ENVIRONMENTAL HEALTH
SERIES
Air Pollution
SELECTED
METHODS
FOR THE
MEASUREMENT
OF AIR
POLLUTANTS
U. S. DEPARTMENT OE HEALTH,
EDUCATION, AND WELFARE
Public Health Service
-------
SELECTED METHODS
FOR THE
MEASUREMENT OE AIR POLLUTANTS
Interbranch Chemical Advisory Committee
U.S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
Public Health Service
Division of Air Pollution
Robert A. Taft Sanitary Engineering Center
Cincinnati, Ohio 45226
May 1965
-------
The ENVIRONMENTAL HEALTH SERIES of reports was estab-
lished to report the results of scientific and engineering studies of
man1^ environment, The community, whether urban, suburban, or
rural, where he lives, works, and plays; the air, water, and earth
he uses and re-uses; and the wastes he produces and must dispose
of in a way that preserves these natural resources. This SERIES of
reports provides for professional users a central source of informa-
tion on the intramural research activities of Divisions and Centers
within the Public Health Service, and on their cooperative activities
with State and local agencies, research institutions, and industrial
organizations. The general subject area of each report is indicated
by the two letters that appear in the publication number; the indica-
tors are
AP Air Pollution
AH Arctic Health
EE Environmental Engineering
FP Food Protection
OH Occupational Health
RH Radiological Health
WP Water Supply
and Pollution Control
Triplicate tear-out abstract cards are provided with reports in
the SERIES to facilitate information retrieval. Space is provided on
the cards for the user's accession number and additional key words.
Reports in the SERIES will be distributed to requesters, as
supplies permit. Requests should be directed to the Division iden-
tified on the title page or to the Publications Office, Robert A. Taft
Sanitary Engineering Center, Cincinnati, Ohio 45ZZ6.
Public Health Service Publication No. 999-AP-ll
-------
PREFACE
A mounting attack on the problems of air pollution has resulted
from growing awareness of the steady degeneration of air quality due
to our increasing urban population, greater industrial activity, and
expanded transportation by automobiles and trucks. Methods of air
analysis are basic tools required for studying pollution processes and
effects, for monitoring the present degrees of pollution, for setting
air quality standards, and for evaluating control efforts. This manual,
addressed to the many chemists newly entering this work, is an effort
to assist in the development of uniform standard methods of analysis.
It provides a channel of communication making available the judgment
and knowledge of a large group of chemists in the Public Health Service.
The methods for determination of pollutants of common interest
presented herein were selected and presented in uniform format by
experienced chemists on the staff of the Division of Air Pollution. The
methods were critically reviewed by the Interbranch Chemical Advi-
sory Committee, which is composed of representatives of the profes-
sional chemical groups in all branches of the Division. An effort was
made to include all important details and provide references to the
original literature for those needing more complete information.
We expect that these and similar methods will be subjected to
rigorous testing procedures by collaborating laboratories having the
confidence of most groups and that they will be found to merit the status
of standard methods. In this connection, we believe that the tests
should examine the critical factors of gas absorption efficiency and the
stability of both the absorbing reagent and the sample reaction products
during the aeration of the sampling process and in the interval before
analysis. An adequate test would involve sampling accurately pre-
pared gas mixtures throughout the applicable concentration range,
with realistic amounts of interfering substances, in a system free
from adsorption losses, such as a flow dilution system. Such testing
will be time consuming. In the interim, this manual provides selected
analytical methods as working tools representing the best judgment of
our staff, on the basis of our experiences with them and the reports
received from others.
The manual was edited by Messrs. Mario Storlazzi and Seymour
Hochheiser. The name of the chemist who selected and prepared each
procedure is indicated at its close. The members of the Interbranch
Chemical Advisory Committee are Dr. A. P. Altshuller, Mr. Gilbert
L. Contner, Mr. Thomas R. Hauser, Mr. Seymour Hochheiser, Mr.
Charles Punte, Dr. Bernard E. Saltzman, Mr. Stanley F. Sleva, Mr.
Mario Storlazzi, and Mr. Elbert C. Tabor. Assistance from many
other staff members is gratefully acknowledged.
At appropriate times new procedures will be added to this col-
lection, and the present ones will be revised. Corrections and con-
structive criticism are welcomed.
Bernard E. Saltzman, Ph. D.
Chairman, Interbranch Chemical
Advisory Committee
-------
CONTENTS
Page
Abstract . vii
Determination of Sulfur Dioxide: West and Gaeke Method A-l
Determination of Sulfur Dioxide: Hydrogen Peroxide Method. B-l
Determination of Nitrogen Dioxide and Nitric Oxide: Saltzman
Method. . . C-l
Determination of Oxidants (Including Ozone): Neutral Buffered-
Potassium Iodide Method. . . . . D-l
Determination of Oxidants (Including Ozone): Alkaline
Potassium Iodide Method. . . E-l
Determination of Aliphatic Aldehydes: 3-Methyl-2-benzo-
thiazolone Hydrazone Hydrochloride (MBTH) Method F-l
Determination of Acrolein: 4-Hexylresorcinol Method . G-l
Determination of Formaldehyde: Chromotropic Acid Method. H-l
Determination of Sulfate in Atmospheric Suspended Particulates:
Turbidimetric Barium Sulfate Method . . 1-1
Determination of Nitrate in Atmospheric Suspended Particulates:
2, 4 Xylenol Method . . . J-l
-------
ABSTRACT
This manual is an effort to assist in the development of uniform
standard methods of analysis of ai-r pollutants. It makes available the
judgment and knowledge of a large group of chemists in the Public
Health Service. Methods of determining pollutants of common interest
are presented in uniform format by chemists on the staff of the Divi-
sion of Air Pollution. The methods were critically reviewed by the
Interbranch Chemical Advisory Committee, which is composed of
representatives of the professional chemical groups in all branches
of the Division. Methods presented are as follows: For determination
of sulfur dioxide, the West and Gaeke and the hydrogen peroxide meth-
ods; for determination of nitrogen dioxide and nitric oxide, the Saltz-
man method; for determination of oxidants, the neutral buffered-
potassium iodide and the alkaline potassium iodide methods; for de-
termination of aliphatic aldehydes, the 3-methyl-2 benzothiazolone
hydrazone hydrochloride method; for determination of acrolein, the
4-hexylresorcinol method; for determination of formaldehyde, the
chromotropic acid method; for determination of sulfate in atmospheric
suspended particulates, the turbidimetric barium sulfate method; and
for determination of nitrate in atmospheric suspended particulates,
the Z, 4 xylenol method.
-------
SELECTED METHODS FOR THE
MEASUREMENT OF AIR POLLUTANTS
Determination of Sulfur Dioxide: West and Gaeke Method"
INTRODUCTION
The West and Gaeke method is applicable to the determination
of sulfur dioxide in outside ambient air in the concentration range
from about 0. 005 to 5 parts per million (ppm). Sulfur dioxide in
the air sample is absorbed in 0. 1 M sodium tetrachloromercurate.
Nonvolatile dichlorosulfitomercurate ion is formed in this process.
Addition of acid-bleached pararosaniline and formaldehyde to the
complex ion produces red-purple pararosaniline methylsulfonic acid,
which is determined spectrophotometrically. The system obeys
Beer's Law up to about 10 ul of sulfur dioxide per 10 ml of absorbing
solution. This method is more sensitive than the hydrogen peroxide
method and is not subject to interference from other acidic or basic
gases or solids such as SOj, H2SO4, NH3, or CaO; however, the
analysis should be completed within 1 week after sample collection,
and the concentrations of ozone and nitrogen dioxide should be less
than that of the sulfur dioxide.
REAGENTS
All chemicals used must be ACS analytical-reagent grade.
Absorbing reagent, 0. 1 M sodium tetrachloromercurate. Dis-
solve 27.2 g {0. 1 mole) mercuric chloride and 11.7 g (O.Z mole)
sodium chloride in 1 liter of distilled water. (CAUTION: Highly
poisonous. If spilled on skin, flush off with water immediately. )
Pararosaniline hydrochloride (0.04%), acid bleached. Dissolve
0. 20 g of pararosaniline hydrochloride in 100 ml of distilled water and
filter after 48 hours. This solution is stable for at least 3 months if
stored in the dark and kept cool. The pararosaniline hydrochloride
used should have an assay of better than 95% and an absorbance maxi-
mum at 543 or 544 m\j.. Pipette 20 ml of this into a. 100-ml volumetric
flask. Add' 6 ml of concentrated HC1. Allow to stand 5 minutes, then
dilute to mark with distilled water. This solution should be pale
yellow with a greenish tint. It can be stored at room temperature in
an amber bottle for a week or for about 2 weeks if refrigerated.
* Prepared by Seymour Hochheiser, Technical Assistance Branch, Division of Air Pollution,
Public Health Service. Approved by the Interbranch Chemical Advisory Committee,
November 1963.
West and Gaeke Method A-
-------
Formaldehyde, 0.2%. Dilute 5 ml of 40% formaldehyde to 1, 000
ml with distilled water. Prepare weekly.
Standard sulfite solution. Dissolve 640 mg sodium metabisul-
fite (assay 65. 5% as SO2) in 1 . 0 liter of water. This yields a solution
of approximately 0.40 mg/ml as SO2- The solution should be stand-
ardized by titration with standard 0.01 N \-, by using starch as indica-
tor, and adjusted to 0. 01Z3 N. Then 1 ml = 150 \L\ SO2 (25°C, 760 mm
Hg). Prepare and standardize freshly.
Starch solution (iodine indicator), 0. 25%. Make a thin paste of
1. 25 g of soluble starch in cold water and pour into 500 ml of boiling
water while stirring. Boil for a few minutes. Store in a glass stop-
pered bottle.
Standard iodine solution, 0. 01 N. Dissolve 12. 69 g of resub-
limed iodine in 25 ml of a solution containing 1 5 g of iodate-free KI;
dilute to the 1, 000-ml mark in a volumetric flask. Pipet exactly 100
ml of this 0. 1 N solution and dilute to 1, 000 ml in a volumetric flask
with 1. 5% KI. This solution can be used as a primary standard if the
weighing is carefully done or it can be checked against a standard
thiosulfate solution. This solution should be stored in an amber bottle,
refrigerated, and then standardized on the day of use.
APPARATUS
Absorber. An all-glass midget impinger (similar to that shown
in Figure 3) or other collection device should be capable of removing
SO2 from an air sample by using 10 ml of absorbing reagent. (Among
the suppliers of midget impingers are Ace Glass Company and Gel-
man Instrument Company. )
Air pump. The air pump should be capable of drawing 2. 5 liters
per minute through the sampling assembly.
Air-metering and flow control devices. These devices ought to
be capable of controlling and measuring flows with an accuracy of - 2
percent. The flow meter should be calibrated for variations in read-
ing with temperature and pressure of the airstream so that the ap-
propriate corrections can be applied.
Thermometer (or other temperature-measuring device). This
device should have an accuracy of - 2°C.
Mercury manometer (or other vacuum-measuring device). This
device should have an accuracy of 0. 2 in. Hg.
Spectrophotometer or colorimeter. This instrument should be
capable of measuring color intensity at 560 m(x, in 1-cm absorbance
cells or larger.
ANALYTICAL PROCEDURE
Collection of samples. Set up a sampling train consisting of,
in order, absorber, trap to protect flow device, flow meter, flow con-
trol device, temperature and vacuum gauge, and air pump. Shield the
A-2 SELECTED METHODS
-------
absorbing reagent from direct sunlight during and after sampling
by covering the absorber with a suitable wrapping such as aluminum
foil to prevent deterioration of sample. All probes and tubing up-
stream from the bubbler should be pyrex glass, stainless steel, or
teflon. Butt-to-butt connections may be made with tygon tubing.
The downstream metering device can be empirically corrected to
atmospheric conditions by conducting a dummy run with an upstream
flow meter in line that is open to the atmosphere.
Pipet exactly 10 ml of absorbing reagent into the absorber.
Aspirate the air sample through the absorber at a rate of 0. 2 to 2. 5
liters per minute (depending upon the concentration of sulfur dioxide
in the atmosphere and the sampling time desired). The sampling
time may vary from a few minutes to 24 hours. For 24-hour sampling,
the absorber selected should be capable of containing 20 ml or more
of absorbing reagent. For best results, the sampling time and rate
should be chosen to provide a concentration of approximately 2 to
4 |il of SC>2 in 10 ml of the absorbing reagent. The dichlorosulfito-
mercurate formed may be stored for 3 days with only a slight de-
crease in strength (about 1 % per day). If samples are stored for
longer periods, a correction factor should be applied. ' The sample
may be stored in the collection device or transferred to a stoppered
glass or polyethylene container.
Analysis. If a mercury precipitate is formed owing to the pre-
sence in the air sample of inorganic sulfides, thiols, or thiosulfates,
it may be removed by filtration or centrifugation. To the clear sample,
adjusted to 10 ml with distilled water to compensate for evaporative
losses, add 1 . 0 ml of acid-bleached pararosaniline solution and 1 . 0 ml
of the 0. Z% formaldehyde solution and mix. In this analysis, reagent
addition and spectrophotometric analysis can be automated.
Treat a 10-ml portion of unexposed sodium tetrachloromercurate
solution in the same manner for use as the blank. If the collecting
reagent remains exposed to the atmosphere during the interval between
sampling and analysis, the blank should be exposed in the same man-
ne r .
Allow ZO minutes for maximum color development and read the
absorbance at 560 m^ in a spectrophotometer using the blank as the
reference.
Calculations. Convert the volume of air sampled to the volume
at standard conditions of Z5°C, 29. 97 in. Hg:
(rn 298. Z
_
s 29. 97 (t + 273. 2) (1)
Vs volume of air in liters at standard conditions
V volume of air in liters as measured by the meter
P barometric pressure in inches of mercury
Pm suction at meter in inches of mercury
t temperature of sample air in degrees centigrade
Ordinarily the correction for pressure is slight and may be
neglected.
West and Gaeke Method A-3
-------
Compute the microliters of sulfur dioxide in the sample by
multiplying the absorbance by the slope of the calibration plot. Then
the concentration is:
ppm SC>2 by volume — —
Vs (2)
PREPARATION OF CALIBRATION CURVE
Pipet exactly 2 ml of standard sulfite solution into a 100-ml
volumetric flask and dilute to mark with absorbing reagent. This final
solution contains 3. 0 (i 1 SO2 per ml.
Add accurately portions of the dilute standard sulfite solution of
0.5, 1. 0, 1. 5, and 2. 0 ml to a series of 10-ml glass stoppered, grad-
uated cylinders and dilute to the marks with absorbing reagent. Con-
tinue with the analysis procedure given above.
Plot the absorbance (optical density) as the abscissa against the
(j. 1 of SOg per 10 ml of absorbing solution on rectangular coordinate
paper. Compute slope of straight line best fitting the data.
DISCUSSION OF PROCEDURE
The error for the combined sampling and analytical technique
is - 10% in the concentration range below 0. 10 ppm with increasing
accuracy with concentration in the range 0. 1 to 1 ppm. The measure-
ments should be reported to the nearest 0. 005 ppm at concentrations
below 0. 15 ppm and to the nearest 0. 01 ppm above 0. 15 ppm.
O-j and NO-, interfere if present in the air sample at concentra-
tions greater than that of SO-?. Interference of NO-p is eliminated by
including 0. 06% sulfamic acid in the absorbing reagent.'' This may,
however, result in losses of SO2 during sampling and during storage
of the sample for more than 48 hours after collection. NO^ inter-
ference may also be eliminated by adding 0-toluidine or sulfamic acid
subsequent to sample collection. °> "
Heavy metals, especially iron salts, interfere by oxidizing di-
chlorosulfitomercurate during sample collection. This interference
is eliminated by including ethylenediaminetetraacetic acid in the ab-
sorbing reagent. Sulfuric acid or sulfate do not interfere. There is
no experimental evidence to indicate that SOj interferes; it probably
hydrolyzes preferentially in the absorbing reagent to form H^SO,^,
rather than combines with sodium tetrachloromercurate to form
the dichlorodisulfitomercurate complex ion. If the latter reaction
prevails, the presence of 803 will result in a positive interference.
If relatively large amounts of solid material are present, a filter
may be used advantageously upstream; however, a loss of SO2 may
occur.
The color produced is independent of temperature in the range
11 to 30°C and is stable for 3 hours. -1
A-4 SELECTED METHODS
-------
Much difficulty with the method has been caused by the use of
impure pararosaniline hydrochloride. *-® A commercial brand is now
available that is specially selected for this procedure (Fisher Scien-
tific Company, catalog No. P-389). The purity of the reagent may be
estimated by comparing the slope of the calibration plot with the value
0. 15 absorbance unit per (J. 1 (obtained with 1-cm cells in a Gary spec-
trophotometer), which corresponds to a molar absorptivity of 36, 700.
REFERENCES
1. West, P.W., Gaeke, G. C. , Fixation of Sulfur Dioxide as
Disulfitomercurate (II), Subsequent Colorimetric Estimation,
Anal. Chem. Z8:1916. 1956.
2. Nauman, R. V. , West, P. W. , Tron, F. , Gaeke, G. C. , A
Spectrophotometric Study of the Schiff Reaction as Applied to
the Quantitative Determination of Sulfur Dioxide, Anal. Chem.
32:1307. I960.
3. Perry, W. H. , Tabor, E. C. , National Air Sampling Network
Measurement of SC>2 and NC>2. Arch. Environmental Health.
4:44. 1962.
4. McCaldin, R. O. , Hendrickson, E. R. , Use of a Gas Chamber
for Testing Air Samplers, J. Amer. Ind. Hyg. Assoc. 20:509.
1959.
5. Welch, A. F. , Terry, J. P., Developments in the Measure-
ment of Atmospheric Sulfur Dioxide, J. Amer. Ind. Hyg.
Assoc. 21:316. I960.
6. Terraglio, F. P. , Manganelli, R. M. , Laboratory Evaluation
of SO2 Methods, Anal. Chem. 34:675. 1962.
7. West, P. W. , Ordoveza, F. , Elimination of Nitrogen Dioxide
Interference in the Determination of Sulfur Dioxide, Anal.
Chem. 34:1324. 1962.
8. Zurlo, N. , Griffini, A. M. , Measurement of Sulfur Dioxide
Content of the Air in the Presence of Nitrogen and Heavy
Metals, Med. d. Lavoro. 5: 330. 1962.
9. Lodge, J. P. , Pate, J. B. , Swanson, G. A. , Ammons, B. E. ,
Nitrogen Dioxide Interference in the Colorimetric Determina-
tion of Atmospheric Sulfur Dioxide. Presented at 148th Nat.
Meeting, Amer. Chem. Soc. Chicago. August 30 Septem-
ber 4, 1964.
10. Pate, J. B. , Lodge, J. P. , Wartburg, A. F. , Effect of Para-
rosaniline in the Trace Determination of Sulfur Dioxide, Anal.
Chem. 34:1660. 1962.
West and Gaeke Method A-5
-------
Determination of Sulfur Dioxide: Hydrogen Peroxide Method"
INTRODUCTION
The hydrogen peroxide method is applicable to the determination
of sulfur dioxide in outside ambient air in the concentration range from
about 0. 01 to 10. 0 ppm. ' Sulfur dioxide in the air sample is absorb-
ed in 0. 03 N hydrogen peroxide reagent (adjusted to about pH 5). The
stable and nonvolatile sulfuric acid formed in this process is titrated
with standard alkali. The method requires only simple equipment and
can be performed by analysts having lesser skills; it is preferable to
the West and Gaeke method if sulfur dioxide is the principal acid or
basic atmospheric gaseous pollutant, or if long storage of samples
(longer than 1 week) is required prior to analysis.
REAGENTS
All chemicals used must be ACS analytical-reagent grade.
Absorbing solution, hydrogen peroxide, 0. 03 N, pH 5. Dilute
3. 4 ml of 30% hydrogen peroxide solution to 2 liters with distilled
water. Determine the alkalinity of the solution by taking a 75-ml por-
tion, adding 3 drops of mixed indicator, and adding approximately
0. 002 N HC1 or HNO3 from a buret until the indicator turns pink (pH 5).
Calculate the amount of acid necessary to adjust the acidity of the bulk
of the absorbent and add the required amount. The zero blank, ob-
tained by titrating 75 ml of the adjusted reagent with 0. 002 N NaOH to
the indicator equivalence point (green), should be not more than 2
drops. The reagent is stable at room temperature for at least 1
month.
Mixed indicator, 0. 1%. Dissolve 0. 06 g bromcresol green and
0. 04 g methyl red in 100 ml of methanol. When stored in an amber
bottle at room temperature, the reagent is stable for at least 6 months.
Standard sulfuric acid solution, 0. 002 N. Prepare this solution
by appropriate dilution of concentrated sulfuric acid. Standardize by
the gravimetric barium sulfate method using a 200-ml portion, or
with a primary standard such as Na2B^Oy 10 H2O. This reagent may
be stored indefinitely without change in strength.
Standard sodium hydroxide solution, 0. 002 N. Prepare 2 liters
of this solution by dilution of 1 N sodium hydroxide with freshly boiled
(COg-free) distilled water. Standardize as follows: Pipet 25 ml of
standard sulfuric acid solution into an Erlenmeyer flask, add 3 drops of
mixed indicator solution, and titrate with the sodium hydroxide reagent
contained in a buret to the green equivalence point. Store the reagent
in a polyethylene or other alkali-resistant bottle and restandardize bi-
monthly.
1 ml of 0. 002 N NaOH 64 (j. g SO2 Z4. 47 u 1 SO2 (25°C,
760 mm Hg).
•^Prepared by Seymour Hochheiser, Technical Assistance Branch, Division of Air Pollution,
Public Health Service. Approved by the Interbranch Chemical Advisory Committee,
November 1963.
Hydrogen Peroxide Method B-l
-------
APPARATUS
Absorber. A standard all-glass impinger or fritted bubbler
(capacity about 300 ml is acceptable). (Among the suppliers are Corn-
ing Glass Company and Fisher Scientific Company. )
Air pump. The air pump should be capable of drawing 1 cfm
through the sampling assembly.
Air-metering and flow control devicej^. These devices should
be capable of controlling and measuring flows with an accuracy of - 2%.
The flow meter should be calibrated for variation in reading with tem-
perature and pressure so that the appropriate corrections can be
applied.
Thermometer (or other temperature-measuring device). This
device should have an accuracy of i Z°C.
Mercury manometer (or other vacuum-measuring device). This
device should have an accuracy of 0. 2 in. Hg.
Buret. The buret should have a 25- or 50-ml capacity graduated
in 0. 1-ml subdivisions, preferably with teflon plug, and should be
capable of measuring volume with an accuracy of 0. 05 ml.
ANALYTICAL PROCEDURE
Collection of samples. Set up a. sampling train consisting of, in
order, impinger, trap to protect flow device, flow meter, flow control
device, temperature and vacuum gauge, and air pump. Measure
75 ml of absorbing reagent into the large impinger. Aspirate air
through the bubbler at a rate of 1 cfm for 30 minutes. Note the read-
ings of the vacuum gauge and thermometer. The downstream meter-
ing device can be empirically corrected to atmospheric conditions by
conducting a dummy run with an upstream flow meter in line that is
open to the atmosphere. If an integrated 24-hour air sample is de-
sired, the sampling rate may be reduced to 1 liter per minute. For
SC>2 concentrations of 0. 3 ppm and greater, the strength of the stand-
ard alkali may be increased or the sampling time shortened. For
concentrations of greater than 0. S ppm, a second impinger should be
connected in series so that a recovery efficiency of 98% is maintained.
All probes and tubing upstream from the impinger should be pyrex
glass, stainless steel, or teflon. Butt-to-butt connections may be
made with short lengths of tygon tubing. The collected sample will
not decompose on standing; consequently, the solution may be titrated
long after sample collection. The sample may be stored in the im-
pinger, which has been stoppered, or transferred to a stoppered glass
or polyethylene container.
Titration. Add 3 drops of mixed indicator solution and titrate
the solution with standard 0. 002 N sodium hydroxide until the color
changes from red to green. A reagent blank is titrated in the same
manner and this result (which should be less than 0. 1 ml) subtracted
from the sample liter.
B-2 SELECTED METHODS
-------
Calculations. Convert the volume of air sampled to the volume
at standard conditions of 25°C, 29. 97 in. Hg:
,, ,, P - Pm Z98.Z (1)
Vs = YX 29.97 X t t 273.2
Vp volume of air in liters at standard conditions
V volume of air in liters as measured by the meter
P = barometric pressure in inches of mercury
Pm suction at meter in inches of mercury
t temperature of sample air in degrees centigrade
Results are computed on the basis of the following reaction:
SO2 +• H2O2 «-H2SO4
Thus the net titer of 0. 002 N NaOH (in ml) multiplied by 24. 47
gives the microliters'of sulfur dioxide. Then the concentration is:
ppm SO2 by volume ——
v s (£>
DISCUSSION OF PROCEDURE
The error for the combined sampling and analytical technique is
± 10% in the concentration range below 0. 1 ppm with increasing accur-
acy with concentration in the range 0. 1 to 1 ppm. The measurements
should be reported to the nearest 0. 01 ppm.
The presence in the air sample of strong acidic gases other than
SO2 or reactive acid solids such as HC1 and NaHSO3 gives erroneously
high results whereas the presence of alkaline gases or reactive basic
solids such as NH-, and CaO gives erroneously low results. H2SO4
does not interfere, since it is not separated from the airstream appreci-
ably, owing to its small particle size, except, perhaps, when the relative
humidity is greater than 85%, which could result in particle sizes of
greater than 1 (j. . SO->, gas, if present, would be a positive interfer-
ence. Sulfates do not interfere. CO2 does not interfere since it is
not absorbed in the acid-absorbing reagent. If relatively large amounts
of solid material are present, a filter may be employed advantageous-
ly upstream; however, a loss of SO2 may occur. The extent of this
loss would depend upon the composition of the particulate matter and
the nature and retentive capacity of the filter used. The acid-base
indicator is not included in the absorbing reagent because it tends to
decompose during sampling, resulting in unreproducible values.
REFERENCES
1. Jacobs, M. B. , Greenburg, L. , Sulfur Dioxide in New York
City Atmosphere, Ind. Eng. Chem. 48:1517. 1956.
2. Jacobs, M. B. , The Chemical Analysis of Air Pollutants,
Interscience, New York. 1960.
3. Craxford, S. R. , Slimming, D.W., Wilkins, E. T. , The
Measurement of Atmospheric Pollution: The Accuracy of
the Instruments and the Significance of the Results, Proceed-
ing of the Harrogate Conference. London, England. 1960.
Hydrogen Peroxide Method B-3
-------
Determination of Nitrogen Dioxide and Nitric Oxide:
Saltzman Method*
INTRODUCTION
The Saltzman method is intended for the manual determination of
nitrogen dioxide in the atmosphere in the range of a few parts per
billion (ppb) to about 5 ppm. Sampling is conducted in fritted bubblers.
The method is also applicable to the determination of nitric oxide after
it is converted to an equivalent amount of nitrogen dioxide by passage
through a permanganate bubbler. Concentrations of both gases of 5
to 100 ppm may be sampled in evacuated bottles. The nitrogen di-
oxide is absorbed in Grie ss-Saltzman reagent. A stable pink color
is produced within 15 minutes and may be read visually or in an appro-
priate instrument. Only slight interfering effects occur from other
gases.
REAGENTS
All reagents are made from analytical-grade chemicals in ni-
trite-free water prepared, if necessary, by redistilling distilled water
in an all-glass still after adding a crystal each of potassium perman-
ganate and of barium hydroxide. They are stable for several months
if kept well stoppered in brown bottles in the refrigerator. The ab-
sorbing reagent should be allowed to warm to room temperature before
use.
N-(l -Naphthyl)-ethylenediamine dihydrochloride, 0. 1%. Dissolve
O.lg of the reagent in 100 ml of water. This is a stock solution.
Absorbing reagent. Dissolve 5 g of sulfanilic acid in almost a
liter of water containing 140 ml of glacial acetic acid. Gentle heating
is permissible, if desired, to speed up the process. To the cooled
mixture, add 20 ml of the 0. 1 % stock solution of N-(l-Naphthyl)-
ethylenediamine dihydrochloride, and dilute to 1 liter. Avoid lengthy
contact with air during both preparation and use, since this will result
in discoloration of reagent because of absorption of nitrogen dioxide.
Standard sodium nitrite solution, 0. 0203 g per liter. One ml of
this working solution produces a color equivalent to that of 10 (il of
nitrogen dioxide (10 ppm in 1 liter of air at 760 mm of mercury and
25°C). Prepare fresh just before use by dilution from a stronger stock
solution containing 2. 03 g of the reagent grade granular solid (drying
is unnecessary) per liter. The stock solution should be stable for
90 days.
Acid permanganate, used for nitric oxide determination. Dis-
solve 2. 5 g of potassium permanganate in about 90 ml water, add 2. 5 g
of concentrated sulfuric acid (or 5.2 ml of 1:3 H2SO4> and dilute to
100 ml with distilled water. Prepare at frequent intervals, since the
keeping quality is not good; discard when an appreciable precipitate of
brown manganese dioxide is noted.
^Prepared by Bernard E. Saltzman, Laboratory of Engineering and Physical Sciences,
Division of Air Pollution, Public Health Service. Approved by the Interbranch Chemical
Advisory Committee, January 1964.
Saltzman Method C-l
-------
APPARATUS
Absorber. A specially ordered all- glass bubbler with a. 60-H-
maximum pore diameter frit (Corning designation "coarse" or Ace
designation "C"), similar to that illustrated in Figure 1, is used.
Acid permanganate bubblers. A midget impinger with a nozzle
about 1 mm in diameter and ground glass joints may be used (Figure 3).
Accumulated deposits of manganese dioxide may be readily cleaned
out by warming with a solution of hydroxylamine hydrochloride or
oxalic acid.
'7 OR 12/5 FEMALE
100-ml BULB
18/7 OR 12/5 MALE
CONCENTRIC WITH FLASK
BOTTOM AND FRITTED
CYLINDER SO THAT INNER
AND OUTER PIECES ARE
INTERCHANGEABLE
FRITTED CYLINDER
CENTERED IN FLASK
BOTTOM. POROSITY IS
CRITICAL MUST BE 60 (i
MAX. PORE DIAMETER.
(ACE DESIGNATION "C"
OR CORNING "COARSE")
FIGURE 1. FRITTED BUBBLER FOR SAMPLING NITROGEN DIOXIDE.
Air-metering device. A glass rotameter capable of accurately
measuring a flow of 0. 4 liter per minute is recommended.
Air pump. An appropriate suction pump capable of drawing the
required sample flow for intervals of up to 30 minutes is suitable.
It is desirable to have a tee connection at the intake. The inlet con-
nected to the sampling train should have an appropriate trap and needle
valve (preferably of stainless steel). The second inlet should have a
valve for bleeding in a large excess flow of clean air to prevent con-
densation of. ac.etic acid vapors from the absorbing reagent, with con-
sequent corrosion of the pump.
C-2
SELECTED METHODS
-------
Spectrophotometer or colorimeter. A laboratory instrument
suitable for measuring the pink color at 550 m|o., with stoppered tubes
or cuvettes, is recommended.
ANALYTICAL PROCEDURE FOR NITROGEN DIOXIDE
Sampling train. Assemble, in order, a fritted absorber, rota-
meter, and pump. Use ground-glass connections upstream from the
absorber. Butt-to-butt glass connections with slightly greased tygon
or pure gum rubber tubing may also be used for connections without
losses if lengths are kept minimal. Since the rotameter operates at
an appreciable vacuum, make one dummy run to calibrate it against
another rotameter or wet test meter installed upstream from the
bubbler and operating at atmospheric pressure. If preferred, the
sampling rotameter may be used upstream from the bubbler provided
occasional checks are made to show that no nitrogen dioxide is lost.
In either case, for accurate measurements, the rotameter must be
kept free from spray or dust.
Sampling procedure. Pipet exactly 10 ml of absorbing reagent
into the fritted bubbler. Draw an air sample through it at the rate of
0.4 liter (or less) per minute until sufficient color has developed (about
10 minutes). Note the total air volume sampled. If the sample air
temperature and pressure deviate greatly from Z5°C and 760 mm Hg,
measure and record the values.
Determination. After collection or absorption of the sample, a
direct red-violet color appears. Color development is complete within
15 minutes at ordinary temperatures. Compare with standards visually
or transfer to stoppered cuvettes and read in a Spectrophotometer at
550 m|j., using unexposed reagent as a reference. Colors may be pre-
served, if well stoppered, with only 3 to 4% loss in absorbance per day;
however, if strong oxidizing or reducing gases are present in the sam-
ple in concentrations considerably exceeding that of the nitrogen dioxide,
the colors should be determined as soon as possible to minimize any
loss.
Standardization. Add graduated amounts of standard sodium
nitrite solution up to 1 ml (measured accurately in a graduated pipet
or small buret) to a series of Z5-ml volumetric flasks, and dilute to
marks with absorbing reagent. Mix, allow 15 minutes for complete
color development, and read the colors.
Good results can be obtained with these small volumes of stand-
ard solution if they are carefully measured. If preferred, however,
larger volumes may be used with correspondingly larger volumetric
flasks.
Calculations. For convenience, standard conditions are taken as
760 mm of mercury and Z5°C; thus, only slight correction by means of
the well-known perfect gas equation is ordinarily required to get V, the
standard volume of the air sample in liters. Quantities of nitrogen di-
oxide may be expressed as microliters, defined as V times the ppm
nitrogen dioxide. It has been determined empirically that 0. 7Z mole
Saltzman Method C-3
-------
of sodium nitrite produces the same color as 1 mole of nitrogen diox-
ide; hence, Z. 03 p. g of sodium nitrite is equivalent to 1 |J-1 of nitrogen
dioxide. * The 1-ml standard is equivalent to 4 n 1 of nitrogen dioxide
per 10 ml of absorbing reagent.
Plot the absorbances of the standard colors, corrected for the
blank, against the milliliters of standard solution. Beer's Law is
followed. Draw the straight line giving the best fit and determine the
slope (the value in milliliters of sodium nitrite intercepted at absor-
bance of exactly 1). This value multiplied by 4 gives the standardiza-
tion factor, M, defined as the number of microliters of nitrogen di-
oxide required by 10 ml of absorbing reagent to give an absorbance of
1. For Z-cm cells the value was 3. 65. Then:
ppm nitrogen dioxide corrected absorbance x M/V (1)
If the volume of the air sample, V, is a simple multiple of M,
calculations are simplified. Thus, for the M value of 3. 65 previously
cited, if exactly 3. 65 liters of air is sampled through a bubbler, the
corrected absorbance is also ppm directly. If other volumes of ab-
sorbing reagent are used, V is taken as the volume of air sample per
10 ml of reagent.
ANALYTICAL PROCEDURE FOR NITRIC OXIDE
Sampling for concentrations of 10 ppm and less. Assemble a
sampling train composed of, in order, rotameter, fritted absorber,
acid permanganate bubbler (with a nozzle rather than fritted inlet),
fritted absorber, and pump. Pipet exactly 10 ml of absorbing reagent
into each fritted absorber (first and third in the train). The second
bubbler in the train should contain 10 ml of the acid permanganate
solution, which may be reused several times. Draw an air sample
through at a rate of 0. 4 liter per minute (or less) until sufficient
color has developed (about 10 minutes). After allowing an additional
15 minutes for full color development, the solution from the third
bubbler may be read in the spectrophotometer and the nitric oxide
computed. Colors too dark to read may be quantitatively diluted with
unexposed absorbing reagent. If a simultaneous determination of
nitrogen dioxide is desired it may be obtained by reading the colored
solution from the first bubbler in a similar manner.
DISCUSSION OF PROCEDURES
Sampling efficiency. The porosity of the fritted bubbler is im-
portant, as well as the flow rate. An efficiency of 95% may be expected
with a flow rate of 0. 4 liter per minute and a maximum pore diameter
of 60 n . Considerably lower efficiencies are obtained with coarser
frits, but these may be utilized if the flow rate is reduced. Since the
quality control by some manufacturers is rather poor, it is desirable
to measure the porosity of a new absorber experimentally as follows:
* Molar volume at 25° C, 760 mm Hq Is 24.47 liters. Molecular weight NaNO2 = 69.00; hence:
I ul NO2= ^= moles NO2 = sr^ x OJ2 x 69.00 = 2.03 x I0'6g NaNO2.
C-4 SELECTED METHODS
-------
Carefully clean the apparatus with dichromate-concentrated sulfuric
acid solution and rinse thoroughly with distilled water. Assemble the
bubbler, add sufficient distilled water to cover the fritted portion, and
measure the vacuum required to draw the first perceptible stream of
air bubbles through the frit. The following equation is then used:
. . 30 s
maximum pore diameter (u) ———
where s is the surface tension of water at the test temperature in dynes
per cm (73 at 18°C, 72 at 25°C, and 71 at 31°C), and P is the measur-
ed vacuum in mm of Hg.
Nitrite equivalent of nitrogen dioxide. Standardization is based
upon the empirical observation that 0.72 mole of sodium nitrite pro-
duces the same color as 1 mole of nitrogen dioxide. Using sodium
nitrite is much more convenient than preparing accurately known gas
samples for standardizing.
Efficiency of nitric oxide conversion. Conversion efficiency of
nitric oxide to nitrogen dioxide by the permanganate bubbler may be
commonly as low as 70%. This depends somewhat upon the quality of
the permanganate solution and the design of the bubbler. Few data
have been published on conversion efficiencies.
Conversion efficiencies of 95 to 100% have been reported recent-
ly for an alternative method using a 17-mm OD glass U tube, con-
taining one sheet of impregnated glass fiber paper cut into 1/4-in.
strips, at a flow rate of 290 ml per minute. (A stack of Z5 sheets of
7-cm-diameter paper is impregnated with 25 ml of 2. 5% Na2Cr2Oy,
2. 5% H2SC>4, and dried in a vacuum oven at 160°F, or on a hot plate
at 200°F Discard top and bottom sheets, store in closed bottle. ) The
useful life of the paper is limited, and it deteriorates rapidly when ex-
posed to reagent vapors downstream from a bubbler. Hence a different
sampling train, composed of rotameter, paper, fritted absorber, and
pump, is used. The analysis yields the total of nitric oxide and nitrogen
dioxide. A separate analysis of the latter gas must be made and de-
ducted to give the concentration of nitric oxide.
Effects of interfering gases. A fivefold ratio of ozone to nitro-
gen dioxide will cause a small interference, the maximal effect occur-
ring in 3 hours. The reagent assumes a slightly orange tint.
A 10-fold ratio of sulfur dioxide produces no effect. A 30-fold
ratio slowly bleaches the color to a. slight extent. The addition of
1% acetone to the reagent before use retards the fading by forming a
temporary addition product with sulfur dioxide. This permits reading
within 4 to 5 hours (instead of the 45 minutes required without the
acetone) without appreciable interferences.
The interferences from other nitrogen oxides and other gases
that might be found in polluted air are negligible.
Saltzman Method C-5
-------
SAMPLING RELATIVELY LARGE CONCENTRATIONS (MORE THAN
5 ppm) WITH EVACUATED BOTTLES
Grab-sample bottles. Ordinary glass-stoppered borosilicate
glass bottles of 30- to 250-m] sizes are suitable if provided with a
mating ground joint attached to a stopcock for evacuation. Calibrate
the volume by weighing with connecting piece, first empty, then filled
to the stopcock with distilled water.
Fifty- or one hundred- milliliter glass syringes are convenient
(although less accurate) for moderately large concentrations.
Sampling for nitrogen dioxide. Sample in evacuated bottles of
appropriate size (30 ml for up to 1 00 ppm, to 250 ml for down to 1
ppm) containing exactly 10 ml (or other convenient volume) of absorb-
ing reagent. First grease the joint lightly with silicone or fluorocar-
bon grease. If a source of vacuum is available at the place of sam-
pling, it is best to evacuate just before sampling to eliminate any un-
certainty about loss of vacuum. A three-way Y stopcock connection
is convenient. One leg is connected to the sample source, one to the
vacuum pump, and the third to a tee attached to the bottle and to
a mercury manometer or accurate gauge. In the first position of the
Y stopcock, the bottle is evacuated to the vapor pressure of the ab-
sorbing reagent, and the actual vacuum is read. In the second posi-
tion of the Y stopcock, the sampling bottle is closed and the vacuum
pump draws air through the sampling line to flush it thoroughly. In
the third position of the Y stopcock, the sampling line is connected
to the evacuated bottle, and the sample is collected. The stopcock
on the bottle is then closed. Allow 15 minutes with occasional shak-
ing for complete absorption and color development. For calculation
of the standard volume of the sample, the pressure is recorded as
the difference between the filled and evacuated conditions, and the
uncorrected volume is that of the bottle plus that of the connection
up to the stopcock minus the volume of absorbing reagent.
Another, more convenient but less accurate field method for
moderately large concentrations is to use 50- or ]00-ml glass syrin-
ges. Ten ml of absorbing reagent is kept in the capped syringes,
and 40 or 90 ml of air is drawn in at the time of sampling. The ab-
sorption of nitrogen dioxide is completed by capping and shaking vigor-
ously for 1 minute, after which the air is expelled. Additional air
may be drawn in and the process repeated several times if necessary
to develop sufficient final color.
The syringe method is also useful when appreciable concentra-
tions of nitric oxide are suspected. Interference caused by the air oxi-
dation of nitric oxide to nitrogen dioxide is minimized by expelling the
air sample immediately after the 1-minute absorption period.
Sampling for nitric oxide. Sample in an evacuated bottle contain-
ing absorbing reagent, as described in the procedure for nitrogen di-
oxide. Close the stopcock and allow sufficient time for the air oxida-
tion of the nitric oxide to be substantially completed (Figure 2), shaking
the bottle at intervals to prevent loss of nitrogen dioxide on the glass.
Read the color in the manner previously described. The nitrogen di-
oxide initially present may be separately determined in a syringe and
deducted if appreciable. The calculated concentration of nitric oxide
may be corrected for incomplete conversion according to Figure 2.
C-6 SELECTED METHODS
-------
Low conversions should be avoided for accurate results. A second
correction for fading of the color (about 3% of the absorbance per day)
may be made for a prolonged absorption period.
2 NO+O2—«-NO2
BASED ON KINETIC DATA OF
SMITH, J. H., J. Am. Chem. Soc
65. 74 (1943)
2 5 10 20 50 100 200 500 1,000
INITIAL ppm NITRIC OXIDE
FIGURE 2. OXIDATION OF NITRIC OXIDE BY AIR AT 25°C.
REFERENCES
1. Ripley, D. L. , Clingenpeel, J. M. , and Hum, R.W., Con-
tinuous Determination of Nitrogen Oxides in Air and Exhaust
Gases, Internal. J. Air and Water Poll. (London) 8: 455-
63. 1964.
2. Saltzman, B. E. , Colorimetric Microdetermination of Nitro-
gen Dioxide in the Atmosphere, Anal. Chem. 26: 1949-55.
1954.
3. Thomas, M. D. , MacLeod, J.A. , Robbins, R. C. , Goettel-
man, R.C., Eldridge, R. W. , and Rogers, L. H. , Automatic
Apparatus for Determination of Nitric Oxide and Nitrogen
Dioxide in the Atmosphere, Anal. Chem. 28: 1810-16. 1956.
Saltzman Method
C-7
-------
Determination of Oxiclants (Including Ozone):
Neutral Buffered-Potassium Iodide Method*
INTRODUCTION
This method ' is intended for the manual determination of oxi-
dants (including ozone) in the range of a few parts per hundred million
(pphm) to about 10 ppm. Ozone, chlorine, hydrogen peroxide, organic
peroxides, and various other oxidants will liberate iodine by this meth-
od. A positive response of about 10% of the ppm nitrogen dioxide oc-
curs. It is customary for convenience to express the results as ozone.
The advantages of this procedure over the alkaline iodide procedure
are simplicity, accuracy, and precision. The analysis must, however,
be completed during the period of 30 minutes to 1 hour after sampling.
Sampling is conducted in midget impingers containing 1% potassium
iodide in a neutral (pH 6.8) buffer composed of 0. 1 M disodium hydro-
gen phosphate and 0. 1 M potassium dihydrogen phosphate. Iodine is
liberated in the absorbing reagent and measured in an appropriate
instrument. Serious interfering effects occur from reducing gases and
dusts .
REAGENTS
All reagents are made from analytical-grade chemicals.
Traces of reducing impurities cause very serious errors.
Double-distilled water, used for all reagents. To distilled water
in an all-glass still, add a crystal each of potassium permanganate and
barium hydroxide, and redistill.
Absorbing reagent. Dissolve 13. 61 g of potassium dihydrogen
phosphate, 14. ZO g of anhydrous disodium hydrogen phosphate (or
35. 82 g of dodecahydratesalt), and 10. OOgof potassium iodide suc-
cessively and dilute the mixture to exactly 1 liter. Age at room tem-
perature for at least 1 day before using. This solution may be stored
for several weeks in a glass stoppered brown bottle in the refrigerator,
or for shorter periods at room temperature. Do not expose to sun-
light.
Standard iodine solution, 0. 05 N. Dissolve successively 1 6. 0 g
of potassium iodide and 3. 173 g of iodine; make to a volume of exactly
500 ml. Age for at least 1 day before using. Standardization is un-
necessary if the weighing is carefully done. (The' solution may also
be standardized by titration with sodium thiosulfate by using starch
indicator. )
* Prepared by Bernard E. Saltzman, Laboratory of Engineering and Physical Sciences,
Division of Air Pollution, Public Health Service. Approved by the Intel-branch Chemical
Advisory Committee, March 1964.
Neutral Buffered-Potassium Iodide Method D-l
-------
APPARATUS
Absorber. All-glass midget impingers with a graduation mark at
10 ml, similar to that shown in Figure 3, are used. (Other bubblers
with nozzle or open-end inlet tubes may be used. Fritted bubblers
tend to give comparatively low results. ) Impingers must be kept
scrupulously clean and dust free. All traces of grease must be re-
moved by treatment with dichromate - concent rate d sulfuric acid solu-
tion followed by tap and distilled water.
Air-metering device. A glass rotameter capable of measuring a
flow of 1 to Z liters per minute with an accuracy of - 2% is recom-
mended.
Air pump. An appropriate suction pump capable of drawing the
required sample flow for intervals of up to 30 minutes is suitable.
It is desirable to have a trap on the inlet to protect the needle valve
and pump against accidental flooding with absorbing reagent and con-
sequent corrosion.
Spectrophotometer. A laboratory instrument suitable for mea-
suring the yellow color at 352 mu., with stoppered tubes or cuvettes
(suitable for ultraviolet use), is recommended.
ANALYTICAL PROCEDURES
Collection of samples. Assemble a train composed of a midget
impinger, rotameter, and pump. Use ground-glass connections up-
stream from the impinger. Butt-to-butt glass connections with slight-
ly greased tygon tubing may also be used for connections without
losses if exposed tubing lengths are kept minimal. Pipet exactly 10
ml of the absorbing solution into the midget impinger and sample at
a flow rate of 1 to 2 liters per minute. Note the total volume of the
air sample. If the sample air temperature and pressure deviate
greatly from 25°C and 760 mm Hg, measure and record these values.
Sufficient air should be sampled so that the equivalent of 0. 5 to 10 u 1
of ozone is absorbed. Sampling periods of longer than 30 minutes
should be avoided. For a flow rate of 2 liters per minute, a 30-minute
sample should yield a sensitivity of 0. 01 ppm. Do not expose the ab-
sorbing reagent to direct sunlight.
Analysis. If appreciable evaporation has occurred, add distilled
water to restore the volume to the 10-ml graduation mark. Transfer
the exposed absorbing reagent (without diluting with rinse water) to a
clean colorimeter tube or cuvette. During the period of 30 to 60 min-
utes after the sampling period, determine the absorbance at 352 mu,,
using a tube or cuvette freshly filled with distilled water as the refer-
ence. A few additional readings at earlier and later times should be
made occasionally when practicable to check on the color stability.
Every few days, determine the blank correction (to be deducted from
sample absorbances) by reading the absorbance of unexposed reagent.
Samples having a color too dark to read may be quantitatively
diluted with additional absorbing reagent, and the absorbance of the
diluted solution read. The dilution factor must then be introduced into
the calculations.
D-2 SELECTED METHODS
-------
Standardization. Freshly prepare 0. 0025 N iodine standard by
pipetting exactly 5 ml of the 0. 05 N standard stock solution into a
100-ml volumetric flask and diluting to mark with absorbing reagent.
Place 0. 2-, 0. 4-, 0. 6-, and 0. 9-ml portions (measured accurately
in a graduated pipet or small buret) of the diluted standard iodine in
separate 25-ml volumetric flasks and dilute to marks with absorbing
reagent. Mix thoroughly. Immediately after preparation of this
known series read the absorbance of each at 352 m \j. in the usual
manne r.
Calculations. For convenience, standard conditions are taken
as 760 mm of mercury and 25°C; thus, only slight correction by means
of the well-known perfect gas equation is required to get V, the stand-
ard volume in liters of the air sampled. Ordinarily this correction
may be omitted. Quantities, customarily expressed in terms of ozone,
may be expressed as microliters, defined as V times ppm ozone.
It has been determined empirically that 1 mole of ozone liberates 1
mole of iodine (12) by this procedure.
Plot the corrected absorbances of the standard colors against
the exact calculated normalities of the corresponding diluted iodine
solutions. Beer's Law is followed. Draw the straight line giving the
best fit and determine the normality of iodine solution intercepted at
an absorbance of exactly 1. This value multiplied by 1.224 x 10
gives the standardization factor M, defined as the number of micro-
liters of ozone required by 10 ml of absorbing reagent to give an ab-
sorbance of exactly 1. For 2-cm cells this value is 4. 8.
Results for samples are computed as follows:
ppm oxidant (expressed as O,) corrected absorbance x M/V (1)
If the volume of the air sample V, is a simple multiple of M, calcu-
lations are simplified. Thus, for the M value of 4. 8 previously cited,
if exactly 4. 8 liters of air are sampled through the impinger, the cor-
rected absorbance is also ppm directly. If other volumes of absorbing
reagent are used, V is taken as the volume of air sample per 10 ml
of absorbing reagent.
DISCUSSION OF PROCEDURE
Sampling efficiency. When two impingers are placed in series,
iodine will very rarely be liberated from the solution in the second
absorber. Thus sampling efficiency is very high. Fritted bubblers,
which also appear to have equally high sampling efficiencies, usually
give, however, less iodine for a given amount of ozone and should not,
therefore, be used. This is due to the complex chemistry of ozone in
iodine solutions.
* Standard molar volume (760 mm Hg, 25°C)=24.47 liters. Hence I fj. mole I2 = 24.47(j.l O3,
and 10 ml I N iodine =5 x I03 fl mole I2 =1.224 x I 0 (j.1 O3.
Neutral Buffered-Potassium Iodide Method D-3
-------
Stability of colors. About 90% of the iodine is liberated by ozone
immediately and the remaining 10% appears to be liberated by a single
slow-reacting component (probably HjPOc; produced by the ozone in a
side reaction) with a half-life of about 10 minutes. Thus the color will
gradually increase until about 45 minutes after sampling, after which
fading will begin. Good results are obtained by reading during the
period of 30 to 60 minutes after sampling.
Oxidants other than ozone will also liberate iodine but at a slower
rate. Some estimate of the presence of such materials or of fading due
to reducing substances can be made for each situation by making oc-
casional measurements over an extended period of time. Use of ana-
lytical-grade reagents and of carefully cleaned glassware reduces
losses of iodine and fading processes. Do not expose the reagent to
direct sunlight, since additional iodine may be released.
Comparison with 2% potassium iodide reagent. A similar rea-
gent, containing 2% potassium iodide in the same buffer that has been
adjusted to pH 7. 0 with sodium hydroxide pellets, is in use. Both
reagents should give comparable results. Color development as well
as fading is slower in the 1% reagent, so that a longer time interval
should be available for accurate reading.
Interferences. The negative interferences from reducing gases
such as sulfur dioxide and hydrogen sulfide are very serious (probably
on a mole-to-mole equivalency). The procedure is very sensitive to
reducing dusts, which may be present in the air or on the glassware.
Losses of iodine occur even on clean glass surfaces, and thus the
manipulations should minimize this exposure.
Elimination of the interference of sulfur dioxide, even when it
was present in as high as hundredfold ratio to oxidant, has been ac-
complished recently by incorporating an extra large (140-ml) ab-
sorbing U-tube in the sampling train upstream from the impinger.
The absorbent, which removes sulfur dioxide without loss of oxidant,
is glass fiber paper impregnated with chromium trioxide. (Drop 15 ml
of aqueous solution containing 2. 5 g chromium trioxide and 0. 7 ml con-
centrated sulfuric acid uniformly over 60 in. 2 of paper, and dry in an
oven at 80 to 90°C for 1 hour. Cut the paper into 1/4- x 1/2-in. strips,
each folded once into a V-shape, pack into the U-tube, condition by
drawing air through tube overnight. ) The absorbent has a long life
(at least 1 month). If it becomes visibly wet from sampling humid air,
it must be dried (with dry air) before further use.
REFERENCES
1. Byers, D. H. , Saltzman, B.E., Determination of Ozone in
Air by Neutral and Alkaline Iodide Procedures, J. Am. In-
dus t. Hyg. Assoc. 19:251-7. 1958.
2. Saltzman, B. E. , Gilbert, N., lodometric Microdetermination
of Organic Oxidants and Ozone, Anal. Chern. 31-1914-20
1959.
°-4 SELECTED METHODS
-------
3. California State Department of Public Health, Tentative
Method of Analysis for Total Oxidant Content of the Atmos-
phere, SDPH 1-20 in "Recommended Methods in Air Pollu-
tion Measurements. " 1960.
4. Saltzman, B. E. , Wartburg, A.F., Jr. Absorption Tube for
Removal of Interfering Sulfur Dioxide in Analysis of Atmos-
pheric Oxidant, Anal. Chem. 37: 779. 1965.
Neutral Buffered-Potassium Iodide Method D-5
GPO 820-519-3
-------
Determination of Oxidants (Including Ozone):
Alkaline Potassium Iodide Method*
INTRODUCTION
This method* is intended for the manual determination of oxi-
dants (including ozone) in the range of a few pphm to about 20 ppm.
Ozone, chlorine, hydrogen peroxide, organic peroxides, and various
other oxidants will liberate iodine by this method. The response to
nitrogen dioxide is limited to 10% by the use of sulfamic acid in the pro-
cedure to destroy nitrite. It is customary for convenience to express
the results as ozone. The advantage of this procedure over the neutral
iodide procedures is that a delay is permissible between sampling and
completion of the analysis. Sampling is conducted in midget impingers
containing 1% potassium iodide in 1 N sodium hydroxide. A stable
product is formed that can be stored with little loss for several days.
The analysis is completed in a laboratory by addition of phosphoric -
sulfamic acid reagent, which liberates the iodine. The yellow iodine
color is read in an appropriate instrument. Serious interfering effects
occur from reducing gases and dusts.
REAGENTS
All reagents are made from analytical-grade chemicals. They
are stable for several months in well-stoppered bottles.
Double-distilled water, used for all reagents. Redistill distilled
water in an all-glass still after adding a crystal each of potassium
permanganate and barium hydroxide.
Absorbing reagent. Dissolve 40. 0 g of sodium hydroxide in al-
most a liter of water, then dissolve 10. 0 g of potassium iodide and
make the mixture to 1 liter. Store in a glass bottle with a screw cap
(with inert liner) or rubber stopper (previously boiled for 30 minutes
in alkali and washed). Age for at least 1 day before using.
Acidifying reagent. Five g of sulfamic acid is dissolved in 100
ml of water, then 84 ml of 85% phosphoric acid is added, and the mix-
ture is made to 200 ml.
Standard potassium iodate solution. Dissolve 0. 758 g of potas-
sium iodate in water and dilute to 1 liter. One ml of this stock solu-
tion is equivalent to 400 (j. 1 of ozone. Prepare a. dilute standard
solution just before it is required by pipetting exactly 5 ml of stock
solution into a 50-ml volumetric flask and making to mark with water.
* Prepared by Bernard E. Saltzman, Laboratory of Engineering and Physical Sciences,
Division of Air Pollution, Public Health Service. Approved by the Interbranch Chemical
Advisory Committee, March 1964.
Alkaline Potassium Iodide Method E-l
-------
APPARATUS
Absorber. All-glass midget impingers with a graduation mark
at 10 ml, similar to that shown in Figure 3, are used. (Other
bubblers with nozzle or open-end inlet tubes may be used. Fritted
bubblers tend to give relatively low results. ) Impingers must be
kept scrupulously clean and dust free. All traces of grease should be
removed by treatment with dichromate-concentrated sulfuric acid
solution (cleaning solution) followed by tap and distilled water.
Air-metering device. A glass rotameter capable of measuring a
flow of 1 to 2 liters per minute with an accuracy of iZ-% is recommend-
ed.
Air pump. An appropriate suction pump capable of drawing the
required sample flow for intervals of up to 30 minutes is suitable. It
is desirable to have a trap on the inlet to protect the needle valve and
pump against accidental flooding with absorbing reagent and consequent
corrosion.
Spectrophotometer. A laboratory instrument suitable for mea-
suring the yellow color at 352 m|j. with stoppered tubes or cuvettes
(suitable for ultraviolet use) is recommended.
ANALYTICAL PROCEDURES
Collection of samples. Assemble a train composed of a midget
impinger, rotameter, and pump. Use ground-glass connections up-
stream from the impinger. Butt-to-butt glass connections with slight-
ly greased tygon tubing may also be used for connections without
losses if lengths are kept minimal. Pipet exactly 10 ml of the absorb-
ing solution into the midget impinger and sample at a flow rate of 1
to 2 liters per minute. Note the total volume of the air sample. If
the sample air temperature and pressure deviate greatly from 25°C
and 760 mm Hg, measure and record these values. Sufficient air
should be sampled so that the equivalent of 1 to 1 5 |i 1 of ozone is ab-
sorbed. If appreciable evaporation has occurred, add distilled water
to restore the volume to the 10-ml graduation mark. If the analysis
is to be completed later, transfer the solution, without rinsing, to a
clean, dry, glass-stoppered, 25-ml, graduated cylinder (or a bottle)
for storage. Prolonged storage may cause "freezing" of glass stoppers.
Analysis. Measure the volume of exposed absorbing reagent in
a 25-ml, glass-stoppered, graduated cylinder. (Do not use rinse
water in any transfers. ) Add from a rapid (serological-type), gradu-
ated pipette exactly one-fifth of this volume of the acidifying reagent
and mix thoroughly. Place the stoppered cylinder in a water bath at
room temperature for 5 to 1 0 minutes to dissipate the heat of neutrali-
zation. Transfer a portion of the sample to a cuvette and determine the
absorbance at 352 m|i with a cuvette containing distilled water as the
reference. Do not delay the reading, since reducing impurities some-
times cause rapid fading of the color.
Prepare a reagent blank by adding 2 ml of the acidifying reagent
to 10 ml of unexposed absorbing reagent. Cool and determine the
blank absorbance. This blank absorbance should be determined each
day and should be subtracted from the absorbances of the samples
E-2 SELECTED METHODS
-------
5 mm
INSIDE
CLEARANCE
3 to 5 mm
T
30
25
20
15
10
25 mm
OD
10 mm OD
§ 24/40, CONCENTRIC WITH
- OUTER PIECE AND WITH
NOZZLE
GRADUATIONS AT 5-ml
INTERVALS, ALL THE
WAY AROUND
NOZZLE ID EXACTLY
I mm; PASSES 0.09 TO 0. II
cfm AT 12 in. H2O VACUUM.
PIECES SHOULD BE INTER-
CHANGEABLE, MAINTAINING
NOZZLE CENTERING AND
CLEARANCE TO BOTTOM
INSIDE SURFACE
FIGURE 3. ALL-GLASS MIDGET IMPINGER (THIS IS A COMMERCIALLY
STOCKED ITEM).
Alkaline Potassium Iodide Method
E-3
-------
Samples may be aliquoted either before or after acidification if
very large concentrations of oxidant are expected. In the former case,
dilute the aliquot to 10 ml with unexposed absorbing reagent and pro-
ceed in the usual manner. In the latter case, dilute the aliquot to
volume with reagent blank mixture. Aliquoting after acidification is
not as reliable and should be used only to save a sample when unex-
pectedly large concentrations of oxidant are encountered. The calcu-
lations should include the aliquoting factor.
Standardization. Add the freshly prepared, dilute, standard
iodate solution in graduated amounts of 0. 10 to 0. 45 ml (measured
accurately in a graduated pipet or small buret) to a series of 25-ml,
glass-stoppered, graduated cylinders. Add sufficient alkaline potas-
sium iodide solution to make the total volume of each exactly 10 ml.
Acidify and determine the absorbance of each standard as with the
samples.
Calculations. For convenience, standard conditions are taken
as 760 mm of mercury and 25°C; thus, usually only slight correction
by means of the well-known perfect gas equation is required to get V,
defined as the standard volume of the air sampled in liters. Ordinarily
this correction may be omitted. Quantities, customarily expressed
in terms of ozone, may be expressed as microliters, defined as V
times ppm ozone. It has been determined empirically that 1 mole of
ozone liberates 0. 65 mole of iodine (!;>) by this procedure. The
strength of the stock standard potassium iodate solution is computed
on the basis of Ij =0= 1/3 KIC>3, and the following:
Standard molar volume (25°C, 760mm) 24.47 liters;
molecular weight K-IO3 214. 02; 1 ml stock solution 400 \i\
0.758x10-3gKI03
Plot the absorbances of the standards (corrected for the blank)
against milliliters of dilute standard iodate solution. Beer's Law is
followed. Draw the straight line giving the best fit and determine the
value in milliliters of the diluted potassium iodate solution intercepted
at an absorbance at exactly 1. This value multiplied by 40 gives the
standardization factor M, defined as the number of microliters of
ozone required by 1 0 ml of absorbing reagent to give a final absorb-
ance of 1. For 2-cm cells this value is 9. 13. Then:
ppm oxidant (expressed as 03) corrected absorbance x— (1)
If the volume of the air sample, V, is a simple multiple of M, calcu-
lations are simplified. Thus, for the M value of 9. 13 previously cited,
if exactly 9. 13 liters of air is sampled through the impinger, the cor-
rected absorbance is also ppm directly. If other volumes of absorbing
reagent are used, V is taken as the volume of air sample per 10 ml
of absorbing reagent.
E-4 SELECTED METHODS
-------
DISCUSSION OF PROCEDURE
Sampling efficiency. When two impingers are placed in series,
iodine will very rarely be liberated from the solution in the second
absorber. Thus, the sampling efficiency is very high. Fritted bub-
blers, which also appear to have equally high sampling efficiences,
usually give, however, less iodine for a given amount of ozone and should
not, therefore, be used. (This is due to the complex chemistry of
ozone in alkaline iodide solution. It appears that hypoiodite is the pri-
mary product, but that some is lost through side reactions, with re-
sulting variation in the stoichiometry. Potassium iodate is a conven-
ient chemical to use for standardization, although iodate is probably not
produced by absorption of ozone. )
Stability of exposed absorbing reagent. Studies have indicated
that most of the losses in exposed reagent occur in the first day. The
reagent may then be stored for as long as a week or more with little
further change. Use of analytical-grade reagents and of carefully
cleaned glassware reduces losses.
Acidification step. Certain irreversible losses of microquanti-
ties of iodine occur during the acidification of alkaline iodide solution.
This is probably the explanation for the relationship of 0. 65 mole of
iodine liberated for each mole of ozone absorbed. Very slow acidifi-
cation will yield less iodine. The most reproducible procedure is to
add the acid rapidly with vigorous stirring.
Interferences. The negative interferences from reducing gases
such as sulfur dioxide and hydrogen sulfide are very serious (prob-
ably on a mole-to-mole equivalency). The procedure is very sensitive
to reducing dusts that may be p.resent in the air or on the glassware.
Losses of iodine also occur even on clean glass surfaces, and thus
the manipulations should minimize this exposure.
Elimination of the interference of sulfur dioxide, even when it
was present in as high as hundredfold ratio to oxidant, has been ac-
complished recently by incorporating an extra large (140-ml) ab-
sorbing U-tube in the sampling train upstream from the impinger.
The absorbent, which removes sulfur dioxide without loss of oxidant,
is glass fiber paper impregnated with chromium trioxide. (Drop 15 ml
of aqueous solution containing 2. 5 g chromium trioxide and 0. 7 ml
concentrated sulfuric acid uniformly over 60 in. of paper, and dry in
an oven at 80 to 90°C for 1 hour. Cut the paper into 1/4- x 1/2-in.
strips, each folded once into a. V-shape, pack into the U-tube, and
condition by drawing air through tube overnight. ) The absorbent has
a long life (at least 1 month). If it becomes visibly wet from sampling
humid air, it must be dried (with dry air) before further use.
Alkaline Potassium Iodide Method E-5
-------
REFERENCES
1. Byers, D. H. , Saltzman, B. E. , Determination of Ozone in
Air by Neutral and Alkaline Iodide Procedures, J. Am.
Indust. Hyg. Assoc. 19:351-7. 1958.
2. Saltzman, B. E. , Gilbert, N. , lodometric Microdetermina-
tion of Organic Oxidants and Ozone, Anal. Chem. 31:1914-
20. 1959.
3. Saltzman, B. E. , Wartburg, A. F. , Jr. Absorption Tube for
Removal of Interfering Sulfur Dioxide in Analysis of Atmos-
pheric Oxidant, Anal. Chem. 37:779. 1965.
E'6 SELECTED METHODS
-------
Determination of Aliphatic Aldehydes: 3-Methvl-2-benzothiazolone
Hydrazone Hydrochloride (MBTH) Method*
INTRODUCTION
The MBTH method is applicable to the determination of total
water-soluble aliphatic aldehydes (measured as formaldehyde) in
ambient air. The results of limited field testing show that as little
as 2 ppb aldehydes in air can be determined when air is sam-
pled at a rate of 0. 5 liter per minute over a Z4-hour period.
Aliphatic aldehydes react with MBTH in the presence of ferric
chloride to form a blue cationic dye in acidic media. The aldehydes
in ambient air are collected in a 0. 05 percent aqueous MBTH solution.
The resulting azine is then oxidized by a ferric chloride-sulfamic
acid solution to form the blue dye, which can be measured at 628 mjo..
REAGENTS
The various reagents are prepared on a weight-volume basis
(i. B. , grams per 100 ml of solution).
Collecting reagent. The collecting reagent is a 0. 05 % aqueous
3-methyl-2-benzothiazolone hydrazone hydrochloride (MBTH) solution.
This colorless solution is filtered by gravity if slightly turbid and is
stable for at least 1 week, after which it becomes pale yellow. Stabil-
ity may be increased by storing in a dark bottle in the cold. MBTH
can be either synthesized^ or purchased (Aldrich or Eastman).
Oxidizing reagent. An aqueous solution containing 1.6% sul-
famic acid and 1.0% ferric chloride is used. Both reagents should
be ACS reagent grade.
Dimedon. Dimedon (5, 5-dimethylcyclohexanedione-1, 3) is
used for the standardization of formaldehyde. Prepare 500 ml of an
aqueous solution containing 1.07 g of dimedon.
Formaldehyde solution. Accurately dilute 2.7 ml of commer-
cially available 37 to 39 % aqueous ACS reagent grade formaldehyde
to a liter with distilled water. This solution will contain approximate-
ly 1 g of formaldehyde oer liter. Standardize this solution by the
following procedure.
Place 50 ml of the dimedon reagent in each of three
clean, dry, glass-stoppered Erlenmeyer flasks and add
to each 10 ml of the formaldehyde stock solution. Shake
the mixtures, let stand overnight (over a weekend if
possible), and filter through previously weighed sintered-
glass (or other filtering) crucibles. Dry the precipitates
^Prepared by Thomas R. Mauser, Field Studies Branch, Division of Air Pollution,
Public Health Service. Approved by the Inter-branch Chemical Advisory Committee,
May 1964.
MBTH Method F-l
-------
in vacuum over phosphorus pentoxide to constant weight.
The gravimetric factor for converting the weight of pre-
cipitate to weight of formaldehyde is 0. 1027. The grams
of CH2O per ml of 37 to 39% solution equals, therefore,
weight of precipitate x 0. 1027 x 100
2. 7
EQUIPMENT
Spectrophotometer or colorimeter. Any instrument capable of
measuring absorbance between 600 and 700 m|j. is acceptable for quan-
titative analysis.
Absorber. Any absorber containing a fritted bubbler of 40- to
80-(J. porosity (Corning coarse frit) and having a capacity of at least
75 ml is acceptable. The absorber used in developing the procedure
was a 100-ml polypropylene test tube.
Air-metering and flow control devices. Any devices capable of
measuring and regulating airflows with an accuracy of t 2 percent are
acceptable.
Air pump. Any pump capable of pulling air through the sampling
assembly at a rate of 0. 5 liter per minute for 24 hours is acceptable.
ANALYTICAL PROCEDURE
Sampling and analysis. Assemble a sampling train in the follow-
ing order: Absorber, trap to protect the flow device, flow-metering
device, flow control device, and air pump. (The flow control and flow-
metering devices may be one piece of equipment such as a precalibrated
limiting orifice. ) After 35 ml of the collecting reagent is added in the
absorber, air is drawn through the system at a rate of approximately
0. 5 liter per minute for 24 hours. When sampling is completed, adjust
the volume of the collecting reagent back to the original 35 ml with dis-
tilled water and allow to stand for 1 hour. This insures complete
reaction of the aliphatic aldehydes with the MBTH. Pipette 1 0 ml of
the sample into a test tube, add 2 ml of the oxidizing reagent, and mix
thoroughly. After it has stood for 12 minutes, the absorbance is mea-
sured at 628 mji against an appropriate blank prepared from nonaerated
laboratory reagents. The amount of aliphatic aldehydes (reported as
formaldehyde) per milliliter test solution is readily ascertained from
the absorbance-concentration curve. Since the volume of air sampled
had been measured, the concentration of aldehydes in the air can be
readily calculated from the following equation:
ppm (total aldehyde as CH?O) = 0814 ^L
FT (1)
where V total volume of collecting reagent 35 ml
C tig aldehyde found (as CH2O) per ml collecting reagent
F airflow-sampling rate in liters per minute
T total sampling time in minutes
0. 814 total (il that one jig CH2O will occupy at 25°C and
760 mm
F-2 SELECTED METHODS
-------
Standardization. For spectrophotometers having an absorbance
range of 0. 0 to 1. 0, five test solutions ranging from 0. 1 to 0. 7 (ig of
formaldehyde per ml of 0. 05% MBTH are prepared. After it has stood
for 1 hour, 10 ml of each test solution is placed in a test tube, and
Z ml of the oxidizing reagent added. After mixing, allow the tube to
stand for at least 1Z minutes for complete color development. The
absorbance is then determined on the spectrophotometer at 6Z8 m(j.
against an appropriate blank; the blank is light yellow. Plot ab-
sorbance versus ^g of formaldehyde per ml of test solution to ob-
tain the calibration curve.
Discussion. The average collection efficiency of formaldehyde
in air has been determined to be 84% when air was sampled at a rate
of 0. 5 liter per minute over a Z4-hour period in 35 ml of collecting
reagent. Collection efficiency data are not available for higher or
lower sampling rates, longer or shorter sampling periods, and larger
or smaller volumes of collecting reagent. The collection efficiency
as well as the sensitivity of the method may be increased or decreased
depending upon the conditions selected for sampling. When sampling
conditions other than those described in the procedure are employed,
the collection efficiency for the new conditions should be determined.
The blank solution for colorimetric analysis may be prepared
from nonaerated laboratory reagents. During the initial determina-
tion of collection efficiency, six bubblers were placed in series. In
no case was any formaldehyde detected past the first bubbler, and no
significant differences were observed in blanks prepared from the
contents of the second bubbler or from nonaerated laboratory reagents.
During repeated determinations, the contents of the first bubbler
showed no difference in formaldehyde content when compared with
blanks prepared from either the contents of the second bubbler or
from laboratory reagents. Consequently, it is unnecessary to have a
second bubbler connected in series in the sampling train.
The molar absorptivity observed for formaldehyde at the wave-
length maxima of 6Z8 mu is 50, 000. The Beer's Law study exhibited
a linear relationship for formaldehyde concentrations of 0. 0 to 1. 72 jig
per ml of test solution over an absorbance range of 0. 0 to Z. 35 when
1. 0-cm cells were employed. The study also demonstrated excellent
reproducibility in absorbance when duplicate samples were analyzed,
and little, if any, deviation from the standard curve was observed
over the entire concentration range reported above.
In the procedure, the addition of the oxidizing reagent to 0. 05%
MBTH test solutions containing formaldehyde gives optimum color
conditions when the concentrations of ferric chloride and sulfamic
acid in the oxidizing reagent are 1. 0 and 1. 6% respectively. Full
color development is observed after 10 minutes oxidation time and
the cplor is stable for at least an additional hour. Increasing the con-
centration of the sulfamic acid in the oxidizing reagent lowers the ab-
sorbance and lengthens the oxidation period; with a lesser concentra-
tion, a persistent turbidity is always observed. Increasing the ferric
chloride content in the oxidizing reagent produces a more colored
blank whereas a decrease results in decreased absorbance.
MBTH Method F-3
-------
When the concentration of the MBTH is increased to more than
0. 05% the solutions become turbid. Smaller concentrations of MBTH
result in a loss of color intensity. A 15% decrease in absorbance is
observed when the concentration of the MBTH is reduced from 0. 05 to
0. 02%, even though the solutions are free of turbidity. The concentra-
tion of the MBTH must be in excess of that of the aliphatic aldehydes
collected. If 60. 4 jig of formaldehyde is absorbed in the 35 ml of
collecting solution, an optical density of 2. 35 is obtained. This amount
of formaldehyde requires 870 (ig of MBTH for complete reaction.
There is 17, 500 |j.g of MBTH in 35 ml of collecting solution, repre-
senting a 20-fold excess. If formaldehyde becomes present in excess,
only a negligible concentration of MBTH is available to react with the
azine, and the final color intensity is very weak. This point may
become very important in the analysis of an air sample.
The time study of the reaction of microgram quantities of form-
aldehyde with 0. 05% MBTH shows that the reaction is complete in
approximately 45 minutes; therefore, a reaction time of 1 hour is
selected for this procedure. Formaldehyde is fairly stable in 0.05%
MBTH since only approximately 5% of the formaldehyde is lost after
standing in the MBTH for 13 days. The samples are, therefore,
stable enough for later analysis.
INTERFERENCES
The following classes of compounds react with MBTH to produce
colored products. These are aromatic amines, imino heterocyclics,
carbazoles, azo dyes, stilbenes, Schiff bases, the aliphatic aldehyde
2, 4-dinitrophenylhydrazones, and compounds containing the p-hydroxy
styryl group. Most of these compounds are not gaseous or water
soluble and consequently should not interfere with the analysis of
water-soluble aliphatic aldehydes in the atmosphere.
REFERENCES
1. Sawicki, E., Hauser, T.R. , Stanley, T.W., and Elbert, W. ,
The 3-Methyl-3-benzothiazolone Hydrazone Test, Anal.
Chem. 33:93. 1961.
2. Hauser, T. R. , and Cummins, R. L. , Increasing the Sensitivity
of 3-Methyl-2-benzothiazolone Hydrazone Test for Analysis
of Aliphatic Aldehydes in Air, Anal. Chem. 36:679. 1964.
3. Yoe, J. H. , and Reid, L. C., Determination of Formaldehyde
with 5, 5-Dimethyl- 1, 3-cyclohexanedione , Ind. Eng. Chem.,
Anal. Ed. 13:238. 1941.
F-4 SELECTED METHODS
-------
Determination of Acrolein: 4-Hexylresorcinol Method*
INTRODUCTION
This method is designed for the determination of acrolein in
the atmosphere over the range of about 20 ppb to at least 10 ppm.
A blue-purple color is formed by the reaction of acrolein with 4-hexyl-
resorcinol in the presence of trichloracetic acid and mercuric chloride.
Owing to its greater sensitivity and specificity, its use is recommend-
ed over that of other available methods. This procedure has been
used satisfactorily in the laboratory but has been field tested to only
a limited extent. 2
REAGENTS
All reagents are analytical grade. Precautions should be taken
in handling most of these solutions since they are corrosive to the
skin or poisonous.
Ethanol (96%).
Trichloracetic acid solution, saturated. It is well to prepare
large quantities of this solution at one time to be sure of uniformity.
It is recommended that the entire contents of the reagent bottle be
dissolved at one time by adding 10 ml of water for each 100 g of the
solid acid and heating on a water bath. (The resulting volume of
solution is about 70 ml per 100 g of solid acid. ) Every new batch of
the solution should be standardized with acrolein. CAUTION: Both
the solid acid and solution are corrosive to the skin. Breathing of
the fumes evolved during preparation of the solution should be avoided.
Mercuric chloride solution. Three g of HgC^ is dissolved in
100 ml of ethanol.
4-Hexylresorcinol solution. Five g of this material (mp 68 to
70°C) is dissolved in 5. 5 ml of 96% ethanol. (This yields about 10 ml
of solution. )
Mixed reagent. Mix, in order, reagents in the following propor-
tions: 5 ml ethanol, 0. 1 ml of 4-hexylresorcinol solution, 0. 2 ml
mercuric chloride solution, and 5 ml saturated trichloracetic acid
solution. The mixed reagent may be stored for a day at room tem-
perature. Prepare the needed quantity by selecting an appropriate
multiple of these amounts. Protect from direct sunlight.
Acrolein, purified. Freshly prepare a small quantity (less than
1 ml is sufficient) by distilling 10 ml of the purest grade of acrolein
commercially available. (The latter material should be stored in a
refrigerator to retard polymerization. ) The distillation should be
done in a hood because the vapors are irritating to the eyes. Reject
the first 2 ml of distillate.
^Prepared by Israel R. Cohen and Bernard E. Saltzman, Laboratory of Engineering and
Physical Sciences, Division of Air Pollution, Public Healfh Service. Approved by Interbranch
Chemical Advisory Committee. May 1964.
4-Hexylresorcinol Method G-1
-------
Acrolein, standard solution. Weigh 0. 1 ml (approximately 84
mg) of freshly prepared, purified acrolein into a 100-ml volumetric
flask, and make to mark with ethanol. Dilute 1 ml of this solution to
100 ml with ethanol to produce the dilute working standard solution
(1 ml 8.4 ug acrolein). Both solutions may.be kept for as long as
a month if properly refrigerated.
NOTE; THIS IS A
STOCK COMMERCIAL
ITEM DIMENSIONS
SIVEN ARE ILLUSTRATIVE
ONLY.
J
c
r
E
)
5 1
E
E
cc
cc
4
I
,
+-
-------
Water bath. Any type of container in which the temperature can
be maintained at 58 to 60°C is acceptable.
Air pump. A suction pump capable of drawing the gas to be sam-
pled through the assembly at the rate of up to 2 liters per minute for
intervals of up to 1 hour is acceptable. There should be a trap at the
inlet to protect the pump from the corrosive reagent.
Air-metering device. A glass rotameter or other device capable
of measuring flows of up to 2 liters per minute with an accuracy of ± 2%
is recommended.
Spectrophotometer or colorimeter. This device should be capable
of measuring the developed color at 605 mji. The absorption band is
rather narrow, and thus a lower absorptivity may be expected in a
broad-band instrument.
ANALYTICAL PROCEDURE
Direct procedure (preferred). The gas is drawn for 30 minutes
at 2 liters per minute or for 60 minutes at 1 liter per minute through a
train of two bubblers, each containing exactly 10 ml of mixed reagent.
An extra bubbler containing water may be added as a trap to protect
the pump. Note the total volume of the air sample. If the sample air
temperature and pressure deviate greatly from 25°C and 760 mm Hg,
measure and record these values. If appreciable evaporation has
occurred, add ethanol to restore the volume to its original graduation
mark. (Excessive evaporation or possible decomposition may occur
if sampling is conducted for longer than 1 hour, or is done of more than
60 liters of air. This volume will suffice to determine as little as 20
ppb acrolein. )
The sample solutions are then immersed in the 60°C bath for
15 minutes to develop the colors. The test tubes are cooled in running
water immediately upon removal from the bath, and the absorbances
are read at 605 m|ji about 15 minutes later. This time may be pro-
longed for up to 2 hours with no appreciable loss in accuracy. Alter-
natively, if no bath is available, the sample solutions may be stored
for 2 hours at room temperature for color development. The absorb-
ances are usually determined in a 1-cm cell. For very small acrolein
concentrations it may be convenient to use a cell with a longer path
length.
A portion of mixed reagent is taken as a blank and treated in the
same manner as the sample solutions.
Alternative procedure for delayed determination. When it is in-
convenient to read the colors immediately after sampling, 96% ethanol
instead of mixed reagent may be used as a collecting reagent. The
bubblers, each containing 10 ml of ethanol, are cooled in ice water
during the sampling period; the sampling procedure is otherwise the
same as above. Do not sample more than 10 liters of air. The con-
centration of acrolein sampled should be at least 0. 1 ppm (for which
5-cm cells are needed for accurate reading of the developed color).
The collected sample may be stored for as long as a week at ice tem-
perature.
4-Hexylresorcinol Method G-3
-------
The determination is completed by mixing exactly 5 ml of the
ethanolic sample solution (or a smaller portion diluted with ethanol
to 5 ml) with the other ingredients in the same proportions as in the
mixed reagent. The colors are then developed and read as described
above in the direct procedure. The absorptivity obtained is 70% of
that by the direct method.
Standardization. Prepare a series of test tubes containing 0,
1, 2, 3, and 4 ml of dilute standard acrolein solution (8. 4 |ji g/ml),
respectively; add to each sufficient ethanol to make exactly 5 ml. To
each tube, add, inorder, exactly 0. 1 ml 4-hexylresorcinol solution,
0. 2 ml mercuric chloride solution, and 5 ml t richloracetic acid solu-
tion. Mix, develop, and read the colors as described in the direct
procedure. Plot the absorbances against the micrograms of acrolein
and determine the slope of the line obtained.
A more accurate, though less convenient, standardization of the
direct procedure is obtained by sampling acrolein-air mixtures from
a mylar bag (about 3 ft ) directly into the mixed reagent. These mix-
tures are prepared by injecting measured volumes of the strong acro-
lein standard solution with a syringe (conveniently of 250- (j.1 capacity)
through a serum bottle cap on a T connection into the airstream as the
bag is filled. Total air volume is computed from the measured flow
rate and filling time.
Calculations.
ppm acrolein = ^-y^ (1)
A absorbance of the reacted sample solution
a absorbance of standards per fig of acrolein
(slope of the standard plot)
2. 29 weight in jig of 1 ul of gaseous acrolein at
25°C, 760 mm Hg
V liters of air sample, corrected to 25°C, 760 mm
Hg by means of the perfect gas equation (this
correction may ordinarily be omitted)
b aliquoting and correction factor. There are
three mathematical cases:
The factor is 1 . 00 for the direct procedure
standardized with gas mixture.
For the direct procedure standardized with
liquids, allowance must be made for the fact
that the standardization yields only 70% of the
absorptivity of gas samples, and final volumes
are 10. 3 ml rather than 10. 0 ml. The factor
is, therefore, 0. 68:
0-70.1M O.b8
G-4 SELECTED METHODS
-------
For the alternative procedure, a half aliquot
is taken in the procedure as described. More-
over, it is desirable to correct for incomplete
absorption of sample. If the estimated collec-
tion efficiency of the total train is e, the factor
is 2.0/e.
The factors b/a x 2. 29 are conveniently combined into a single
standardization constant.
Add the ppm values computed for the contents of each bubbler in
the sampling train to get the total present in the sample.
DISCUSSION OF PROCEDURE
Absorption efficiency. The collection efficiency, when mixed
reagent is used for sampling, is 70 to 80% in the first bubbler and 95%
in the first two bubblers, even with a 40- to 50-liter sample. (It
appears likely that use of an absorber with a finer frit, similar to
that shown in Figure 1 or Figure 5, would raise these efficiences.
The collection efficiency is lower when ethanol is used as the
absorbing reagent, since the volatile acrolein is not fixed by chemical
reaction but is merely in solution. Satisfactory collection efficiency
(80 to 90%) can be obtained with two bubblers in series at ice tempera-
ture if sample volumes are limited to less than 10 liters. Use of a
dry ice-acetone bath permits sampling of greater air volumes at
smaller concentrations.
Applicability of Beer's Law. The absorbances at 605 mji are
linear for at least 1 to 30 p.g of acrolein in the 10-ml portions of mixed
reagent. The absorptivities of the colored product for the direct and
alternative methods are 0. 50 and 0. 35 (J.g~ ml cm" respectively.
With the alternative method, for example, using a cell with a 1-cm path
length, the standard color containing 1 ml of dilute standard solution
(which thus contains 8. 4 |j.g of acrolein in 10. 3 ml total volume) should
have an absorbance of 0. 35 x 8. 4/ 10. 3 0. 29.
Interferences. There is no interference from ordinary quantities
of sulfur dioxide, nitrogen dioxide, ozone, and most organic air pollu-
tants. A'Slight interference occurs from dienes: 1.5% for 1,3-buta-
diene, and 2% for 1, 3-pentadiene. The red color produced by some
other aldehydes and undetermined materials does not interfere in the
spectrophotometric measurement.
REFERENCES
1. Cohen, I. R. , and Altshuller, A. P, , A New Spectrophotometric
Method for the Determination of Acrolein in Combustion
Gases and in the Atmosphere, Anal. Chem. 33:726-33. 1961.
2. Altshuller, A. P. , and McPherson, S. P. , Spectrophotometric
Analysis of Aldehydes in the Los Angeles Atmosphere, J. Air
Poll. Control Assoc. 13:109-11. 1963.
4-Hexylresorcino'l Method G-5
-------
92 mm
FLAT BOTTOM
L 28-mm _J
I OD |
? 24/40, CONCENTRIC
WITH OUTER PIECE
SHAPE BEND SO THAT
INNER PIECE PASSES
FREELY THROUGH OUTER
JOINT; UPPER AND
LOWER TUBE SECTIONS
ARE PARALLEL TO OUTER
PIECE.
9-mm - DIAMETER FRITTED
DISC. POROSITY MUST BE
AS SPECIFIED. (FOR HIGH
ABSORPTION EFFICIENCY
SPECIFY 60 TO 70 V- MAXIMUM
PORE DIAMETER.) PIECES
SHOULD BE INTERCHANGEABLE,
MAINTAINING CLEARANCE
TO BOTTOM INSIDE SURFACE
AT 2 TO 5 mm.
FIGURE 5. ALL-GLASS MIDGET BUBBLER WITH FRITTED-DISC INLET.
G-6
SELECTED METHODS
GPO 82O—519—4
-------
Determination of Formaldehyde: Chromotropic Acid Method*
INTRODUCTION
Formaldehyde in the ambient air can be determined by using the
chromotropic acid method in the concentration range of about 0. 01 to
at least 200 ppm. To measure 0. 01 ppm of formaldehyde it is neces-
sary to sample about 60 liters of air. A purple monocationic chromo-
gen is formed when formaldehyde reacts with a chromotropic acid-
sulfuric acid solution. Compounds such as formic acid, dextrose,
methanol, and others, which decompose under the test conditions to
yield formaldehyde, will also be measured by this method. It has
been used extensively to measure formaldehyde in synthetic atmos-
pheres and has been used satisfactorily to measure formaldehyde in
city atmospheres. '
REAGENTS
Chromotropic acid, 4, 5-dihydroxy-2, 7-naphthalenedisulfonic
acid. The chromotropic acid presently commercially available is
practical grade; be certain, therefore, to recheck the calibration
curve with each new supply.
Sampling solution, 0. 1% chromotropic acid in concentrated
sulfuric acid. Dissolve 1.0 g of chromotropic acid in concentrated
sulfuric acid and dilute to 1 liter. (DANGER: keep off skin and eyes. )
The solution is stable for at least 1 month when stored in bottles pro-
tected from light.
Iodine, 0. 1 normal (approximate). Dissolve 25 g of potassium
iodide in about 25 ml of water, add 12.7 g of iodine and dilute to 1 liter.
Iodine, 0. 01 normal. Take a 100-ml portion of the 0. 1 normal
iodine solution and dilute to 1 liter. Standardize against sodium thio-
sulfate or arsenious oxide.
Starch solution, 1%. Make a paste of 1 g of soluble starch and
2 ml of water, and slowly add the paste to 100 ml of boiling water.
Cool and store in a stoppered bottle.
Buffer solution. Dissolve 80 g of anhydrous sodium carbonate
in about 500 ml of water. Add 20 ml of glacial acetic acid and dilute
to 1 liter. The pH is adjusted to 9- 6 (t 0. 1) by using acetic acid or
sodium carbonate.
Sodium bisulfite, 1%. Dissolve 1 g of NaHSOj in 100 ml of water.
Stock formaldehyde solution. Prepare a solution containing ap-
proximately 1 g of formaldehyde per liter of solution by pipetting 3 ml
of 37 to 39% reagent grade formaldehyde into a 1-liter volumetric
flask and diluting to the mark with distilled water. Standardize this
stock solution as described below in the standardization section.
'•'Prepared by Stanley IT. Sleva, Air Pollution Training, Training Program, Public Health
Service. Approved by Interbranch Chemical Advisory Committee. July 1964.
Chromotropic Acid Method H-l
-------
Dilute standard formaldehyde solution. One hundred ml of this
stock formaldehyde solution is diluted to 1 liter with distilled water
just before it is needed for preparation of the calibration curve. The
formaldehyde concentration of this diluted solution is about 100 g/ml.
APPARATUS
Samplers. An all-glass absorber, similar in design to that
shown in Figure 1, with nozzle or fritted-tube inlet is recommended.
If a fritted tube is used, a frit with maximum pore diameter of about
175 (J., equivalent to Corning EC or Ace Glass A, is recommended.
Air pump. A pump capable of pulling at least 2 liters of air per
minute for 60 minutes through the sampling train is required.
Air-metering and flow control devices. Devices capable of
measuring and controlling airflows with an accuracy of t 2% are
needed. The flow meter calibration should provide for temperature
and pressure corrections.
Thermometer (or other temperature-measuring device. ) This
device should have an accuracy of 1 2°C.
Mecury manometer (or other vacuum-measuring device. ) This
device should have an accuracy of - 5 mm Hg.
Spectrophotometer or colorimeter. This device should be cap-
able of measuring color intensity at 580 mp..
ANALYTICAL PROCEDURE
Assemble the sampling train in the following order: Bubbler,
manometer, flow-metering device, trap to protect pump, flow control
device, and pump. Measure 10 ml of sampling solution into each
bubbler. Draw the air to be sampled through the sampling train at a
rate of up to 2 liters per minute. After sampling, transfer resulting
solution to a pyrex test tube.
Analysis. Heat is necessary to obtain full color development.
This may be accomplished by actually heating the sample solutions in
a 100°C bath for 15 minutes or by the heat of reaction resulting from
the addition of 1 ml of water to each 10 ml of sample solution. The
color development procedure decided upon should also be used in pre-
paring the standard calibration curve. After full color development,
cool the sample solutions to about 25°C, transfer to proper cells, and
read the absorbance against a blank at 580 mp.. The blank solution
is 10 ml of 0. 1% chromotropic acid solution, treated in the same
manner as the air-sampled solution.
STANDARDIZATION
Standardization of stock formaldehyde solution. Pipet 1 ml of
stock formaldehyde solution into one flask and 1 ml of water into an-
other flask. Add 25 ml of 1% sodium bisulfite and 1 ml of 1% starch
solution into each flask. Titrate these solutions with 0. 1 normal
iodine to a dark blue color. Destroy the excess iodine by adding a
few drops of 0. 05 normal sodium thiosulfate, then return to a faint
blue color by carefully adding 0. 01 normal iodine.
H-2 SELECTED METHODS
-------
Chill the flasks in an ice bath and add 25 ml of chilled sodium
carbonate buffer to each flask. Place the flasks in an ice bath for an
additional 10 minutes and then titrate the liberated sulfite to the faint
blue color with 0. 01 normal iodine. The volume of 0. 01 normal iodine
solution used in the blank titration is subtracted from the sample ti-
tration. Since 1 ml of 0. 01 normal iodine solution is equivalent to
0. 15 mg of formaldehyde, the concentration of the standard formalde-
hyde solution in (ig per ml can be determined by the equation:
Hg of formaldehyde /ml V xN xl.5x!04 (1)
V ml of 0. 01 normal iodine solution used to titrate the
liberated sulfite corrected for blank titration
N exact normality of the 0.01 normal iodine solution.
h
Preparation of calibration curve. Transfer separately exactly
ZO, 15, 10, 5, and Z. 5 ml of the dilute standard formaldehyde solution
to five 100-ml volumetric flasks and dilute each to the mark with dis-
tilled water. These five test solutions should contain approximately
ZO, 15, 10, 5, and Z. 5 |j.g, respectively, of formaldehyde per ml
of test solution. Pipet 1 ml of each test solution into separate 10-ml
volumetric flasks. Add to each volumetric flask about 7 ml of 0. 1%
chromotropic acid solution (CAUTION: heat of reaction) and cool to
room temperature; then dilute to the mark with additional 0. 1%
chromotropic acid solution. The heat of reaction resulting from the
addition of the chromotropic acid to 1 ml of aqueous formaldehyde
solution is usually sufficient to develop the purple color fully. The
additional treatment of transferring the contents of the volumetric
flasks to pyrex test tubes and then heating at 100°C for 15 minutes
will guarantee full color development. Allow the solutions to cool
to about Z5°C and then measure the absorbance of each test solution
against a. blank at 580 m\i . The blank solution consists of 1 ml of
distilled water treated in the same manner as the test solution. The
formaldehyde concentration in the final color-developed solution is
approximately Z, 1.5, 1, 0. 5, and 0. Z5 ^g/ml. Prepare a calibra-
tion curve by plotting absorbance versus the formaldehyde concentra-
tion in fig/ml of the final color-developed solution.
Calculations. Correct the volume of air sampled to the volume
at standard conditions of Z5°C and 760 mm Hg:
v v x - x
VF 760 (t + 273) U'
Vs volume of air in liters at standard conditions
V volume of air in liters as measured at sampling condi-
tions
P barometric pressure in mm of mercury
Pm suction at meter in mm of mercury
t temperature of the sampled air, °C
Chromotropic Acid Method H-3
-------
The concentration of formaldehyde in the sampled atmosphere
may be calculated by using the following equations:
. .. C x B , ,
ppm (vol) 1 Z3 y I')
., , , , 3 C x B x 1000
fig of formaldenyde/m — (j;
vs
Where
m is cubic meters of air
C is the concentration of formaldehyde in (ig/ml of the
final color-developed solution obtained from calibra-
tion curve
B is the total ml of sampling solution
V is the volume of sampled air in liters at standard condi-
tions of 25°C and 760 mm Hg
1. 23 is the vapor density of formaldehyde in fig/ (J.1 calculated
at 25°C and 760 mm Hg
DISCUSSION OF PROCEDURE
Sampling efficiency. The use of sampling collectors with fritted
stems and flow rates up to 1 liter per minute give collection efficiencies
of at least 95% with a single sampler.
Stability of colored reaction product and sampling solution. An
increase in absorbance of the reaction product of about 3% is obtained
after it has stood for 1 day, and about 10%, after 8 days.
The chromotropic acid sampling solution can be kept for at
least 2 months if the solution is kept in bottles protected from light.
It is important to protect the sampling solution from sunlight during
the actual sampling period. On a bright day, the solution tends to
become straw or light tan in color if unprotected. Wrapping the sam-
pling apparatus with aluminum foil is a convenient method of eliminat-
ing this problem.
Interferences. The chromotropic acid procedure has very little
interference from other aldehydes. Saturated aldehydes give less than
0. 01% positive interference, and the unsaturated aldehyde acrolein
results in a few percent positive interference. Ethanol and higher
molecular weight alcohols and olefins in mixtures with formaldehyde
are negative interferences, 1 but concentrations of alcohols in air are
usually much smaller than formaldehyde concentrations, which creates
no grave problems.
Phenols result in a 10 to 20% negative interference when present
at an 8 to 1 excess over formaldehyde. They are, however, ordinarily
present in the atmosphere at lesser concentrations than formaldehyde,
which create.s no significant problem.
Ethylene and propylene in a 10 to 1 excess over formaldehyde
resulted in a 5 to 10 % negative interference, and 2-methyl-l, 3-
butadiene in a 15 to 1 excess over formaldehyde showed a 15% negative
interference. Aromatic hydrocarbons also constitute a negative inter-
ference.
H-4 SELECTED METHODS
-------
Interferences of olefins and aromatic hydrocarbons can be sub-
stantially reduced by using an aqueous sodium bisulfite solution as a
collecting medium in place of the chromotropic sulfuric acid sampling
solution and making minor modifications in the procedure. This
aqueous solution has a lower collection efficiency for these interfering
substances.
REFERENCES
1. Altshuller, A. P. , Miller, D. L. , Sleva, S. F. , Determination
of Formaldehyde in Gas Mixtures by the Chromotropic Acid
Method, Anal. Chem. 33'621. 1961.
2. Altshuller, A. P. , and McPherson, S. P. , Spectrophotometric
Analysis of Aldehydes in the Los Angeles Atmosphere, J. Air
Poll. Control Assoc. 13:109. 1963.
3. Altshuller, A. P. , et al. , Analysis of Aliphatic Aldehydes
in Source Effluents and in the Atmosphere. Anal. Chim.
Acta. 25:101. 1961.
Chromotropic Acid Method H-5
-------
Determination of Sulfate in Atmospheric Suspended Participates:
Turhidimetric Barium Sulfate Method *
INTRODUCTION
Suspended particulate matter is collected over a 24-hour period
on an 8- by 10-inch glass fiber filter by using a high-volume sampler. 1
A water extract of the sample is treated with barium chloride to form
barium sulfate. The turbidity caused by the barium sulfate is a mea-
sure of the sulfate content. Aliquoting is adjusted so that samples
containing 1 to ZO |j.g/m (the expected range of atmospheric samples)
can be measured. The sensitivity of the turbidimetric analytical pro-
cedure is 50 (ig of sulfate. Nephelometrically, as little as Z jig of
sulfate can be measured.
REAGENTS
All reagents are made from analytical-grade chemicals.
Hydrochloric acid (10 normal). Dilute 80 ml of concentrated
reagent grade hydrochloric acid to 100 ml with distilled water.
Glycerol-alcohol solution. Mix 1 volume of glycerol with Z
volumes of absolute ethyl alcohol (reagent grade).
Barium chloride. Use ZO- to 30-mesh crystals.
Standard sulfate solution (100 |j.g SO| per ml). Dissolve 0. 148
g of anhydrous sodium sulfate (dry if necessary) in distilled water and
dilute to 1 liter.
EQUIPMENT
High-volume sampler. A motor blower filtration system with a
sampling head, which can accommodate an 8- by 10-inch glass fiber
filter web and is capable of an initial flow rate of about 60 ft per min-
ute, is used and is shown in Figure 6. These samplers are available
from General Metals Works, Box 30, Bridgetown Road, Cleves, Ohio;
and Staplex Company, 774 Fifth Avenue, Brooklyn 3Z, N. Y. , among
others.
Glass fiber filters. Use 8- by 10-inch size, Mine Safety Appli-
ances Company, 1106 BH or any comparable make.
Refluxing apparatus. Use lZ5-ml flask fitted with reflux con-
denser and hot plate.
Funnels and Whatman No. 1 filter paper.
Cuvettes. Use cuvettes with a 1-inch light path and plastic
stoppers.
*As used by the National Air Sampling Network.
Prepared by Norman A. Huey, Laboratory of Engineering and Physical Sciences,
Division of Air Pollution, Public Health Service. Approved by the Interbranch Chemical
Advisory Committee, July 1964.
Turbidimetric Barium Sulfate Method I-1
-------
FIGURE 6. TYPICAL SAMPLER ASSEMBLY (ABOVE) AND HIGH-VOLUME AIR
SAMPLER (BELOW).
1-2
SELECTED METHODS
-------
Pipettes. Use ZO-, 4-, and 1-ml pipettes.
Spectrophotometer or colorimeter. This device should be suit-
able for measurement at 500 mu.
PROCEDURE
Sampling. Using the Hi-Vol sampler, collect the particulates
from approximately Z, 000 m of air. Twenty-four hours is the usual
sampling period. The air volume is calculated from the sampling
time and the average of airflow measurements taken at the start and
end of the sampling period.
Sample preparation. The sample filter is folded upon itself
along the 10-inch axis to facilitate storage and transportation. This
fold may result in a nonhomogeneous area in the sample. All sample
aliquoting is, therefore, made across the fold. Using a wallpaper
cutter or other suitable device and a straight edge, cut a 3/4- by 8-
inch strip from the filter. Place this in the refluxing apparatus with
25 ml of distilled water and reflux for 90 minutes. Filter through
Whatman No. 1 paper, rinsing with distilled water till 50 ml of fil-
trate is obtained.
Analytical procedure. Place a ZO-ml portion of the prepared sam-
ple into a clean, dry, 1-inch cuvette. Add 1 ml of 10 N HC1, 4 ml of
the glycerol-alcohol solution, and mix. Determine the absorbance at
500 mn against a reference cuvette containing distilled water. This
reading is subtracted from the final reading. It corrects for unmatched
cuvettes and other impurities in the sample. Add approximately 0. Z5 g
of barium chloride crystals and shake until dissolved. Let stand for
40 minutes at room temperature (20 to 30°C). Measure the absorbance
at 500 m|j.against the reference cuvette containing distilled water.
A standard sulfate solution should be analyzed with each batch of
samples. Deviations up to 5% from the standard curve can be expected.
Occasionally it is advisable to determine the percentage recovery by
adding known amounts of sulfate to clean filters and determining the
amounts found, using the entire procedure including refluxing. The
percentage recovery should be close to 100.
Standardization. Obtain a standard curve by analyzing ZO ml
of a series of standards containing Z to 60 |JL g SO| per ml. Coordinates
of the curve are absorbance and total sulfate in jig (40 to 1,200).
Calculations.
|i.g SO| per m3 FC/V
F sample aliquot factor 30
C number of u g of SO| found
V sample air volume in m
Turbidimetric Barium Sulfate Method 1-3
-------
DISCUSSION OF PROCEDURE
Collection media. Although most past data have been gathered
on Mine Safety Appliance Company glass fiber filters, other filters are
available from H. Reeve Angel ik Company, Union Industrial Equip-
ment Company, Carl Schleicher & Schuell Company, and the Gelman
Instrument Company.
Glass fiber filters are not sulfate free. The MSA filters have
been found to contain about 4 mg per 8- by 10-inch sheet. It is
advisable to check whatever sampling media are used. This sulfate
can be removed by water wash prior to sampling if desirable. When
this is not practical, results must be corrected accordingly.
The analytical method can also be applied to samples collected
on membrane filters and with electrostatic precipitators.
Modification of analytical method sensitivity. To decrease
sensitivity, use a smaller sample portion diluted to 20 ml with dis-
tilled water. To increase sensitivity, use a larger sample portion
or, in extreme cases, measure nephelometrically.
Critical variables and their control. Measurement is dependent
upon the amount, the size, and the suspension of the barium sulfate
particles.
Parameters that must be controlled are stability of the suspension
of colloidal particles, sulfate concentration, barium ion strength, pH,
temperature, and aging of the barium chloride solution. Glycerol
acts as a stabilizer for the colloid, while alcohol promotes precipita-
tion of the sulfate. Use. of solid crystals of Bad? eliminates the prob-
lem of barium ion strength and solution aging. Sulfate concentration is
maintained within the limits of the method, and pH is controlled by
addition of HC1. Variations in temperature of 20-to 30°C do not appear
to have a significant effect.
Precision of method. The method has been shown to have an
11% coefficient of variation.
REFERENCES
1. Air Pollution Measurements of the National Air Sampling
Network 1957-1961. Public Health Service Publication
No. 978. U.S. Government Printing Office, Washington,
D.C.
2. Pate, J. B. , Tabor, E.G., Analytical Aspects of Glass Fiber
Filters, Am. Ind. Hyg. Assoc. J. 23:145-150. 1962.
3. Parr, S. W. , Staley, W. D. , Determination of Sulfur by
Means of the Turbidimeter, Ind. Eng. Chem. Anal. Ed 3:
66-67. 1931.
4. Keily, H.J., Rodgers, L. B. , Nephelometric Determination
of Sulfate Impurities in Certain Reagent Grade Salts, Anal
Chem. 27:759. 1955.
1-4 SELECTED METHODS
-------
Determination of Nitrate in Atmospheric Suspended Particulates:
2,4Xylenol Method*
INTRODUCTION
Suspended particulate matter is collected over a 24-hour period
on an 8- by 10-inch glass fiber filter by using a high-volume sampler.
A water extract is obtained and used to nitrate 2, 4 xylenol. The ni-
trated 2, 4 xylenol is separated from other water-soluble colored
substances by means of extraction with toluene and sodium hydroxide.
The color of the purified caustic extract is compared with that of
standards to estimate the nitrate content. Aliquoting is adjusted
so that samples containing 0. 1 to 10 |ig/m , (the expected range of
atmospheric samples) can be measured. Sensitivity is 5 |o.g of nitrate
in up to 5 ml of water.
REAGENTS
Reagents are made from analytical-grade chemicals.
Sulfuric acid solution, 85%. Cautiously add 480 ml of concen-
trated sulfuric acid to 117 ml of water, mixing well and cooling during
the addition.
Xylenol solution (1%). Mix 5 ml of 2, 4 xylenol with 500 ml
glacial acetic acid. This solution is stable for months when kept in
a brown bottle.
Sodium hydroxide solution (0.4 normal). Dissolve 16 g sodium
hydroxide in distilled water and dilute to 1 liter. Store in a plastic
bottle.
Stock standard solution (100 (j.g NO^/ml). Dissolve 0. 163 g
potassium nitrate and dilute to 1 liter with distilled water.
Dilute standard solution (20 |qg NO^)ml). Pipette 5 ml of stock
solution into a. 25-ml volumetric flask, dilute to mark with distilled
water, and mix.
Toluene.
EQUIPMENT
High-volume sampler. A motor blower filtration system with a
sampling head, which can accomodate an 8- by 10-inch glass fiber
filter web and is capable of an initial flow rate of about 60 ft per
minute, is used and is shown in Figure 6. These samplers are
available from General Metals Works, Box 30, Bridgetown Road,
Cleves, Ohio; and Staplex Company, 774 Fifth Avenue, Brooklyn 32,
N. Y. , among others.
#As used by the National Air Sampling Network.
Prepared by Norman A. Huey, Laboratory of Engineering and Physical Sciences,
Division of Air1 Pollution, Public Health Service. Approved by the Interbranch Chemical
Advisory Committee, July 1964.
2, 4 Xylenol Method J-l
-------
Glass fiber filters. Use the 8- by 10-inch size, Mine Safety
Appliances Company, 1106 BH, or any comparable make.
Refluxing apparatus. Use a 125-ml flask fitted with reflux con-
denser and hot plate.
Water bath, 60°C.
Funnels and Whatman No. 1 filter paper.
Volumetric flasks. Use Z5-ml, glass-stoppered flasks .
Volumetric pipettes. Use 15-, 10-, 5- and 1-ml pipettes.
Test tubes. Use 25-mm tubes with polyethylene caps.
Separatory funnels. The funnels should have a 250-ml capacity.
Cuvettes. Cuvettes with a 3/4-inch light path are recommended.
Cotton. Surgical-grade cotton is required.
Spectrophotometer or colorimeter. This device should be suit-
able for measurements at 435 mji.
PROCEDURE
Sampling. Using the Hi-Vol sampler, collect the particulates
from approximately 2, 000 m^ of air. Twenty-four hours is the usual
sampling period. The air volume is calculated from the sampling
time and the average of the airflow measurements taken at the start
and end of the sampling period.
Since only 1% of the sample is used for the nitrate measurement,
the remainder of the sample is left for further analyses. A smaller air
volume may be sampled provided that a larger portion is used in the
method. Only 20 m of air is needed for the nitrate measurement.
Sample preparation. To facilitate storage and transportation,
the sample filter is folded upon itself along the 10-inch axis. This
fold may result in a nonhomogeneous area in the sample, and so all
sample aliquoting is made across the fold. Using a wallpaper cutter
or other suitable device and a straight edge, cut a 3/4- by 8-inch strip
from the filter. Place this in the refluxing device with 25 ml of dis-
tilled water and reflux for 90 minutes. Filter through Whatman No. 1
paper, rinsing with distilled water until 50 ml of filtrate is obtained.
Analytical procedure. To a 5-ml sample portion in a 25-mm
test tube, add 15 ml of 85% sulfuric acid; mix and allow to cool. Add
1 ml of xylenol reagent, mix, and place in a 60°C water bath or oven
for 30 minutes. Cool and transfer with distilled water to a 250-ml
separatory funnel. Dilute to about 80 ml with distilled water and then
add 10 ml of toluene. Shake gently for about 2 minutes. Allow to
stand till layers separate (about 10 minutes), then discard the lower
aqueous layer. Rinse the toluene with about 20 ml of distilled water.
Discard the aqueous layer. Add exactly 10 ml of 0. 4 normal sodium
hydroxide solution and shake gently for 5 minutes. Allow to stand till
clear. Place cotton pledgets in funnel stems. Draw lower aqueous
layer through the cotton pledget and into the cuvette. Measure the
J-2 SELECTED METHODS
-------
absorbance against a reagent blank in a suitable spectrophotometer
at 435 mp.. Determine the nitrate concentration by reference to the
standard curve.
A standard solution should be analyzed with each batch of samples.
Deviations up to 5% from the standard curve can be expected.
Occasionally it is advisable to determine the percentage recovery
by adding known amounts of nitrate to clean filters and determining the
amounts found, using the entire procedure including refluxing. The
percentage recovery should be close to 100.
Standardization. Obtain the standard curve by analyzing 5 ml
of a series of standards containing 0 to 20 |j. g of nitrate per ml. Co-
ordinates of the curve are absorbance and total nitrate in |j.g (0 to 100).
Calculations.
fig NO3 per m3 FC/V
F sample aliquot factor 120
C number of p.g NOo found
V sample air volume in m
DISCUSSION OF PROCEDURE
Collection media. Although most past data have been gathered on
Mine Safety Appliance Company glass fiber filters, other filters are
available from H. Reeve Angel & Company, Union Industrial Equip-
ment Company, Carl Schleicher & Schuell Company, and the Gelman
Instrument Company. The analytical method can also be applied to
samples collected on membrane filters and with electrostatic pre-
cipitators.
Significant amounts of nitrate are not generally found in the MSA
glass fiber filters. It is, however, advisable to check whatever sam-
pling medium is used.
Method blank. The Whatman No. 1 filter papers used to filter
the refluxed sample contain nitrate and may add as much as 60 u.g of
NO3'to the filtered sample. This can be corrected mathematically or
the filter papers can be made nitrate free by water washing before use.
If not corrected, the method will give results about 0. 3 (jig/m3 higher
than actual.
Modification of analytical-method sensitivity. It is necessary
that the nitration be conducted according to the proportions set up in
the method; that is, 5 ml of sample, 15 ml of 85% H2SO4, and 1 ml of
xylenol reagent. If a smaller aliquot than 5 ml is desired, dilute this
aliquot to 5 ml with distilled water and proceed as usual. If more sen-
sitivity is needed, increase the sample aliquot and the sulfuric acid
proportionally, or reduce the amount of toluene and sodium hydroxide.
Emulsions during extraction. The separatory funnels should be
shaken gently for a long period of time rather than vigorously for a
short period of time, to avoid the formation of emulsions.
2, 4 Xylenol Method J-3
-------
Interferences. Most colored material is eliminated from the
sample by the extraction procedure. In cases where this is not true,
the color is corrected by subtracting the optical density of an equal
sample portion carried through the procedure without 2, 4 xylenol.
A negative interference is caused by chloride above a concen-
tration of 100 fig/ml in the prepared sample.
Significant amounts of nitrite do not usually occur in suspended
air particulates and do not, therefore, constitute an interference with
this method; however, nitrite does interfere in the analytical procedure.
Analytical results on samples containing equivalent amounts of nitrate
and nitrite may be as much as 80% high.
Oxidizing agents may react chemically with xylenol to form a
colored complex or to deplete the quantity necessary for nitration,
causing either a positive or negative interference.
Precision of method. The method has been shown to have an 8%
coefficient of variation.
REFERENCES
1. Air Pollution Measurements of the National Air Sampling
Network 1957-1961. Public Health Service Publication No.
978, U.S. Government Printing Office, Washington, D. C.
2. Barnes, H. , A Modified 2:4 Xylenol Method for Nitrate
Estimation, Analyst. 75:388. 1950.
3. Pate, J.B., Tabor, E.G., Analytical Aspects of Glass Fiber
Filters, Am. Ind. Hyg. Assoc. J. 23:145-150. 1962.
J-4 SELECTED METHODS
-------
BIBLIOGRAPHIC: Interbranch Chemical Advisory Com-
mittee. Selected methods for the measurement of air
pollutants. PHS Publ. No. 999-AP-ll. 1965. 54pp.
ABSTRACT: This manual is an effort to assist in the
development of uniform standard methods of analysis
of air pollutants. It makes available the judgment
and knowledge of a large group of chemists in the
Public Health Service. Methods of determining pol-
lutants of common interest are presented in uniform
format by chemists on the staff of the Division of Air
Pollution. The methods were critically reviewed by
the Interbranch Chemical Advisory Committee, which
is composed of representatives of the professional
chemical groups in all branches of the Division.
Methods presented are as follows: for determination
of sulfur dioxide, the West and Gaeke and the hydro-
gen peroxide methods; for determination of nitrogen
dioxide and nitric cxide, the Saltzman method; for
determination of oxidants, the neutral buffered-
potassium iodide and the alkaline potassium iodide
BIBLIOGRAPHIC: Interbranch Chemical Advisory Com-
mittee. Selected methods for the measurement of air
pollutants-. PHS Publ. No. 999-AP-ll. 1965. 54pp.
ABSTRACT: This manual is an effort to assist in the
development of uniform standard methods of analysis
of air pollutants. It makes available the judgment
and knowledge of a large group of chemists in the
Public Health Service. Methods of determining pol-
lutants of common interest are presented in uniform
format by chemists on the staff of the Division of Air
Pollution, The methods were critically reviewed by
the Interbranch Chemical Advisory Committee, which
is composed of representatives of the professional
chemical groups in all branches of the Division.
Methods presented are as follows: for determination
of sulfur dioxide, the West and Gaeke and the hydro-
gen peroxide methods; for determination of nitrogen
dioxide and nitric oxide, the Saltzman method; for
determination of oxidants, the neutral buffered-
potassium iodide and the alkaline potassium iodide
BIBLIOGRAPHIC: Interbranch Chemical Advisory Com-
mittee. Selected methods for the measurement of air
pollutants. PHS Publ. No. 999-AP-ll. 1965. 54pp.
ABSTRACT: This manual is an effort to assist in the
development of uniform standard methods of analysis
of air pollutants. It makes available the judgment
and knowledge of a large group of chemists in the
Public Health Service. Methods of determining pol-
lutants of common interest are presented in uniform
format by chemists on the staff of the Division of Air
Pollution. The methods were critically reviewed by
the Interbranch Chemical Advisory Committee, which
is composed of representatives of the professional
chemical groups in all branches of the Division.
Methods presented are as follows: for determination
of sulfur dioxide, the West and Gaeke and the hydro-
gen peroxide methods; for determination of nitrogen
dioxide and nitric oxide, the Saltzman method; for
determination of oxidants, the neutral buffered-
potassium iodide and the alkaline potassium iodide
ACCESSION NO.
KEY WORDS:
Measurement
Recommended
Methods
Manual Methods
Air Pollution
Sulfur Dioxide
Nitrogen Dioxide
Nitric Oxide
Oxidants
Aliphatic
Aldehydes
Acrolein
Formaldehyde
Sulfate
Nitrate
ACCESSION NO.
KEY WORDS:
Measurement
Re c omme nde d
Methods
Manual Methods
Air Pollution
Sulfur Dioxide
Nitrogen Dioxide
Nitric Oxide
Oxidants
Aliphatic
Aldehydes
Acrolein
Formaldehyde
Sulfate
Nitrate
ACCESSION NO.
KEY WORDS:
Measurement
Recommended
Methods
Manual Methods
Air Pollution
Sulfur Dioxide
Nitrogen Dioxide
Nitric Oxide
Oxidants
Aliphatic
Aldehydes
Acrolein
Formaldehyde
Sulfate
Nitrate
-------
methods; for determination of aliphatic aldehydes,
the 3-methyl-2-benzothiazolone hydrazone hydro-
chloride method; for determination of acrolein, the
4-hexylresorcinol method; for determination of
formaldehyde, the chromotropic acid method; for
determination of sulfate in atmospheric suspended
particulates, the turbidimetric barium sulfate meth-
od; and for determination of nitrate in atmospheric
suspended particulates, the 2, 4 xylenol method.
methods; for determination of aliphatic aldehydes,
the 3-methyl-2-benzothiazolone hydrazone hydro-
chloride method; for determination of acrolein, the
4-hexylresorcinol method; for determination of
formaldehyde, the chromotropic acid method; for
determination of sulfate in atmospheric suspended
particulates, the turbidimetric barium sulfate meth-
od; and for determination of nitrate in atmospheric
suspended particulates, the 2,4 xylenol method.
methods; for determination of aliphatic aldehydes,
the 3-methyl-2-benzothiazolone hydrazone hydro-
chloride method; for determination of acrolein, the
4-hexylresorcinol method; for determination of
formaldehyde, the chromotropic acid method; for
determination of sulfate in atmospheric suspended
particulates, the turbidimetric barium sulfate meth-
od; and for determination of nitrate in atmospheric
suspended particulates, the 2, 4 xylenol method.
------- |