EPA-650/4-74-047
NOVEMBER 1974
Environmental Monitoring Series
^V6^jc;c^
i
-------
Research reports of the Office of Research and Development, Environmental
Protection Agency, have been grouped into five series. These five broad categories
were established to facilitate further development and application of environmental
technology. Elimination of traditional grouping was consciously planned to
foster technology transfer and a maximum interface in related fields. The
five series are:
I. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL MONITORING series.
This series describes research conducted to develop new or improved methods
and instrumentation for the identification and quantification of environmental
pollutants at the lowest conceivably significant concentrations. It also includes
studies to determine the ambient concentrations of pollutants in the environment
and/or the variance of pollutants as a function of time or meteorological factors.
Copies of this report are available free of charge to Federal employees, current
contractors and grantees, and nonprofit organizations - as supplies permit -
from the Air Pollution Technical Information Center, Environmental Protection
Agency, Research Triangle Park, North Carolina 27711; or, for a fee, from
the National Technical Information Service, Springfield, Virginia 22161.
-------
EPA-650/4-74-047
AN EVALUATION OF TGS-ANSA
PROCEDURE FOR DETERMINATION
OF NITROGEN DIOXIDE IN AMBIENT AIR
by
Robert G. Fuerst and John H. Margeson
Quality Assurance and Environmental Monitoring Laboratory
Program Element 1HA327
National Environmental Research Center
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina
November 1974
-------
This report has been reviewed by the Office of Research and Development,
Environmental Protection Agency, and approved for publication. Approval
does not signify that the contents necessarily reflect the views and policies
of the Environmental Protection Agency, nor does mention of trade names
or commercial products constitute endorsement or recommendation for use.
Publication No. EPA-650/4-74-047
-------
ACKNOWLEDGMENTS
The authors wish to thank Dr. Eugene Sawicki and other
members of the Laboratory Methods Research Section for providing
the initial method write-up describing the TGS-ANSA procedure
and for helpful discussions during the procedure review.
m
-------
CONTENTS
Page
Abstract v
Sections
I Introduction 1
II Experimental 3
III Results and Discussion 7
IV Conclusions 18
V Future Work 19
VI References 20
VII Appendices 22
TABLES
No_.
1. Ruggedness Test Format 11
2. Summary of Ruggedness Test Results 15
FIGURES
1. NO- Permeation Rate for Device 7-35 4
A-l. Sampling Train 32
A-2. Flowmeter 33
D-l. Sampling Train 46
D-2. Flowmeter 47
IV
-------
ABSTRACT
A detailed method write-up describing the TGS-ANSA manual
procedure for measurement of NOp in ambient air was developed. The
method involves sampling for 24 hours with a restricted-orifice bubbler
immersed in a triethanolamine, o-methoxyphenol, sodium metabisulfite
3
solution. The range of the method is approximately 20 to 700 ug/m .
The method was evaluated to determine its usefulness. This involved
a review of the procedure, as developed, to judge the adequacy of the
development work and ruggedness testing, as described by Youden.
The method was shown to be free from interferences such as: NO,
SOp, 0.,, CO, and NH, and possesses a constant-high collection efficiency,
93%. The ruggedness test showed the method to be insensitive to normal
variations in: time between sample collection and analysis, storage con-
ditions after sample collection, flow rate, COp concentration, sampling
time, and orifice size. The time interval between the addition of the
diazonium salt forming reagent and the diazonium salt coupling reagent
is critical and must be carefully controlled.
The method appears to be a reliable procedure for the measurement
of NOp in ambient air.
The method will now be subjected to a collaborative test to determine
its repeatability, reproducibility, and bias.
-------
SECTION I
INTRODUCTION
Since the promulgation in the Federal Register of the reference
method for the determination of nitrogen dioxide in the atmosphere, '
the inadequacies of the method have been brought forth. Researchers
(2) (3)
within^ ' and outsidev ' of EPA found a variable collection efficiency
and a positive nitric oxide interference. After further evaluation,
the Administrator on June 14, 1972, stated that the reference method
for measuring nitrogen dioxide was suspected of being unreliable and
(4)
was being withdrawn. Recently, ' EPA has chosen three tentative methods
for replacement of the original reference method:
a. a manual arsenite-alkali method.
b. a continuous Saltzman procedure.
c. a continuous chemiluminescence procedure.
The Administrator in his proposal for the consideration and comment on
these three methods also asked any interested persons to submit information
and comments pertinent to other new methods for N0? detection.
Since the task of Methods Standardization Branch (MSB), Quality
Assurance and Environmental Monitoring Laboratory (QAEML), is to standardize
methods for making air pollution measurements with particular emphasis on
the reference methods, we were interested in the three proposed methods
and any new methods.
-------
(5)
A new manual method* ' for the detection and analysis of NCL in
ambient air was chosen to be included in the MSB laboratory evaluation
program due to its reported high collection efficiency (93%) and freedom
from suspected interferences. The method is based on the sampling of
NOp from ambient air using an aqueous solution of triethanolamine
containing small amounts of o-methoxyphenol and sodium metabisulfite,
with subsequent measurement of the nitrite ion by a conventional
diazotization-coupling reaction. The work reported here describes an
evaluation of this method.
-------
SECTION II
EXPERIMENTAL
The specific reagents and procedures used in this evaluation were
exactly the same as those specified in the method write-up. (See
Appendix A)
A. Generation of N0? Test Atmospheres
The various test atmospheres in this evaluation were generated using
a permeation device and known amounts of clean dilution air. This procedure
has been described by O'Keeffe and Ortman* ' and Scaringelli et al. ' '
An FEP-TefIon-sleeve, glass reservoir permeation device developed by
the National Bureau of Standards (NBS) and the Environmental Protection
(9)
Agency (EPA) was used as the source of NO^. This device (No. 7-35) was
calibrated gravimetrically* ' and had a permeation rate of 1.188 j^ 0.002
Mg N02/min (95% C.I.) at 25.0 + 0.1°C. The rate constancy of this device
was well established as shown by the data in Figure 1.
The temperature of the device was controlled by a water-jacketed
condenser, which was maintained at 25.0 j^0.1°C by a Forma Temp., Jr. con-
stant temperature bath. The N0? was flushed from the condenser with dry
nitrogen at approximately 50 cc/min. The flushing nitrogen was obtained from
an A-type cylinder of extra dry grade nitrogen. This was passed through a
column of molecular sieve (6-16 mesh, type 4-A) and indicating Drierite.
The dilution air was compressed house air which was passed through an air
filter (Wilkerson Corporation Model No. 1237-2F) to remove dirt particles and
aerosols, indicating silica gel (6-16 mesh) and activated charcoal (6-16 mesh).
-------
'?£
(.. .•••& •?&#•#?
i
UJ
-------
A blank, consisting of a 24-hour sampling of dilution air plus flushing
nitrogen with no permeation device in the system, showed a NCL concentration
of less than 2 yg NO^/m . Thus, the generation system was free from inter-
ferences.
B. Sampling System
Five sampling trains were placed in parallel to a common inlet glass
manifold. In this way each recorded effect was an average of five deter-
minations. Each sampling train sampled the test atmosphere at approximately
200 cc/min. by using a 27-gauge, stainless-steel hypodermic needle as the
critical orifice. A Gast Model 0211 oil-less vacuum pump was used to main-
tain a pressure drop across each orifice of approximately 0.7 of an atmosphere.
The time of sampling was either 20 or 24 hours.
The total flow through the sampling trains was measured and compared to
the summation of the individual train flows. This is a check to detect any
leaks in the system. Differences of greater than 10% constituted a basis
for rejecting a sample.
C. Flow Measurement
All flow measurements were made using a wet test meter (1 s,/rev, 10 a/rev)
or a bubbler flow meter. All flow measurements were an average of an initial
and a final flow. The total dilution air flow never varied more than one per-
cent in any 24-hour sampling period, based on differences in initial and
final readings.
D. Analysis
Using a Beckman Model B spectrophotometer at a wavelength of 550 nm with
one centimeter cells, the absorbance of each sample was read against a blank,
-------
following the analytical procedure of the method.
E. Concentration of Carbon Dioxide
The carbon dioxide used in these experiments was obtained from two
different A-type cylinders with concentrations of 1060 ppm C02 in nitrogen
and 99.9% C02- Both cylinders were previously checked for NO and NOp by a
NO-NO^-NO chemiluminescent monitor. None was detected.
F. Restricted Orifice Bubbler
The restricted-orifice bubblers specified in the method were obtained
from a local glassblower. Only those orifices meeting the method
specifications were used.
-------
SECTION III
RESULTS AND DISCUSSION
A. Procedure Review
The procedure used by MSB in standardizing a method involves a
critical investigation of the method in three phases. Phase one is a
procedure review. This consists of evaluating the method on its potential
for making meaningful measurements, based on the write-up, obtained from,
and conversations with, the developers.
Phase two consists of a laboratory evaluation to determine how well
the method measures the pollutant of interest when challenged by variations
in the procedure which might occur in the field use of the method.
If a method proves to be reliable after MSB's evaluation, it can be
subjected to a collaborative test designed to determine its precision
(repeatability and reproducibility) and its accuracy (bias). The collabora-
tive test is the final phase of the standardization process and is a measure
of the performance of the method in actual use.
Following this procedure, a copy of the TGS-ANSA method was obtained
from the developers, the laboratory Methods Research Section of the Chemistry
and Physics Laboratory, for procedure review.
The method write-up specifies bubbling ambient air through a solution
containing triethanolamine, o-methoxyphenol, and sodium metabisulfite. This
converts N02 gas to nitrite ion (NOp), which is then assayed by dia.zotization
and coupling using sulfanilamide and the ammonium salt of 8-anilino-l-
naphthalene-sulfonic acid (ANSA). The absorbance of the pink-purple dye is
read at 550 nm and the valves converted to nitrite ion concentration by use
of a calibration curve.
7
-------
The function of the triethanolamine (TEA) is to provide a basic
collecting media. When used by itself, the (TEA) produces an overall
collection efficiency of 85%' ' with a fritted glass bubbler. The
(12)
o-methoxyphenol(guaiacol) increases the collection efficiency/ '
It is also relatively stable, among phenoxides, in alkaline solution.
This reagent when added to the (TEA) improves the overall collection
efficiency to 93% using a restricted glass orifice.
The developers found that the triethanolamine and guaiacol system
(TG) showed reduced efficiency with age and developed a yellow color.
It was suspected that the guaiacol was forming quinones with age which
affected the efficiency and produced the yellow color. A free radical
inhibitor, sodium metabisulfite, was added to reduce the formation of
quinones. With the addition of the sulfite ion, it was noted that the
dye formed in the sulfanilamide, n-(l-naphthyl)ethylene-diamine dihydro-
chloride reaction was being bleached; therefore, new diazotization-coupling
reagents had to be found.
Knowing from previous work that ANSA would be stable under these
conditions, the developers tried this coupling reagent with various
diazonium salt precursors; sulfanilamide in HC1 proved to give the most
reproducible results. A novel feature of this analytical system is the
high range of analysis, up to 4.0 ug/ml of NCL, possible without sample
dilution.
The developers also showed data that the TGS-ANSA method was both
constant in overall efficiency (93%) from 20 to 700 pg/m and free from a
-------
number of probable interferences such as: NO, S02» 03, NH.,, CO, CH20,
and phenol.
With these and other facts brought forth by the developers, the
TGS-ANSA method was judged to be sufficiently well developed to proceed
directly to the laboratory evaluation without further development. A
copy of the write-up, developed as a result of this procedure review, is
given in Appendix A. It differs from the original only in minor technical
modifications and editorial changes.
B. Ruggedness Testing
1. Design
Once a method is deemed ready for laboratory testing (Phase II), it
is desirable to subject the method to slight variations in important para-
meters as would be expected to occur in normal usage . This can be
accomplished by ruggedness testing. This is done by studying selected
variables at two levels; the nominal level stated in the method write-up,
and a challenging level. A procedure has been developed by Youden^ ' to
determine the effect of a variable by comparing the results obtained at the
two levels. To accomplish this, seven^ variables are chosen for study and
their nominal levels designated A to G. A challenging level is then selected
and denoted by the corresponding lower case letter, a to g. A series of eight
' Schemes for examining the effect of a larger or smaller number of
variables are available.
(14)
-------
experiments are then conducted using various combinations of either
nominal or challenging values for each variable. The format for these
experiments is shown in Table 1.
Each of the eight experiments produces a result, denoted as s, t,
u, v, w, x, y, and z. Examination of the format in Table 1 reveals that
by summing the group of experiment results in which a given nominal value
was involved and subtracting from it the sum of the group of results in
which the corresponding challenging value was involved, the effect of all
other variables are canceled. If the grouped results are divided by the
number in each group, the above subtraction will yield the average effect or
difference between the nominal and challenging conditions.
For example, the average effect of variable E is calculated using:
E-e = s + u + x + z - t + v + w + y
4 4
A complete set of equations for calculating the effect of A-a, B-a, etc.
are given in Appendix B.
It should be noted that the results of the ruggedness test will not
completely describe the effect of varying a given parameter. The results
only show the effect of the range of variation used in the experiment. If
the effect is shown to be significant, further experimentation will be needed
to define the exact relationship.
Thus, the ruggedness test design permits the screening of the effect of
seven variables with only eight experiments. Without this design, it would
require 2 or 128 experiments to investigate the effect of seven variables
at two levels.
10
-------
Table 1. RUGGEDNESS TEST FORMAT
EXPERIMENTS
1 2 3 4 5 6 7 S
A
B
C
D
E
F
G
A
B
c
D
e
f
9
A
b
C
d
E
f
g
A
b
c
d
e
F
G
a
B
C
d
e
F
9
a
B
c
d
E
f
G
a
b
C
D
e
/
G
a
b
c
D
E
F
9
' OBSERVED RESULTS
s t u v v/ x y z
-------
2. Selection of Variables
In evaluating any method there are, of course, many variables
that could be studied, but the following were deemed most important:
a. N02 concentration
A = 70 ug N02/m3
a = 600 ug N02/m
The effect of various concentrations of N02 on the method
had been previously evaluated in the determination of collection efficiency.
However, the effect of other variables in association with the N02 concen-
3
tration was not known. Therefore, N02 concentrations of 70 and 600 pgN02/m
were chosen to cover the range of the method.
b. Flow rate
3
B =« ^200 cm /min.
3
b = ",350 cm /min.
3
The method requires a flow rate of 180 to 220 cm /min. Since
the collection efficiency of a method can be affected by the rate of delivery
of the sample to the absorbing solution, it was decided to examine the effect
of flow rates. Accordingly, nominal and challenging flows of 180 to 220 and
310 to 340 cm /min, respectively were selected.
c. C02 concentration
C = ambient
c = ambient + 250 ppm
C02 absorbed in the absorbing solution will produce a change in
pH which can, in turn, effect the collection efficiency. To test the
significance of this effect, 250 ppm of C02 was added to the ambient (nominal)
12
-------
level of C02>
d. Orifice size
D = 0.3 to 0.4 mm
d = 0.6 mm
Orifice size can affect collection efficiency by controlling
the surface area of the bubbles produced in the solution. A test of the
effect of an orifice diameter outside the prescribed 0.3 to 0.4 mm was made
by using 0.6 mm for the challenging value.
e. Time between collection and analysis
E = 2-4 days
e = 2 weeks +_ 2 days
This parameter was chosen because of the possibility of color
formation in the absorbing solution if the effectiveness of the free radical
inhibitor was reduced on aging of the collected samples. Samples were stored
on the laboratory bench and analyzed at the indicated times.
f. Storage conditions after sampling
F = in the dark
f = on the laboratory bench
The use of a manual method, in practice, usually involves
shipping the collected samples to a central laboratory for analysis. During
shipment, of course, the samples are in the dark. Subsequent exposure to
light prior to analysis could accelerate color formation if the free radical
inhibitor was not effective. Accordingly, samples were stored in the dark
and on the laboratory bench for the times called for in the ruggedness test
13
-------
format, 2-4 days or 2 weeks.
g. Sampling time
G = 24-hours
g = 20-hours
When a method specifies taking a 24-hour sample, sampling
periods of less than 24 hours sometimes occur when the 24-hour period
terminates at the end of the working day. Since the effect of this
variation in sampling time had not been studied, it was included as a
variable. The challenging level was set at four hours less than the
nominal value.
3. Conducting the Ruggedness Test
The parameters chosen for the ruggedness test were incorporated
into the format shown in Table 1 and the experiments conducted in random
order (2, 3, 5, 7, 4, 1, 8, 6). The individual and average results for
each experiment are given in Appendix C. It should be noted that the
results are expressed in percent. This was calculated by dividing the con-
centration found by the concentration of NOp generated. This normalization
of the results was necessary before the effect of the different parameters
could be determined because, the method is obviously sensitive to NOp con-
centration.
The results in Appendix C were substituted into the equations of
Appendix B and the effect of each parameter was calculated. The net results
are shown, ranked in order of decreasing absolute magnitude, in Table 2.
14
-------
Table 2. SUMMARY OF RUGGEDNESS TEST RESULTS
Variable
Orifice size
NOp concentration
Time between collection
and analysis
Flow rate
Storage conditions after
sampling
COp concentration
Time of sampling
Levels
D = 0.3 - 0.4 mm
d = 0.6 mm
A = 70 vg N02/m33
a = 600 ng NOp/m
E = 2-4 days
e = 2 weeks
B = 200 cc/min
b = 350 cc/min
F = in dark
f = on bench
C = ambient
c = ambient + 250 ppm
G = 24 hours
g = 20 hours
Difference, %
-7.4
-2.6
2.5
2.0
1.8
1.6
1.0
15
-------
4. Results
Inspection of the data shows that six of the seven variables
examined (N02 concentration, time between collection and analysis, flow
rate, storage conditions after sampling, COp concentration, and sampling
time) gave differences in response of only 1.0 to 2.6%. Since the
standard deviation for the collection efficiency of the method (see section
4.1.1, Appendix A) is 2%, these differences do not appear significant.
Changing the orifice size from its nominal value of 0.3 to 0.4 mm to 0.6
mm, however, produced a difference of -7.4%. Numerically, this appears to
be significant; however, the fact that the value is negative indicates that
increasing the orifice size produced an increase in the method response
(collection efficiency). An increase in orifice size should, if anything,
reduce the collection efficiency because the total surface area of the air
bubbles is being reduced. Thus, this result may be anomalous. No further
experimentation is planned to investigate this point.
Subsequent to this work, the TGS-ANSA method was used by the
Analytical Chemistry Branch of QAEML to analyze a large number of collected
samples. During this work, it was found that the time interval between
formation of the diazonium salt of sulfanilamide and addition of the ANSA
coupling reagent, in the analytical scheme, was critical. This led us to
examine the effect of this variable. The experiments involved used intervals
of 2, 4, 8, 16, 32 and 64 minutes and measured the absorbance produced.
The results showed that time intervals up to eight minutes had no effect on
absorbance; at the 16 minute interval the absorbance was significantly
decreased.
16
-------
Based on these results and a report on the use of the method,
issued by ACB, a revised-improved write-up was generated. A copy is
included as Appendix D. Attention is directed to the caution statements
in Sections 6.2.9 and 7.2.
17
-------
SECTION IV
CONCLUSIONS
The TGS-ANSA method is insensitive to normal variations in: time
between sample collection and analysis, flow rate, storage conditions
after sample collection, COp concentration, sampling time, and (most
likely) orifice size.
No interferences have been detected in the method.
Thus, the TGS-ANSA method appears to be a reliable procedure for
the measurement of N0? in ambient air , provided the revised version of
the method is followed.
18
-------
SECTION V
FUTURE WORK
This will involve additional distribution of the revised method
write-up to interested laboratories and soliciting the results of their
experience in using the method. This information should aid in further
refinement of the method.
The revised method will also be subjected to a collaborative test
(tentatively scheduled for May, 1974) to determine its repeatability,
reproducibility and bias.
MSB will carry out experiments, as time becomes available, to optimize
the time interval between formation of the diazonium salt and addition of
the coupling reagent (Section 7.2 - Appendix D); specifications on reagent
stability will also be optimized.
19
-------
SECTION VI
REFERENCES
1. Federal Register. 36_, pp. 8186-8187, April 30, 1971.
2. Hauser, T. R., Shy, C. M. Environmental Science and Technology, 6_,
p. 890-894 (1972).
3. Merryman, E. L. et al. Environmental Science and Technology, _7,
1056-1059 (1973).
4. Federal Register, 38_, No. 110, p. 15174, June 8, 1973.
5. Mulik, J. D., Fuerst, R. G., Meeker, J. R., Guyer, M., Sawicki, E.
"A New Twenty-four Hour Manual Method of Collection and Colorimetric
Analysis of Atmospheric NO-." Presented at the 165th ACS National
Meeting in Dallas, Texas, April 8-13, 1973.
6. O'Keeffe, A. E. and Ortman, G. C. Analytical Chemistry, 38_, p. 760
(1966).
7. Scaringelli, F. P., Frey, S. A. and Saltzman, B. E. Journal of the
American Industrial Hygiene Association, 28, p. 260 (1967).
8. Scaringelli, F. P., O'Keeffe, A. E., Rosenberg, E. and Bell, J. P.
Analytical Chemistry, 42_, p. 871 (1970).
9. NBS Technical Note 585, p. 26, Available from: Superintendent of
Documents, Government Printing Office, Washington, D. C. 20402. Price
70 cents.
10. Rook, H. L., Fuerst, R. G. and Margeson, J. H. Progress Report: EPA-NBS
Study to Determine the Feasibility of Using NOp Permeation Devices as
Standards, December 1972-January 1973.
20
-------
11. Levaggi, P. A., Siu, W., Feldstein, M., J.A.P.C.A.. 23_, 30-3 (1973),
12. Nash, T. Atmospheric Environment, 4_, 661-665 (1970).
13. Youden, W. J., "Statistical Techniques for Collaborative Tests,"
Association of Official Analytical Chemists, March 1967.
14. Plackett, R. L. and Burman, J.. P. Biometrika,33, 305 (1946).
21
-------
SECTION VII
APPENDICES
A. "Tentative Method for Determination of Nitrogen Dioxide in
the Atmosphere (TGS-ANSA Procedure)."
B. Equations for Calculating Ruggedness Test Results.
C. Data from Ruggedness Test.
D. Revised, February 1974, method write-up.
22
-------
Appendix A
ENVIRONMENTAL PROTECTION AGENCY
METHODS STANDARDIZATION BRANCH
QUALITY ASSURANCE AND ENVIRONMENTAL MONITORING LABORATORY
NATIONAL ENVIRONMENTAL RESEARCH CENTER
RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711
NOVEMBER 1973
TENTATIVE METHOD FOR THE DETERMINATION OF NITROGEN DIOXIDE
IN THE ATMOSPHERE (TGS-ANSA)3
aA tentative method is one which has been carefully drafted from
available experimental information, reviewed editorially within
the Methods Standardization Branch and has undergone extensive
laboratory evaluation. The method is still under investigation
and therefore is subject to revision.
23
-------
1. Principle and Applicability
1.1 Nitrogen dioxide is collected by bubbling air through a
solution of triethanolamine, o-methoxyphenol and sodium metabisulfite.
The nitrite ion produced during sampling is determined colormetrically
by reacting the exposed absorbing reagent with sulfanil amide and
8-anilino-l-naphthalenesulfonic acid.
1.2 The method is applicable to collections of 24-hour samples
in the field and subsequent analysis in the laboratory.
2. Range and Sensitivity
2.1 The range of the analysis is 0.025 to 4.0 yg NOl/ml. Beer's
law is obeyed throughout this range. With 50 ml of absorbing reagent and
3
a sampling rate of 200 cm /min for 24-hours, the range of the method is
20 to 700 yg/m nitrogen dioxide.
2.2 A concentration of 0.025 yg NO^/ml will produce an absorbance
of approximately 0.013 using 1 cm cells.
3. Interferences
3
3.1 At a nitrogen dioxide concentration of 100 yg/m the following
pollutants, at the levels indicated, do not interfere: ammonia,. 205 yg/m ;
carbon monoxide, 154,000 yg/m ; formaldehyde, 750 yg/m ; nitric oxide, 734
333 o
yg/m ; phenol, 150 yg/m ; ozone, 400 yg/m and sulfur dioxide, 439 yg/m .
3.2 A temperature of 40°C during collection of sample had no effect
on recovery.
24
-------
4. Precision and Accuracy
4.1 Precision and Accuracy
4.1.1 On making measurements from standard nitrogen dioxide atmos-
pheres, prepared by using permeation devices, a relative standard deviation
of 2% and a collection efficiency of 93% were determined throughout the
range of the method.
4.2 Stability
4.2.1 The absorbing reagent is stable for 3 weeks before sampling and
the collected samples are stable for 3 weeks after sampling.
5. Apparatus
5.1 Sampling. A diagram of a suggested sampling apparatus is shown
in Figure A-l .
5.1.1 Probe. Teflon, polypropylene, or glass tube with a polypropylene
or glass funnel at the end.
5.1.2 Absorption tube. Polypropylene tubes 164 x 32 mm. equipped with
polypropylene two-port closures. Rubber stoppers cause high and varying blank
values and should not be used. A glass tube restricted orifice is used to
disperse the gas. The tube, approximately 8 mm O.D.-6 mm. I.D., should be
152 mm long with the end drawn out to 0.3-0.6 mm. I.D. ' The tube should be
positioned so as to allow a clearance of 6 mm from the bottom of the absorber.
5.1.3 Moisture trap. Polypropylene tube equipped with a two port closure.
The entrance port of the closure is fitted with tubing that extends to the bottom
of the trap. The unit is loosely packed with glass wool to prevent moisture
entrainment.
This specification was modified from the original 0.3 to 0.4 mm. to reflect
the results of the ruggedness test.
25
-------
5.1.4 Membrane Filter, 0.8-2.0 microns porosity.
5.1.5 Flow Control Device. Any device capable of maintaining a
constant flow through the sampling solution between 180-220 cm /min. A
2
typical flow control device is a 27 gauge hypodermic needle, three-eights
inch long. (Most 27 gauge needles will give flow rates in this range.)
The device used should be protected from particulate matter. A membrane filter
is suggested. Change filter after collecting 10 samples.
5.1.6 Air Pump. Capable of maintaining a pressure differential of at
least 0.6-0.7 of an atmosphere across the flow control device. This value
(2)
includes the minimum useful differential, 0.53V ' atmospheres, plus a safety
factor to allow for variations in atmospheric pressure.
5.1.7 Calibration Equipment. Flowmeter for measuring airflows up to
275 cm /min. within +_ 2%, stopwatch, and a precision wet test meter (1 liter/
revolution).
5.2 Analysis
5.2.1 Volumetric Flasks. One each 200, 250, 1000 ml; 6 each 100 ml.
5.2.2 Pipets, volumetric. Two each 0.5; one each 3, 4, 5, 6, 10 ml.
5.2.3 Pipets serological, graduated in 1/10 ml divisions. One each 1,
5 ml.
5.2.4 Test Tubes. Each approximately 20 x 150 mm.
5.2.5 Spectrophotometer. Capable of measuring absorbance at 550 nm.
5.2.6 Graduated cylinder. One each 50 ml.
26
-------
6. Reagents
6.1. Sampling
6.1.1 Triethanolamine [N^H.OH)^]. Reagent grade.
6.1.2 o-Methoxyphenol (o-CH3OCgH4OH). Also known by its trivial name,
guaiacol. Reagent grade. Melting point 27-28°C.
6.1.3 Sodium Metabisulfite (Na2S205). ACS reagent grade.
6.1.4 Absorbing Reagent - Dissolve 20g of triethanolamine, 0.5g of
o-methoxyphenol, and 0.250g of sodium metabisulfite consecutively in 500 ml
of distilled water. Dilute to one liter with distilled water. Mix thoroughly.
The solution should be colorless. This solution is stable for four weeks, if
kept refrigerated.
6.2 Analysis
6.2.1 Hydrogen Peroxide (H,,02). ACS reagent grade, 30%.
6.2.2 Sulfanilamide [4-(H2N)CgH4S02NH2]. Melting point 165-167°C.
6.2.3 8-Anilino-l-napthalenesulfonic acid ammonium salt (ANSA) (8-CgHgNH-l
C10H6SO-NHj)-
6.2.4 Sodium Nitrite. [NaNO^L ACS reagent grade. Assay of 97% NaN02
or greater.
6.2.5 Methanol, absolute [CH3OH]. ACS reagent grade (Acetone free).
6.2.6 Hydrochloric acid, [HC1]. Concentrated. ACS reagent grade.
6.2.7 Hydrogen Peroxide Solution. Dilute 0.2 ml of 30% hydrogen peroxide
to 250 ml with distilled water. This solution can be used for a month if
protected from light and refrigerated.
27
-------
6.2.8 Sulfa^ilamide Solution (2.0% in 4N^HC1). Dissolve 2.0 g of
sulfanilamide in 33 ml of concentrated HC1 and dilute to 100 ml with
distilled water. Mix. This solution can be used for a month, if
refrigerated.
6.2.9 ANSA Solution. Dissolve O.lg ANSA in 50 ml absolute methanol.
Dilute to 100 ml with absolute methanol. Mix. Keep stoppered when not in
use. This solution can be used for a month, if refrigerated.
6.2.10 Standard Nitrite Solution. Dissolve sufficient desiccated
sodium nitrite and dilute with distilled water to 1000 ml so a solution
containing 1000 pgNOZ /ml is obtained. The amount of NaNO^ to use is
calculated as follows:
G = UQO 10Q
A X
where
G = Amount of NaNO^, grams.
1 .500 = Gravimetric factor in converting N0~ into NaNOp
A = Assay, percent
7. Procedures
7.1 Sampling. Assemble the sampling apparatus, as shown in Figure A-l
Components upstream from the absorption tube may be connected, where required,
with teflon or polypropylene tubing; glass tubing with dry ball joints; or
glass tubing with butt-to-butt joints with tygon, teflon or polypropylene.
Add exactly 50 ml of absorbing reagent to the calibrated absorption tube
28
-------
(8.1.3). Disconnect funnel, insert calibrated flowmeter (8.1.1) into
the end of the probe and measure flow before sampling. Denote as F,.
3
If flow rate before sampling is not between 180-220 cm /min replace the
flow controlling device and/or check the system for leaks. Start sampling
only after obtaining an initial flow rate in this range. Sample for 24-hours
and measure the-flow after sampling by again inserting a calibrated flowmeter
into the probe, after removing the funnel. Denote as F^.
7.2 Analysis. Replace any water lost by evaporation during sampling
by adding distilled water up to the calibrated mark on the absorption tube.
Mix well. Pipet 5 ml of the collected sample into a test tube, add 0.5 ml
of the peroxide solution and mix vigorously for approximately 15 seconds.
Add 2.7 ml of sulfanilamide solution and mix vigorously for about 30 seconds.
Then pipet 3 ml of the ANSA solution, mix vigorously for about 30 seconds.
Mechanical mixing is recommended. Prepare a blank in the same manner using
5 ml of unexposed absorbing solution. Determine absorbance at 550 nm against
the blank solution using 1 cm cells. The color is stable for 30 minutes.
Read pg NOZ/ml from the calibration curve (Section 8.2).
7.3 Spectrophotometer cells must be rinsed thoroughly with distilled
water, acetone, and dried, otherwise a film will build up on the cell walls.
8. Calibration and Efficiencies
8.1 Sampling
8.1.1 Calibration of Flowmeter. (See Figure A-2.) Using a wet test meter
and a stopwatch, determine the rates of air flow (cm /min) through the flow-
29
-------
meter at a minimum of four different ball positions. Plot ball
position versus flow rate.
8.1.2 Flow Control Device. The flow control device results in a
constant rate of air flow through the absorbing solution and is determined
in 7.1.
8.1.3 Calibration of Absorption Tube. Calibrate the polypropylene
absorption tube (Section 5.1.2) by first pipeting in 50 ml of water or
absorbing reagent. Scribe the level of the meniscus with a sharp object,
go over the area with a felt-tip marking pen, and rub off the excess.
8.2 Calibration Curve. Dilute 5.0 ml of the 1000 pg NO^/ml solution
to 200 ml with absorbing reagent. This solution contains 25 pg N
Pipet 0.5, 4, 10, 16 ml of the 25 (ig N0"/ml solution into 100 ml volumetric
flasks and dilute to the mark with absorbing reagent. These solutions
contain 0.125, 1.0, 2.5, 4.0 iig NO^/ml , respectively. Run standards as
instructed in 7.2. Plot absorbance vs ug NO^/ml . A straight line should
be obtained.
8.3 Efficiencies. An overall average efficiency of 93% was obtained
from test atmospheres having a nitrogen dioxide concentration of 20 to 700
3
pg/m .
9. Calculation
9.1 Sampling
9.1.1 Calculate volume of air sampled.
u - Fi + F? K
V - ] „ 2 x T x 10'6
30
-------
V = Volume of air sampled^ .
F, = Measured flow rate before sampling, cm /min.
3
F~ = Measured flow rate after sampling, cm /min.
T = Time of sampling, min.
10 = Conversion of cm to m .
9.1.2 Uncorrected Volume. The volume of air sampled is not corrected
to S.T.P., because of the uncertainty associated with 24-hour average tem-
perature and pressure values.
9.2 Calculate the concentration of nitrogen dioxide as yg N0?/m .
yg N02/m3 - (ug NCs/ml) X 50
V X (0.93)a
50 = Volume of absorbing reagent used in sampling, ml.
V = Volume of air sampled, m .
0.93 = Overall efficiency of method.
9.2.1 If desired, concentration of nitrogen dioxide may be calculated
as ppm NO^.
ppm = (ygN02/m3) X 5.32 X 10"4
10. References
1. Mulik, J. D., Fuerst, R. G. , Meeker, J. R., Guyer, M., Sawicki, E.
"A Twenty-Four Hour Method for the Collection and Manual Colorimetric
Analysis of Nitrogen Dioxide. Presented at the 165th ACS National
Meeting in Dallas, Texas, April 8-13, 1973.
2. Lodge, J. P., Jr., Pate, J. B., Ammons, B. E., Swanson, G. A. "The Use
of Hypodermic Needles as Critical Orifices in Air Sampling."
J.A.P.C.A. 16, 197-200 (1966).
The correction for collection efficiency was added to the method after
the ruggedness test. 31
-------
BUBBLER
TRAP
Figure A-l. Sampling train.
-------
OJ
OJ
OPEN
TO
ATMOSPHERE
RATE CONTROL VALVE
PUMP
FLOWMETER
Figure A-2. Flownieter.
-------
Appendix B. Equations for Calculating Ruggedness Test Results,
,~ . S^U^Vt-U t+V+X + Z
—: « - - * —— •
4 4
_ U+V+V/+X
4 ' 4
4
f V+V/+Z _
/=" 4 " 4
4 4
34
-------
Appendix C. Data from Ruggedness Test.
3
Expt. Result NOo, yg/m ... yg N09/ml Mean
No^_ Generated- Found Found^ Response, % Response, %
1 s 76.5 69.9 0.422 91.4 92 9
76.4 68.7 0.414 89.9
76.4 69.6 0.433 91.1
76.4 73.6 0.443 96.3
76.5 73.4 0.443 95.9
2 t 78.4 72.1 0.169 92.0 86 0
78.3 62.5 0.142 79.8
78.2 67.9 0.157 86.8
78.5 67.9 0.152 86.5
78.3 66.5 0.155 84.9
3 u 77.1 73,1 0.615 94.8 95 4
77.0 72.6 0.615 94.3
77.1 72.9 0.596 94.6
77.1 74.3 0.615 96.4
77.2 74.8 0.605 96.9
4 v 76.7 68.5 0.690 89.3 94 1
76.7 68.7 0.704 89.6
76.8 66.7 0.651 86.8
76.8 86.1 0.857 112.1
77.5 71.7 0.681 92.5
5 w 594.7 591.0 3.038 99 4 99 4
594.6 587.8 2.951 98 9
592.8 570.0 2.953 96.2
593.7 606.9 3.095 102 2
593.7 595.6 3.038 100.3
6 x 591.2 580.5 3.413 98.2 99 4
591.6 578.3 3.481 97.8
592.5 592.2 3.577 99.9
592.2 590.9 3.604 99.8
591.8 599.8 3.575 101.4
7 y 590.4 552.2 5.301 93.5 89 1
590.6 490.3 4.776 83.0
591.0 505.7 4.733 85.6
590.9 546.2 5.254 92 4
590.7 537.3 5.094 91.0
8 z 592.1 557.8 4.351 94.2 90 9
592.5 503.9 4.001 85.0
591.8 536.1 4.171 90.6
592.1 545.6 4.452 92 1
592.1 547.1 4.399 92.4
35
-------
APPENDIX D
ENVIRONMENTAL PROTECTION AGENCY
METHODS STANDARDIZATION BRANCH
QUALITY ASSURANCE AND ENVIRONMENTAL MONITORING LABORATORY
NATIONAL ENVIRONMENTAL RESEARCH CENTER
RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711
FEBRUARY 1974
TENTATIVE METHOD FOR THE DETERMINATION OF NITROGEN DIOXIDE
IN THE ATMOSPHERE (TGS-ANSA)a
aA tentative method is one which has been carefully drafted from
available experimental information, reviewed editorially within
the Methods Standardization Bran.ch and has undergone extensive
laboratory evaluation. The method is still under investigation
and therefore is subject tc revision.
36
-------
1. Principle and Applicability
1.1 Nitrogen dioxide is collected by bubbling air through a
solution of triethanolamine, o-methoxyphenol and sodium metabisulfite.
The nitrite ion produced during sampling is determined colormetrically
by reacting the exposed absorbing reagent with suIfanil amide and 8-
anilino-1-naphthalenesulfonic acid, ammonium salt..
1.2 The method is applicable to collections of 24-hour samples in
the field and subsequent analysis in the laboratory.
2. Range and Sensitivity
2.1 The range of the analysis is 0.025 to 4.0 ug NOl/ml. Beer's
law is obeyed throughout this range. With 50 ml of absorbing reagent and a
sampling rate of 200 cm /min for 24-hours, the range of the method is 20 to
T
/UU ug/m~ nitrogen dioxide.
2.2 A concentration of 0.025 ug NOl/ml will produce an absorbance
of approximately 0.025 using 1 cm cells.
3. Interferences
3.1 At a nitrogen dioxide concentration of 100 ug/m the follov/ing
pollutants, at the levels indicated, do not interfere: ammonia, 205 ug/m ;
3 3
carbon monoxide, 154,000 ug/m ; formaldehyde, 750 ug/m ; nitric oxide, 734
ug/m ; phenol, 150 ug/m ; ozone, 400 ug/m and sulfur dioxide, 439 uQ/m .
3.2 A temperature of 40°C during collection of sample had no effect
on recovery.
37
-------
4. Precision and Accuracy
4.1 Precision and Accuracy
4.1.1 On making measurements from standard nitrogen dioxide atmos-
pheres, prepared by using permeation devices, a relative standard deviation
of 2% and a collection efficiency of 93% were determined throughout the
range of the method.
4.2 Stability
4.2.1 The absorbing reagent is stable for 3 weeks before sampling and
the collected samples are stable for 3 weeks after sampling.
5. Apparatus
5.1 Sampling. A diagram of a suggested sampling apparatus is shown
in Figure D-l. '
5.1.1 Probe. Teflon, polypropylene, or glass tube with a polypropylene
or glass funnel at the end.
5.1.2 Absorption tube. Polypropylene tubes 164 x 32 mm. equipped with
polypropylene two-port closures. Rubber stoppers cause high and varying blank
values and should not be used. A glass tube restricted orifice is used to
disperse the gas. The tube, approximately 8 mm O.D.-6 mm. I.D., should be
152 mm long with the end drawn out to 0.3-0.6 mm. I.D. The tube should be
positioned so as to allow a clearance of 6 mm from the bottom of the absorber.
•5.1.3 "Moisture trap.Polypropylene tube equipped with a two port closure-.
The entrance port of the closure is fitted with tubing that extends to the
bottom of the trap. The unit is loosely packed with glass wool to prevent
rroisture entrainment.
38
-------
5.1.4 Membrane Filter, 0.8-2.0 microns porosity.
5.1.5 Flow Control Device. Any device capable of maintaining a
3
constant flow through the sampling solution between 180-220 cm /min.
2
A typical flow control device is a 27 gauge hypodermic needle, three-
eights inch long. (Most 27 gauge needles will give flow rates in this
range.) The device used should be protected from particulate matter.
A membrane filter is suggested. Change filter after collecting 10 samples.
5.1.6 Air Pump. Capable of maintaining a pressure differential of at
least 0.6-0.7 of an atmosphere across the flow control device. This value
(2)
includes the minimum useful differential, 0.53X ' atmospheres, plus a safety
factor to allow for variations in atmospheric pressure.
5.1.7 Calibration Equipment. Flowmeter for measuring airflows up to
3
275 cm /min. within +_ 2%, stopwatch, and a precision wet test meter (1 liter/
revolution).
5.2 Analysis
5.2.1 Volumetric Flasks.. Two each 250, 1000 ml; three each 200; 7 each
100 ml; one 500 ml.
5.2.2 Pipets, volumetric. One each, 2, 3, 9, 10, 20 and 50 nil; seven 5
5.2.3 Pipets serological, graduated in 1/10 ml divisions. One eoch 1,
5 ml.
5.2.4 Test Tubes. Each approximately 20 x 150 nun.
5.2.5 Spectrophotometer. Capable of measuring absorbance at 550 m:i.
5.2.6 Graduated cylinder. One each 50 ml.
39
-------
6. Reagents
6.1 Sampling
6.1.1 Triethanolamine [N^H.OH).,]. Reagent grade.
6.1.2 o-Methoxyphenol (o-CH3OCgH4CH). Also known by its trivial
name, guaiacol. Reagent grade. Melting point 27-28°C. (Caution: Technical
grade material will not meet this specification and should not be used).
6.1.3 Sodium Metabisulfite (Na^SpOr).' ACS reagent grade.
6.1.4 Absorbing Reagent - Dissolve 20g of triethanolamine, 0.5g of
o-methoxyphenol, and 0.250g of sodium metabisulfite consecutively in 500 ml
of distilled water. Dilute to one liter, with distilled water. Mix thorough-
ly. The solution should be colorless. This solution is stable for three weeks,
if kept refrigerated.
6.2 Analysis
6.2.1 Hydrogen Peroxide (H20p). ACS reagent grade, 30%.
6.2.2 Sulfanilamide [4-(H2N)CgH4S02NH2]. Melting point 165-167°C.
6.2.3 8-Anil ino-1-naphthalenesulfonic acid Ammonium salt (ANSA) (8-C,H-l,'H-
0 3
l-C10H6SO~r,'H*). Minimum analysis, 98%.
6.2.4 Sodium Nitrite, [NaN02]. ACS reagent grade. Assay of 97% NaN02
or greater.
6.2.5 Methanol, absolute [CH-jOH]. ACS reagent grade.
6.2.6 Hydrochloric acid, [HC1]. Concentrated. ACS reagent grade.
6.2.7 Hydrogen Peroxide Solution. Dilute 0.2 ml of 30;^ hydrogen peroxide
to 250 ml with distilled water. This solution can be used for a month if pro-
tected from light and refrigerated.
40
-------
6.2.8 Sulfanilamide Solution (2.0^ in 4^HC1). Dissolve 2.0g of
sulfanilamide in 33 ml of concentrated HC1 and- dilute to 100 ml with
distilled water. Mix. This solution can be used for two weeks, if
refrigerated.
6.2.9 ANSA Solution. (0.12 W/v). Dissolve O.lg ANSA in 50 ml absolute
nethanol. Dilute to 100 ml with absolute irethanol in a volumetric flask.
Mix. Keep stoppered, when not in use, to minimize evaporative losses. Pre-
pare fresh daily. ( CAUT Ip.f j_: Older reagent may result in lower absorbance).
6.2.10 Standard Nitrite Solution. Dissolve sufficient desiccated
sodium nitrite and dilute with distilled water to 1000 ml so a solution
containing 1000 ygNO^/ml is obtained. The amount of NaNOp to use is
calculated as follows:
G •
x ,00
where
G = Amount of NaNCL, grams.
1.500 = Gravimetric factor in converting N0? into NaiNOo
A = Assay, percent
7. Procedures
7.1 Sampling. Assemble the sampling apparatus, as shown in Figure D-l.
Components upstream from the absorption tube may be connected, where required,
with teflon or polypropylene tubing; glass tubing with dry ball joints; or
glass tubing with butt-to-butt joints with tygon, teflon or polypropylene.
Add exactly 50 ml of absorbing reagent to the calibrated absorption tube
41
-------
(8.1.3). Disconnect funnel, insert calibrated flowmeter (8.1.1) into
the end of the probe and measure flow before sampling. Denote as F,.
If flow rate before sampling is not between 180-220 cm /min replace the
flow controlling device and/or check the system for leaks. Start sampling
only after obtaining an initial flow rate in this range. Sample for 24-
hours and measure the flow after sampling by again inserting a calibrated
flowmeter into the probe, after removfng the funnel. Denote as F?.
7.2 Analysis. Replace any water lost by evaporation during sampling
by adding distilled water up to the calibrated mark on the absorption tube.
Mix well. Pipet 5 ml of the collected sample into a test tube, add 0.5 ml
of the peroxide solution and mix vigorously for approximately 15 seconds.
Add 2.7 ml of sulfanilamide solution and mix vigorously for about 30 seconds.
Then pipet 3 ml of the ANSA solution, mix vigorously for about 30 seconds.
The ANSA must be added within 6 minutes of mixing the sulfanilamide solution.
(CAUTION: Longer time intervals will result in lowered absorbance values).
Prepare a blank in the same manner using 5 ml of unexposed absorbing solution.
The absorbance of the blank should be approximately the same as the y-inter-
cept in the calibration curve (Section 8.2). Determine absorbance at 550 nm
with distilled water in the reference cell using 1 cm cells. The color can
be read anytime from 1 to 40 minutes after addition of the AHSA. Read
ug NOZ/ml from the calibration curve (Section 8.2).
7.3 SpectrophotoiiiGter cells must be rinsed thoroughly with distilled
water, acetone, and dried, otherwise a film will build up on the cell walls.
8. Calibration and Efficiencies
8.1 Sampling
42
-------
8.1.1 Calibration of Flowmeter. (See Figure D-2.) Using a wet test
2
meter and a stopwatch, determine the rates of air flow (cm /min) through.
the flowmeter at a minimum of four different ball positions. Plot ball
position versus flow rate.
8.1.2 Flow Control Device. The flow control device results in a
constant rate of air flow through the absorbing solution and is determined
in 7.1.
8.1.3 Calibration of Absorption Tube. Calibrate the polypropylene
absorption tube, (Section 5.1.2) by first pipeting in 50 ml of water or
absorbing reagent. Scribe the level of the meniscus with a sharp object,
go over the area with a-felt-tip marking pen, and rub off the excess.
8.2 Calibration Curve. Dilute 5.0 ml of the 1000 ug NO^/ml solution
u
to 250 ml with absorbing reagent. This solution contains 20 ug NOp/ml .
Dilute 5.0 ml of the 20 pg NOZ/rcl standard to 200 ml with absorbing reagent.
This solution contains 0.50 pg NOZ/ml . Prepare calibration standards by
pipeting the indicated volume of the standard into volumetric flasks and
diluting to the mark with absorbing reagent.
Final Concentration
Volume of Standard :Vo1ume ml yg N
10 ml of 0.50 pg NO^/ml 100 0.05
20 ml of 0.50 ug N0~/inl 100 0.10
2 nl of 20 yg f,'0~/ml 200 0.20
Use 0.50 ug/ml Standard Directly ~~ 0.50
5 ml of 20 ug NO^/ml Standard 100 1.00
9 nil of 20 pg NO^/ml Standard . 100 1.80
43
-------
Run standards, plus a blank, as instructed in 7.2. Plot absorbance vs
ug NOl/ml. A straight line should be obtained with a slope of approximately
0.5 absorbance units/yg NOl/ml, and a y-intercept (i.e., zero ug N09/ml) of
•Q ' C. C-
approximately 0.01 absorbance units. The absorbance is linear up to a con-
centration of 4.0 u'g MOZ/ml, absorbance of 1.9. Therefore, if samples
exceed the absorbance of the highest calibration standard and the above
absorbance is within the range of the spectrometer, the calibration curve
can be extended by including higher concentration standards. If a higher
absorbance range is not available, samples must be diluted with absorbing
reagent until the absorbance is within'the ranqp of th». hi^st standard.
8.3 Efficiencies. An overall average efficiency of 93% was obtained
from t.pst atmospheres having a nitroqen dioxide concentration of 20 to 700
ug/m .
9. Calculation
9.1 Sampling
9.1.1 Calculate volume of air sampled.
V = F1 * F2 x T x 10"6
2
V = Volume of air sampled,, m .
F-i = Measured flow rate before sampling, cm /min.
3
Fp = Measured flow rate after sampling, cm /min.
T = Time of sampling, min.
10" = Conversion of cm to m .
9.1.2 Uncorrected Volume. The volume of air sampled is not corrected
to S.T.P., because of the uncertainty associated with 24-hour average
44
-------
temperature and pressure values.
^>
9.2 Calculate the concentration of nitrogen dioxide as pg N02/i"J.
v:g fi02/in3 = (t:g NOij/ml) X 50
V X (0.93)
50 = Yolir;* of absorbing reagont used in sampling, nil.
3
V = Volume of air sar.'.plod, ni .
0.93 = Overall efficiency of ir.etiiod.
9.2.1 If desired, concentration of nitrogen dioxide may be calculouoJ
as pp;n HO.,.
pp;n = (i.::i;02/n3) X 5.32 X 10"4
10. References
1. X'jli';, J. D., Fuerst, R. G., Meeker, J. R., Guyer, fl., Sawicki, E.
"A Twenty-Four Hour Method for the Collection and Manual Colorirr.otric
Analysis of Nitrogen Dioxide. Presented at the 165th ACS National
Meeting in Dallas, Texas, April 8-13, 1973.
2. Lodgo, J. P., Jr., Poco, J. B., Ammons, B. E., Swanson, G. A. "The
Use of Hypodermic Needles as Critical Orifices in Air Sampling."
J.A.P.C.A. 1_6, 197-200 (1966).
45
-------
BUBBLER
TRAP
Figure D-l. Sampling train.
-------
OPEN
TO
ATMOSPHERE
RATE CONTROL VALVE
PUMP
FLOWMETER
Figure D-2. Flowmeter.
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-650/4-74-047
3. RECIPIENT'S ACCESSIOI»NO.
4. TITLE AND SUBTITLE
AN EVALUATION OF TGS-ANSA RROCEDURE FOR DETERMINATION
OF NITROGEN DIOXIDE IN AMBIENT AIR
6. REPORT DATE
November 1974
6. PERFORMING ORGANIZATION CODE
7. AUTHORIS)
Robert G. Fuerst and John H. Margeson
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
10. PROGRAM ELEMENT NO.
Environmental Protection Agency
Quality Assurance and Environmental Monitoring Lab.
National Environmental Research Center
Research Triangle Park, N.C. 27711
1HA327
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
A detailed method write-up describing the TGS-ANSA manual procedure for measure-
ment of NO- in ambient air was developed. The method involves sampling for 24 hours
with a restricted-orifice bubbler immersed in a triethanolamine, o-methoxyphenol,
sodium metabisulfite solution. The range of the method is approximately 20 to 700
ug/m . The method was evaluated to determine its usefulness. This involved a review
of the procedure, as developed, to judge the adequacy of the development work and
ruggedness testing, as described by Youden.
The method was shown to be free from interferences such as: NO, S0?, 0VCO, and
NH~ and posseses a constant-high collection efficiency, 93 %. The ruggedness test
showed the method to be insensitive to normal variations in: time between sample col-
lection and analysis, storage conditions after sample collection, flow rate, C0? con-
centration, sampling time, and orifice size. The time interval between the addition
of the diazonium salt forming reagent and the diazonium salt coupling reagent is
critical and must be carefully controlled.
The method appears to be a reliable procedure for the measurement of N0? in am-
bient air. ^
The method will now be subjected to a collaborative test to determine its
repeatability, reproducibility, and bias.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Nitrogen dioxide measurement
Method evaluation
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATi l-'icld/Group
18. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report I
Unclassified
21. NO. OF PAGES
54
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
48
------- |