EPA-650/4-74-031
July 1974
Environmental Monitoring Series
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EPA-650/4-74-031
EVALUATION OF TRIETHANOLAMINE
PROCEDURE FOR DETERMINATION
OF NITROGEN DIOXIDE
IN AMBIENT AIR
E. Carol Ellis and John H. Margeson
Quality Assurance and Environmental Monitoring Laboratory
Task No. 015
Program Element No. IHA327
ROAP No. 26AAF
ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
National Environmental Research Center
Research Triangle Park, N. C. 27711
July 1974
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Research reports of the Office of Research and Development, Environ-
mental Protection Agency, have been grouped jnto five scries.
Thc'.si- live broad categories were established to facilitate- further
development and application of environmental technology, Elimination
ol traditional grouping was> consciously planned to lo.slc.-r technology
and a maximum interface in related fields. The five series
are:
1. 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 con-
ceivably significant concentrations. It also includes studies to
determine the ambient concentrations of pollutants in the environment
ancl/or the variance of pollutants as a function of time or meteorologi-
cal I actors.
Copies ol 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 22151.
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ABSTRACT
A detailed method write-up describing the triethanolamine (TEA)
manual procedure for measurement of nitrogen dioxide in ambient
air was developed. The method involves sampling for 24 hours with
a fritted bubbler immersed in 0.1N TEA collecting solution. The
3
range of the method is approximately 20 to 700 gg/m .
The method was evaluated to determine its usefulness for meas-
uring nitrogen dioxide in ambient air. This involved a review of
the procedure as developed and subsequent laboratory experiments
to better define some obscure points in the procedure. The con-
stancy of the method's collection efficiency, the addition of
n-butanol to enhance the collection efficiency and the need to use
fritted bubblers as gas dispersers to assure high collection
efficiency were the main points investigated in these experiments.
The results indicated a constant collection efficiency over the
method's range both with and without any added n-butanol using
either frits or restricted-orifice bubblers; however, the collection
efficiency using frits is about 80%, while the efficiency drops to
about 50% using restricted-orifice bubblers.
Further work on the method does not seem warranted at this
time because the availability of other methods which show more
promise for the measurement of NO in ambient air.
2
m
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CONTENTS
List of Figures v
List of Tables v
Acknowledgments v""
Sections
I Conclusions 1
II Introduction 2
III Experimental 3
IV Results and Discussion 5
V Additional Experiments and Results 9
VI References 10
VII Appendices 11
Bibliographic Data Sheet 28
IV
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FIGURES
No. Page
1. Collection Efficiency vs. NOg Concentration Using
Fritted Bubblers 6a
2. NOo Concentration Detected vs. NCL Concentration Sampled
for TEA Absorbing Solution (frits) 6b
3. Collection Efficiency vs. NC^ Concentration Using
Restricted-Orifice Bubblers 7a
4. N(L Concentration Detected vs. N(L Concentration Sampled
for TEA (restricted bubblers) 7b
TABLES
No. Page
1. Effect of Aging on N02 Recovery in Collected Samples 9a
2. Comparison of S-NEDA and S-ANSA Analytical Systems 9b
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ACKNOWLEDGMENTS
The authors wish to thank Mr. Dario Levaggi and others at
the San Francisco Bay Area Air Pollution Control District for
assistance and helpful discussions during the procedure review.
vi
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SECTION I
CONCLUSIONS
The TEA method has a high collection efficiency of 80%
using fritted bubblers for gas dispersion. The use of a frit is
a disadvantage to the method, because the frit porosity needs to
be checked periodically and these bubblers are easily broken
under normal usage. The collection efficiency obtained by using
the more preferable restricted-orifice bubbler is 50%, too low to
(4 5}
warrant its use. Other manual N02 methods* '' are available
that have high collection efficiencies of 80% or greater using
restricted-orifice bubblers. Since Methods Standardization Branch
plans to standardize only the most promising methods for N02
measurements, it appears that further work on the TEA method is
not justified at this time.
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SECTION II
INTRODUCTION
The Methods Standardization Branch (MSB) of the Quality Assurance
and Environmental Monitoring Laboratory (QAEML), has the responsibility
to evaluate and standardize various methods for measuring air pollutants
to determine their utility. In the case of nitrogen dioxide, the Federal
Register reference Method* ' has been shown to be highly inadequate. ' '
In light of this, the reference method for measuring nitrogen dioxide was
withdrawn and the Environmental Protection Agency (EPA) chose three
(4)
tentative methodsv ' for replacement of the original reference method.
Interested persons were asked to comment on the three procedures as well
as to offer suggestions of other methods for consideration. Additional
manual methods* ' 'were suggested; one of these was the TEA liquid-absorber
method.
In the TEA method, ' air is pulled through an aqueous solution of
triethanolamine (TEA) and a small amount of n-butanol; nitrogen dioxide
present in the sampled air volume is absorbed by the solution. A sub-
sequent colorimetric analysis of the exposed collecting solution indicates
the concentration of NOp in the air sample. This report describes a
laboratory evaluation of the TEA method.
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SECTION III
EXPERIMENTAL
All reagents and procedures used in this evaluation are described
in Appendix A. The method write-up therein is a slightly modified
version of the TEA method developed by Levaggi and co-workers. '
A. Test Atmosphere Generation
Test atmospheres containing known concentrations of NCL were generated
by diluting the effluent from a MCL-permeation device with controlled
(789^
volumes of purified air. This procedure has been well documented. ' ' '
Three permeation devices of the FEP-teflon sleeve, glass reservoir
type* ' developed jointly by NBS and EPA were employed in the study.
They were gravimetrically calibrated 'throughout the study oeriod
and all showed a constant permeation rate at constant temperature.
Device No. 25-7 with a low permeation rate, 0.690 ± .003 ygN02/min,
was used for generating N02 concentrations up to 300 ug/m . The other
devices (Nos. 25-2 and 19-2) were used simultaneously to create the
high NOp concentrations (300 to 700 yg/m ) and have a combined per-
meation rate of 1.952 +_ .003 qg/min.
For sampling and calibration, the permeation device was housed
in a water-circulated condenser maintained at 25.0 ±0.1°C by a
constant temperature bath. A stream of dry nitrogen at approximately
3
100 cm /min was passed over the device to flush the NOp from the
condenser into a dilution chamber. The dilution air was compressed
(housed) air purified by passage through silica gel for drying, air
filters for particle removal, and finally a mixture of activated charcoal
(6-14 mesh), molecular sieve (6-16 mesh, type 4A), and silica gel (6-16 mesh)
for removal of any N02 and hydrocarbons.
3
-------
A blank consisting of a 24-hour sampling of dilution air plus
flushing nitrogen with no permeation device in the system, showed a
NOp background of less than 2.5 pg NOp/m . Thus the generation
system was free of NCL interference.
B. Sampling
Samples were collected in quintuplicate according to the
method described in Appendix A.
C. Flow Measurement
The flow rate for each absorption tube was measured before
and after sample collection with a soap-bubble flow meter. The
total flow rate into the inlet manifold was also measured immedi-
ately before and after sampling for comparison with the sum of
the individual flows to detect any system leaks. Samples with
a final flow that differed by more than 10% from the initial flow
were rejected. Total dilution air flows in the NOp generation
system were measured before and after sampling using a wet test
meter (1 Ji/rev or 10 fc/rev). The dilution air flow never varied
more than one percent in any 24-hour sampling period.
D. Bubblers
Fritted bubblers with a porosity of 60 to 100 urn were used
for dispersion as described by the method. The restricted-orifice
bubblers used in some experiments were 0.5 - 0.7 mm I.D.
E. Analysis
After sampling the tubes were disconnected from the sample
manifold. Water lost by evaporation was replaced and an aliquot of
the sample was analyzed as described in the method. A Beckman
Model "B" Spectrophotometer was used for the absorbance measurements.
4
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SECTION IV
RESULTS AND DISCUSSION
The first phase of method standardization by MSB is a orocedure
review and subsequent laboratory evaluation, if necessary. The former
involves assessing the method developers' recommended procedure as to its
potential for making meaningful measurements. Accordingly, a visit was
made to the developers of the TEA method to gain insight into the method's
development and to see how the method performed under optimum conditions,
i.e. when used by persons trained in the method. The results of the visit
indicated that a laboratory evaluation would be necessary. In particular,
further study was needed to determine the constancy of the collection
efficiency over the useful range, 0-700 ygNOp/m ; to determine the effect
of n-butanol on the collection efficiency of the TEA solution; and to
investigate replacement of the recommended fritted bubblers by restricted-
orifice bubblers as gas dispersers.
The collection efficiency is of utmost importance because it is a
measure of the overall method response to sampling NOp. It includes both
the method's absorption efficiency (percentage of N02 trapped chemically
or physically in the absorbing solution during sampling) and stoichiometric
factors (equivalency of nitrogen dioxide gas to nitrite ion in the absorb-
ing solution). Mathematically the collection efficiency (percent) is
expressed as the ratio of the concentration of N02 detected to the concen-
tration of NOg sampled multiplied by 100. The slope from a plot of
collection efficiency vs. concentration of IWL sampled indicates how the
-------
collection efficiency varies with concentration. If the slope is signifi-
cantly different from zero, the method has no utility because its response
would depend on N02 concentration. On the other hand, if the collection
efficiency is essentially constant, then the slope from a plot of concen-
tration detected vs. concentration sampled gives the average collection
efficiency directly.
Two series of experiments were designed for the laboratory evaluation
of the TEA method. In the first series, three TEA absorbing solutions were
exposed to N02 over the range 30-700 ygNOp/m using the fritted bubblers
recommended by the method; in the second series restricted-orifice bubblers
replaced the fritted bubblers. The three absorbing solutions were 0.1N TEA
with n-butanol added at three concentrations levels (3ml/I, 0.5ml/I and 0.0ml/I),
The collection efficiency as a function of N02 concentration is shown
in Figure 1 for the three TEA absorbing solutions using the fritted bubblers.
The slope for each curve from a least squares linear regression fit is
essentially zero thus, indicating a constant collection efficiency across
the range of interest. The collection efficiency is also independent of
n-butanol level studied as evidenced by the near superposition of the three
curves in Figure 1.
To obtain the average collection efficiency over the pertinent concen-
tration range for each absorbing solution, the slope from a plot of ML con-
centration detected vs. N02 concentration sampled is determined for each
solution. From the slope of the least squares linear regression curve in
Figure 2, the average collection efficiency for the TEA-O.Oml n-butanol/I
-------
O)
O
1 I 0.0
100.01
•0.0
B0.0
•70.0
B0.0
A: TEA-3.Oml/A n-Butanol +
B: TEA-0.5ml/!i. n-Butanol A
C: TEA-O.Oml/«, n-Butanol O
Concentration N02 Sameled (yg/m )
F1gure !. Conectlon Efficiency vs. NO, Concentration «.,«, FHt« BUbblers.
-------
SBB.ES T
co
CO
at
O
-------
solution is 78.8%. Similar plots also indicate average collection
efficiencies of about 80% for the other two TEA solutions. This
method for obtaining the average collection efficiency is to be
preferred over using the y-intercept value from a plot like
Figure 1 as the average collection efficiency. The curve in
Figure 2 not only provides a direct and accurate average collection
efficiency, but also its linearity is indicative of the constancy
of the collection efficiency over the concentration range of
interest. Associated with a linear regression analysis, an often-
used indicator of the strength of the linear relationship between
the two variables under consideration (in this case concentration
detected vs. concentration sampled) is the correlation coefficient or
r value. The closer the |r| is to 1.0 then the stronger is the
linear correlation between the two variables. In the case of
Figure 2, r = 0.996.
The results of the experiments using restricted-orifice
bubblers as seen from Figure 3 again show a constant collection
efficiency independent of NO^ concentration sampled or of n-butanol
level in the TEA absorbing solution. Though constant, the average
collection efficiency drops by about 30% when using restricted-
orifice bubblers. This lower collection efficiency (47%)
is shown in Figure 4 for the TEA-0.0 ml n-butanol/I.
In summary, the collection efficiency over the concentration range
studied, is constant and independent of n-butanol level in the absorbing
solution using either frits or restricted-orifice bubblers; however, the
collection efficiency using frits is about 80%, while the efficiency drops
to about 50% for restricted-orifice bubblers. Since there appears to be no
-------
O)
•r—
U
(J
O)
•7BJ.B
BS.G3
BB.B
5S.B
BB9J8
HB.Qi
HB.B
35.68
A: TEA-O.Bml/j, n-Butanol -«-
B: TEA-O.Oml/j, n-Butanol O
Concentration NOp Sampled (ng/m )
Figure 3. Collection Efficiency vs. N02 Concentration Using Restricted-Orifice
Bubblers.
-------
en
3.
-o
QJ
a
c
o
(U
U
o
CM
HSTB.B T
HBB.B
3SB.B
3BB.B
2SBJ.SB • •
Z0B.B!
ISB.B
IBB.B
SB.B
B.BT
NOg Concentration Sampled (gg/m )
Figure 4. N02 Concentration Detected vs. NOp Concentration Sampled for TEA (restricted-
orifice bubblers).
-------
advantage to adding n-butanol to the TEA absorbing solution, Its addition
Is not recommended in the method write-up in Appendix A. The recommended
TEA procedure uses fritted bubblers and has an average collection efficiency
of 78.8$ over the range 0-700 yg/m NOp. Experimental data are found in
Appendix B.
12
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SECTION V
ADDITIONAL EXPERIMENTS & RESULTS
During the course of the laboratory evaluation, it was a simple
matter to collect stability data on the absorbing solutions. Collected
samples were analyzed immediately, then again at one week and three week
intervals after collection. There were no significant differences noted
in the amount of NOp detected for any of the analyses (Table 1). Addition-
ally, the TEA absorbing solutions were all found to be stable for at least
a month after preparation when stored in glass containers placed on the
bench top.
A large number of the collected samples were also analyzed by an
alternate colorimetric procedure.:^ The collection efficiencies obtained
by the sulfanilamide - 8-Anilino-l-naphthalenesulfonic acid Ammonium salt
(S-ANSA) procedure were consistently about 10% higher than those obtained by
the method's recommended analytical procedure^ - diazotization of sulfanilamide
and coupling to N-(l-Naphthyl)-ethylenediamine Dihydrochloride (S-NEDA). Results
comparing the two analytical procedures are shown in Table 2. Though some-
what puzzling, no explanations can be given for the differences noted between
the two analytical procedures and no further investigations seem warranted
at this time, because the scope of the evaluation of the TEA method did not
call for optimization.
13
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Table 1. Effect of Sample Age on Collection Efficiency.
N02 Sailed n-Butano, Level
(ug/m (ma/a) Immediately 1st week 3rd week Mean(%)
0.0 83.8 91.7 97.8 91.1
35.7a 0.5 82.9 89.8 94.1 88.9
3.0 88.0 100. 99.9 95.9
Q.O 84.3 89.2 90.1 87.9
99.9 0.5 84.2 87.4 91.6 87.7
3.0 89.9 95.1 91.9 92.3
a 0.0 79.7 87.5 89.6 85.6
201 0.5 82.9 91.9 95.0 89.9
3.0 86.0 92.1 95.5 91.2
0.0 92.2 94.6 89.7 92.2
304 0.5 88.8 92.1 88.1 89.7
3.0 89.0 90.6 87.2 88.9
83.8
82.9
88.0
84.3
84.2
89.9
79.7
82.9
86.0
92.2
88.8
89.0
85.0
88.7
90.5
81.1
82.6
82.7
77.5
82.5
84.9
75.6
77.9
81.3
91.7
89.8
100.
89.2
87.4
95.1
87.5
91.9
92.1
94.6
92.1
90.6
84.6
85.1
86.7
83.2
85.4
85.0
76.5
78.5
81.1
80.4
81.6
83.7
97.8
94.1
99.9
90.1
91.6
91.9
89.6
95.0
95.5
89.7
88.1
87.2
81.6
87.6
86.1
85.4
85.6
84.5
85.6
85.1
87.3
80.5
82.7
85.0
0.0 85.0 84.6 81.6 83.7
395 0.5 88.7 85.1 87.6 87.1
3.0 90.5 86.7 86.1 87.8
0.0 81.1 83.2 85.4 83.2
490 0.5 82.6 85.4 85.6 84.5
3.0 82.7 85.0 84.5 84.1
0.0 77.5 76.5 85.6 79.9
587 0.5 82.5 78.5 85.1 82.0
3.0 84.9 81.1 87.3 84.4
0.0 75.6 80.4 80.5 78.8
701 0.5 77.9 81.6 82.7 80.7
3.0 81.3 83.7 85.0 83.3
a: Samples were not properly sealed initially and evaporative losses
caused the seemingly increased results with aging.
14
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Table 2. Comparison of S-NEDA and S-ANSA Analytical Systems.
Collection Efficiency (%)
Sampled TEA - 0.0 mfc n-Butanol/fc
. '
(yg/m3) S-NEDA S-ANSA
35.7 83.8 96.2
53.2 77.2 89.5
99.9 84.3 91.1
201 79.7 88.6
208 85.6 91.8
301 78.7 94.0
304 92.2 97.8
395 85.0 88.3
423 83.7 96.4
490 81.1 87.8
587 77.5 90.1
602 82.4 91.9
701 75.6 82.9
15
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SECTION VI
REFERENCES
1. Federal Register. 36, 8186 (April 30, 1971).
2. Mauser, T. R. and Shy, C. M., Environ. Sci. Techno!.. 6_, 890 (1972).
3. Merryman, E. L. ejt aj_., Environ. Sci. Technol.. ]_, 1056 (1973).
4. Federal Register. 38, 15174 (June 8, 1973).
5. Mulik, J. D. et al_., Environ. Anal. Chem.,To be published.
6. Levaggi, D. A. e£ alL, J. Air Pollut. Contr. Ass.. 23_, 30 (1973).
7. O'Keeffe, A. E. and Ortman, G. C., Anal. Chem., 38, 760 (1966).
8. Scaringelli, F. P. e_t al_., Amer. Indus. Hyg. Ass. J.. 28, 260 (1967).
9. Scaringelli, F. P. et al_., Anal. Chem.. 42_, 871 (1970).
10. National Bureau of Standards Technical Note 585, p. 26. Available from:
Superintendent of Documents, Government Printing Office, Washington, D.C.
20402, 70 cents.
11. Rook, H. L. e_t al_., "Operation Characteristics of N02 Permeation Devices."
Presented at the 167th American Chemical Society Meeting, Los Angeles,
Calif., March 31-April 5, 1974, Paper No. 61.
16
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SECTION VII
APPENDICES
APPENDIX A
TENTATIVE METHOD FOR THE DETERMINATION OF NITROGEN DIOXIDE IN
THE ATMOSPHERE (TRIETHANOLAMINE PROCEDURE)3
A 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.
17
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1. Principle and Applicability
1.1 Nitrogen dioxide is collected by bubbling air through an
aqueous triethanolamine^ ' solution. The nitrite ion produced during
sampling is determined colorimetrically via diazotization of sulfanil amide
and subsequent coupling with N-(l-naphthyl)-ethylenediamine to form an azo
dye.
1.2 The method is applicable to collection 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 0.04 to 2.0 yg NOg/ml. Beer's law
is obeyed throughout this range (0 to 1.0 absorbance units). With 50 ml
of absorbing reagent and a sampling rate of 200 cm /min for 24-hours, the
3
range of the method is 20 to 700 yg/m (0.01 to 0.4 ppm) nitrogen dioxide.
2.2 A concentration of 0.04 yg NOZ/ml will produce an absorbance of
approximately 0.016 with 1 cm cells.
3. Interferences
3.1 Nitric oxide at concentrations as high as 740 yg/m in the
3 CM
presence of 40 - 170 yg/m N02 does not affect the N02 analyses. '
3.2 The potential SOo interference is eliminated by converting it
(2)
to sulf ate ion with hydrogen peroxide prior to analysis/ '
3.3 Ozone at atmospheric concentrations does not affect analysis
for N02.
4. Precision, Accuracy and Stability
4.1 Precision. Insufficient data are available to state the precision
of the method.
18
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4.2 Accuracy. No accuracy data are available.
4.3 The absorbing reagent is stable for up to 5 weeks without
refrigeration. Collected samples are stable for at least 3 weeks prior
to analysis.
5. Apparatus.
5.1 Sampling. A diagram of a suggested sampling apparatus is shown
in Figure 1.
5.1.1 Probe. Teflon, polypropylene, or glass tube with a glass or
polypropylene funnel at the end.
5.1.2 Absorption Tube. Polypropylene tubes 164 x 32 mm, equipped with
polyproylene two-port closures. A gas dispersing tube with a fritted end
of 60 to 100 urn porosity is used in conjunction with the tube. Frits need
be screened as to exact porosity only for initial usage. The maximum use-
able pore diameter is about 160 pm.
5.1.2.1 Measurement of Maximum Pore Diameter of Frit. Carefully clean
the frit with dichromate-concentrated sulfuric acid cleaning solution and
rinse well with distilled water. Insert through one hole of a two-hole
rubber stopper and install in a test tube containing sufficient distilled
water to cover the fritted portion. Attach a vacuum source to the other
hole of the rubber stopper and measure the vacuum required to draw the
first perceptible stream of air bubbles through the frit. Apply the
following equation:
maximum pore diameter, pm = -5^-
s = Surface tension of water (dynes/cm) at the test temperature (73 at
18°C, 72 at 25°C and 71 at 31°C).
P = Measured vacuum, mmHg.
19
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5.1.3 Moisture Trap. Polypropylene tube equipped with 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.
5.1.4 Membrane Filter. 0.8-2.0 ^m porosity to protect the flow control
device from parti cul ate matter. The filter should be replaced after collect-
ing ten samples.
5.1.5 Flow Control Device. Any device capable of maintaining a con-
stant flow through the absorbing solution between 180-220 cm /min. A typical
flow control device is a 27-gauge hypodermic needle, ' three-eights inch
long.
5.1.6 Air Pump. Capable of maintaining a pressure differential of at
least 0.6 - 0.7 atm across the flow control device. This value includes
/3\
the minimum useful differential, ' 0.53 atm, plus a safety factor to allow
for variations in atmospheric pressure.
5.1.7 Calibration Equipment. Flow meter for measuring air flows up to
275 cm /min within +2%, stopwatch, and a soap-bubble flow meter (100 ml).
5.2 Analysis
5.2.1 Glassware. Appropriate vol. flasks, pi pets, graduated cylinders
and test tubes to prepare reagents and standard solutions and to oerform
colorimetric analyses.
5.2.2 Spectrophotometer. Instrument capable of measuring absorbance
at 530 nm.*
* The wavelength of maximum absorbance for the azo dye should be determined.
Different manufacturers' lots of NEDA have different absorption peak
maximas.
20
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6. Reagents
6.1 Sampling
6.1.1 Triethanolamine [N(C2H4OH)3]. Reagent grade.
6.1.2 Absorbing Solution. Dissolve 15g of triethanolamine (TEA) in
500 ml of distilled H20. Dilute to one liter with distilled water. The
solution is stable for at least one month without refrigeration.
6.2 Analysis
6.2.1 Hydrogen Peroxide (H202). ACS reagent grade, 30%.
6.2.2 Sulfanilamide [4-(H2N)CgH4S02NH2] melting point 165-167°C.
6.2.3 N-(l-Naphthyl)-ethylenediamine dihydrochloride (NEDA). Best
grade available.
6.2.4 Sodium Nitrite, (NaN02). ACS reagent grade. Assay of 97% NaN02
or greater.
6.2.5 Phosphoric Acid (HjPO^). ACS reagent grade, 85%.
6.2.6 Hydrogen Peroxide Solution. Dilute 0.2 ml of 30% H202, to 250
ml with distilled water. The solution may be used for a month if protected
from light and refrigerated.
6.2.7 Sulfanilamide Solution. Dissolve 20g sulfanil amide in 700 ml
distilled water. Add, with mixing, 50 ml concentrated H-PO. and dilute to
one liter. The solution is stable for one month, if refrigerated.
6.2.8 NEDA Solution. Dissolve 0.5g of NEDA in 500 ml distilled water.
The solution is stable for one month, if refrigerated and protected from
light.
6.2.9 Standard Nitrite Solution. Prepare a liter of 100 ygNOZ/ml for
a stock nitrite standard. The amount of NaNO,, to use is calculated as follows:
21
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G = 1.500 x 100%
A "TO"
where
G = amount of NaNCL* grams
1.500 = gravimetric factor in converting N02 into NaN02
A = assay per cent
10 = dilution factor
7. Procedure
7.1 Sampling. Assemble the sampling apparatus as shown in Figure
1. Components up stream 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 on
polypropylene. Add exactly 50 ml of absorbing reagent to the (calibrated)
absorption tube. Disconnect funnel, insert calibrated flowmeter and
measure flow before sampling. If flow rate before sampling is not between
180 and 220 cm /min, replace the flow control 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 the sampling
period.
7.2 Analysis. Replace any water lost by evaporation during
sampling by adding distilled water up to 50 ml; mix well. Pi pet 5 ml of
the collected sample into a test tube; add 0.5 ml of the peroxide solution,
5 ml sulfanilamide solution and 0.7 ml NEDA solution with thorough mixing
after the addition of each reagent. Prepare a blank in the same manner
using 5 ml of unexposed absorbing reagent. Allow the color to develop for
22
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10 minutes, then measure the absorbance of sample against the blank at 530 nm.
Read pgNOl/ml from the calibration curve (Section 8.2). Samples with an
absorbance greater than 1.0 must be reanalyzed after diluting an aliquot (less
than 5 ml) of the collected sample with unexposed absorbing reagent to 5 ml.
8. Calibration and Efficiencies
8.1 Sampling
8.1.1 Calibration of Flowmeter. Using a soap-bubble flow meter and a
o
stopwatch, determine the rates of air flow (cm /min) through the flowmeter
at a minimum of 4 different flows. Plot meter position versus flow rates.
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 Section 7.1.
8.2 Calibration Curve. Dilute the stock standard nitrite solution
(Section 6.2.9) 50:1 with TEA absorbing solution to prepare a working
standard solution containing 2.0 yg NOl/ml. To a series of test tubes
pipet 0.1, 0.5, 1.0, 2.0, 3.0, 4.0, and 5.0 m
-------
Fl + F? fi
V = ' 2 * x t x 10~°
3
V = volume of air sampled, m
3
F, = measured flow rate before sampling, cm /min
F« = measured flow rate after sampling, cm /min
t = time of sampling, min
-6 "3 "\
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
temperature and pressure values.
3
9.2 Calculate the concentration of nitrogen dioxide as yg/m N0? using:
ug/m3N02 = (yg/mlNOg) 50
V x 0.79
50 = volume of absorbing reagent used in sampling, ml
V = volume of air sampled, m
0.79 = collection efficiency
If desired, concentration of NOp may be calculated as ppm NCL using
ppm N02 = yg/m3N02 x 5.32 x 10"4
10. References
1. Levaggi, D. A. et al_., J. Air Pollut. Cont. Ass.. 23, 30 (1973).
2. Jacobs, M. B. and Hochheiser, S., Anal. Chem.. 30_, 426 (1958).
3. Lodge, J. P. ejt al_., J. Air Pollut. Cont. Ass.. 16., 197 (1966).
24
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, INVERTED
FUNNEL
ro
ui
V ^)
** HYPODERMIC
NEEDLE
^^
o
f~
"\ j
\
AIR
PUMP
BUBBLER
TRAP
Figure 1. Sampling train.
-------
APPENDIX B. Laboratory Evaluation Data: Fritted Bubblers-
N09 Sampled
N02 Detected (ug/m3)
Collection Efficiency (%}
(ug/m3)
35.7
53.2
99.9
104
201
208
301
304
395
404
423
490
538
587
602
701
QL
n-Butanol Level (m/a)
3.0
32.1
30.6
47.4
46.8
87.9
91.8
93.1
93.8
173
173
194
196
229
254
273
268
358
356
303
318
335
333
400
410
447
452
490
508
512
521
572
569
0.5
29.6
29.6
44.4
41.3
83.9
84.2
91.4
93.3
171
163
180
179
231
228
270
270
360
342
308
324
336
344
409
401
442
435
493
476
559
506
5E8
564
0.0
29.8
38.7
84.3
89. Q
160
178
237
280
335
336
354
398
445
455
497
530
dl
n-Butanol Level (m£/a)
3.0
90.2
85.8
89.7
88.0
88.0
91.8
89.5
90.2
85.9
86.1
93.3
94.2
76.1
84.4
89.9
88.1
90.8
90.2
74.9
78.7
79.2
78.7
81.7
83.6
83.1
84.0
83.4
86.4
85.1
86.5
81.5
81.2
0.5
82.9
82.9
83.4
77.6
84.1
84.3
87.9
89.7
84.9
81.0
86.5
86.1
76.7
75.7
88.9
88.7
90.8
86.5
76.2
80.1
79.4
81.3
83.4
81.8
82.2
80.9
84.0
81.1
92.9
84.0
75.4
80.3
0.0
83.8
77.2
84.3
85.6
79.7
85.6
78.7
92.2
85.0
83.2
83.7
81.1
82.7
77.5
82.4
75.6
26
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APPENDIX B. Laboratory Evaluation Data: Restricted-Orifice Bubblers.
N0? Detected (yg/m3) Collection Efficiency (%)
N02 Sampled at at
dig/m3) n-Butanol Level (IDE/A) n-Butanol Level (ma/a)
0.5 0.0 0.5 0.0
34.2 17.9 18.3 52.4 53.4
17.6 18.1 51.3 52.8
19.3 56.3
305 158 136 51.8 55.7
156 144 51.1 44.4
170 47.1
497 234 229 47.1 45.9
242 233 48.5 46.9
247 49.5
693 345 318 49.9 45.9
345 344 49.8 49.7
330 47.7
27
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TECHNICAL REPORT DATA
(Pk-asc rcatl Infirm nuns on llif n i crse before owi/i/t ling)
1 REPORT NO
EPA-650/4-74-031
3 RECIPIENT'S ACCESSION-NO.
4 TITLE AND SUBTITLE 2
"An Evaluation of the Tn'ethanolamine Procedure for the
Determination of Nitrogen Dioxide in Ambient Air."
5. REPORT DATE
July 1974
6. PERFORMING ORGANIZATION CODE
7 AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO
E. Carol Ellis and John H. Margeson
9 PERFORMING OR~ANIZATION NAME AND ADDRESS
Methods Standardization gXRgXftXttXMgB Branch
Quality Assurance and Environmental Monitoring Laboratorfy
National Environmental Research Center
Research Triangle Park, N. C. 27711
10 PRCiGRAM ELEMENT NO
1HA327
11 CONTRACT/GRANT NO
12 SPONSORING AGENCV NAME AND ADDRESS
Environmental Protection Agency, NERC
Quality Assurance & Environmental Monitoring Laboratory
Methods Standardization Branch
ResearchTriangle Park, N. C. 27711
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
IS. SUPPLEMENTARY NOTES
16. ABSTRACT
A detailed method write-up describing the tnetnanoiamine (TEAJ manual pro-
cedure for measurement of nitrogen dioxide in ambient air was developed. The method
involves sampling for 24 hours with a fritted bubbler immersed in 0.1N TEA collecting
solution. The range ofthe method is approximately 20 to 700 ug/m3.
The method was evaluated to determine its usefulness for measuring nitrogen dioxid
in ambient air. This involved a review of the procedure as developed and subsequent
laboratory experiments to better define some obscure points in the procedure. The con-
stancy of the method's collection efficiency, the addition of n-butanol to enhance the
collection efficiency and the need to use fritted bubblers as gas dispersers to assure
high collection efficiency were the main points investigated in these experiments. The
results indicated a constant collection efficiency over the method's range both with
and without any added n-butanol using either frits or restricted-orifice bubblers; how-
ever, the collection efficiency using frits is about 80%, while the efficiency drops to
about 50% using restricted-orifice bubblers.
Further work on the method does not seem warranted at this time, because the
availability of other methods which show more promise for the measurement of NO? in
ambient air.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b IDENTIFIERS/OPEN ENDED TERMS C COSATI I leM/Croup
nitrogen dioxide
triethanolamine
manual method
ambient air
analysis
3 DISTRIBUTION STATEMENT
unlimited
19 SECURITY CLASS {1 Ills Report I
unclassified
21 NO OF PAGES
34
20 SECURITY CLASS (Tliu page/
unclassif i ed
22 PRICE
EPA Form 2220-1 (9-73)
28
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