EPA-650/4-74-048
NOVEMBER 1974
Environmental Monitoring Series
3D
O
O
ol
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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.
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EPA-650/4-74-048
AN EVALUATION OF ARSENITE PROCEDURE
FOR DETERMINATION OF NITROGEN
DIOXIDE IN AMBIENT AIR
by
Michael E. Beard and John H. Margeson
Program Element No. 1HA327
ROAP No. 26AAF
NATIONAL ENVIRONMENTAL RESEARCH CENTER
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK. N. C. 27711
November 1974
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This report has been reviewed by the Environmental Protection Agency
and approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the Agency,
nor docs mention of trade names or commercial products constitute
endorsement or recommendation for use.
ACKNOWLEDGMENTS
The authors wish to thank Mr. Robert G. Fuerst of Methods
Standardization Branch, QAEML for his calibrations of the N0?
permeation devices used in this study. We would also like to
thank Mr. John C. Puzak of Analytical Quality Control Branch,
QAEML for his assistance in preparing regression equations and
other statistical data.
11
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CONTENTS
Section Page
LIST OF TABLES iv
LIST OF FIGURES iv
I. INTRODUCTION 1
II. EXPERIMENTAL 2
III. RESULTS AND DISCUSSION 6
IV. CONCLUSIONS 21
V. FUTURE WORK 21
VI. REFERENCES 22
VII. APPENDICES 25
TECHNICAL REPORT DATA SHEET 40
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LIST OF TABLES
Table Page
1. Effect of Nitric Oxide on Collection Efficiency 9
2. Eight Combinations of Seven Factors Used to Test the
Ruggedness of an Analytical Method 14
3. Arsenite Method Ruggedness Test - Format 18
4. Summary of Ruggedness Test Evaluation 20
LIST OF FIGURES
Figure Page
1 Percent Collection Efficiency of the Arsenite Method
As a Function of N02 Concentration 7
A-l Sampling Train 35
A-2 Flowmeter 36
IV
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AN EVALUATION OF ARSENITE PROCEDURE FOR DETERMINATION
OF NITROGEN DIOXIDE IN AMBIENT AIR
INTRODUCTION
The Environmental Protection Agency (EPA) promulgated an
annual average of 100 micrograms-per-cubic meter (yg/m ) of nitrogen
dioxide (NOp) as a national primary ambient air quality standard.
The standard and a 24-hour reference method for determining compliance
were published in the Federal Register on April 30, 1971.^ ' The
reference method was later found to have a variable collection efficiency
and a positive interference from nitric oxide (NO). ' ' ' These de-
ficiencies were considered serious and led EPA to search for new methods
for measuring NO- in ambient air.
(5)
Christie et al.v ' reported a 95% collection efficiency of N00 in
c
sodium hydroxide solutions containing 0.1% sodium arsenite. This method
was investigated and adapted for field use by the Analytical Laboratory
Branch (ALB) of the Quality Assurance and Environmental Monitoring
Laboratory (QAEML) of EPA. ALB's preliminary investigation showed the
arsenite (Christie) method to have a collection efficiency of 85%. '
Thus, the arsenite method overcame the major deficiency of the original
reference method and was chosen as one of three candidate reference
methods published in the Federal Register as replacements for the
original reference method. '
Investigation of the arsenite method was continued in order to
establish its reliability. This report contains the results of an
1
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evaluation of the mathod made by the Methods Standardization Branch
(MSB) of QAEML. MSB is responsible for standardizing methods used
in determining compliance with the national ambient air quality
standards. This standardization process includes: 1) a review of
the method write-up to insure that it is clearly written and technically
accurate and, 2) a laboratory evaluation to determine if the method will
perform according to the specifications of the write-up. The laboratory
evaluation may include investigation or verification of such factors as
stoichiometry, collection efficiency, concentration range or effect of
interferents. The extent of the evaluation depends on how well the method
has been developed and documented.
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 colla-
borative test is the final phase of the standardization process and is
a measure of the performance of the method in actual use.
II. EXPERIMENTAL
A. General
The method used for the preliminary phase of this evaluation
is described in the Federal Register; ' The information gained in the
preliminary evaluation was used to modify the original method write-up.
The modified procedure was used as the basis for the final evaluation
and is given in Appendix A. Basically, the method consists of drawing
ambient air through a tube having a restricted orifice immersed in 50 ml
-------
of a solution containing 0.1 N NaOH and 0.1% w/w sodium arsenite. The
NOo in the ambient air is converted to nitrite ion. The concentration
of nitrite ion is determined colorimetrically by formation of a purple
azo-dye.
B. Sampling
Samples were collected in quintuplicate by attaching 5
sampling tubes to a common manifold. The flow rate for each tube was
measured before and after sample collection as directed in the method.
The total flow rate into the common manifold was also measured immediate-
ly before and after sampling and was compared with the sum of the in-
dividual flows to insure that there were no leaks in the system. Samples
with a final flow more than 10% different from the initial flow were re-
jected.
C. Flow Control
The samples were collected at a rate of approximately 200cm /min
by using a 27 gauge hypodermic needle as a critical orifice as suggested
by the method. A Gast Model 0211 oil-less vacuum pump was used to main-
tain a pressure drop across the orifice of approximately 0.6-0.7 atmos-
pheres. The total sampling time ranged from 20 to 24-hours.
D. Analysis
After sampling was completed, the tubes were disconnected from
the manifold. Water lost by evaporation during the sampling 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 measure-
ments.
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E. Test Atmosphere Generation
1. Nitrogen Dioxide
Test atmospheres containing known amounts of NCL were
generated by diluting the effluent from a gravimetrically calibrated
NCL permeation device with various measured amounts of purified air.
(0\
This procedure has been described by O'Keefe and Ortman, ' and
Scaringelli ejt al_. ' ' The permeation device was made by the Micro-
chemical Analysis Section of the National Bureau of Standards (NBS)
and was calibrated frequently at intervals between sampling periods.
The stability of permeation rates from these devices with respect to
time has been well established.^ '
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. constant temperature bath. The NCL was flushed from the jacket by a
3
flow of 100 cm /min dry N,,. The permeation rate for the device was
1.184 j^O.OOl yg/min. (Based on 66 weighings).
Purified air was obtained by passing compressed (House)
air through silica gel for drying, treating with ozone to convert any NO
to N02, and finally by passing through activated charcoal (6-A mesh),
molecular sieve (6-16 mesh, type 4A), and silica gel (6-16 mesh) to
remove any N02 and hydrocarbons.
2. Nitric Oxide
NO was introduced to the test atmospheres by means of a
"T" connection in the N02 system. A Kjeldahl trap following the "T"
insured mixing of the NO with the test atmosphere. A cylinder of NO in
N~ was analyzed by gas-phase titration with 03 as described in the
4
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Federal Register ' and found to contain 100 ppm N0(122,700 yg/m )
o
and 3.0 ppm N02(5644 yg/m ). Because of the N02 "impurity" in the
NO cylinder, it was necessary to calculate the exact N02 and NO con-
centrations using:
P.R. yg/min x 103L + Y_ 5644 yg N02/m3 = yg N02/m3
X L/min m3 X
and Y L/min (122,700 yg NO/m3) = yg NO/m3
X L/min
where
P.R. = permeation rate of N02 device
X = total dilution air flow rate
Y = NO flow rate
For test atmospheres containing a 4:1 ratio of NO:N02 approximately
80% of the N02 was from the permeation tube and 20% from the N02 impurity
in the NO cylinder. For the atmospheres containing a 1:1 NO:N02 ratio
95% of the N02 was from the permeation tube and 5% from the NO cylinder.
3. Carbon Dioxide
C02 was added to the test atmosphere by means of a "T"
connection, as in the addition of NO (see 2). The C02 was supplied
from one of two cylinders containing 1060 ppm (XL in N2 and 99.9% C02.
Each cylinder was checked and found to be free of NO and N02 impurities
by means of a chemiluminescent N0-N02-N0 monitor. The C02 concentration
in each test atmosphere was calculated using:
F x C = C
COp C02 C02
Ftotal
-------
where F = flowrate from COp cylinder
total = combined flow rates in manifold
C = concentration of C09 in cylinder
COp L.
C = concentration of COp added to test atmosphere.
No attempt was made to control the COp concentration in the purified air.
Thus, the final COp concentration was the ambient concentration, plus
the amount added from the cylinder.
III. RESULTS AND DISCUSSION
A. Collection Efficiency
The preliminary evaluation of the arsenite method began with
an investigation of the collection efficiency. Establishing the collection
efficiency was essential because the original reference method had shown a
50% non-linear variation in collection efficiency over the concentration
(2)
rangev ' of the method and the arsenite method was only a modification
of the original method.
The collection efficiency was determined by sampling test
atmospheres containing 43.6? 77.7, 105, 106, 329, 449, 470, 644, and
743 yg NOp/m . The samples were collected and analyzed according to the
procedure described in the Federal Register: ' Collection efficiencies
(percent) were calculated by the ratio of NO,, recovered (as nitrite ion)
to N02 generated x 100 and are shown as a function of NO- concentration
in Figure 1. Data for this figure is found in Appendix B. The least
squares regression equation for the data is:
% CE = 82.46 - 0.00085 (ygN02/m3)
The intercept of the equation (82.46) represents the collection efficiency
of the method and the slope (-.00085) shows no significant change in
An NOp-permeation device with a rate of 0.723 pg/min was used to obtain
this level.
6
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100
95
90
C
tu
u
I 85
u
Z 80
O
o a
o
o
©
o
o
8
o o o
0 e
o
P
o
o
o
75
70
65
60
8
O
©
o
8
% COLLECTION EFFICIENCY = 82.46 0.00085 (/ugN02/m3)
100
200
300 400 500
N02 CONCENTRATION, jjg/m3
600
700
800
Figure 1. Percent collection efficiency of the arsenite method as a function of N02 concentration.
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collection efficiency over the concentration range examined.
The arithmetic mean of the collection efficiencies obtained
from the data in Appendix B is 82.2% with a relative standard deviation
(RSD) of 4.5%. This is similar to the variability of other impinger
(9)
collection systems. ' More importantly, the data verifies that the
variable collection efficiency of the original reference method has indeed
been overcome by the arsenite modification.
B. Nitric Oxide Effect
The next step in the evaluation of the arsenite method
was an investigation of the response of the method to nitric oxide (NO).
The original reference method had shown an appreciable positive inter-
(2 3 4)
ference from NO. ' ' ' The mechanism by which the NC interfere is
believed to be described by the reaction
NO + N02 + 2"OH-> 2N02 + H20
In this reaction the NO interference depends on both the NO and N02 con-
centrations; therefore, it was necessary to sample test atmospheres con-
taining various ratios of NO:N02 in order to 'evaluate their effect on
the method.
3
Test atmospheres containing approximately 100 ygNOp/m and
NO:N02 ratios (w/w) of 0:1, 1:1 and 4:1 were generated and sampled accord-
ing to the method described in the Federal Register: ' Collection
efficiencies were calculated as in III.A. and are shown in Table 1.
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Table 1. Effect of Nitric Oxide on Collection Efficiency.
NO:N02*
w/w
0:1
0:1
1:1
1:1
4:1
4:1
Mean Collection
Efficiency
%
78.1
82.6
90.5
82.2
89.2
85.1
Standard
Deviation
%
2.7
1.3
1.0
1.5
1.4
1.0
*N02 concentration 103 to 106 ygN02/m3.
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The atmospheres which contained only N(L (0:1) gave
collection efficiencies of 78.1% and 82.6% (average 80.4 +3.2) and
were used as a basis for comparison to measure the effect of the atmo6.
spheres containing NO. The test atmospheres containing a 1:1 ratio
gave collection efficiencies of 90.5% and 82.2% (average 86.4 +_5.9).
By comparing the 1:1 values with the 0:1 values, it is difficult to
draw any conclusions because of the variability of the data.
The 4:1 ratios gave values of 89.2% and 85.1% (average 87.2 +
2.9). Comparing the base value (0:1) of 80.4 +_ 3.2 with the 4:1 value
of 87.2 +_ 2.9, the effect of the NO becomes significant. However, the
difference is small.
Additional work is needed to define the actual effect of NO
in the arsenite method. However, it is important to note that the effect
of the NO in the arsenite method is not as severe as that of the original
(2}
reference method indicated by Hauser and Shy.x '
C. Other Factors Evaluated
1. Orifice Diameter
The normal value for the diameter of the glass orifice
in the bubbler was originally 0.4 mm. One lot of glass orifices supplied
by a local glass blowing shop were examined and found to range from 0.4 mm
to 0.9 mm. No significant difference in collection efficiency was found
using orifice diameters between 0.4 and 0.8 mm. Therefore, the middle
value and the range of orifices tested, 0.6 +_0.2 mm, was adopted in place
of 0.4 mm.
10
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Pressure drops across the glass orifice in the sampler
were between 10 and 16 mm Hg for the orifice diameters used. These
pressure drops should have had no significant effect on the pressure
drop across the critical orifice used for flow control.
2. Analytical System
The diazotation-coupling reaction used to detect
nitrite in this analysis is well documented in the literature. How-
ever, certain parameters in the analysis were deemed worthy of investi-
gation to insure that the arsenite modification had not affected them.
The optimum pH and time for color development were
investigated and found to be 2.0 and 10 minutes, respectively. The
color was stable for at least 30 minutes after development.
The stability of a collected N02 sample was in-
vestigated by analyzing a sample containing approximately 0.55 yg NO^/ml
(equivalent to 100 yg NO^/m ) at 0, 1, 4 and 41 days after collected.
No significant change in concentration was found.
Since the pH, time for color development, and sample
stability were found to be as described by the method and related
litereature, no changes in the original specifications were necessary.
D. Preliminary Assessment
At this point in the investigation, a preliminary assess-
ment of the arsenite method was made. The constant collection efficiency
and lower response to NO overcame the most serious problems associated
with the original reference method. Therefore, it was decided that a
11
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further, more detailed, evaluation was warranted. The original
method write-up, used in the preliminary experiments, was edited
and modified to its present form (Appendix A) incorporating the in-
formation gained in the preliminary studies. This version of the
method was then subjected to further investigation to determine the
effect of various parameters which had not previously been evaluated.
E. Ruggedness Testing
1. Design
The second phase of the evaluation involved a test
designed to determine the sensitivity of important operational para-
meters to slight changes similar to those encountered in normal use.
This type of evaluation is called ruggedness testing. It is accomplish-
ed by conducting a series of controlled experiments in which selected
parameters are varied at two levels: the nominal level stated in the
method write-up and a challenging level. The results obtained using the
nominal procedure are compared with the results obtained using the
variation in order to determine the effect of the variable. Parameters
which significantly effect the method response can then be more carefully
controlled, thereby improving the method.
An ingenious scheme for determining the individual
effects of variations in several parameters with a minimum number of
experiments has been described by Youden.^ *' Seven d parameters are
a Schemes for examining the effect of a larger or smaller number of
(13)
parameters are available/ '
12
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chosen for testing and their nominal values are denoted by A, B,
C, D, E, F, and G. A challenging value for these parameters is then
selected and denoted by a, b, c, d, e, f, and g. A series of eight
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 2.
Each of the eight experiments produces a result, de-
noted as S, T, U, V, W, X, Y, and Z. Examination of the format in
Table 2 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 A is cal-
culated using
A-a = S+T+U+V - VI+X+Y+Z
4 4
A complete set of equations for calculating the effect of A-a, B-b, etc.
are given in Appendix C.
It should be noted that the results of the ruggedness
test will not completely describe the effect of varying a given para-
meter. The results only show the effect of the range of variation used
13
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Table 2. Eight Combinations of Seven Factors Used to Test the
Ruggedness of an Analytical Method
Determination Number
Factor
Value
A or a
B or b
C or c
D or d
E or e
F or f
G or g
Observed
Result
1
A
B
C
D
E
F
G
S
2
A
.B
c
D
e
f
g
T
3
A
b
C
d
E
f
g
U
4
A
b
c
d
e
F
G
V
5
a
B
C
d
e
F
g
W
6
a
B
c
d
E
f
G
X
7
a
b
C
D
e
f
G
Y
8
a
b
c
D
E
F
g
Z
14
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in the experiment. If the effect is shown by the test to be signi-
ficant, a series of tests controlling various levels of that para-
meter are then necessary to describe the exact relationship.
2. Selection of Parameters
Several parameters were considered to be subject
to variation and possibly critical to the performance of the arsenite
method.
a. Concentration
The effect of various concentrations of N0? on
the arsenite method had been previously evaluated in the determination
of the collection efficiency. However, the effect of other variables in
association with the NCL concentration was not known. Therefore, NCL
3
concentrations of 65 and 700 pgNO/m were chosen to cover the range of
the method.
b. Temperature
Methods used in the field are always subjected
to extremes of temperature that can affect the collection efficiency of
the method. The sampling devices used in most 1^ networks are equipped
with warming devices to eliminate the cold or near freezing temperatures.
Therefore, a temperature of 25°C was selected for the nominal condition and
35°C was chosen for the challenge.
c. Orifice Size
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 0.6 +_
0.2 mm was made by using 0.6 mm for the nominal value and 1.0mm for the
15
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challenging value.
d. Flow Rate
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. The nominal and
3
challenging flows selected were 180 to 220 and 310 to 340 cm /min,
respectively.
e. Sodium Arsenite Concentration
The original work by Christie determined the
optimum amount of NaAs02 for N02 absorption by adding gaseous N02 to
solutions containing various amounts of NaAs02 and then shaking the
mixture. ' Since this experiment does not duplicate the dynamic
solution process of the sampling system, it was decided to examine
NaAsOp concentration. The nominal value was l.Og/L, as described in
the method,and the challenging value was set at 0.8g/L.
f. Carbon Dioxide Concentration
Merryman reported a decrease in collection
efficiency of an arsenite-type procedure with a COp concentration of
2000 ppm/ ' However, he showed no effect with C02 near the ambient
level of 300 ppm. Thus, a test to determine the effect of C02 concen-
trations slightly above the ambient level was conducted. The nominal
value for C02 was the existing ambient concentration. The challenging
concentration used was the nominal value, plus 300 ppm.
16
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g. System Blank
The format described by Youden provides for
evaluation of seven variables. If the performance of the method is well
documented and understood, a complete set of seven variables may be
tested. When the method does not meet these requirements, it is
advisable to replace one of the variables with a system blank. It
should be noted here that the system blank is unlike the customary
blank in which the concentration of NC^ would be zero. The system
blank is merely a mathematical balance of all the variable conditions
(12)
in the experiment. ' If this experiment yields a low difference we
may conclude that there were no uncontrolled factors which are critical
to the performance of the method. Thus, a system blank was chosen for
the seventh and final experiment in the ruggedness test.
3. Conducting the Ruggedness Test
a. Test Plan and Results
The parameters chosen for the ruggedness test
were incorporated into the format previously described and are shown in
Table 3. The experiments were conducted in random order (6, 1, 3, 7,
8, 2, 5, and 4) and the individual and average results for each
determination are given in Appendix D. It should be noted that the
results are expressed in per cent. This was calculated by dividing the
concentration found by the concentration of NCL generated. This
normalization of the results was necessary before the effect of the
different parameters could be determined because, the method is obviously
17
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00
Table 3. Arsenite Method Ruggedness Test Format
Determination Number
Factor Value
N0? Concentration
A = 65ug/m3 a = 700ug/m3
Absorber Temperature
B = 25°C b = 35°C
Orifice Size
C = 0 . 6mm c = 1 . Omm
Flow Rate
D = 200cm /mi n d = 300cm /mi n
Sodium Arsenite Cone.
E = l.Og/L e = 0.8g/L
COp Concentration
F = Ambient f = Ambient+300
System Blank
G = g, No variation
Observed Resul t
1
65y.g/m
25°C
0.6mm
200cm /mi n
l.Og/L
Ambient
-
S
2
65
25
1.0
200
0.8
Amb. + 300
-
T
3
65
35
0.6
300
1.0
Amb. +300
-
U
4
65
35
1.0
300
0.8
Ambient
-
V
5
700
25
0.6
300
0.8
Ambient
_
W
6
700
25
1.0
300
1.0
Amb. +300
_
X
1_
700
35
0.6
200
0.8
Amb. +300
_
Y
8
700
35
1.0
200
1.0
Ambient
_
Z
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sensitive to NOp concentration.
The results in Appendix D were substituted into
the equations of Appendix C and the effect of each parameter was
calculated. The net results are shown ranked in order of absolute
magnitude in Table 4.
b. Results
1. Carbon Dioxide Concentration
The most significant effect on the arsenite
method was due to the C02 concentration. The positive value of 18.3%
indicates that the recovery of NCL is significantly reduced by the
presence of an additional 300 ppm COo (over ambient) in the air sample.
Thus, C02 is a negative interferent in the method.
2. Flow Rate
The recovery of NOp was apparently reduced
3 3
by 14.4% by flow rates of 300 cm /min instead of the 200 cm /min required
by the method. However, this effect may be related to the increased COp
intake at the higher flow rate rather than the flow rate alone.
3. Orifice Size
The negative 2.6% value obtained for this
variable indicates the 1.0mm orifice has a slightly greater recovery
than the 0.6mm orifice. The preliminary evaluation of this variable
indicated that increasing the orifice size had the reverse of this
result, although the magnitude did not appear to be significant. The
small magnitude of this result and the possible contradiction between
19
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Table 4. Summary of Ruggedness Test Evaluation.
Rank Factors Difference
1. C(L Concentration 18.3
Ambient vs Ambient + 300
2. Flow Rate 14.4
3 3
^200cm /min vs 'vSnOcm /min
3. Orifice Size (-) 2.6
0.6mm vs 1.Omm
4. N02 Concentration (-) 1.9
65ug/m3 vs 700 Mg/m3
5. NaAsOp Concentration (-) 1.5
l.Og/L vs 0.8g/L
6. Temperature 1.2
25°C vs 35°C
7. Experiment Blank 1.1
20
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the preliminary evaluation and the ruggedness test are considered
to be of no consequence.
4. Other Parameters
The values obtained for the N0? concen-
tration, NaAs02 concentration, temperature, and system blank were 1.9,
-1.5, 1.2 and 1.1%, respectively. These values indicate that the effects
of these variations were insignificant. The small difference obtained
for the system blank indicates that there were no critical factors uncon-
trolled in the test.
IV. CONCLUSIONS
The arsenite method has a constant-high collection efficiency over
the entire range of the method. The method is insensitive to normal
variations in: orifice bubbler diameter, temperature of the absorbing
solution during sampling, and concentration of sodium arsenite. However,
NO and C02 are positive and negative interferents, respectively; sample
flow rate may also be a variable affecting the method response and should
be closely controlled.
Before an assessment can be made as to the utility of the arsenite
method for measuring N02 in ambient air, the effect of the above inter-
ferents, and flow rate, on the method response needs to be quantiated.
(Present-incomplete data indicate that the interference from NO is small,
approximately 10%).
V. FUTURE WORK
Future work will.involve determining if the reduced method response
attributed to flow rate, as a result of the ruggedness test, was caused
by increasing the N02 sampling rate and/or COn consumption.
21
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Additional combinations of NO plus N(L and C(L plus NCL will
be sampled to quantify the effect of these interferents on the method
response. The experiments will be designed so that equations can be
developed from the data that will allow calculation of the effect of
NO or C0? concentration (in combination with N0?) on the method response.
This information will allow a judgment to be made as to the practical
magnitude of the interferences and consequently the utility of the method
for making NOp measurements. If both the interferences are minimal, the
method could be used as is and the fact documented with the equations.
If either of the interferences is too high, further development of the
method to eliminate the interference(s) would be recommended.
VI. REFERENCES
1. Federal Register, 36, April 30, 1971, National Primary and Secondary
Ambient Air Quality Standards, p. 8186-8187, Appendix F, p. 8199-8200.
2. Mauser, T. R. and Shy, C. M., Environmental Science and Technology, 6_,
10, 1972, p. 890-894.
3. Heuss, J. M., Nebel, G. J., and Colucci, J. M., Journal of the Air
Pollution Control Association, 21_, 9, 1971, p. 535-548.
4. Merryman, E. L., Spicer, C. W. and Levy, A., Environmental Science and
Technology, 7, 11, 1973, p. 1056-1059.
5. Christie, A. A., Lidzey, R. G., and Radford, D. W. F., Field Methods for"
the Determination of Nitrogen Dioxide in Air, Analyst, 95, May 1970,
p. 519-524.
6. Wheeler, V. A., Knapp, K. T., and Thompson, R. J., "Aqueous Absorbing
Solutions for Ambient Monitoring of Nitrogen Dioxide," presented at
22
-------
165th National Meeting American Chemical Society, April 1973.
7. Federal Register, 3JS, 110, June 8, 1973, Reference Method for
Determination of Nitrogen Dioxide, p. 15174-15176.
8. O'Keefe, A. E. and Ortman, G. C., "Primary Standards for Trace Gas
Analysis," Analytical Chemistry, 38, p. 760, (1966). .
9. Scaringelli, F. P., Frey, S. A. and Saltzman, B. E., "Evaluation of
Teflon Permeation Tubes for Use with Sulfur Dioxide," Journal of the
American Industrial Hygiene Association, 28, p. 260, (1967).
10. Scaringelli, F. P., O'Keefe, A. E., Rosenburg, E., and Bell, 0. P.,
"Preparation of Known Concentrations of Gases and Vapors with Per-
meation Devices Calibrated Gravimetrically," Analytical Chemistry,
42_, 8, p. 871, (1970).
11. 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.
12. Youden, W. J., "Statistical Techniques for Collaborative Tests," 1967,
p. 29-32, Association of Official Analytical Chemists, Washington,
D. C. 20044. Price $2.00.
13. Plackett, R. L., and Burman, J. P., "The Design of Optimum Multi-
factorial Experiments," Biometrika, 3_3, 305 (1946).
23
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VII. Appendices
A. Tentative Method for the Determination of Nitrogen
Dioxide in the Atmosphere (Sodium Arsenite Procedure).*
B. Collection Efficiency vs Concentration.
C. Equations for Evaluation of the Ruggedness Test.
D. Arsenite Method Ruggedness Test Data.
*A tentative method is one that has been carefully drafted from
available experimental information, reviewed editorially within
the Methods Standardization Branch, and undergone extensive
laboratory evaluation. The method is still under investigation
and, therefore, is subject to revision.
25
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APPENDIX A. TENTATIVE METHOD FOR THE DETERMINATION OF NITROGEN DIOXIDE
IN THE ATMOSPHERE (SODIUM ARSENITE PROCEDURE)
1. Principle and Applicability
1.1 Nitrogen dioxide is collected by bubbling air through a sodium
hydroxide-sodium arsenite solution to form a stable solution of sodium
A
nitrite. The nitrite ion produced during sampling is reacted with phos-
phoric acid, sul fenilar.ide, and N-l-(naphthyl)ethylenediamine dihydro-
chlorids to form an azo dye and then determined colorimetrically.
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 N0"/ml. Beer's lav/
is obeyed through this range (0 to 1.0 absorbance units). With 50 ml
absorbing reagent and a sampling rate of 200 cm /min for 24-hours, the
nge of the net hod is 20 to 750 ;;g/m (0.01 to 0.4 ppm) nitrogen dioxide.'
2.2 A concentration of 0.04-tS NO-Vml-v;i 11 produce-en-absorbance of
approximately 0.02 with 1-cm cells.
3. Interferences
3.1 Nitric oxide is a positive interferent. The presence of NO can
2
increase the NO- response by 5 to 15?. of the N02 sampled.
3.2 -.The interference of sulfur dioxide is eliminated by converting
it to sulfate ion \vith hydrogen peroxide before analysis.
4. Precision, Accuracy and Stability
4.1 The relative standard deviations for sampling N02 concentrations
of 78, 105 and 329 ug/m are 3, 4 and 22, respectively.
27
-------
4.2 No accuracy data are available.
4.3 Collected samples are stable for at least 6 weeks.
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 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 vary-
ing 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 rrm long with the end drawn out to 0.3 » 0.8 mm I.Dia'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 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. Of 0.8 to 2.0 microns porosity.
5.1.5 Flow Control Device. Any device capable of maintaining i. con-
stant flow through the sampling solution between 180-220 cm/min. A typical
flow control device is a 27 gauge hypodermic needle, three-eights inch long.
(Most 27 gouge needles will give flow rates in this range.) The device
used should be protected from particulate matter. A membrane filter is
^a'This specification was modified after the completion of our study by addition-
al information obtained from other investigators. '
28
-------
.suggested. Changs 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 includes the minimum useful differential, 0.53 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).
' i
. 5.2 Analysis
5.2.1 Voluretric Flasks. 50, 100, 200, 250, 500, 1,000 ml.
; 5.2.2 Graduated Cylinder. 1,000 ml.
\;
..-.; 5.2.3 Pipets. 1, 2, 5, 10, 15 ml volumetric; 2 ml, graduated in
11' '
-.ST'T^r-"1 ?**--*-~^-
., I/ lo fill ifi (.cTva ii .
5.2.4 Test Tubes, approximately 20 x 150 mm.
5.2.5 Spectrophotoreter. Capable of measuring absorbance at 540 nm.
,>
:','6. Reagents
6.1 Sampling
*: 6.1.1 Sodium Hydroxide. ACS Reagent Grade.
6.1.2 Sodium Arsenite. ACS Reagent Grade.
6.1.3 Absorbing Reagent. Dissolve 4.0 g sodium hydroxide in distill'
t
;
-------
6.2.2 N-(l-Naphthyl)-ethylenediamine dihydrochloride (NEDA). Best
grade available.
, 6.2.3 Hydrogen Peroxide. ACS Reagent Grade, 30».
6.2.4 ScdiuT, Nitrite. Assay of 972 NaN02 or greater.
6.2.5 Phosphoric Acid. ACS Reagent Grade, 85%.
6.2.6 Sulfanilamide Solution. Dissolve 20 g sulfanilamide in 700
ml distilled water. Add, with mixing, 50 ml concentrated phosphoric acid and
dilute to 1,000 ml. This solution is stable for one month, if refrigerated.
6.2.7 NEDA Solution. Dissolve 0.5 g of NEDA in 500 ml of distilled
water. This solution is stable for one month, if refrigerated and protected
from light.
6.2.8 Hydrogen Peroxide Solution. Dilute 0.2 ml of 30/J hydrogen
peroxide to 250 ml with distilled water. This solution may be used for cnc
month, if protected from light and refrigerated.
6.2.9 Standard Nitrite Solution. Dissolve sufficient desiccated
sodium nitrite and dilute with distilled water to 1,000 ml so that a
solution containing 1,000 ug NOl/ml is obtained. The amount of NaNO- to
use is calculated as follows:
-- r 1.500 v 100
= 5
G = Amount of NoNOp grams.
1.500 = Gravin-etric factor in converting NOp into NaNOp.
A = Assay, percent.
30
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7. Procedure
7.1 Sampling. Assemble the sampling apparatus as shown in
FigureAl. 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 (8.1.3). Disconnect funnel, insert calibrated
flowmeter, and treasure flov/ before sampling. If flow rate before sampling
is not betv:een 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 ranga. Sample for 24 hours and measure the flow after
the sampling period.
7.2 Analysis. Replace "any water lest by evaporation d-jring sampling
by adding distilled water up to the calibration mark on the absorption tube.
i
Pipet 10 ml of the collected sample into a test tube. Pipet in 1 ml hydrogen
peroxide solution, 10 ml sul fanilamide solution, and 1.4 ml NEDA solution
with thorough mixing after the addition of each reagent. Prepare a blank in
the same manner'using 10 ml of unexposed absorbing reagent. After a 10-minute
color-doveloprrent interval, measure the absorbance at 540 nm against the blank,
Read pg NOl/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 10 ml) of the collected sample with unexposed absorbing reagent.
31
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8. Calibration and Efficiencies
8.1 Sampling
/-
8.1.1 Calibration of Flcwmeter. (See Figure 2). Using a wet test
3
meter and a stopwatch, determine the rates of air flow (cm /min) through
the flcwmeter at a minimum of four different ball positions. Plot ball
positions versus flcv.1 rates.
8.1.2 Flow Control Device. The flow control device results in a
constant rate of air flow through the absorbing solution. The flow rate
is determined in Section 7.1.
8.1.3 Calibration of Absorption Tube. Calibrate the polypropylene
absorption tube (Section 5.1.1) by first pipeting in 50 ml of water or
absorb"! r.g ;c-c;r,t. Scribe the level of the meniscus with a sharp object,
go over the' area with a felt-tip marking pan, and rub off the excess.
8.2 Calibration Curve. Dilute 5.0 rn,l of the 1,000 yg NO^/ml
solution to 200 ml with absorbing reagent. This solution contains 25 yg
NO^/ml. Pipot 1, 1, 2, 15, and 20 ml of the 25 yg N0"/ml solution into 100-,
50-, 50-, 250-, and 250- ml volumetric flasks and dilute to the mark with
absorbing recrent. The solutions contain 0.25, 0.50, 1.00, 1.50 and 2.00
pg NO^/nl, respectively. Run standards as instructed in 7.2, including
the blank. Plot absorbance vs. ug NOl/ml. A straight line with a slope
of 0.13 j_ 0.02 absorbance units/ug N0"/ml, passing through the origin,
should be obtained.
32
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8.3 Efficiencies. An overall average efficiency of 82% was
obtained over the range of 40 to 750 wg/m NOp-
9. Calculation
9.1 Sair.pl ing
9.1.1 Calculate volu~.-2 of air sampled.
F + F '
X T X 10
V = Volume of air sampled, m .
F, = Measured flow rate before sampling, cm /min.
3
F? = Measured flow rate after sampling,-cm /min.
T = Time of sampling, min.
-6 3 3
10" = Conversion of on 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.
9.2 Calculate the concentration of nitrogen dioxide as yg NO^/m
using:
pg N02/m3 = (ug Np;/rr.l) X 50
V X 0.82
50 = Volurr.e of absorbing reagent used in sampling, ml.
V c Voluirc of air sair.pled, m .
0.82 - . Collection efficiency.
9.2.1 If desired, concentration of nitrogen dioxide may be calculated
as p.p.m. fiOp using:
p.p.m. H02 = (ug Hb2/m3) X 5.32 X 10"4
33
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10. References
1. Christie,A. A. e_t al_. "Field Methods for the Determination of
Nitrogen Dioxide in Air." Analyst 95. 519-524 (1970).
2. Unpublished results, Environmental Protection Agency, Research
Triangle Park, N. C. 27711.
3. Merryman, E. L. e_t a]_. "Effects of NO, C02> CH4> H20 and Sodium
Arscnite on N'Op Analysis." Presented at the Second Conference on
Natural Gas Research and Technology in Atlanta, Georgia on June 5,
1972.
4. Jacobs, M. B. and Hochheiser, S., "Continuous Sampling and Ultramicro-
determination of Nitrogen Dioxide in Air," Anal. Chem. 30, 426
(1953). -
5. Lodge, J. P. et_ aj_. "The Use of Hypodermic Needles as Critical
Orifices in Air Sampling." J.A.P.C.A., 1_6., 197-200 (1966).
34
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BUBBLER
TRAP
Figure A-1. Sampling train.
CO
en
-------
CO
CT>
OPEN
TO
ATMOSPHERE
RATE CONTROL VALVE
PUMP
FLOWMETER
Figure A-2. Flowmeter.
-------
Appendix B. Collection Efficiency vs Concentration.
N0? Generated N09 Found Collection Mean Standard
* - , Deviation
43.6 35.8 82.1 84.1 2.3
77.7 63.7 82.0 82.5 2.9
105 83.3 79.3 78.1 2.7
106 87.8 82.8 82.6 1.3
N09 Found
£
3
37.3
37.0
35.8
35.4
37.7
61.8
62.9
63.7
64.6
67.7
77.5
84.8
83.3
83.1
81.8
88.1
89.3
87.8
85.7
87.0
280
280
273
284
267
366
367
351
362
362
429
428
417
511
502
486
512
490
632
616
601
613
617
Collection
Efficiency
85.6
84.9
82.1
81.2
86.5
79.5
81.0
82.0
83.1
87.1
73.8
80.8
79.3
79.1
77.9
83.1
84.2
82.8
80.8
82.1
85.1
85.1
83.0
86.3
81.2
81.5
81.7
78.2
80.6
80.6
91.3
91.1
88.7
79.3
78.0
75.5
79.5
76.1
85.1
82.9
80.9
82.5
83.0
329 273 83.0 84.1 2.0
449 351 78.2 80.5 1.4
470 428 91.1 90.4 1.4
644 486 75.5 77.7 1.8
743 601 80.9 82.9 1.5
37
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Appendix C. Equations for Evaluation of the Ruggedness Test.
1. A-a = S + T + U + V - VI + X + Y + Z
4 4
2. B-b = S + T + M + X - U + V + Y + Z
4 4
3. C-c = S + U + VI + Y - T + V + X + Z
4 4
4. D-d = S + T + Y + Z - U + V + W + X
4 4
5. E-e = S + U + X + Z - T + V + VI + Y
4 4
6. F-f = S +-V+'Vr+ Z - T + U + X + Y
4 4
7. G-g = S + V + X + Y - T + U + VI'+ Z
4 4
\ .'
38
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Appendix D. Arsenite Method Ruggedness Test Data.
Determination No. NO, Generated NCL Found % Response
yg/m3
Mean Observed Result
Designation
65.9
66.6
66.4
66.3
736
735
722
741
61.8
62.8
59.0
63.2
58.4
48.4
52.0
52.9
52.0
52.6
93.8
36.
39.
38.0
39.3
39.0
53.
54.
54.1
53.
53.
617
:593
596
595
560
485
498
478
473
443
541
551
551
549
576
696
707
698
696
716
95.
89.
95.
72.7
78.1
79.4
78.1
79.0
54.5
59.5
57.2
59.2
58.7
80.7
82.4
81.6
80.7
80.2
83.8
80.6
81.0
80.8
76.1
66.0
67.8
65.0
64.
60,
74.9
,3
.3
76.
76.
76.0
79.8
93.9
95.4
94.2
93.9
96.6
92.6
77.5
57.8
.81.1
80.5
64.7
76.7
94.8
39
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-650/4-74-048
3. RECIPIENT'S ACCESSION-NO.
4..TITLE AND SUBTITLE
5. REPORT DATE
An Evaluation of Arsenit« Procedure for
Determination of Nitrogen Dioxide in Ambient Air
November 1974
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Michael E. Eeard and John H. Margeson
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Quality Assurance and Environmental Monitoring
Laboratory
Methods Standardization Branch
Research Triangle Park. N.C. 27711
10. PROGRAM ELEMENT NO.
1HA327
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Protection Agency
National Environmental Research Center
Research Triangle Park, N.C. 27711
13. fXPE Of REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Report describes and evaluates the sodium arsenite manual procedure for
measurement of NC>2 in ambient air. The evaluation included ruggedness
testing, as described by Youden. The results showed a constant-high
collection efficiency of 82 ±3.7% over the entire range. The method involves
sampling for 24 hours with a restricted-orifice bubbler immersed in a
NaAsO2~NaOH collecting solution. The range of the method is approx-
imately 20 to 750 ug/m . The method was insensitive to normal variations in
orifice bubbler diameter, temperature of the absorbing solution during sampling,
and concentration of arsenite. However, the ruggedness test identified NO
and CC>2 as positive and negative interferents, respectively; sample flow
rate may also be a variable affecting the method response.
An assessment of the usefulness of the method was deferred until the
effects of the above interferents and of the flow rate have been quantitated.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
13. DISTRIBUTION STATEMENT
Release unlimited
19. SECURITY CLASS (This Report)
jxjone
21. NO. OF PAGES
45
20. SECURITY CLASS (This page)
None
22. PRICE
EPA Form 2220-1 (9-73)
40
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