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NITROGEN DIOXIDE BACKUP DATA REPORT (ID-182)
This backup report was revised May, 1991
Introduction
The general procedure for the air sample collection and analysis of nitrogen dioxide
(NO2) is described in OSHA Method No. ID-182
(11.1.). In the past, NO2 was collected using a combination
tube consisting of triethanolamine-impregnated molecular sieve (TEA-IMS).
Nitrite contamination of the TEA-IMS was occasionally noted, was lot dependent,
and highly variable. Air samples were taken with a flow rate of less than 0.05 L/min. Analysis
was performed by either colorimetric or polarographic methods.
Presently, it is required to water-wash the molecular sieve before triethanolamine
(TEA) impregnation to remove any soluble salts that may contribute to background measurement or
act as an interference (i.e. nitrite or soluble chloride salts). The evaluation of Method No.
ID-182 examines the use of the combination tube,
and a three-tube sampling device at a flow rate of approximately 0.2 L/min.
The four-fold increase in sample flow rate during collection should assist in
detecting low levels of NO2 and help minimize any impact from sorbent
contamination. Analysis is performed by ion chromatography (IC).
This method was evaluated when the Permissible Exposure Limit (PEL) was a 5 ppm Ceiling. The
OSHA Final Rule PEL for NO2 is currently 1 ppm. A 15-min
sampling time was used. Short descriptions of the components used for the evaluation are listed below.
Generation System
All generation of nitrogen dioxide test atmospheres, and hence all experiments, with one
exception, were performed using the equipment shown in Figure 1.
The detection limit study did not use a test atmosphere generation for sample spiking and
collection. Instead, samples were spiked with solutions of sodium nitrite.
Nitrogen dioxide permeation tubes (Thermedics Inc., Woburn, MA) were used as the contaminant
source for all of the generation experiments except the conversion factor experiment. A cylinder
of nitric oxide (NO) in nitrogen and oxidizer tubes were used to determine conversion factors.
Permeation rates during the other experiments were determined by measuring the weight loss of
three permeation tubes over a given period of time. A constant temperature of 35 °C was
used. As shown below, the calculated overall NO2 permeation rate
for the three tubes was 89.09 µg/min.
Time Elapsed
(min) | Weight Loss
(µg) | Diffusion Rate
(µg/min) |
|
4,335
5,700
10,105
10,095 |
387,600
513,400
904,200
882,100 |
89.41
90.07
89.48
87.38 |
| |
| Ave. 89.09 ± 1.17 µg/min |
The NO2 produced from the permeation source was diluted with a small
amount of filtered air and then mixed, using a glass mixing chamber, with filtered, tempered air.
A flow, temperature and humidity control system (Miller-Nelson Research Inc., Model
HCS-301) was used to condition the diluent air for mixing. A Teflon sampling
manifold was attached to the mixing chamber. Flow rates for the diluent air were determined
using a dry test meter. Contaminant gas flows were measured using mass flow controllers and
soap bubble flowmeters.
Sampling Media
Three different TEA-IMS sampling systems were commercially available for
NO2 sampling at the beginning of the evaluation. The three devices are
designed to simultaneously collect NO2 and nitric oxide (NO).
Preliminary studies conducted on the three different systems indicated the SKC collection device
(1) listed below was the most suitable sampling device to collect NO and NO2.
A short description of each device is listed:
- NO2-NO collection device (Cat. No. 226-40, SKC, Eighty Four, PA):
The sampling device consists of three separate glass tubes, two TEA-IMS tubes
and an oxidizer tube. Each glass tube is flame sealed. Both sample collection tubes consist of
400 mg TEA-IMS. The oxidizer contains approximately 1 g of a chromate compound.
Either TEA-IMS tube can be used separately to monitor NO2.
When sampling for both NO and NO2, the three tubes are connected with
Tygon tubing such that the oxidizer tube is placed between the two TEA-IMS sampling
tubes. The tubes used during the experiments were from lot no. 374.
- SKC combination tube (Cat. No. 226-40 discontinued, SKC):
This combination tube contained all three sections in a single tube. Two 400 mg sections of
TEA-IMS were separated by a 800 mg oxidizer section. This tube has been discontinued
by SKC and replaced with the device mentioned above. The tubes used were from lot no. 306.
- Supelco combination tube (Supelco, Bellefonte, PA):
This tube is similar in construction to the SKC lot no. 306 sampling tube (2) listed above
with one exception. The Supelco tube uses a smaller mesh size of molecular sieve. Lot no.
582-99 was used for a Sampling and Analysis experiment.
SKC collection devices (1) and (2) listed above are identical except device (1) has a physical
segregation of sorbents and oxidizer.
Due to low recoveries found during a preliminary study with Supelco sampling tubes, these tubes
were excluded from the experiments.
Sample Collection
Air samples were collected from the Teflon manifold using calibrated Du Pont model P125 low
flow pumps (flow rates of 0.175-0.200 L/min) for all experiments except for the
Desorption Efficiency (DE) (Analysis - Section 1) determination. This experiment used low flow
pumps to spike the TEA-IMS material with gaseous NO2.
The analysis experiment was designed to determine the amount of gas collected and not
necessarily the sampling capability at this flow rate. A flow rate of 0.010 L/min with SKC
Model 222-3-10 low flow pumps were used for the DE study.
Sample Analysis
Samples prepared for all experiments were analyzed by IC using the conditions specified in the
method (11.1.). For the conversion of NO2 to nitrite ion, a conversion
factor (C.F.) of 0.72 had been proposed (11.2.) to use in result calculations. Later experiments
revealed an average C.F. of 0.63 (11.3.-11.5.).
A C.F. of 0.63 was used to for all air sample experiments in this evaluation which
were performed below 10 ppm NO2.
Evaluation
The following experiments were performed for the evaluation of Method No. ID-182:
- Analysis - (DE) of spiked samples
- Sampling and Analysis - generation and analysis of NO2 samples
- Collection efficiency and breakthrough of TEA-IMS sampling tubes
- Storage stability of sampling tubes
- Sampling at different humidities
- Analytical method comparison
- Analytical detection limit determinations
- Determination of conversion factor for NO2 concentrations of 10 to 200 ppm.
The preliminary sampling and analysis experiment using Supelco tubes is discussed in Section 9.
A statistical protocol (11.6.) was used to evaluate results. Data were subjected to the
Bartlett's (11.7.) and an Outlier test (11.8.) to determine homogeneity of variance and identify any extraneous data.
1. Analysis (Desorption Efficiency, DE)
Procedure: A total of 20 spiked samples (8 samples at 0.5 and 6 samples at 1 and 2
times the Transitional PEL) were prepared and analyzed. Samples were prepared by spiking known
amounts of NO2 gas into TEA-IMS solid sorbent tubes.
The spiked concentrations were approximately 2.5, 5.0, and 10 ppm of nitrogen dioxide. These
concentrations are about 0.5, 1, and 2 times the OSHA Transitional PEL. Recoveries at these
levels represent the analytical DE. Results also provide information regarding the extent of
variability for the analytical portion of the method. Details for this experiment are discussed below:
1.1. SKC lot no. 374 sampling tubes were used.
1.2. Known NO2 gas concentrations were prepared by using a ten-fold
dilution of the NO2 permeation source with tempered air (50% RH and
25 °C). Samples were dynamically spiked using calibrated SKC low flow rate pumps. The
pumps slowly drew the diluted NO2 contaminant gas into the TEA-IMS
tubes. Samples were taken for measured time periods at a flow rate of approximately 0.010 L/min.
Results: The results of the analysis study are presented in Table 1.
All data passed the Bartlett's test. One result tested as an outlier and was omitted. Results
were pooled. The data (Table 1) indicates acceptable precision and accuracy (11.6.) for the
analytical portion of the method and does not indicate a need for a desorption correction factor.
The coefficient of variation for analysis (CV1) was 0.021 and the
average analytical or spiked recovery was 106%.
2. Sampling and Analysis
Procedure: A total of 18 samples (6 samples at each of the three test levels) were
collected from dynamically generated test atmospheres and analyzed. Generation and analysis of
NO2 was the same as mentioned in the Introduction. Sample results
from the dynamic generation provide the overall error and precision of the sampling and
analytical method. Overall error should be ±25% and was calculated using the following
equation (11.6.):
Overall error = ± [ | mean bias | + 2CVT ] × 100%
2.1. SKC sampling tubes, lot no. 306, were used for this experiment.
2.2. Samples were taken for 15-min sampling periods at concentrations of approximately
0.5, 1, and 2 times the OSHA Transitional PEL. The relative humidity and temperature of the
generation system were set at 50% and 25 °C.
Results: The results of the sampling and analysis experiment are shown in
Table 2. The sampling and analysis data also show acceptable precision
and accuracy (11.6.). All data passed both the outlier and Bartlett's test and results were
pooled. The pooled coefficients of variation for spiked CV1 (pooled),
generated CV2 (pooled) samples, as well as the overall CVT (pooled), are as follows:
CV1 (pooled) = 0.021
CV2 (pooled) = 0.033
CVT (pooled) = 0.034
The overall bias was 13% high. Overall error was acceptable (< ±25%) and was ±19.8%.
3. Collection Efficiency and Breakthrough
-
3.1. Collection Efficiency
Procedure: Samples were generated to measure the sorbent collection efficiency at about 9.5 ppm NO2.
3.1.1. SKC sampling tubes, lot no. 306, were used to collect the NO2
at 50% RH and 25 °C. These were the combination tubes; each glass tube contained two sections
of TEA-IMS separated by an oxidizer section.
3.1.2. Using the same generation system described in the Introduction, six samples were collected
at 2 times the OSHA Transitional PEL for 15 min.
3.1.3. The amount of NO2 vapor collected in the first and second sections of
the tubes was measured. The collection efficiency was calculated by dividing the amount
collected in the first solid-sorbent section by the total amount of
NO2 collected in both sections.
Results: Results are reported in Table 3. Collection
efficiency was adequate at two times the Transitional PEL with an average recovery of 97%.
3.2. Breakthrough
Procedure: Samples were generated at a concentration greater than the evaluation
levels to determine the extent of NO2 breakthrough from the first
solid sorbent tube into a second tube. The calculated breakthrough should be less than 5%.
3.2.1. Four sampling tubes (SKC lot no. 374) were connected to backup tubes and then to
sampling pumps. Air samples were collected for 15 min at a concentration of approximately 4 times
the Transitional PEL. The generation system was set at 30% RH and 25 °C. The low humidity
level was used as a "worst case" test since the presence of water is necessary for the
conversion reaction of NO2 to NO2¯
to proceed (11.1., 11.3.).
3.2.2. Breakthrough was assessed by analyzing both tubes and dividing the amount collected in
the second solid-sorbent tube by the total amount collected in both sections.
Results: The amount of breakthrough is shown in Table 3.
Breakthrough studies indicate the sorbent tube capacity for NO2 is
adequate for air concentrations at least to 21 ppm (using air volumes and flow rates described).
Small amounts of NO2 were detected on the backup tubes during both
collection efficiency and breakthrough studies. This could be from contamination rather than
actual breakthrough. although sample results are blank corrected, blank readings can be variable
(see Section 7 and Table 7 for further information regarding blanks).
Regardless of blank contamination or breakthrough, the breakthrough recoveries for both studies
are less than 5% and are considered acceptable.
4. Storage Stability
A study was conducted to determine any effects on storage of TEA-IMS samples
containing known amounts of NO2. A storage period of approximately 1
month was used. The procedure used is discussed below:
4.1. The determination was performed using SKC lot no. 306 tubes.
4.2. Twenty-four samples were generated at the OSHA Transitional PEL as described in the Introduction.
4.3. These samples were stored at 20 to 25 °C and were placed laboratory bench for the duration of the storage period.
4.4. Six samples were analyzed after 1, 5, 15, and 29 days.
Results: The results of the storage stability study are shown in Table 4.
Collected samples are stable at room temperature. The mean of samples analyzed after 29 days was
within ±5% of the mean of samples analyzed after one day. Samples may be stored in normal
environmental conditions found in a laboratory setting for a period of 29 days after sampling
without producing a significant change in results.
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5. Humidity Study
Procedure: A study was conducted to evaluate any effects on recovery when sampling
at different humidities. A contaminant flow conditioned at different relative humidities and a
constant temperature of 25 °C was generated using the system described in the Introduction.
Relative humidities of 30, 50, and 80% were used. SKC lot no. 374 tubes were used and six
samples were generated at each humidity level.
Results: Results are shown in Table 5. Data from sampling
at different humidities displayed no apparent effect on sampling efficiency. As shown in
Table 5, an analysis of variance (F test) was performed on the data to
determine if any significant difference existed in different humidity group results. The average
recovery across the three different humidity levels was also considered. The calculated F value
is below the critical value and a significant effect from humidity does not appear to exist.
Evidence of a slight increase in average recovery is apparent with an increase in humidity.
However, the increase is within the variability of the method and also does not appear as significant.
Therefore, the humidity study did not reveal a significant difference in recoveries or variance
when sampling at 30, 50, and 80% RH (25 °C).
6. Comparison of Analytical Methods
The IC method was compared to a reference method to determine if any significant disagreement
existed between the 2 methods. The previous analytical method, the differential pulse polarographic
(DPP) procedure (11.9.), was used as the reference analytical method. TEA-IMS
samples were taken using the generation system described in the Introduction.
Procedure: Eighteen samples were generated and analyzed by IC. Since both
analytical procedures use the same desorbing solution [(1.5% triethanolamine (TEA)], an aliquot
was taken from each sample and analyzed by the polarographic method.
Results: A linear regression comparison of the two methods is shown in
Figure 2 (the dotted line shown in Figure 2 represents ideal agreement
between the two methods. The solid line represents the observed agreement). Results of the
comparison between the IC and DPP method are also shown in Table 6.
The comparison of the DPP and IC analytical methods show excellent correlation and agreement.
The correlation coefficient (r) of 0.99 and a slope value of 1.0194 ± 0.0295 are very
close to ideal values. An r and slope value equal to 1 would indicate ideal correlation and
agreement between the two analytical methods. Over the concentration range tested the IC method
results show an increase of 1.9% when compared to polarographic method results. The slightly
higher recoveries of the IC procedure indicate that some of the bias noted (Section 2) can be
attributed to the analytical portion of the method. The background levels inherent in the
treated sorbent and erratic blank readings probably contribute to the positive bias also.
7. Analytical Detection Limits
Procedure: Qualitative and quantitative detection limits were determined by
analyzing low concentration samples and blanks. The samples were prepared by spiking solutions
containing 3 mL of 1.5% TEA with sodium nitrite solutions. The spiking was performed using a
calibrated micropipette. Samples and blanks were analyzed using a 50 µL sample injection
loop and a conductivity cell sensitivity range setting of 3 microsiemens.
7.1. Qualitative detection limit: The Rank Sum Test (11.10.) was used for the determination of
the qualitative detection limit of the IC analysis of NO2 (as nitrite).
7.2. Quantitative detection limit: The International Union of Pure and Applied Chemistry (IUPAC)
detection limit equation (11.11.) was used to calculate the detection limit.
Results: The results are listed in Table 7 and graphically
displayed in Figure 3. The qualitative detection limit is 0.07 ppm
NO2. The quantitative detection limit is 0.19 ppm NO2.
A 50 µL sample injection loop was used for all analyses in this evaluation. If necessary, a
larger sample loop can be used to achieve a lower limit of detection. In the past, blank
contamination was a serious problem and consequently caused high detection limits; blank
levels were occasionally 0.5 to 1 times the Transitional PEL when using a 0.05 L/min flow rate
for calculations. Soluble chloride salts can also elevate the detection limit. If the amount of
chloride in the sample is large (>5 µg/mL), the nitrite ion appears as a shoulder on the
chloride peak during IC analysis. Using the data reduction system described in Section 2 of the
method (11.1.), chloride peak areas from non-water washed TEA-IMS
tubes were 5 times greater than the water-washed sorbent. Nitrite peaks appeared
as shoulders on the chloride peaks of the non-water washed sorbent.
Water-washing decreased the chloride content to the point where good separation was
noted between the chloride and nitrite peaks.
8. Conversion Factor (C.F.)
As described in OSHA Method No. ID-182 (11.1.), the proposed factor for the
conversion of NO2 gas to the nitrite ion is concentration dependent.
If the reaction is stoichiometric, a C.F. of 0.5 would be seen experimentally. In practice,
however, this is not the case. For concentrations below 10 ppm, the average C.F. is 0.6 to 0.7
as reported by. Morgan et. al. (11.12.), in a previous study (11.9.), and by numerous others
(11.2-11.5.). For concentrations of 0 to 10 ppm NO2,
a factor of 0.63 was adopted by OSHA (11.9.) and NIOSH (11.13.). The factor was not well
defined at higher concentrations and needed further evaluation. The following procedure was used
to experimentally determine the C.F. for concentrations greater than 10 ppm:
8.1. A cylinder of NO in nitrogen (Air Products Co., 1.05% NO) was used as the contaminant
source. The rapid depletion of the NO2 permeation tubes precluded
their use for this experiment. The same generation system shown in Figure 1 was used with the
gas cylinder replacing the permeation tubes as the contaminant source. The NO2
was produced by flowing a diluted NO mixture through oxidizer sections, which converted the
NO to NO2 before collection.
8.2. The generation system was set at 50% RH and 25 °C.
8.3. Samples were taken using impingers containing 1.5% TEA solutions for variable time periods
at different concentration ranges. These TEA solutions were used in an attempt to avoid any
extraneous background contribution from solid sorbent desorption or intrinsic contamination from
the tubes. Samples were taken at a flow rate of 0.025 L/min to assure complete oxidation of the
NO and to provide sufficient residence time of NO2 in the TEA solutions.
Results: The results for C.F. calculations from 10 to 200 ppm are listed in
Table 8. Data in Table 8 show the conversion factors for
NO2 concentrations from 10 to 200 ppm. The conversion factor for the
10 to 100 ppm concentration range averaged 0.50; at about 200 ppm the factor was 0.37. Further
work may be necessary to determine why the factor decreased at the 200 ppm level. Another study
indicated no breakthrough of NO at this concentration (11.14.). Previous sample results and the
toxicology of NO2 indicate a 200 ppm NO2
sample collected in an industrial setting is unlikely. A correction factor and further work at
this concentration level was not pursued for these reasons. The conversion factor is further
discussed in reference 11.14.
9. Sampling and Analysis - Supelco Tubes
A preliminary evaluation of the combination tube manufactured by Supelco was conducted using
the same conditions and equipment mentioned in the Introduction. Samples were collected using
the procedure mentioned in Section 2. Results are listed in Table 9. This data indicates a sample
loss of approximately 30% when sampling at approximately 0.2 L/min. The loss could be associated
with a difference in mesh size (Supelco tubes contain a smaller mesh molecular sieve than SKC
tubes), flow rate differences or a poorly prepared lot. The original methodology for sampling
NO2/NO with this type of tube specified a flow rate of less than or
equal to 0.05 L/min. The four-fold increase in flow rate may be causing premature
breakthrough. The residence time of the sampled gas may not be sufficient at 0.2 L/min for this tube.
10. Discussion
Two different lots of SKC tubes were used for the evaluation. The combination tube consisting
of all three sections in a single tube (lot no. 306) was commercially available at the beginning
of the evaluation. This tube was used for the sampling and analysis, collection efficiency, and
storage stability experiments. Design changes were instituted and a three tube collection device
was produced to offer greater convenience when sampling NO2 or both NO
and NO2 simultaneously. The three-tube collection device,
lot no. 374, was used for the remaining studies. The two SKC devices are identical except the
sorbent and oxidant are contained in three separate glass tubes for the three tube device.
The data generated during the evaluation of the method indicates an acceptable alternative to
the polarographic method. The ion chromatographic method offers an accurate and precise
determination of NO2 exposures. A concentration-dependent conversion factor is
required in calculations and the molecular sieve solid sorbent must be water-washed
before impregnation and tube packing.
11. References
- 11.1. Occupational Safety and Health Administration Technical Center:
Nitrogen Dioxide in Workplace Atmospheres (Ion Chromatography),
by J.C. Ku (USDOL/OSHA-SLTC Method No. ID-182). Salt Lake City, UT. Revised 1991.
11.2. Saltzman, B.E.: Colorimetric Microdetermination of Nitrogen
Dioxide in the Atmosphere. Anal. Chem. 26:1949 (1954).
11.3. Gold, A.: Stoichiometry of Nitrogen Dioxide Determination in
Triethanolamine Trapping Solution. Anal. Chem. 49:1448-50 (1977).
11.4. Blacker, J.H.: Triethanolamine for Collecting Nitrogen Dioxide in
the TLV Range. Am. Ind. Hyg. Assoc. J. 34:390 (1973).
11.5. Vinjamoori, D.V. and Chaur-Sun Ling: Personal Monitoring Method
for Nitrogen Dioxide and Sulfur Dioxide with Solid Sorbent Sampling and Ion Chromatographic Determination.
Anal. Chem. 53:1689-1691 (1981).
11.6. Occupational Safety and Health Administration Analytical Laboratory:
Precision and Accuracy Data Protocol for Laboratory Validations. In OSHA Analytical Methods Manual.
Cincinnati, OH: American Conference of Governmental Industrial Hygienists (Pub. No. ISBN: 0-936712-66-X), 1985.
11.7. National Institute for Occupational Safety and Health:
Documentation of the NIOSH Validation Tests by D. Taylor, (DHEW/NIOSH Pub. No. 77-185). Cincinnati, OH, 1977.
11.8. Mandel, J. In Treatise on Analytic Chemistry. 2nd ed. Kolthoff,
I.M. and Elving, P.J., ed. New York: John Wiley and Sons, Inc., 1978. p 282.
11.9. Occupational Safety and Health Administration Analytical Laboratory:
OSHA Analytical Methods Manual (USDOL/OSHA-SLCAL Method No. ID-109).
Cincinnati, OH: American Conference of Governmental Industrial Hygienists (Pub. No. ISBN: 0-936712-66-X), 1985.
11.10. Dixon, W.J. and F.J. Massey, Jr.: Introduction to Statistical Analysis.
2nd ed. New York: McGraw-Hill Book Co., 1957. pp 289-292.
11.11. Analytical Methods Committee: Recommendations for the Definition,
Estimation and Use of the Detection Limit. Analyst 112(2):199-204 (1987).
11.12. Morgan, G.B., C. Golden, and E.C. Tabor: "New and Improved
Procedures for Gas Sampling and Analysis in the National Air Sampling Network" Paper presented
at the 59th Annual Meeting of the Air Pollution Control Association, San Francisco, CA, 1966.
11.13. National Institute for Occupational Safety and Health:
NIOSH Manual of Analytical Methods by D. Taylor, (DHEW/NIOSH Pub. No. 78-175).
Cincinnati, OH, 1978. Method no. S320.
11.14. Occupational Safety and Health Administration Technical Center:
Nitric Oxide Backup Data Report (ID-190) by J.C. Ku. Salt Lake City, UT. Revised 1991.
Table 1
Analysis*
Nitrogen Dioxide
|
| Level** |
------0.5 × PEL----- | |
------ 1 × PEL----- | |
------ 2 × PEL----- |
|
µg
taken | µg
found | DE | |
µg
taken | µg
found | DE | |
µg
taken | µg
found | DE |
|
|
12.35
15.48
12.59
15.72
13.26
12.28
12.08
14.97 |
12.50
16.35
13.11
16.80
13.90
13.10
12.55
16.46 |
1.01
1.06
1.04
1.07
1.05
1.07
1.04
1.10 |
|
23.78
29.82
27.44
25.25
24.88
31.10 |
24.38
24.12
29.31
27.00
26.33
33.36 |
1.03
***
1.07
1.07
1.06
1.07 |
|
58.36
53.06
52.14
65.68
57.08
52.33 |
60.68
54.42
54.95
68.36
61.73
54.91 |
1.04
1.03
1.05
1.04
1.08
1.05 |
| |
n
Mean
Std Dev
CV1 |
|
8
1.06
0.027
0.025 |
|
5
1.06
0.017
0.016 |
|
6
1.05
0.017
0.016 |
| |
|
CV1 (pooled) = 0.021
Ave. DE = 1.06 |
DE = Desorption efficiency
* SKC tubes, lot no. 374, were used
** Transitional PEL of 5 ppm NO2 was used
*** Excluded from statistical analysis as an outlier |
|
Table 2
Sampling and Analysis*
Nitrogen Dioxide
|
| Test Level** | Found
µg | Air Vol
(L) | Found
ppm | Taken
ppm | Recovery
(in %) |
|
| 0.5 × PEL |
14.46
12.32
10.59
14.37
16.03
15.02 |
2.59
2.23
1.94
2.62
2.81
2.67 |
2.97
2.94
2.90
2.92
3.03
2.99 |
2.64
2.64
2.64
2.64
2.64
2.64 |
113
111
110
111
115
113 |
| |
|
n
Mean
Std Dev
CV2 |
6
112
1.8
0.016 |
| |
| 1 × PEL |
28.77
23.61
21.01
27.59
28.24
29.17 |
2.59
2.23
1.94
2.62
2.81
2.67 |
5.90
5.63
5.76
5.60
5.34
5.81 |
5.06
5.06
5.06
5.06
5.06
5.06 |
117
111
114
111
106
115 |
| |
|
n
Mean
Std Dev
CV2 |
6
112
3.9
0.035 |
| |
| 2 × PEL |
56.83
46.99
38.21
53.06
55.53
54.39 |
2.59
2.23
1.94
2.62
2.81
2.67 |
11.66
11.20
10.47
10.76
10.50
10.83 |
9.45
9.45
9.45
9.45
9.45
9.45 |
123
119
111
114
111
115 |
| |
|
n
Mean
Std Dev
CV2 |
6
115
4.8
0.042 |
| |
CV2 (pooled)
Ave. Recovery |
= 0.033
= 113% |
CVT (pooled)
Overall Error |
= 0.034
= ±19.8% |
| |
* SKC tubes, lot no. 306, were used
** Transitional PEL of 5 ppm NO2 was used |
|
Table 3
Collection Efficiency
(25 °C and 50% RH)
|
| ------ µg NO2 Found ----------- | |
| Sample No. | First Section | Second Section | % Collection Efficiency |
|
1
2
3
4
5
6 |
56.83
46.99
38.21
53.06
55.53
54.39 |
2.32
ND
ND
2.19
1.98
2.30 |
96.1
100.0
100.0
96.0
96.6
95.9 |
| |
| Average | 97.4 |
| |
| Note: | (1) | SKC tubes, lot no. 306, were used |
| (2) | Sampling rate
Sampling time | =
= | 0.2 L/min
15 min |
| (3) | Concentration | = | approximately 2 times OSHA Transitional PEL |
| (4) | ND | = | None detectable < 0.24 µg NO2¯
(3-mL sample volume) |
Breakthrough Study
(25 °C and 30% RH)
|
| ------ µg NO2 Found ----------- | |
| Sample No. | 1st Tube | 2nd Tube | % Breakthrough |
|
1
2
3
4 |
103.8
104.5
105.1
103.2 |
3.34
ND
3.31
ND |
3.1
0
3.1
0 |
| |
| Average | 1.6 |
| |
| Note: | (1) | 1st and 2nd tube | = | SKC tubes, lot no. 374, were used |
| (2) | Sampling rate
Sampling time | =
= | 0.175 L/min
15 min |
| (3) | Generation concentration | = | 21 ppm NO2 |
| (4) | ND | = | None detectable < 0.24 µg NO2¯
(3-mL sample volume) |
|
Table 4
Storage Stability Test*
Nitrogen Dioxide
|
| Storage Day | Found
µg | Air Vol
(L) | Found
ppm | Taken
ppm | Recovery
(%) |
|
| Day 1 |
28.77
23.61
21.01
27.59
28.24
29.17 |
2.59
2.23
1.94
2.62
2.81
2.67 |
5.90
5.63
5.76
5.60
5.34
5.81 |
5.06
5.06
5.06
5.06
5.06
5.06 |
117
111
114
111
106
115 |
| |
| n
Mean
Std Dev
CV | 6
112
3.9
0.035 |
| |
| Day 5 |
25.74
23.56
20.69
26.52
29.32
28.41 |
2.61
2.23
1.93
2.60
2.72
2.61 |
5.24
5.61
5.70
5.42
5.73
5.79 |
5.04
5.04
5.04
5.04
5.04
5.04 |
104
111
113
108
114
115 |
| |
| n
Mean
Std Dev
CV | 6
111
4.2
0.038 |
| |
| Day 15 |
24.56
22.64
20.56
28.27
29.50
28.69 |
2.61
2.23
1.93
2.60
2.72
2.61 |
5.00
5.40
5.66
5.78
5.76
5.84 |
5.04
5.04
5.04
5.04
5.04
5.04 |
99.2
107
112
115
114
116 |
| |
| n
Mean
Std Dev
CV | 6
111
6.4
0.058 |
| |
| Day 29 |
27.34
23.95
23.66
27.58
28.41
31.92 |
2.61
2.23
1.93
2.60
2.72
2.61 |
5.57
5.71
6.52
5.64
5.55
6.50 |
5.04
5.04
5.04
5.04
5.04
5.04 |
111
113
129
112
110
129 |
| |
| n
Mean
Std Dev
CV | 6
117
9.2
0.079 |
| |
| * SKC tubes, lot no. 306 were used |
| |
|
Table 5
Relative Humidity Test (25 °C)*
Generated NO2 Concentration = 2.64 ppm
|
| RH, % | 34 | 50 | 80 |
|
| NO2 Found, ppm |
2.74
2.73
2.65
3.11
2.73
2.77 |
2.79
2.94
2.90
2.92
3.03
2.99 |
2.88
2.81
2.79
2.91
3.10
2.86 |
| |
| n
Mean, ppm
Std Dev, ppm
CV
Recovery |
6
2.79
0.16
0.058
106% |
6
2.93
0.083
0.028
111% |
6
2.89
0.11
0.038
109% |
| |
F test results: Fcalc = 2.078, Fcrit = 6.36, p < 0.01
* SKC tubes, lot no. 374, were used |
|
Table 6
Comparison of Methods*
[Ion Chromatographic (IC) vs. Polarographic (DPP)]
|
0.5 × PEL**
-- ppm Found -- |
1 × PEL**
-- ppm Found -- |
2 × PEL**
-- ppm Found -- |
| IC | DPP | RR | IC | DPP | RR | IC | DPP | RR |
|
3.41
3.43
3.57
3.40
3.46
3.39 |
3.17
3.19
3.27
3.19
3.33
2.82 |
1.076
1.075
1.092
1.066
1.039
*** |
5.93
6.21
6.21
5.95
5.88
6.15 |
5.55
6.03
5.91
5.61
5.58
6.00 |
1.068
1.030
1.051
1.061
1.054
1.025 |
10.11
10.20
10.73
10.33
10.11
11.96 |
10.11
10.39
10.23
10.09
10.03
10.49 |
1.000
0.982
1.049
1.024
1.008
1.140 |
| |
n
Mean
Std Dev
CV |
5
1.070
0.020
0.018 |
6
1.048
0.017
0.016 |
6
1.034
0.057
0.055 |
| |
* SKC tubes, lot no. 374, were used
** Transitional PEL of 5 ppm NO2 was used
*** Excluded from statistical analysis as an outlier
RR = Relative ratio, IC Found (ppm)/DPP Found (ppm) |
|
Linear Regression Comparison (also see Figure 2)
|
Correlation coefficient (r) | = 0.9938 |
|
| Slope (b) | = 1.0194 |
| Intercept (a) | = 0.1587 |
| Std dev of slope (Sb) | = 0.0295 |
Table 7
Qualitative Detection Limit - Nitrogen Dioxide
Rank Sum Test
For n(s) = n(b) = 10
|
| ------------------------- NO2 -- (as nitrite) --------------------------- |
| Rank |
0.08 µg/mL
Peak Area
|
0.16 µg/mL
Peak Area
|
0.32 µg/mL
Peak Area
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20 |
0.50
0.57
0.70
0.72
0.83
1.03
1.05
1.13
1.13
1.16
1.86
1.89
1.89
1.89
1.93
1.99
2.10
2.10
2.16
2.18 |
RBL
RBL
RBL
RBL
RBL
RBL
RBL
RBL
RBL
RBL
STD
STD
STD
STD
STD
STD
STD
STD
STD
STD |
0.50
0.57
0.70
0.72
0.83
1.03
1.05
1.13
1.13
1.16
2.14
2.29
2.41
2.46
2.58
2.77
2.79
2.83
2.90
2.93 |
RBL
RBL
RBL
RBL
RBL
RBL
RBL
RBL
RBL
RBL
STD
STD
STD
STD
STD
STD
STD
STD
STD
STD |
0.50
0.57
0.70
0.72
0.83
1.03
1.05
1.13
1.13
1.16
4.02
4.15
4.33
4.49
4.61
4.64
4.67
4.78
4.81
4.96 |
RBL
RBL
RBL
RBL
RBL
RBL
RBL
RBL
RBL
RBL
STD
STD
STD
STD
STD
STD
STD
STD
STD
STD |
| |
Rb =
C = | 55
99.9% | 55
99.9% | 55
99.9% |
| |
| Qualitative detection limit for nitrogen dioxide = 0.08 µg/mL or 0.24 µg
(3-mL sample volume). This corresponds to a concentration of 0.07 ppm NO2
for a 3-L air volume. |
| |
| Note: | (1) RBL | = Reagent Blank |
| (2) STD | = Standard |
| (3) Peak Area | = measured peak area/100,000 |
|
Table 7 (Cont.)
Quantitative Detection Limit - Nitrogen Dioxide (as NO2¯)
|
| Sample No. | Blank
Peak Area | 0.08 µg/mL
Peak Area | 0.16 µg/mL
Peak Area | 0.32 µg/mL
Peak Area |
|
1
2
3
4
5
6
7
8
9
10 |
0.50
0.57
0.70
0.72
0.83
1.03
1.05
1.13
1.13
1.16 |
1.86
1.89
1.89
1.89
1.93
1.99
2.10
2.10
2.16
2.18 |
2.14
2.29
2.41
2.46
2.58
2.77
2.79
2.83
2.90
2.93 |
4.02
4.15
4.33
4.49
4.61
4.64
4.67
4.78
4.81
4.98 |
| |
n
Mean
Std Dev
CV |
10
0.88
0.25
0.282 |
10
2.00
0.12
0.062 |
10
2.61
0.27
0.105 |
10
4.55
0.30
0.067 |
| |
Peak Area = measured peak area/100,000
The quantitative detection limit is calculated using the equation: |
| |
| Cld = k(sd)/m |
Cld = 10(0.248)/10.83 = 0.23 µg/mL |
| |
| Where: |
| Cld = |
the smallest reliable detectable concentration an analytical instrument can determine at a given confidence level |
| k = |
10, thus giving confidence that any detectable signal will be greater than or equal to an average blank reading plus ten times the standard deviation (area reading > Blave + 10sd) |
| sd = |
standard deviation of blank readings |
| m = |
analytical sensitivity or slope as calculated by linear regression
Quantitative detection limit = 0.23 µg/mL (as nitrite) or 0.69 µg
(3-mL sample volume). This corresponds to 0.19 ppm NO2 for a 3-L air volume. |
| |
|
Table 8
Nitrogen Dioxide Conversion factor
|
| NO2 ppm | Samples | Std Dev | CV | Mean* |
|
12.89
25.20
49.79
97.90
192.57 |
7
7
6
6
7 |
0.038
0.037
0.022
0.020
0.025 |
0.074
0.070
0.043
0.044
0.068 |
0.519
0.533
0.517
0.450
0.368 |
| |
| * Average conversion factor. This was calculated from sample results and assumed a 100% recovery. |
| |
|
Table 9
Sampling and Analysis (Supelco Tubes)*
Nitrogen Dioxide
|
| Test Level** | Found
µg | Air Vol
(L) | Found
ppm | Taken
ppm | Statistics |
|
| 0.5 × PEL |
5.80
6.25
7.71
8.52
5.06
8.71 |
2.19
1.90
1.71
2.24
2.40
2.56 |
1.41
1.75
2.40
2.02
1.12
1.81 |
2.62
2.62
2.62
2.62
2.62
2.62 |
| |
| n
Mean
Std Dev
CV | 6
66.9%
17.0
0.26 |
| |
| 1 × PEL |
15.91
12.73
11.45
15.82
16.27
18.94 |
2.19
1.90
1.71
2.24
2.40
2.56 |
3.86
3.56
3.56
3.75
3.60
3.93 |
5.08
5.08
5.08
5.08
5.08
5.08 |
| |
| n
Mean
Std Dev
CV | 6
73.0%
3.2%
0.043 |
| |
| 2 × PEL |
30.11
22.77
22.48
28.63
31.14
34.04 |
2.19
1.90
1.71
2.24
2.40
2.56 |
7.31
6.35
6.99
6.79
6.90
7.07 |
9.66
9.66
9.66
9.66
9.66
9.66 |
| |
| n
Mean
Std Dev
CV | 6
71.4%
3.3%
0.047 |
| |
* Supelco tubes, Lot No. 582-99, were used
** Transitional PEL of 5 ppm NO2 was used |
| |
| CV(pooled) = 0.15 Ave. Recovery = 70.4% Overall Error = ±59.6% |
|
A block diagram of the major components of the dynamic generation system is
shown below. The system consists of four essential elements, a flow,
temperature and humidity control system, a nitrogen dioxide vapor generating
system, a mixing chamber and an active sampling manifold.
Figure 1
Linear Regression Comparison
Ion Chromatographic vs. Polarographic Analysis of Nitrogen Dioxide
Dotted Line = Ideal Agreement Between Methods
Solid Line = Found Agreement Between Methods
Figure 2
Detection Limit
Figure 3
|
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