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AMMONIA BACKUP DATA REPORT
This report was revised June, 1990
Introduction
The general procedure for the air sample collection and analysis of ammonia
is described in OSHA Method No. ID-188 (10.1.). The validation of this
method examines the use of a glass sampling tube containing 500 mg of carbon
bead impregnated with sulfuric acid (CISA). Sampling tubes were made
in-house and also obtained from Supelco Inc. (Bellefonte, PA). During the
validation these commercial tubes became available and were used for
experiments not completed. The in-house and commercially prepared tubes are
identical except the tube manufactured by Supelco has a 250-mg backup
section. The in-house tubes were prepared using the method of Bishop,
Belkin and Gaffney (10.2.) with a minor modification. A dilute sulfuric
acid pre-wash of the carbon bead sorbent was performed when preparing the
in-house tubes.
This method was evaluated when the OSHA Time Weighted Average (TWA)
Permissible Exposure Limit (PEL) for ammonia was 50 ppm. As of this
writing, the OSHA Final Rule Limit for exposure to ammonia is now a
Short-Term Exposure Limit (STEL) of 35 ppm.
The method has been validated for TWA samples using sampling flow rates
of about 0.10 liter per minute (L/min) and sampling times of 3 to 4 h. An
evaluation of four types of ammonia detector tubes was carried out
simultaneously with the method validation. The results of the detector tube
study are reported in OSHA Product Evaluation No. 7 (10.3.). A preliminary
test was also conducted on ammonia dosimeter tubes obtained from Wilson
Safety Products (Reading, PA). The testing of the dosimeter tubes was
discontinued since these tubes could not measure concentrations above 50 ppm
ammonia during the experiments.
The validation of OSHA Method No. ID-188 (10.1.) consisted of the
following experimental protocol:
- Analysis of spiked samples.
- Analysis of dynamically generated samples having concentrations of
approximately 0.5, 1, and 2 times the TWA PEL. Test atmospheres were
generated using 50% RH and 25°C.
- Collection efficiency and breakthrough studies of the CISA sampling
tubes.
-
Determination of the storage stability of ammonia collected with CISA
tubes.
- Determination of any variation in results when sampling at high and
low RH.
- Comparison of the ion chromatographic method with the ISE method for
the determination of ammonia in workplace atmospheres.
- Determination of the qualitative and quantitative detection limits.
- Collection and analysis of ammonia samples employing Supelco tubes
and comparison with tubes produced in-house.
A generation system, shown in Figure 1, was used for simultaneous testing
of detector tubes and continual sampling devices. All generations of
ammonia test atmospheres, and hence all experiments, with two exceptions,
were performed using the apparatus shown in Figure 1. The analysis and
detection limit studies did not use test atmospheres; these samples were
spiked with solutions of ammonium sulfate.
Ammonia Gas Concentration
Ammonia in nitrogen (certified standard, 0.99% ammonia, Air Products Co.,
Long Beach, CA) was used as the contaminant source. The concentration of
ammonia in the cylinder was verified by the following technique:
- The undiluted gas stream from the cylinder was sampled with a gas
syringe and then injected into 0.1 N sulfuric acid contained in
septum-capped vials.
- These samples were analyzed for ammonia with an Orion Model 9512
Ammonia Ion Specific Electrode (ISE) and an Orion Model EA940
IonAnalyzer (10.4.). The results are shown below:
Theoretical NH3
|
Found NH3 (µg)
|
Recovery %
|
SD
|
CV
|
Spikes (µg): |
|
60.5 60.5 60.5 60.5 |
56.8 59.8 54.2 50.2 |
93.9 98.8 89.6 83.0 |
|
|
|
|
|
6.70 |
0.073 |
Average |
|
91.3 |
|
|
The ammonia aliquot results were compared to the manufacturer's stated
concentration value. The average spiked sample recovery was 91.3% of the
stated value and the CV was 0.073. The manufacturer's stated value was used
for all calculations. The lower recoveries were considered to be due to
variability in analysis and not due to a change in the stated cylinder
concentration. The ISE method has displayed a significant amount of
variability in results and slightly lower than expected recoveries.
Internal quality control data and results of ISE samples generated during
this evaluation are evidence of this variability and decreased recovery when
using the ISE method.
Generation System Components
The ammonia gas was 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. Moisture and other contaminants were removed from
the diluent air by using a charcoal, molecular sieve and Drierite filtering
system. A Teflon sampling manifold and connections were attached to the
mixing chamber. Diluent air flow was determined using a dry test meter
(Singer Co., Model No. DTM 115) before, during, and after each experiment.
Ammonia flow rates were controlled by a mass flow controller (Tylan Model FC
260), and were measured before and after each experiment with a soap bubble
flow-meter. During each experiment the flow rate was monitored using the
readout (LED display) for the mass flow controller.
Sample Collection
Air samples were collected from the manifold using Du Pont Model P125 pumps
(Du Pont Co. Wilmington, DE) calibrated at flow rates of about 0.1 L/min for
all generation experiments. Specific sampling times are mentioned in the
procedures for each experiment.
Sample Analysis
Samples, blanks and prepared standards were analyzed for ammonium ion by ion
chromatography (10.1.). Analyses and data reduction were performed using a
Dionex Model 2010i Ion Chromatograph interfaced to a Hewlett-Packard 3357
Laboratory Automation System. An IBM AT Personal Computer with AutoIon 400
software was used during later analyses. All sample results were calculated
using a concentration-response curve with peak areas used for signal
measurement. Sample results were statistically examined for outliers and
homogeneous variance. Possible outliers were determined using the American
Society for Testing and Materials (ASTM) test for outliers (10.5.).
Homogeneity of the coefficients of variation was determined using the
Bartlett's test (10.6.).
- 1. Analysis (Spiked Samples)
Procedure: Twenty-one spiked samples (7 samples at each test level) were
prepared and analyzed. The spiked concentrations correspond to
approximately 0.5, 1 and 2 times the TWA PEL when using a 24-L air
volume. Recoveries represent the desorption efficiency and also provide
precision and accuracy data for the analytical portion of the method.
1.1. Three sets of spiked samples were prepared using the following
procedure:
1.1.1. A concentrated solution of ammonium sulfate [(NH4)2SO4] was
prepared by dissolving a weighed amount of (NH4)2SO4 ("Baker
Analyzed" Reagent, ACS) in deionized water (DI H2O).
1.1.2. Aliquots of this solution were injected into in-house
prepared sorbent tubes using a calibrated micropipette.
1.1.3. Sufficient (NH4)2SO4 solution was added so that the tubes in
each set would contain an amount of ammonia expected after
collection from atmospheres at approximately 0.5, 1, and 2
times the PEL, respectively.
1.1.4. The spiked tubes were allowed to stand overnight at room
temperature.
1.2. The carbon beads were removed from each tube and desorbed with DI
H2O and analyzed as mentioned in the method (10.1.). The glass tube
was also rinsed with DI H2O. Blanks were also prepared in the same
fashion.
Results: The results are given in Table 1. All data were used except
for one sample (2 × TWA PEL) which appeared contaminated with an unknown
substance and gave baseline irregularities during analysis. All results
passed the outlier and Bartlett's tests and were pooled. The analytical
coefficient of variation (CV1) was 0.031 and recovery was 99.7%.
2. Sampling and Analysis
Procedure: Twenty-four samples were taken from the dynamic generation
system mentioned in the Introduction. Sample results from the dynamic
system provide the overall error and precision of the sampling and
analytical method. Overall error (OE) should be within ±25% and is
calculated using the following equation (10.7.):
Overall Error = ± [|mean bias| + 2CVT] × 100%
2.1. Samples were collected from gas streams (50% RH and 25°C)
containing ammonia at approximately 0.5, 1, and 2 times the TWA PEL.
2.2. In-house prepared tubes containing beaded activated carbon with 5%
(by weight) sulfuric acid as described in the method (10.1.) and
similar tubes prepared by Supelco were taken side-by-side.
2.3. Two to four samples were collected during each generation
experiment. Three to four samples were desired, but in several
cases pump failure ended the determination.
2.4. Collection rates were about 0.1 L/min. Collection times were 3 to
4 h.
2.5. Samples were desorbed with 50 or 100 mL of DI H2O and analyzed.
Results: Sample results are listed in Table 2 and are only for the
in-house tubes. Supelco tube results are similar. The in-house tube
samples collected at 50% RH (Table 2) show good precision and accuracy.
The total coefficient of variation (CVT) was 0.050 and the OE (total) was
±10.9%. Bias was less than 1%.
3. Collection Efficiency and Breakthrough Studies
3.1. Collection Efficiency:
Procedure: Test atmospheres were generated and samples were taken
to measure the sorbent collection efficiency at the upper
concentration limit of the validation.
-
3.1.1. A determination of the collection efficiency was performed
using five Supelco tubes in which ammonia at 2 times the TWA
PEL was collected. Two samples were collected at 30% and
three samples at 80% RH. Samples were taken for
approximately 200 min. The amounts of ammonia collected in
the first and second sections of the tubes were determined.
3.1.2. The collection efficiency was calculated by dividing the
amount collected in the first section by the total amount of
ammonia collected in the first and second sections.
Results: The results are given in Table 3. The collection
efficiency was 100%. No ammonia was detected in the backup
sections. The results indicate that the collection efficiency is
excellent.
3.2. Breakthrough:
Procedure: Samples were generated at a concentration greater than
the validation level to determine the extent of breakthrough from
the first solid sorbent section into a second section.
-
3.2.1. The possibility of breakthrough of ammonia during sampling
was examined by collecting six samples at approximately 5
times the TWA PEL for 335 min, using Supelco tubes.
Generation conditions were 50% RH and 25°C.
3.2.2. The main sections were each desorbed in 250 mL of DI H2O. To
facilitate detection of any breakthrough, the backup sections
were each desorbed in 10 mL of DI H2O.
Results: The results given in Table 3 show the overall recovery was
94.6% and the CV was 0.032. Ammonia was not detected in the backup
sections, indicating no evidence of breakthrough.
- 4. Storage Stability of Ammonia Samples Collected on CISA
Procedure: A long-term evaluation of sample media stability was done to
assess any potential problems if delays in sample analyses occur.
- 4.1. Supelco tube samples were collected from a gas stream adjusted to
50% RH, 25°C and an ammonia concentration of approximately 50 ppm.
4.2. A collection time of about 3.5 h was used.
4.3. Samples were capped and stored for various periods up to 29 days
before preparation and analysis. Samples were stored in a desk
drawer.
Results: The results given in Table 4 indicate a slight loss of ammonia
(<10%) during approximately one month of storage. The slight decrease in
recovery does not appear detrimental to the overall accuracy of the
method. Samples can be stored for at least 29 days before analysis.
5. Humidity Tests
Procedure: Samples were collected at high (80%) and low (30%) RH using
similar conditions mentioned in Section 2, where samples were collected
at 50% RH. Supelco and in-house tubes were taken side-by-side. Sample
recoveries for these three humidity levels were examined to determine any
significant differences.
Results: The low and high RH results are given in Table 5; the 50% RH
results are shown in Table 2. Results listed are for in-house tubes
only. Supelco tubes gave similar results. Sampling at different
humidities displayed no apparent effect on recovery. An analysis of
variance (F test) was performed on the data to determine any significant
difference among or within the different humidity groups. Variance at
each concentration level (0.5, 1, and 2 times the TWA PEL) was compared
across the 3 humidity levels (25-30, 50, and 80% RH). The variance among
and within the different concentration groups gave acceptable calculated
F values with the exception of the data at the TWA PEL. At this
concentration only three samples were collected at the low humidity
level; these recoveries were lower than expected and appeared to be due
to a dilution problem during ammonia generation. The reference method
bubbler samples taken side-by-side also gave lower than expected results.
The test at low RH was one of the first experiments conducted. This
anomalous behavior was not observed for any of the other data.
The recoveries across the 3 different humidity levels were also
considered. No evidence of any significant constant increase or decrease
in average recovery was apparent when generation data are compared at
different humidity levels. Therefore, the data indicate no apparent
humidity effect on recovery.
-
6. Method Comparison
Procedure: The CISA sampling and ion chromatography (IC) analytical
method was compared to a reference method to determine if any significant
disagreement existed between the two methods. The bubbler sampling and
ISE analytical method (10.4.) was chosen as the reference method. The
comparison was conducted as described below:
6.1. Side-by-side samples of CISA tubes (both commercial and in-house
tubes) and bubblers containing 0.1 N sulfuric acid were collected at
25°C and 25-30%, 50%, and 80% RH. Du Pont Model P4000 pumps were
used to collect bubbler samples. Bubbler collection rates were
1 L/min and collection times were 3 to 4 h. The bubbler solutions
were analyzed using an Orion Model 9512 Ammonia ISE and an Orion
Model EA940 IonAnalyzer (10.4.).
6.2. The CISA tubes were sampled and analyzed using the procedures
described in the Introduction.
Results: The results are given in Table 6. Each CISA and bubbler sample
value listed is an average value of two to four samples. Each comparison
is for samples collected side-by-side. Statistical treatments are also
given. Each sample comparison is based on the averages of the CISA and
bubbler samples collected side-by-side. Linear regression comparison
calculations are also given. The results of the two methods show the
CISA sampling and corresponding IC analytical method has an overall
positive bias of approximately 7% (slope = 1.07 ± 0.0387) when compared
to the bubbler method. Complete listings of individual CISA and bubbler
sample results are given in the Appendix.
- 7. Analytical Detection Limits
Procedure: The qualitative detection limit for the analysis of ammonia
by IC was calculated using the Rank Sum Test (10.8.). A modification or
derivation of the International Union of Pure and Applied Chemistry
(IUPAC) detection limit equation (10.9.) was used to determine the
quantitative detection limit. At the sensitivity level tested, blank
readings and the standard deviation of the blank were equal to zero. The
lack of a blank signal does not satisfy a strict interpretation of the
IUPAC detection limit when using the equation shown in Table 7. The
quantitative detection limit for this method is calculated using the
standard deviation of a standard below the range of the expected
detection limit as a substitute for the blank readings. The procedure
used for sample preparation to determine detection limits is discussed
below:
-
7.1. Low concentration ammonia samples were prepared from an ammonium
chloride solution (1,000 µg/mL as NH3). The sample concentrations
were 0.05, 0.1, 0.2, and 0.5 µg/mL ammonia.
7.2. All solutions were made in 0.005 N sulfuric acid. This is the
concentration expected when a typical 500-mg section of acid-treated
carbon beads from a sample tube is desorbed with 100 mL of DI H2O.
7.3. A blank sample was prepared containing the same sulfuric acid
concentration as the ammonia samples.
7.4. Samples were analyzed by IC with a 50-µL sample loop and
30-microsiemens detector setting.
Results: The qualitative and quantitative detection limits (Table 7) are
0.20 and 0.50 µg NH3/mL solution, respectively. Using a 24-L air volume
and a 50-mL sample volume, the qualitative limit is 0.60 ppm and the
quantitative limit is 1.5 ppm ammonia in air. For a 7.5-L air sample,
these limits are 1.9 and 4.8 ppm, respectively.
8. Collection of Ammonia Samples - Supelco Tubes
Procedure: Experiments were done with in-house sampling tubes and tubes
prepared by Supelco. Side-by-side sampling at varied humidity and
concentration levels was performed to compare both tubes. Recoveries
were compared and a t-test was used to determine if any significant
difference in results existed between the two tubes (10.10.).
Results: The results are shown in Table 8. Separate Supelco tube
results are also shown in Table 8. The results indicate the two
different sets of tubes compare well with each other in their ability to
collect and retain ammonia. A t-test (10.10.) showed no significant
difference between recoveries for the two different sets of tubes.
The backup sections of the Supelco tubes were also analyzed. All
backup results were non-detected when the samples were analyzed shortly
after desorption. A very small peak eluting at the same time as ammonia
developed after solutions stood for 1 week.
9. Conclusions
The sample determinations shown in Tables 1 and 2 are well within NIOSH
or OSHA accuracy and precision guidelines (10.6., 10.7.). Collection
efficiency, breakthrough, and storage stability are adequate. A humidity
effect was not noted. The comparison of the bubbler with the IC method
showed a positive linear regression slope of 1.07. This is to be
expected since overall recoveries of the bubbler method were about 9%
lower than expected (theoretical) and IC sample recoveries exhibited
minimal bias. The sampling and analysis data for bubbler samples (three
different RH and concentration levels) gave an overall recovery of 91.0%
and a CV of 0.091. In general, the lowest recoveries for the bubbler
samples were measured during preliminary experiments before improvements
were made in the ISE procedure. Results for all samples taken and
analyzed by IC or ISE are shown in the Appendix.
Detection limits are adequate for 4-h exposure determinations. For
STEL measurements, larger sample volumes will need to be taken over the
15-min sampling period. It is recommended to use 0.5 L/min for STEL
assessments (total air volume = 7.5 L). although no STEL experiments
were performed during this evaluation, a literature reference (10.2.)
experiment conducted at a sampling rate of 0.5 L/min for 12 min at a
concentration of 25 ppm indicated no detectable breakthrough. The
experimenters also indicated the theoretical capacity of the sampling
tube is 8.5 mg ammonia.
The method for collecting ammonia with CISA tubes and analysis by IC
is a precise and accurate method for the determination of ammonia in
workplace atmospheres.
10. References
- 10.1. Occupational Safety and Health Administration Technical Center:
Ammonia in Workplace Atmospheres - Solid Sorbent by R.G. Adler
(OSHA-SLTC Method No. ID-188). Salt Lake City, UT. Revised 1991.
10.2. Bishop, R.W., F. Belkin and R. Gaffney: Evaluation of a New
Ammonia Sampling and Analytical Procedure. Am. Ind. Hyg. Assoc.
J. 47: 135-137 (1986).
10.3. Occupational Safety and Health Administration Analytical
Laboratory: Ammonia Detector Tubes (PE-7). Salt Lake City, UT.
1987.
10.4. Occupational Safety and Health Administration Analytical
Laboratory: OSHA Analytical Methods Manual (USDOL/OSHA-SLCAL
Method No. ID-164). Cincinnati, OH: American Conference of
Governmental Industrial Hygienists (Pub. No. ISBN:
0-936712-66-X), 1985.
10.5. Mandel, J.: Accuracy and Precision, Evaluation and Interpretation
of Analytical Results, The Treatment of Outliers. In Treatise On
Analytical Chemistry, 2nd Ed., edited by I. M. Kolthoff and P. J.
Elving. New York: John Wiley and Sons, 1978. pp. 282-285.
10.6. National Institute for Occupational Safety and Health:
Documentation of the NIOSH Validation Tests by D. Taylor, R.
Kupel and J. Bryant (DHEW/NIOSH Pub. No. 77-185). Washington,
D.C.: U.S. Government Printing Office, 1977. pp. 1-12.
10.7. 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.
10.8. National Bureau of Standards: Experimental Statistics by M.G.
Natrella (U.S. Dept. of Commerce/NBS Handbook 91). Washington,
D.C.: U.S. Government Printing Office, 1966. Chapter 16, pp 8-14.
10.9. Long, G.L. and J.D. Windfordner: Limit of Detection, A Closer
Look at the IUPAC Definition. Anal. Chem. 55: 712a-724a (1983).
10.10. Osol, Arthur, ed.: Remington's Pharmaceutical Sciences. Easton,
PA: Mack Publishing Co., 1980. pp. 113-114.
Table 1
Analysis - Spiked NH3 Samples
(OSHA-TWA PEL)* |
µg NH3 Taken |
µg NH3 Found |
F/T |
n |
Mean |
Std Dev |
CV |
AE |
(0.5 × TWA PEL) |
348.0 348.0 348.0 348.0 348.0 348.0 348.0 |
341.0 361.0 342.0 326.0 338.0 339.0 358.0 |
0.9799 1.0374 0.9828 0.9368 0.9713 0.9741 1.0287 |
|
|
7 |
0.987 |
0.035 |
0.035 |
8.3 |
(1 × TWA PEL) |
818.0 818.0 818.0 818.0 818.0 818.0 818.0 |
841.0 855.0 825.0 828.0 830.0 848.0 872.0 |
1.0281 1.0452 1.0086 1.0122 1.0147 1.0367 1.0660 |
|
|
7 |
1.030 |
0.021 |
0.020 |
7.1 |
(2 × TWA PEL) |
1636.0 1636.0 1636.0 1636.0 1636.0 1636.0 |
1540.0 1610.0 1543.0 1674.0 1609.0 1536.0 |
0.9413 0.9841 0.9432 1.0232 0.9835 0.9389 |
|
|
6** |
0.969 |
0.034 |
0.035 |
10.1 |
F/T |
= |
Found/Taken |
AE |
= |
Analytical Error (± %) |
Bias |
= |
-0.003 |
CV1 (pooled) |
= |
0.031 |
Analytical Error (Total) |
= |
±6.5% |
|
* |
Levels are approximate. |
** |
Seven samples were taken; however, one sample was omitted due to baseline irregularities occurring during analysis. |
|
Table 2
Sampling and Analysis
(50% RH and 25°C)
(OSHA-TWA PEL) |
ppm NH3 Taken |
ppm NH3 Found |
F/T |
n |
Mean |
Std Dev |
CV |
OE |
(0.5 × TWA PEL) |
34.2 34.2 34.2 30.7 30.7 |
35.1 36.1 39.6 29.8 29.5 |
1.0263 1.0556 1.1579 0.9707 0.9609 |
|
|
5 |
1.034 |
0.079 |
0.077 |
18.8 |
(1 × TWA PEL) |
45.4 45.4 45.4 50.3 50.3 50.3 50.1 50.1 50.1 |
49.2 46.9 47.4 47.0 47.6 48.2 51.2 50.3 51.0 |
1.0837 1.0330 1.0441 0.9344 0.9463 0.9583 1.0220 1.0040 1.0180 |
|
|
9 |
1.005 |
0.049 |
0.049 |
10.3 |
(2 × TWA PEL) |
100.7 100.7 100.7 100.7 98.5 98.5 98.5 101.8 101.8 101.8 |
94.9 94.5 91.9 97.6 96.1 97.8 93.5 98.5 95.9 100.2 |
0.9424 0.9384 0.9126 0.9692 0.9756 0.9929 0.9492 0.9676 0.9420 0.9843 |
|
|
10 |
0.957 |
0.025 |
0.026 |
9.4 |
F/T |
= |
Found/Taken |
OE |
= |
Overall Error (± %) |
Bias |
= |
-0.009 |
CV2 (pooled) |
= |
0.048 |
Overall Error |
= |
±10.5% |
CVT (pooled) |
= |
0.050 |
Overall Error (Total) |
= |
±10.9% |
|
Table 3
Collection Efficiency and BreakthroughCollection Efficiency - Supelco Tubes50 % RH and 25 °C
Sample |
ppm |
|
Collection |
ppm Ammonia Found |
Collection |
No. |
Ammonia |
RH (%) |
Time (min) |
1st Sec. |
2nd Sec. |
Eff. (%) |
|
|
|
|
|
|
|
1 2 3 4 5 |
99.5 99.5 101.3 101.3 101.3 |
30 30 80 80 80 |
190 190 215 215 215 |
87.8 91.6 103.4 105.5 102.8 |
ND ND ND ND ND |
100 100 100 100 100 |
|
Samples were collected at approximately 0.1 L/min flow rate.ND = None detected. Detection limit = 1.5 ppm NH3 |
|
Breakthrough - Supelco Tubes50 % RH and 25°C
-------------------------NH3 Found------------------------- |
NH3 Taken |
|
µg |
Air Vol (L) |
ppm |
ppm |
% Recovery |
|
|
5189 5012 5218 4968 4802 5426 |
29.52 29.83 29.27 29.61 28.79 32.94 |
252 241 256 241 239 236 |
258 258 258 258 258 258 |
|
|
|
n Mean Std Dev CV |
= = = = |
6 244 7.94 0.032 |
|
|
94.6 |
Samples were collected at about 0.1 L/min for 335 min at approximately 5 × TWA PEL. No ammonia was detected in the backup sections. |
Table 4
Storage Stability Test - 1 × TWA PEL, 50 % RH, 25°C
|
-------------------------Found------------------------- |
Taken |
|
Storage Day |
µg |
Air Vol (L) |
ppm NH3 |
ppm NH3 |
% Recovery |
|
Day 1 |
705.3 606.7 656.6 |
18.70 16.63 17.89 |
54.1 52.4 52.7 |
53.3 53.3 53.3 |
|
|
n Mean Std Dev CV |
3 53.1 0.907 0.017 |
|
|
100 |
Day 5* |
672.2 620.8 |
19.26 16.54 |
50.1 53.9 |
53.3 53.3 |
|
|
n Mean Std Dev CV |
2 52.0 2.69 0.052 |
|
|
98 |
Day 9 |
614.0 609.6 555.2 |
17.64 17.50 17.04 |
50.0 50.0 46.8 |
53.3 53.3 53.3 |
|
|
n Mean Std Dev CV |
3 48.9 1.85 0.038 |
|
|
92 |
Day 15 |
664.4 609.6 661.0 |
18.37 18.29 19.05 |
51.9 47.8 49.8 |
53.3 53.3 53.3 |
|
|
n Mean Std Dev CV |
3 49.8 2.05 0.041 |
|
|
93 |
Day 29 |
570.4 536.4 546.3 |
17.03 15.98 16.62 |
48.1 48.2 47.2 |
50.1 50.1 50.1 |
|
|
n Mean Std Dev CV |
3 47.8 0.551 0.012 |
|
|
95 |
* One result was deleted due to pump failure.All samples were collected using Supelco tubes. Some of the sampling tubes used had been stored 11 months prior to use. Storage times reported are from the day of collection to the day of analytical preparation. |
Table 5
NH3-IC Humidity Study25-30% RH and 25°C
(OSHA-TWA PEL) |
ppm NH3 Taken |
ppm NH3 Found |
F/T |
n |
Mean |
Std Dev |
CV |
OE |
(0.5 × TWA PEL) |
34.0 34.0 34.0 34.3 34.3 34.3 24.3 24.3 24.3 |
28.7 29.4 29.6 34.0 31.9 31.3 24.4 23.5 23.1 |
0.8441 0.8647 0.8706 0.9913 0.9300 0.9125 1.0041 0.9671 0.9506 |
|
|
9 |
0.926 |
0.057 |
0.062 |
19.8 |
(1 × TWA PEL) |
55.0 55.0 55.0 |
44.8 43.0 46.5 |
0.8145 0.7818 0.8455 |
|
|
3 |
0.814 |
0.032 |
0.039 |
26.4 |
(2 × TWA PEL) |
99.6 99.6 99.6 99.5 99.5 99.5 |
90.0 95.0 94.6 101.8 101.4 100.4 |
0.9036 0.9538 0.9498 1.0231 1.0191 1.0090 |
|
|
6 |
0.976 |
0.048 |
0.049 |
12.2 |
F/T |
= |
Found/Taken |
OE |
= |
Overall Error (± %) |
Bias |
= |
-0.076 |
CV2 (pooled) |
= |
0.055 |
Overall Error (Total) |
= |
±18.7% |
|
80% RH and 25°C
(OSHA-TWA PEL) |
ppm NH3 Taken |
ppm NH3 Found |
F/T |
n |
Mean |
Std Dev |
CV |
OE |
(0.5 × TWA PEL) |
29.2 29.2 29.2 24.2 24.2 24.2 |
27.3 28.6 29.0 22.1 22.2 22.3 |
0.9349 0.9795 0.9932 0.9132 0.9174 0.9215 |
|
|
6 |
0.943 |
0.034 |
0.036 |
13.0 |
(1 × TWA PEL) |
50.2 50.2 50.2 48.1 48.1 48.1 |
48.4 47.0 49.1 41.6 45.6 40.9 |
0.9641 0.9363 0.9781 0.8649 0.9480 0.8503 |
|
|
6 |
0.924 |
0.053 |
0.058 |
19.2 |
(2 × TWA PEL) |
101.3 101.3 101.3 |
105.8 98.0 102.6 |
1.0444 0.9674 1.0128 |
|
|
3 |
1.008 |
0.039 |
0.038 |
8.5 |
F/T |
= |
Found/Taken |
OE |
= |
Overall Error (± %) |
Bias |
= |
-0.052 |
CV2 (pooled) |
= |
0.047 |
Overall Error (Total) |
= |
±14.5% |
|
Table 6
Comparison of Sampling and Analytical Methods
RH
|
IC Found (ppm)
|
ISE Found (ppm)
|
RR
|
25-30% |
29.2 32.4 23.7 44.8 93.2 101.2 |
29.7 28.6 22.9 44.4 88.9 94.4 |
0.983 1.133 1.035 1.009 1.048 1.072 |
50 % |
36.9 29.7 47.8 47.6 50.9 94.7 95.8 98.2 |
29.1 29.2 44.9 42.5 53.3 88.7 79.3 99.7 |
1.268 1.017 1.065 1.120 0.955 1.068 1.208 0.985 |
80% |
28.3 22.2 48.1 42.7 102.1 |
25.3 23.0 46.4 46.2 92.1 |
1.119 0.965 1.037 0.924 1.109 |
RR = Relative Recovery = IC Found/ISE FoundEach comparison listed is the average value for all CISA and bubbler samples collected side-by-side for a given experiment.IC samples were collected using CISA tubes and analyzed by ion chromatography.ISE samples were collected using bubblers containing 0.1 N H2SO4 and analyzed by ISE. |
Linear Regression Comparison (all analyses)
|
Correlation Coefficient (r) |
= |
0.9890 |
Slope (b) |
= |
1.0698 |
Intercept (a) |
= |
-0.5028 |
Std Dev of Slope (Sb) |
= |
0.0387 |
|
Table 7
Determination of Qualitative Detection Limit
µg/mL NH3
|
|
Integrated Area/1000
|
BLANK |
|
0, 0, 0, 0, 0, 0 |
0.050 |
|
0, 0, 0, 0, 0, 0 |
0.100 |
|
0, 0, 1.202, 1.238, 1.015, 1.314 |
0.200 |
|
2.314, 2.571, 2.739, 3.033, 2.897, 2.886 |
0.500 |
|
6.403, 6.934, 7.515, 7.306, 7.975, 8.667 |
|
Rank Sum
|
|
|
a |
= |
0.01 (two-tailed test) |
n1 |
= |
6 (no. of 0.200 µg/mL determinations) |
n2 |
= |
6 (no. of blank determinations) |
n |
= |
n1 + n2 = 12 |
R |
= |
69 (sum of ranks for 0.200 µg/mL) |
Rn |
= |
n1(n + 1) - R = 9 |
R(table) |
= |
23 |
Therefore, Rn is not equal to or greater than R(table), and both sample populations are significantly different.Qualitative detection limit = 0.20 µg ammonia per mL, or 10.0 µg in a 50-mL sample volume. This corresponds to a 0.60 ppm ammonia for a 24-L air volume. |
Determination of Quantitative Detection Limit
|
-----------------Ammonia (as NH3) (µg/mL)----------------- |
Sample No.
|
|
0.100 PA
|
|
0.200 PA
|
|
0.500 PA
|
1 2 3 4 5 6 |
|
0 0 1.202 1.238 1.015 1.314 |
|
2.314 2.571 2.739 3.033 2.897 2.886 |
|
6.403 6.934 7.515 7.306 7.975 8.667 |
n Mean Std Dev CV2 |
|
6 0.795 0.623 0.784 |
|
6 2.740 0.261 0.095 |
|
6 7.467 0.793 0.106 |
PA = Integrated Peak Area (NH3)/1000 |
IUPAC Method
|
|
Using the equation: |
Cld = k(sd)/m |
Where: |
|
Cld |
= |
the smallest detectable concentration an analytical instrument can determine at a given confidence level. |
k |
= |
10, thus giving 99.99% confidence that any detectable signal will be greater than or equal to an average blank or low standard reading plus ten times the standard deviation. |
sd |
= |
standard deviation of blank or low standard readings. |
m |
= |
analytical sensitivity or slope as calculated by linear regression. |
Minimum detectable signal: |
Cld = 10(0.623)/0.01238 Cld = 378 ppb = 0.50 µg/mL |
The quantitative detection limit = 0.50 µg ammonia per mL, or 25 µg in a 50-mL sample volume. This corresponds to a 1.5 ppm ammonia concentration for a 24-L air volume. |
Table 8
Side-by-Side Comparison of Supelco Tubes and In-house Carbon Bead Tubes
Level
|
RH
|
ppm NH3 Found, Lab Prep
|
ppm NH3 Found, Supelco
|
0.5 × TWA PEL
Mean Std Dev CV2 ppm taken % recovered |
25 |
24.4 23.5 23.1 23.7 0.666 0.028 24.3 97.5 |
23.4 24.1 23.4 23.6 0.404 0.017 24.3 97.1 |
|
0.5 × TWA PEL
Mean Std Dev CV2 ppm taken % recovered |
80 |
22.1 22.2 22.3 22.2 0.100 0.005 24.2 91.7 |
19.9 20.6 20.2 20.2 0.351 0.017 24.2 83.5 |
|
1 × TWA PEL
Mean Std Dev CV2 ppm taken % recovered |
30 |
44.8 43.0 46.5 44.8 1.750 0.039 55.0 81.5 |
48.4 47.6 48.8 48.3 0.611 0.013 55.0 87.8 |
|
1 × TWA PEL
Mean Std Dev CV2 ppm taken % recovered |
50 |
51.2 50.3 51.0 50.9 0.473 0.009 50.1 101.6 |
48.1 48.2 47.2 47.8 0.551 0.012 50.1 95.4 |
|
2 × TWA PEL
Mean Std Dev CV2 ppm taken % recovered |
30 |
101.8 101.4 100.4 101.2 0.721 0.007 99.5 101.7 |
87.8 91.6
89.7 2.69 0.030 99.5 90.1 |
|
2 × TWA PEL
Mean Std Dev CV2 ppm taken % recovered |
80 |
105.8 98.0 102.6 102.1 3.92 0.038 101.3 100.8 |
103.4 105.5 102.8 103.9 1.418 0.014 101.3 102.6 |
|
t-test comparison:A student t-test calculation was carried out comparing the individual Supelco tube recoveries with the individual in-house tube recoveries. These samples were taken side-by-side. |
tcalc |
= |
1.129 |
|
df = 33 |
|
|
|
tTable |
= |
2.750 |
(p < 0.01) |
|
df = 30 |
(2-tailed) |
tTable |
= |
2.704 |
(p < 0.01) |
|
df = 40 |
(2-tailed) |
|
The calculated value for t was less than the Table values. Therefore, the Supelco and in-house tube results are likely from the same population, and compare well with each other. |
NH3-Supelco TubesAll RH Levels
(OSHA-TWA PEL) |
ppm NH3 Taken |
ppm NH3 Found |
F/T |
n |
Mean |
Std Dev |
CV |
OE |
(0.5 × TWA PEL) |
24.3 24.3 24.3 24.2 24.2 24.2 |
23.4 24.1 23.4 19.9 20.6 20.2 |
0.9630 0.9918 0.9630 0.8223 0.8512 0.8347 |
|
|
6 |
0.904 |
0.076 |
0.084 |
26.4 |
(1 × TWA PEL) |
55.0 55.0 55.0 50.1 50.1 50.1 |
48.4 47.6 48.8 48.1 48.2 47.2 |
0.8800 0.8655 0.8873 0.9601 0.9621 0.9421 |
|
|
6 |
0.916 |
0.043 |
0.047 |
17.9 |
(2 × TWA PEL) |
99.5 99.5 101.3 101.3 101.3 |
87.8 91.6 103.4 105.5 102.8 |
0.8824 0.9206 1.0207 1.0415 1.0148 |
|
|
5 |
0.976 |
0.070 |
0.072 |
16.8 |
F/T |
= |
Found/Taken |
OE |
= |
Overall Error (± %) |
Bias |
= |
-0.070 |
CV2 (pooled) |
= |
0.069 |
Overall Error (Total) |
= |
±20.9% |
|
Dynamic Generation System forProduction of Ammonia Atmospheres
Figure 1
Appendix
NH3-IC (All Data) Results
(OSHA-TWA PEL) |
ppm NH3 Taken |
ppm NH3 Found |
F/T |
n |
Mean |
Std Dev |
CV |
OE |
(0.5 × TWA PEL) |
34.0 34.0 34.0 34.3 34.3 34.3 24.3 24.3 24.3 34.2 34.2 34.2 30.7 30.7 29.2 29.2 29.2 24.2 24.2 24.2 |
28.7 29.4 29.6 34.0 31.9 31.3 24.4 23.5 23.1 35.1 36.1 39.6 29.8 29.5 27.3 28.6 29.0 22.1 22.2 22.3 |
0.8441 0.8647 0.8706 0.9913 0.9300 0.9125 1.0041 0.9671 0.9506 1.0263 1.0556 1.1579 0.9707 0.9609 0.9349 0.9795 0.9932 0.9132 0.9174 0.9215 |
|
|
20 |
0.958 |
0.071 |
0.075 |
19.1 |
(1 × TWA PEL) |
55.0 55.0 55.0 45.4 45.4 45.4 50.3 50.3 50.3 50.1 50.1 50.1 50.2 50.2 50.2 48.1 48.1 48.1 |
44.8 43.0 46.5 49.2 46.9 47.4 47.0 47.6 48.2 51.2 50.3 51.0 48.4 47.0 49.1 41.6 45.6 40.9 |
0.8145 0.7818 0.8455 1.0837 1.0330 1.0441 0.9344 0.9463 0.9583 1.0220 1.0040 1.0180 0.9641 0.9363 0.9781 0.8649 0.9480 0.8503 |
|
|
18 |
0.946 |
0.085 |
0.090 |
23.3 |
(2 × TWA PEL) |
99.6 99.6 99.6 99.5 99.5 99.5 100.7 100.7 100.7 100.7 98.5 98.5 98.5 101.8 101.8 101.8 101.3 101.3 101.3 |
90.0 95.0 94.6 101.8 101.4 100.4 94.9 94.5 91.9 97.6 96.1 97.8 93.5 98.5 95.9 100.2 105.8 98.0 102.6 |
0.9036 0.9538 0.9498 1.0231 1.0090 0.9424 0.9384 0.9126 0.9692 0.9756 0.9929 0.9492 0.9676 0.9420 0.9843 1.0444 0.9674 1.0128 |
|
|
19 |
0.971 |
0.038 |
0.039 |
10.7 |
F/T |
= |
Found/Taken |
OE |
= |
Overall Error (± %) |
Bias |
= |
-0.041 |
CV2 (pooled) |
= |
0.071 |
Overall Error (Total) |
= |
±18.3% |
|
NH3-ISE (All Data) Results
(OSHA-TWA PEL) |
ppm NH3 Taken |
ppm NH3 Found |
F/T |
n |
Mean |
Std Dev |
CV |
OE |
(0.5 × TWA PEL) |
34.0 34.0 34.3 34.3 34.3 24.3 24.3 24.3 24.3 34.2 34.2 34.2 30.7 30.7 30.7 29.2 29.2 29.2 24.2 24.2 24.2 24.2 |
29.0 30.4 29.0 27.4 29.3 22.6 23.0 22.8 23.3 29.4 29.4 28.4 30.3 28.9 28.4 24.6 25.3 26.2 23.2 23.5 22.2 23.2 |
0.8529 0.8941 0.8455 0.7988 0.8542 0.9300 0.9465 0.9383 0.9588 0.8596 0.8596 0.8304 0.9870 0.9414 0.9251 0.8425 0.8664 0.8973 0.9587 0.9711 0.9174 0.9587 |
|
|
22 |
0.902 |
0.054 |
0.059 |
21.7 |
(1 × TWA PEL) |
55.0 55.0 55.0 55.0 45.4 45.4 45.4 45.4 50.3 50.3 50.1 50.1 50.1 50.2 50.2 50.2 48.1 48.1 |
42.7 46.3 45.5 43.1 43.9 51.5 42.2 42.0 42.4 42.5 48.2 53.1 58.6 41.8 48.2 49.1 47.6 44.7 |
0.7764 0.8418 0.8273 0.7836 0.9670 1.1344 0.9295 0.9251 0.8429 0.8449 0.9621 1.0599 1.1697 0.8327 0.9602 0.9781 0.9896 0.9293 |
|
|
18 |
0.931 |
0.112 |
0.120 |
31.0 |
(2 × TWA PEL) |
99.6 99.6 99.6 99.5 99.5 99.5 100.7 100.7 98.5 98.5 98.5 101.8 101.8 101.3 101.3 101.3 |
82.1 96.9 87.7 93.6 92.6 97.0 86.6 90.9 84.0 65.5 88.3 98.3 101.2 97.0 86.9 92.3 |
0.8243 0.9729 0.8805 0.9407 0.9307 0.9749 0.8600 0.9027 0.8528 0.6650 0.8964 0.9656 0.9941 0.9576 0.8578 0.9112 |
|
|
16 |
0.899 |
0.080 |
0.089 |
28.0 |
F/T |
= |
Found/Taken |
OE |
= |
Overall Error (± %) |
Bias |
= |
-0.090 |
CV2 (pooled) |
= |
0.091 |
Overall Error (Total) |
= |
±27.2% |
|
|