3.1. Safety Precautions

3.1.1. Refer to appropriate IC instrument manuals and the Standard Operating Procedure (SOP) for proper instrument operation (5.14.).

3.1.2. Observe laboratory safety regulations and practices.

3.1.3. Sodium azide is highly toxic and presents a severe explosion hazard if shocked or heated. Use appropriate personal protective equipment such as safety glasses, goggles, gloves, and lab coat when handling this chemical. Prepare solutions in an exhaust hood. Store unused solutions in a refrigerator or dispose of properly.

3.2. Equipment

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Chromatographic equipment which allows for analyte contact with metal surfaces MAY reduce the amount of azide present. It is recommended to use equipment in which samples have minimal or no contact with metal surfaces. Analysts should avoid using metal spatulas when weighing azide compounds, or IC pre-column or columns contaminated with heavy metals.

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3.2.1. Ion chromatograph (Model 4000i or 4500i Dionex, Sunnyvale, CA) equipped with a variable UV detector.

3.2.2. Automatic sampler (Dionex Model AS-1) and sample vials (0.5 mL).

3.2.3. Laboratory automation system: Ion chromatograph interfaced to a data reduction system (AutoIon 450, Dionex).

3.2.4. Separator and guard columns, anion (Model HPIC-AS9 and AG9, Dionex).

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Note: The pH of the eluant must be maintained between 2-11 and hydroxide ion must not be present in significant amounts if Dionex AS9 and AG9 columns are used. Irreversible damage to the columns (guard and separator column) will result.

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3.2.5. Disposable syringes (1 mL).

3.2.6. Plastic or Teflon^®-coated spatulas used for weighing NaN₃.

3.2.7. Miscellaneous volumetric glassware: Micropipettes, 10-mL volumetric flasks, 25-mL Erlenmeyer flasks, graduated cylinders, and beakers.

3.2.8. Scintillation vials, glass, 20-mL, with polypropylene- or Teflon^®-lined caps.

3.2.9. Equipment for eluant degassing (vacuum pump, ultrasonic bath).

3.2.10. Analytical balance (0.01 mg).

3.2.11. Exhaust hood.

3.3. Reagents - All chemicals should be at least reagent grade.

3.3.1. Principal reagents:

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CAUTION:

NaN3 can be a dangerous chemical, and can cause an explosion when shocked or heated. It is also a skin irritant and a hypotensive agent. Avoid skin contact and handle this chemical and any solutions with care. Do not dry NaN3 in a drying oven!

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Sodium carbonate (Na₂CO₃)
 Sodium bicarbonate (NaHCO₃)
 Sodium azide (NaN₃)
 Hydrochloric acid (HCl)
 Deionized water (DI H₂O) - specific conductance <10 µS.

3.3.2. Eluent and desorbing solution (0.9 mM Na₂CO₃ + 0.9 mM NaHCO₃):

Dissolve 0.191 g Na₂CO₃ and 0.151 g NaHCO₃ in 2.0 L DI H₂O. Sonicate this solution and degas under vacuum for 15 min. Prepare weekly.

3.3.3. Azide (N₃^-) stock standard (1,000 µg/mL):

Prepare the azide stock standard in an exhaust hood. Carefully weigh 1.5476 g of NaN₃ (Aldrich Chemical Company, Inc., Milwaukee, WI). Dissolve and dilute to 1.0 L with DI H₂O. Prepare monthly.

3.3.4. Azide (N₃^-) standard solutions (100, 10, and 1 µg/mL):

Perform serial dilutions of the 1,000 µg/mL N₃^- stock standard using volumetric pipets and flasks. Dilute to the mark with eluant. Prepare every two weeks. The larger standards (100 and 10 µg/mL) can be used as working standards, if necessary.

3.3.5. Dispose of azide or azide solutions according to the chemical manufacturer, and local or federal waste disposal guidelines. A method for disposal of aqueous azide solutions recommended by the Royal Society of Chemistry (5.15.) is to dilute the solution greatly with water and then run to waste.

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CAUTION:

Do not dispose of untreated azides or concentrated azide solutions by pouring down sink drains.

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3.4. Working Standard Preparation

3.4.1. Prepare N₃^- working standards in the ranges specified below:

Working Std (µg/mL)	Std Solution (µg/mL)	Aliquot (mL)	Eluant Added (mL)
0.05	1.0	0.5	9.5
0.10	1.0	1.0	9.0
0.20	1.0	2.0	8.0
0.50	1.0	5.0	5.0
0.75	1.0	7.5	2.5
1.00	1.0	*	*
* Already prepared in Section 3.3.4.

3.4.2. To prepare 10 mL of each working standard, pipette an appropriate aliquot (Aliquot column listed above) of the 1.0 µg/mL standard solution into a scintillation vial or Erlenmeyer flask. Add the specified amount of eluant (Eluant Added column). As an alternative, pipet each aliquot into a 10-mL volumetric flask and dilute to volume with eluant.

3.5. Sample Preparation - Air Samples

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Note:

Samples desorbed in the field (Section 2.7.) are ready for analysis (Section 3.7.).

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3.5.1. Remove filter cassette and tube samples from the refrigerator and allow them to warm to room temperature.

3.5.2. Tube Samples:

Carefully remove the end glass wool plug. The sorbent should always be removed from the glass tube via the opposite end of collection (i.e. backup section is removed first). This will minimize the possibility of contamination from any collected particulate.

3.5.3. Transfer each section of the ISG and glass wool plugs and place in separate 25-mL Erlenmeyer flasks or 20-mL scintillation vials. Place the front glass wool plug and front ISG section (150 mg) in one container and place the middle and end glass wool plug in another container with the backup ISG section (75 mg).

3.5.4. Pipette 3.0 mL of desorbing solution into each container. Cap each flask tightly and allow the solution to sit for at least 60 min. Swirl the solution occasionally.

3.5.5. Filter Samples:

Carefully remove each filter from the cassette and place into individual 20-mL scintillation vials. Add 5.0 mL of desorbing solution to each vial. Cap each vial tightly and allow the solution to sit for at least 60 min. Swirl the solution occasionally.

3.6. Sample Preparation - Wipe and Bulk Samples

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Note: Samples desorbed in the field (Section 2.7.) are ready for analysis (Section 3.7.).

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3.6.1. Remove wipe and bulk samples from the refrigerator and allow them to warm to room temperature.

3.6.2. Weigh out representational aliquots of bulks.

3.6.3. Carefully transfer wipe samples, and previously weighed aliquots of bulk samples to separate labeled 20-mL scintillation vials and add 10.0 mL of desorbing solution into each vial. Cap each vial tightly and allow the solution to sit for at least 60 min. Swirl the solution occasionally.

3.7. Sample Analysis

3.7.1. Pipette a 0.5- to 0.6-mL portion of each standard or sample solution into separate automatic sampler vials. Place a filtercap into each vial. The large filter portion of the cap should face the solution.

3.7.2. Load the automatic sampler with labeled samples, standards, and blanks.

3.7.3. Set up the ion chromatograph in accordance with the SOP (5.14.)

Typical operating conditions for a Dionex 4500i with a variable wavelength UV detector and an automated sampler are listed below:

Ion Chromatograph
Eluant:	0.9 mM Na2CO3/0.9 mM NaHCO3
Column temperature:	ambient
Anion pre-column:	AG9
Anion separator column:	AS9
Variable UV wave length:	210 nm
Variable UV output range:	0.01 AU
Sample injection loop:	50 µL
Pump
Pump pressure:	500 psi
Flow rate:	1 mL/min
Chromatogram
Run time:	12 min
Peak retention time:	8 to 9 min for N3-

3.7.4. Follow the SOP for further instructions regarding analysis (5.14.).

3.8. Calculations

3.8.1. After the analysis is completed, retrieve the peak areas or heights for the azide anion. Obtain hard copies of chromatograms from a printer. An example chromatogram of a solid sorbent sample collected at an hydrozoic acid concentration of approximately 2 × PEL is shown below:

Example chromatogram of a solid sorbent sample collected at an hydrozoic acid concentration of approximately 2 × PEL

Sample Name: AZS-124			Detector: VDM-1
REPORT	VOLUME	DILUTION	POINTS	RATE	START	STOP	AREA	REJECT
External	1	1	3605	5Hz	0.00	12.02	100000
Peak No.	Retention Time (Min)		Component Name			--------Peak---------
1	0.77					28,132	1,527,608
2	1.67					1,193,355	26,810,606
3	3.48					612,318	19,049,090
4	5.28					53,446	791,025
5	5.72					20,583	286,812
6	8.42		Azide			196,012	4,072,104
7	9.50		Nitrate			550,223	12,829,040

3.8.2. Prepare a concentration-response curve by plotting the peak areas or peak heights versus the concentration of the N₃^- standards in µg/mL.

3.8.3. Calculate the air concentration of NaN₃ (in mg/m³) for each filter or sorbent sample:

WSA = (µg/mL N3-)(SV)(GF)SA

mg/m3 NaN3 = WSA - WB AV

Where:

WSA	=	Total µg of NaN3 in the sampleWB = Total µg of NaN3 in the blank sample
µg/mL N3-	=	Amount found (from curve)
SV	=	Solution volume (mL) from Section 3.5.3.
(GF)SA, NaN3/N3-	=	Gravimetric factor = 1.5476
AV	=	Air volume (L)

3.8.4. Calculate the total concentration of NaN₃ (in µg) in each wipe or bulk sample using the appropriate equation:

µg NaN3 = WSA - WB	(Wipe Samples)
NaN3 % (w/w) = WSA × 100% S × F	(Bulk Samples)

Where:

S	=	Sample wt, mg = Aliquot of bulk taken in Section 3.6.2.
F	=	1,000 µg/mg

3.9. Reporting Results

3.9.1. Add the PVC filter and sorbent results together for each sample. Report this sum result to the industrial hygienist as mg/m³ NaN₃ (total).

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Note:

Vapor phase and particulate results should be combined to determine compliance and to minimize confusion. Although the vapor phase is a ppm value, the OSHA regulation stipulates "sodium azide" as sodium azide or as hydrozoic acid (5.13.). The total exposure to both phases needs to be considered for compliance and the results need to be reported as either total mg/m3 NaN3 or total ppm HN3 to minimize confusion. If it is necessary to determine the ppm amount of HN3, see the Appendix.

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3.9.2. Wipe sample concentrations are reported as total micrograms or milligrams of NaN₃.

3.9.3. Bulk sample results are reported as approximate percent by weight sodium azide. Due to differences in sample matrices between bulks and analytical standards, bulk results are approximate.

1. An analysis of 24 spiked samples was performed (8 samples each at 2 ×, 1 ×, and 0.5 × the Ceiling PEL) to evaluate desorption efficiency (DE).
   
2. A sampling and analysis of 18 samples (6 samples each at 2 ×, 1 ×, and 0.5 × Ceiling PEL) collected from dynamically generated test atmospheres at 50% RH. to determine bias and overall error.
   
3. A determination of the sampling media collection efficiency at approximately 0.26 ppm (2 × Ceiling PEL).
   
4. A determination of potential breakthrough.
   
5. An evaluation of storage stability at room (20 to 25°C), refrigerator (0 to 4°C), and freezer (-10 to -14°C) temperatures for 64 collected samples.
   
6. A determination of any significant effects on results when sampling at different humidities.
   
7. A determination of the qualitative and quantitative detection limits.
   
8. Evaluation of a pre-filter/cassette assembly or foam for use during sampling.
   
9. Determination of stability of NaN₃ on wipe sampling media.
   
10. Summary.

Where i is the respective sample pool being examined.

4.1. Analysis

Twenty-four samples were prepared by adding known amounts of NaN₃ (as N₃^-) stock solution to the ISG tubes to determine desorption efficiencies (DEs) for the analytical portion of the method.

4.1.1. Procedure: Sampling tubes containing ISG were spiked using a 25-µL syringe (Hamilton Microliter ^®/Gastight^® Syringe, Hamilton Co., Reno, NV). Spikes were 0.5, 1.0, and 2.0 µg N₃^-. These levels correspond approximately to 0.5, 1, and 2 times the Ceiling PEL for a 5-L air sample at a 1-L/min flow rate.

4.2. Sampling and Analysis

To determine the precision and accuracy of the method, known concentrations of HN₃ were generated, samples were collected and then analyzed. A block diagram of the generation system used is shown in Figure 1.

4.2.1. Procedure:

1. Test atmospheres of HN₃ were generated using a syringe pump (Model 355 syringe pump, Sage Instruments, Cambridge, MA) and a dynamic generation system. To prepare the atmospheric concentrations, a 1,000 µg/mL azide solution (prepared from NaN₃, EM Science, Cherry Hill, NJ) was used. For each HN₃ atmosphere generated, 100 µL of concentrated HCl was added to 10 mL of the azide solution to drive the reaction of NaN₃ to HN₃. The HCl/NaN₃/H₂O solution was immediately loaded into a 10-mL disposable syringe driven between 0.13 and 0.52 mL/h through 60 cm of a Teflon^® needle (KF30TF needle, Hamilton Co., Reno, NV) into a glass mixing chamber. The mixing chamber was connected to a filtered and humidified airstream.
    
2. Dynamic generation system
   A Miller-Nelson Research Inc. flow, temperature, and humidity control system (Model HCS-301, Monterey, CA) was used to control and condition the airstream. All generation system fittings and connections were Teflon^®. The HN ₃ concentrations were varied by either adjusting the dilution airstream volume or the speed of the syringe pump delivering the azide. The dilution airstream was adjusted using the mass flow controller of the Miller-Nelson system. The system was set to generate test atmospheres at 50% RH and 25°C.
    
3. The total flow rate of the generation system was measured using a dry test meter.
    
4. Side-by-side solid-sorbent and impinger samples were taken from the sampling manifold using constant-flow pumps. Alpha 1 pumps (E.I. Du Pont de Nemours & Co., Wilmington, DE) and Gilian^® Gil-Air SC pumps (Gilian Instrument Corp., W. Caldwell, NJ) were used for impinger and ISG samples, respectively. For the ISG samples, pump flow rates were approximately 1 L/min and sampling time was 5 min. For impinger samples, a 1 L/min sampling rate for 15 min was used. Generation system concentrations were approximately 0.5, 1, and 2 times the OSHA Ceiling PEL.

4.2.2. An independent source was used for NaN₃ analytical standard preparations (Aldrich Chemical Company, Inc., Milwaukee, WI). All samples and standards were analyzed in accordance with Section 3 of this method.

4.2.3. Results: The results are shown in Table 2) and spiked sample (Table 1) results each passed the Bartlett's test and were pooled to determine a total CV (CV_T) for the sampling and analytical method. For the experiments, the pooled coefficients of variation, bias, and OE are as follows:

CV1 (pooled) = 0.023;	CV2 (pooled) = 0.051
CVT (pooled) = 0.052;	bias = -0.022;	OE = ±12.6%

4.3. Collection Efficiency

Procedure: Six commercially-prepared sampling tubes were used for collection at a concentration of approximately 2 times the OSHA Ceiling PEL for 5 min at 1 L/min (50% RH and 25°C). The amounts of HN₃ vapor collected in the first section (150 mg of sorbent) and second section (150 mg) were determined. The collection efficiency (CE) was calculated by dividing the amount of HN₃ collected in the first section by the total amount of HN₃ collected in the first and second sections.

Results: The results in Table 3 show a CE of 100%. No HN₃ was found in the second sorbent section for the CE experiment.

4.4. Breakthrough

(Note: Breakthrough is defined as >5% loss of analyte through the sampling media at 50% RH)

Procedure: The same procedure as the CE experiment (Section 4.3.) was used with two exceptions: The generation concentration was increased to a level approximately 9 times the Ceiling PEL, and samples were taken at 1 L/min for 30 min.

The amount of breakthrough for each sampling tube was calculated by dividing the amount collected in the second section by the total amount of HN₃ collected in the first and second sections.

Results: No breakthrough of HN₃ into the second section was found. Results are shown in Table 4.

4.5. Storage Stability

Procedure: Two tests were conducted to assess storage stability. The first was a preliminary study of storage at room temperature (20 to 25°C) after HN₃ collection. Twenty-four samples were taken near the OSHA Ceiling PEL of 0.1 ppm. After collection, all samples were stored under normal laboratory conditions (20 to 25°C) on a lab bench and were not protected from light. Six samples were initially desorbed and analyzed, then six samples were desorbed and analyzed after various periods of storage (5, 15, and 32 days).

An additional test was conducted by generating 40 samples (4 room-temperature samples at day 15 were discarded due to analytical problems) for a temperature-dependent storage stability test, including 4 control samples (used for day 0). The samples were separated into 3 groups and each group consisted of 4 samples per storage period. A group was stored at either room, refrigerated, or freezer temperature. The same analytical procedure as the previous storage test was used. Samples were analyzed after 0, 7, 15, and 30 days.

Results: As shown in Table 5a and the graph below, the results of the first test show the mean of samples analyzed after 32 days was only 77% of the value of day 0. Table 5b and the graph below show the results of the second study at different temperatures. The recovery is only 77% of the value of day 0 after a 30-day storage at room temperature. This drastic change was not noted for samples stored at refrigerated or freezer temperatures; however, a slight decrease in sample recoveries (93 - 94%) after 30 days was apparent.

Storage Stability Results

4.6. Humidity Study

Procedure: A study was conducted to determine any effect on results when samples are collected at different humidities. Samples were taken using the generation system and procedure described in Section 4.2. Test atmospheres were generated at 25°C and at approximately 0.5, 1, and 2 times the OSHA Ceiling PEL. Relative humidities of 30%, 50%, and 80% were used at each concentration level tested.

Results: Results of the humidity tests are listed in Table 6. An F test was used to determine if any significant effect occurred when sampling at different humidities. As shown, the calculated F values are less than critical F values (5.19.) for all the concentrations tested and no significant difference in results occurred across the humidity ranges tested.

4.7. Qualitative and Quantitative Detection Limit Study

Procedure: Low concentration samples were prepared by spiking desorbing solutions (Section 3.3.2.) with aliquots of aqueous standards prepared from NaN₃ (Section 3.3.4.). These samples were analyzed using a 50-µL sample injection loop and a variable wavelength UV detector setting of 0.01 absorbance unit (AU). A derivation of the International Union of Pure and Applied Chemistry (IUPAC) detection limit equation (5.20.) was used to calculate detection limits.

4.8. Pre-filter Evaluation

Procedure: Past research regarding aerosols (5.21.) has indicated that particulate in the air sampled may penetrate any glass wool plugs and the sorbent when using conventional sampling tubes. A pre-filter can be used to assist in capturing particulate before entry into the sampling tube. A study was conducted to evaluate the possibility of HN₃ reacting with a pre-filter/cassette or foam sampling device to capture NaN₃ or other particulate. Evaluations were performed using either ISG sampling tubes with pre-filter sampling assemblies (PVC filter/spacer support/cassette), or with polyurethane foam [foam used in the combination sampling device for SO₂ (Type II tube), OSHA Method No. ID-200] for particulate collection.

A test was conducted by taking four ISG samples without pre-filters side-by-side with four ISG samples connected with pre-filters. This test was repeated with foam plugs instead of the pre-filters. Samples were taken such that the test atmosphere entered the pre-filter or foam first and then entered the ISG. Short pieces of Tygon^® tubing were used to connect the cassettes and ISG sampling tubes. All samples were taken at a flow rate of about 0.8 L/min for 5 min. The generation system concentration was approximately 1.5 times the Ceiling PEL.

Results: The results of the comparison of ISG samples taken, with and without pre-filter or foam, are shown in Tables 8a and 8b, respectively. As shown, a difference in the amount of HN₃ collected was not noted between the pre-filter/ISG and ISG, or foam/ISG. The PVC pre-filter/cassette or the foam does not appear to inhibit the collection of HN₃ when using the sampling conditions stated in Section 2. The PVC filter/cassette assembly is recommended for particulate sample collection. The foam may be validated for use in the future to develop a combination sampling device for collection of both NaN₃ and HN₃. The ability of the foam to effectively capture NaN₃ needs to be further examined.

4.9. Stability of NaN₃ on Wipe Sampling Media

Procedure: A determination of the stability of NaN₃ was conducted using 37-mm glass fiber filters (Cat. no. 61715, Gelman Instrument Company, Ann Arbor, MI) and smear tabs (Lot. no. 3034, Whatman LabSales Inc., Hillsboro, OR). The stability of sodium azide on PVC membranes has been previously reported as stable up to 10 days of storage (5.6.). Glass fiber filters or smear tabs were spiked using a 25-µL syringe (Hamilton Microliter^®/Gastight^® Syringe, Hamilton Co., Reno, NV). Solution spikes contained between 7 and 15 µg NaN₃. Filters were allowed to dry and were stored for 3 days on a lab bench, then refrigerated until analysis.

Results: The precision and accuracy results for glass fiber filters and smear tabs are shown below (F/T = Found/Theoretical recovery):

Collection Media		N		Mean (F/T)		Std Dev		CV
Glass Fiber Filters		5		1.001		0.036		0.036
Smear Tabs		5		0.412		0.134		0.325

The recovery data shows that azide is unstable on cellulose media and stable on glass fiber filters.

4.10. Summary

The validation results indicate the method meets both the NIOSH and OSHA criteria for accuracy and precision (5.17., 5.18.). Performance during collection efficiency, breakthrough, and humidity tests is adequate. Although it appears that the recovery dramatically decreases when storing collected samples at room temperature after 15 days, no losses were found when storing the sampling tubes after sample collection in a refrigerator or freezer. It is recommended to analyze samples within 10 days if samples are stored without refrigeration and within 30 days if refrigeration is used. Detection limits are adequate when samples are taken for 5 min at 1 L/min. The method is adequate for monitoring occupational exposures to the OSHA Ceiling PEL.

5. References

5.1. Westwood, L.C. and E.L. Stockes: Determination of Azide in Environmental Samples by Ion Chromatography. Ion Chromatographic Analysis of Environmental Pollutants, Vol. 2, edited by J.J. Mulick and E. Sawicki. Ann Arbor, MI. Ann Arbor Science, 1979. p.141.

5.2. Roberson, C.E. and C.M. Austin: Colorimetric Estimation of Milligram Quantities of Inorganic Azides. Anal. Chem. 29:854-855 (1957).

5.3. Williams, K.E., G.G. Esposito, and D.S. Rinehart: Sampling Tubes for the Collection of Selected Acid Vapors in Air. Am. Ind. Hyg. Assoc. J. 42:476-478 (1981).

5.4. Zehner, J.M. and R.A. Simonaitis: Gas Chromatographic Determination of Hydrazoic Acid. J. Chromatogr. Sci. 14:493-494 (1976).

5.5. Puskar, M.A., S.M. Fergon and L.H. Hecker: A Short-Term Solid Sorbent Determination of Hydrazoic Acid in Air. Am. Ind. Hyg. Assoc. J. 52(1):14-19 (1991).

5.6. National Institute for Occupational Safety and Health: Azide particulates (Method No. P&CAM 369). Cincinnati, OH: National Institute for Occupational Safety and Health, 1982.

5.7. Occupational Safety and Health Administration Salt Lake Technical Center: Azide by Ion Chromatography (Stopgap Method - Unpublished) by J. Germ, Salt Lake City, UT, 1985.

5.8. National Research Council, Committee on Hazardous Substances in the Laboratory: Prudent Practice for Handling Hazardous Chemical in Laboratories, Washington D.C.: National Academy Press, 1981. pp.145-147.

5.9. Kleinhofs, A., W.M. Owais, and R.A. Nilan: Azide. Mutat. Res. 55:165-195 (1978).

5.10. Owais, W.M., A. Kleinhofs, and R.A. Nilan: In Vivo Conversion of Sodium Azide to a Stable Mutagenic Metabolite in Salmonella Typhimuriun. Mutat. Res. 68:15-22 (1979).

5.11. Hawley, G.G., ed. The Condensed Chemical Dictionary, 8th rev. ed. New York: Van Nostrand Reinhold Co., 1971.

5.12. Yost, D.M., and H. Russell, Jr.: Systematic Inorganic Chemistry, New York: Prentice-Hall, Inc., 1946. Ch. 3, pp.122-131.

5.13. "Sodium azide" Federal Register 54:12 (19 Jan. 1989). pp 2540.

5.14. Occupational Safety and Health Administration Salt Lake Technical Center: Ion Chromatography Standard Operating Procedure (Ion Chromatographic Committee). Salt Lake City, UT. In progress.

5.15. Bretherick, L, ed.: Hazards in the Chemical Laboratory, 4th ed. London: Royal Society of Chemistry, 1986. pp. 491-492.

5.16. Mandel, J.: Accuracy and Precision, Evaluation and Interpretation of Analytical Results, The Treatment of Outliers. In Treatise On Analytical Chemistry. 2nd ed., Vol. 1, edited by I. M. Kolthoff and P. J. Elving. New York: John Wiley and Sons, 1978. pp. 282-285.

5.17. 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). Cincinnati, OH: National Institute for Occupational Safety and Health, 1977. pp. 1-12.

5.18. Occupational Safety and Health Administration Salt Lake Technical Center: Evaluation Guidelines of the Inorganic Methods Branch. In OSHA Analytical Methods Manual. 2nd ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists, 1991.

5.19. Dowdy, S. and S. Wearden: Statistics for Research. New York: John Wiley and Sons, 1983. Chapter 8.

5.20. Long, G.L. and J.D. Winefordner: Limit of Detection – A Closer Look at the IUPAC Definition. Anal. Chem. 55:712A-724A (1983).

5.21. Fairchild, C.I., and M.I. Tillery: The Filtration Efficiency of Organic Vapor Sampling Tubes against Particulates. Am. Ind. Hyg. Assoc. J. 38:277-283 (1977).

 

Table 1 Azide (as N3-) Analysis - Desorption Efficiency (DE)
(OSHA-PEL)
Taken (µg N3-)	Found (µg N3-)	DE (F/T)	N	Mean	Std Dev	CV
(0.5 × PEL)
0.500 0.500 0.500 0.500 0.500 0.500 0.500 0.500	0.500 0.515 0.520 0.500 0.505 0.510 0.465 0.525	1.000 1.030 1.040 1.000 1.010 1.020 0.930 1.050
			8	1.010	0.037	0.037
(1 × PEL)
1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000	0.995 0.985 0.995 1.000 1.015 0.995 0.995 1.000	0.995 0.985 0.995 1.000 1.015 0.995 0.995 1.000
			8	0.998	0.008	0.008
(2 × PEL)
2.000 2.000 2.000 2.000 2.000 2.000 2.000 2.000	1.980 1.960 2.000 1.990 1.975 2.010 2.035 1.970	0.990 0.980 1.000 0.995 0.988 1.005 1.018 0.985
			8	0.995	0.012	0.012
F/T = Found/Taken DE = Desorption Efficiency CV1 (Pooled) = 0.023 Average DE = 1.001
The average DE is very close to 1.0; therefore, a DE correction is not necessary.

Table 2 Hydrazoic Acid Sampling and Analysis - Ceiling PEL Determination * (25°C and 50% RH)
(OSHA-PEL)
Taken (ppm HN3)	Found (ppm HN3)	Recovery (F/T)	N	Mean	Std Dev	CV	OE (±%)
(0.5 × PEL)
0.057 0.057 0.057 0.057 0.057 0.057	0.053 0.058 0.053 0.061 0.056 0.054	0.930 1.018 0.930 1.070 0.982 0.947
			6	0.980	0.056	0.057	13.4
(1 × PEL)
1.130 1.130 1.130 1.130 1.130 1.130	0.129 0.121 0.135 0.117 0.122 0.121	0.992 0.931 1.038 0.900 0.938 0.931
			6	0.955	0.050	0.053	15.1
(2 × PEL)
0.263 0.263 0.263 0.263 0.263 0.263	0.259 0.267 0.252 0.251 0.276 0.272	0.985 1.015 0.958 0.954 1.049 1.034
			6	0.999	0.040	0.040	8.01
F/T = Found/Taken Bias = -0.022 CV2 (Pooled) = 0.051 CVT (Pooled) = 0.052 Overall Error (Total) = ±12.6%
*Samples were taken for 5 min.

Table 3 Collection Efficiency (2 × PEL, 25°C & 50% RH)
	------------------ppm HN3 -------------------
Sample No.	First Section	Second Section	% Collection Efficiency
1 2 3 4 5 6	0.259 0.267 0.252 0.251 0.273 0.273	ND ND ND ND ND ND	100.0 100.0 100.0 100.0 100.0 100.0
Notes: Sampled at 1 L/min for 5 min. Samples desorbed using a sample solution volume of 3.0 mL ND = None detectable (<0.001 ppm HN3)

Table 4 Breakthrough Study (25°C and 50% RH)
	------------------ppm HN3 -------------------
Sample No.	First Section	Second Section	% Breakthrough
1 2 3 4 5 6 7 8	0.933 0.940 0.897 0.889 0.938 0.891 0.913 0.925	ND ND ND ND ND ND ND ND	0 0 0 0 0 0 0
Notes: Sampled at 1 L/min for 30 min Due to the large concentration generated and the analytical sensitivity, the front ISE sections of sampling tubes were desorbed using larger sample solution volumes of 10.0 mL. ND = None detectable (<0.001 ppm HN3)

Table 5a Preliminary Test Storage Stability - HN3 (1 × PEL, 25°C, and 50% RH)
Day	Air Vol	Found	Taken	--------------Statistical Analysis-------------
	(L)	(--ppm HN3--)		N	Mean	Std Dev	CV	Recovery (%)
0	4.21 4.21 4.21 4.21 4.21 4.21	0.129 0.121 0.135 0.117 0.122 0.121	0.130 0.130 0.130 0.130 0.130 0.130
				6	0.124	0.007	0.053	95.4
5	4.21 4.21 4.21 4.21 4.21 4.21	0.116 0.124 0.116 0.121 0.117 0.114	0.130 0.130 0.130 0.130 0.130 0.130
				6	0.118	0.004	0.032	90.8
15	3.92 3.92 3.92 3.92 3.92 3.92	0.106 0.106 0.107 0.113 0.101 0.101	0.130 0.130 0.130 0.130 0.130 0.130
				6	0.106	0.004	0.042	81.3
32	4.21 4.21 4.21 4.21 4.21 4.21	0.096 0.099 0.104 0.100 0.108 0.092	0.130 0.130 0.130 0.130 0.130 0.130
				6	0.100	0.006	0.057	76.8

Table 5b Storage Stability - HN3 at Room, Refrigerated and Freezer Temperatures (Known HN3 Concentration = 0.108 ppm at 50% RH)
Temperature:	Room			Refrigerated		Freezer
Day	Air Vol (L)		Found (ppm)	Air Vol (L)	Found (ppm)	Air Vol (L)	Found (ppm)
0	3.05 3.05 3.05 3.05		0.116 0.120 0.097 0.099	* * * *	* * * *	* * * *	* * * *
	N Mean Std Dev CV2 Recovery	= = = = =	4       0.108 0.012 0.108 100%		* * * *		* * * *
7	3.54 3.54 3.54 3.54		0.121 0.115 0.095 0.087	3.05 3.05 3.05 3.05	0.098 0.126 0.105 0.116	3.54 3.54 3.54 3.54	0.127 0.108 0.098 0.104
	N Mean Std Dev CV2 Recovery	= = = = =	4       0.105 0.016 0.154 96.8%		4       0.111 0.012 0.111 103%		4       0.109 0.013 0.115 101%
15	+ + + +		+ + + +	3.54 3.54 3.54 3.54	0.120 0.102 0.100 0.106	3.05 3.05 3.05 3.05	0.129 0.101 0.102 0.110
	N Mean Std Dev CV2 Recovery	= = = = =	+ + + + +		4       0.107 0.009 0.084 99.1%		4       0.111 0.013 0.117 102%
30	3.54 3.54 3.54 3.54		0.089 0.076 0.085 0.082	3.05 3.05 3.05 3.05	0.104 0.103 0.102 0.097	3.54 3.54 3.54 3.54	0.104 0.091 0.104 0.103
	N Mean Std Dev CV2 Recovery	= = = = =	4       0.083 0.0055 0.066 76.9%		4       0.102 0.003 0.031 94.0%		4       0.101 0.006 0.063 93.1%
* Same as day 0 for room temperature + Due to poor precision and analytical difficulties, data are deleted from statistical analysis and are not presented graphically in Section 4.5.

Table 6 Humidity Test - HN3 (0.5 × PEL & 25°C)
% RH	30	50	80
ppm HN3 Taken	0.061	0.057	0.057
ppm HN3 Found	0.068 0.058 0.063 0.057 0.062 0.058 0.062 0.059	0.053 0.058 0.053 0.061 0.056 0.054	0.057 0.065 0.047 0.067 0.046 0.051
N Mean (ppm) Std Dev (ppm) CV Ave Recovery	8        0.061 0.004 0.060 100%	6        0.056 0.003 0.057 98.0%	6        0.056 0.009 0.163 97.4%

At the 99% confidence level:
	Fcrit = 6.11	Fcalc = 0.12 (2, 17 degrees of freedom)
Fcrit > Fcalc; therefore, no significant difference in results was noted across the humidity levels tested.

Humidity Test - HN3 (1 × PEL & 25°C)
% RH	30	50	80
ppm HN3 Taken	0.124	0.130	0.121
ppm HN3 Found	0.122 0.129 0.131 0.125	0.129 0.121 0.135 0.117 0.122 0.121	0.119 0.124 0.118 0.115 0.115 0.122
N Mean (ppm) Std Dev (ppm) CV Ave Recovery	4        0.127 0.004 0.032 102%	6        0.124 0.007 0.053 95.5%	6        0.119 0.004 0.031 98.2%

At the 99% confidence level:
	Fcrit = 6.70	Fcalc = 3.42 (2, 13 degrees of freedom)
Fcrit > Fcalc; therefore, no significant difference in results was noted across the humidity levels tested.

Humidity Test - HN3 (2 × PEL & 25°C)
% RH	30	50	80
ppm HN3 Taken	0.202	0.263	0.206
ppm HN3 Found	0.203 0.214 0.202 0.210 0.200 0.203 0.215	0.259 0.267 0.252 0.251 0.276 0.272	0.218 0.199 0.213 0.191 0.182 0.196
N Mean (ppm) Std Dev (ppm) CV Ave Recovery	7        0.207 0.006 0.030 102%	6        0.263 0.010 0.040 99.9%	6        0.200 0.014 0.068 97.0%

At the 99% confidence level:
	Fcrit = 6.23	Fcalc = 2.11 (2, 16 degrees of freedom)
Fcrit > Fcalc; therefore, no significant difference in results was noted across the humidity levels tested.

Table 7 Qualitative and Quantitative Detection Limits (IUPAC Method)
		---------HN3 (as N3-) Level-----------
	Sample No.	0.02 µg/mL PA	0.05 µg/mL PA	0.10 µg/mL PA
	1     2     3     4     5     6     7	5.07 5.31 4.65 4.78 4.16 4.42 5.61	15.19 17.03 14.10 14.87 12.35 14.41 13.44	42.23 36.72 40.02 36.29 39.73 40.21 38.18
	N     Mean     Std Dev     CV	7        4.86 0.507 0.104	7        14.48 1.468 0.101	7        39.05 2.108 0.054
PA = Integrated Peak Area (N3-)/100,000 The blank and 0.01 mg/mL integrated peak areas, and their standard deviations (Std Dev) were all equal to zero.
Using the equation:          Cld = k(sd)/m Where: Cld = the smallest reliable detectable concentration an analytical instrument can determine at a given confidence level. k = 3 (Qualitative Detection Limit, 99.86% Confidence) = 10 (Quantitative Detection Limit, 99.99% Confidence) sd = standard deviation of the reagent blank (Rbl) readings. m = analytical sensitivity or slope as calculated by linear regression. Cld = 3(0.507)/438.6 = 0.00347 µg/mL as N3- for the qualitative limit. Cld = 10(0.507)/438.6 = 0.01156 µg/mL as N3- for the quantitative limit. Qualitative detection limit = 0.0104 µg N3- (3-mL sample volume) or 0.001 ppm HN3 (5-L air volume). Quantitative detection limit = 0.0348 µg N3- (3-mL sample volume) or 0.004 ppm HN3 (5-L air volume).

Table 8a Comparison Study - With/Without Pre-filter (Known Concentration = 0.131 ppm HN3) (25°C, and 50% RH)
	With Pre-filter		Without Pre-filter
Sample Set #	Air Vol, L	ppm HN3 Found	Air Vol, L	ppm HN3 Found
1 2 3 4	3.41 3.41 3.41 3.41	0.124 0.140 0.134  0.098*	3.38 3.38 3.38 3.38	0.141 0.138 0.131 0.114
N Mean Std Dev CV Recovery		3         0.133 0.008 0.061 101%		4         0.131 0.012 0.092 100%
* Outlier
Notes: A 37-mm PVC filter was used as the pre-filter in a polystyrene cassette. Sampling Time = 5 min Flow Rate = 0.825 to 0.829 L/min Sample Solution Volume for Desorption = 3.0 mL
At the 99% confidence level: tcrit = 9.92                 tcalc = -0.615 (2 degrees of freedom) tcrit > tcalc; therefore, no significant difference in results was noted across the two sets tested.

Table 8b Comparison Study - With/Without Foam (Known Concentration = 0.141 ppm HN3) (25°C, and 50% RH)
	With Foam		Without Foam
Sample Set #	Air Vol, L	ppm HN3 Found	Air Vol, L	ppm HN3 Found
1 2 3 4	3.35 3.35 3.35 3.35	0.129 0.140 0.138 0.155	3.43 3.43 3.43 3.43	0.155 0.135 0.140 0.154
N Mean Std Dev CV Recovery		4         0.141 0.011 0.077 100%		4         0.146 0.010 0.069 104%
Notes: Type II containing 150 mg-ISG glass jacket was used. The dimensions of the front portion of the glass jacket are 12-mm o.d., 10-mm i.d., and 25-mm long and is used for collecting azide particulate. The second part of the glass tube contains ISG and is used for collecting HN3. The dimensions of the second part are 6-mm o.d., 4-mm i.d., and 50-mm long. Both ends of the sampling tube are sealed with plastic caps (see Method No. ID-200 for a graphic description of the Type II glass jacket used). Foam analyzed after sampling contained 0.004 ppm as HN3 (average). Sampling Time = 5 min Flow Rate = 0.627 to 0.787 L/min Sample Solution Volume for Desorption = 3.0 mL
At the 99% confidence level: tcrit = 5.84                 tcalc = -0.0055 (3 degrees of freedom) tcrit > tcalc; therefore, no significant difference in results was noted across the two sets tested.

Block Diagram of the Laboratory Generation System

Figure 1

The system shown above was used to generate dynamic test atmospheres. The system consists of four essential elements:

1. A flow-temperature-humidity control system,
   
2. An HN₃ vapor generating system,
   
3. A mixing chamber, and
   
4. An active sampling manifold.

Appendix WHA = (µg/mL N3-)(SV)(GF)HA   ppm HN3 = WHA × MV AV × MW

Where:

AV	=	Air volume
WHA	=	µg HN3
(GF)HA, HN3/N3-	=	Gravimetric factor = 1.0238
MV	=	Molar volume (L/mol) = 24.45 (25°C and 760 mmHg)
MW	=	Molecular weight for HN3 = 43.0 (g/mol)
SV	=	Solution volume
µg/mL N3-	=	Sample result taken from concentration-response curve