BROMINE BACKUP DATA REPORT (ID-108)

Introduction

The general procedure for collection and analysis of bromine (Br₂) air samples is described in OSHA method no. ID-108 (10.1.). Briefly, Br₂ is collected in a midget fritted glass bubbler (MFGB) containing a buffer (0.0030 M NaHCO₃ / 0.0024 M Na₂CO₃) collection solution. In this basic solution, Br₂ disproportionates to produce bromide (Br¯) and bromate (BrO₃-) (10.2.) which can be determined by ion chromatography (IC). This method has been evaluated using 30-L, 60-min samples. The concentrations tested were near the OSHA Time Weighted Average (TWA) Permissible Exposure Limit (PEL) of 0.1 ppm.

1. Experimental Protocol

The evaluation consisted of the following experiments or discussions:

1. Analysis of a total of 18 spiked samples.
2. Analysis of a set of 18 samples which were taken from dynamically generated test atmospheres.
3. Determination of the collection efficiency and the breakthrough when using MFGB.
4. Storage stability tests for six samples collected at the PEL.
5. Determination of the detection limit of the method.
6. Comparison of methods.
7. Assessment of the precision and accuracy of the method.
8. Conclusions - including a discussion of changes in the PEL since this evaluation was performed.

2. Analysis

Samples (six samples at each of three test levels) were prepared by spiking appropriate amounts of standardized Br₂ into collection solutions. The spiked samples were prepared and analyzed to determine analytical precision and accuracy.

Procedure:   Samples were prepared by adding known amounts of a standardized stock Br₂ solution to 10 mL of collection solution. The spikes consisted of 17.8, 35.5, and 71.1 µg of Br₂, which corresponded to about 0.5, 1, and 2 times the PEL if sampling at 0.5 L/min for 60 min.

2.1. Standardization of Br₂ stock solution:

A Br₂ stock solution was prepared from a Br₂ permeation tube by bubbling the Br₂ vapor through a collection solution for a given period of time. This stock solution was then analyzed by IC. The concentration of the stock solution was 35.57 µg/mL as Br₂ (29.64 µg/mL as Br¯).

2.2. Three sets of spiked samples were prepared by adding 0.5, 1.0, and 2.0 mL, respectively, of the Br₂ stock solution into 10-mL volumetric flasks and diluted to volume with collection solution. Each set consisted of 6 samples.

2.3. The analytical procedure described in OSHA method no. ID-108 (10.1.) was followed.

Results:   The results of the analytical experiment are presented in Table 1. The overall analytical recovery was 98.3% which does not indicate a need for an analytical correction factor.

3. Sampling and Analysis

Procedure:   A standard generator [Model 350, Analytical Instrument Development Inc. (AID), Avondale, PA] containing Br₂ permeation tubes (from AID) was used as the source for generating dynamic test atmospheres of Br₂. A sampling manifold, constructed from glass and Teflon, was attached to the generator. Samples (6 samples at each of the three test levels) were collected from the manifold using concentrations of 0.5, 1, and 2 times the OSHA TWA PEL (0.1 ppm).

3.1. The permeation rate of the Br₂ permeation tubes was determined by measuring their respective weight loss at a constant temperature of 30 °C ± 0.1 °C over a given period of time. The permeation rates are shown in Table 2. Two different sizes of permeation tubes were used.

3.2. The flow rates of the diluent air and saturated gas stream of bromine from the generator were measured with a soap bubble flow meter to determine the concentration of the generated gas.

3.3. Three sets of six samples were collected individually at about 0.05, 0.1, and 0.2 ppm Br₂. Samples were collected using personal sampling pumps at a sample flow rate of about 0.5 L/min for 60 min.

Results:   The results of sampling and analysis are shown in Table 3. Known (Taken) concentrations listed were calculated from the permeation tube weight loss and flows of Br₂ gas and diluent air.

4. Collection Efficiency (CE) and Breakthrough

Procedure - CE:   Two MFGBs containing 10 mL of collection solution were connected in series. Six of these series samples were collected at a concentration of 0.2 ppm for 60 min at 0.5 L/min. The amount of Br₂ vapor collected in each MFGB was then measured.

Results:   The CE of the first MFGB was calculated by dividing the amount of Br₂ collected in the first MFGB by the total amount of Br₂ collected in the first and second MFGB. The results are reported in Table 4. The CE was 100%.

Procedure - Breakthrough:   Two MFGBs in series, as mentioned above, were prepared. Three of these series samples were taken at 0.2 ppm. A flow rate of 0.5 L/min and sampling times of 60, 120, and 240 min were used.

Results:   Breakthrough was calculated by dividing the amount of Br₂ collected in the second MFGB by the total amount of Br₂ collected in the first and second MFGBs. The results are given in Table 5. The breakthrough was 2.4% after 240 min.

5. Storage Stability

A study was conducted to assess the storage stability of collected Br₂ in the collection solution.

Procedure:   Six samples were generated as described in Section 3. The samples were transferred into 10-mL volumetric flasks. These flasks were then tightly closed and stored on top of a lab bench at normal laboratory temperatures. The samples were analyzed after 1, 5, 15, and 30 day storage periods.

Results:   The results of the storage stability study are shown in Table 6. These results indicate that samples may be stored under normal laboratory conditions for a period of at least 30 days.

6. Detection Limit

Procedure:   Samples containing small amounts of Br¯ were prepared in the collection solution and then analyzed by IC. The Rank Sum Test was used for the determination of the qualitative detection limit. The test is a non-parametric or a distribution-free test. The quantitative limit was determined by examining the variation (CVs) in results of these samples.

Results:   The results of the Rank Sum Test are shown in Table 7. As shown, the qualitative detection limit as Br₂ is 0.02 µg/mL (99% confidence level). The quantitative limit is 0.09 µg/mL as Br₂, or 0.9 µg in a 10 mL sample volume. This corresponds to 0.005 ppm Br₂ for a 30-L air volume. The CV at this level was about 0.11.

7. Analytical Method Comparison

The previous ion specific electrode (ISE) procedure (10.3.) used by OSHA was chosen as the reference analytical method to which the results of the IC method were compared.

7.1. Analytical procedure for ISE (10.3)

7.1.1. A low level ionic strength adjuster (ISA) was prepared by diluting 20 mL ISA (5 M sodium nitrate) to 100 mL with deionized water.

7.1.2. Three sets of spiked samples were prepared by adding 5, 10, and 20 mL, respectively, of Br₂ stock solution, 1 mL of ISA, and 50 µL of concentrated nitric acid into 100-mL volumetric flasks and then diluting to volume with collection solution. These samples corresponded to 1.78, 3.56, and 7.11 µg/mL Br¯ and were compared to those samples prepared in Section 2.2.

7.1.3. Two different concentrations of Br¯ standards were prepared from potassium bromide to check the slope (-58.0 mV) of the ISE.

7.1.4. Samples were analyzed using an Orion model 94-35A specific ion electrode and an Orion Model 901 millivolt meter.

7.2. Results:   The comparison data of the ISE reference and IC methods are shown in Table 8.

7.3. Discussion:   In basic solution, Br₂ disproportionates to produce Br¯ and BrO₃¯ according to the following equation (10.2.):

3Br₂  +  6OH¯  ---->  5Br¯  +  BrO₃¯  +  3H₂O     (basic solution)

The mole ratio of Br₂ per Br¯ is 1.2. As the pH is lowered, Br¯ and BrO₃¯ may react with each other to gradually convert back to Br₂ according to the following equation (10.4).:

BrO₃¯  +  5Br¯  +  6H⁺  ---->  3Br₂  +  3H₂O     (acidic solution)

Results of Br₂ concentration obtained from the ISE were much lower than that from the IC, which was likely due to the change in pH after nitric acid is added. Therefore, results obtained from IC analysis are more accurate and reliable than ISE results.

8. Precision and Accuracy

The data, based on the NIOSH statistical protocol (10.5.), are presented in Tables 1 and 3. The pooled coefficients of variation for spiked (CV₁ [pooled]) and generated (CV₂ [pooled]) samples and the overall CV_T (pooled) are:

The bias was -0.056 and overall error was ±19%. Overall error was calculated as:

OE_i  =  ± [|mean bias_i|  +  2CV_i] × 100%

where  i  is the respective sample pool being examined.

9. Conclusions

The analytical, sampling and analytical, collection efficiency, breakthrough, storage stability, and detection limit experiments displayed acceptable data. A negative bias was noted for the sampling and analysis experiment conducted at two times the TWA PEL; however, the collection efficiency experiment at this concentration indicated no Br₂ was passing into the next bubbler.

The MFGB sampling and IC analytical method for Br₂ has shown to be an acceptable alternative to determining compliance with the OSHA PEL of 0.1 ppm (TWA). The ability of the method to determine compliance to the STEL of 0.3 ppm Br₂ is dependent on the detection limit and potential breakthrough at this concentration. A detection limit of 0.9 µg or 0.018 ppm Br₂ (15-min sample, 7.5-L total air volume) is more than adequate for STEL measurements. Breakthrough was not evident at 60 to 120 min and was only 2.4% at a 240-min sampling time (0.2 ppm concentration). Breakthrough is not expected to occur at 0.3 ppm for a 15-min sampling time. Therefore, it is recommended to sample for TWA or STEL samples at 0.5 L/min as demonstrated in this method.

10. References

10.1 Occupational Safety and Health Administration Technical Center: Bromine in Workplace Atmospheres by J. Ku (USDOL/OSHA-SLTC Method No. ID-108). Salt Lake City, UT. Revised 1990.

10.2. Cotton, F.A. and G. Wilkinson: Advanced Inorganic Chemistry -- A Comprehensive Text. 2nd rev. ed. New York: Interscience Publishers, 1966. pp. 569-570.

10.3. Orion Research Incorporated: Instruction Manual, Halide Electrodes, Model 94-35. Cambridge, MA: Orion Research Incorporated, 1982.

10.4. Blaedel, W.J. and V.W. Meloche: Elemental Quantitative Analysis -- Theory and Practice. 2nd ed. New York: Harper and Row, Publishers, 1963. p. 854.

10.5. 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.