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CHLORINE BACKUP DATA REPORT (ID-101)
This Backup Report was revised May, 1991 Introduction The OSHA sampling and analytical method for chlorine is discussed in reference 9.1. The principle of sampling is described in reference 9.2. The analytical procedure is based on an iodometric technique which uses a residual chlorine electrode (RCE) for detection (9.3.). The validation of the chlorine method consisted of the following experimental studies:
The details with respect to each of these items are discussed in the following sections. All experiments were based on the ability of the method to collect and analyze a 15-L air sample for each concentration tested. The sample preparation and analytical technique used during the method evaluation follow that described in reference 9.4. A revised method (9.1.) is also available.
Note: The revised version of the method (9.1.) differs in one major point from reference 9.4.: Preparation of samples and standards for analysis. It is now recommended to prepare samples and standards in 0.1% sulfamic acid solutions rather than the deionized water previously used (9.5.). 1. Generation A dynamic standard generator (Model 350, Analytical Instrument Development Inc., Avondale, PA) was used for generating test atmospheres of chlorine. The system is further described in reference 9.6. Two chlorine permeation vials were used as the chlorine source. The permeation vials were maintained at a constant temperature of 30 ± 0.1 °C. The chlorine concentration was determined from the weight loss of the permeation vial over a measured time period and was calculated according to the equation listed in Appendix A. After the chlorine was produced it was then diluted with tempered air so that a controlled concentration at 80% RH and 25 °C was achieved. Flow rates for the generation system were measured with a soap bubble flow meter to accurately determine dilution and the final concentration of the gas. Samples were taken from a glass sampling manifold which was attached to the generation system. The majority of samples were collected in sets of six at one of three concentrations, about 0.5, 1, or 2 ppm chlorine. 2. Analysis Procedure: Samples containing 0.1% sulfamic acid were spiked with standardized chlorine solutions. This test determined the precision and accuracy of the analysis portion of the method. Results: The results are shown in Table 1. Average analytical recovery was 96.7% and the coefficient of variation (CV1) was 0.03 for the three sets of spiked samples. 3. Sampling and Analysis Procedure: Samples were collected in 0.1% sulfamic acid solutions at three different chlorine concentrations using the generation system described in Section 1. Midget fritted glass bubblers (MFGB) were used to disperse the air samples in the sulfamic acid solutions. This test determined the precision and accuracy of the sampling and analysis portion of the method. Results: Sampling and analysis data are presented in Table 2. The NIOSH Statistical Protocol (9.7.) developed for evaluation of methods under the Standards Completion Program (SCP) was used as a guide for the determination of precision and accuracy from this data. The precision for this method using these statistical procedures is:
The average recovery for sampling and analysis over all levels was 99.4%. Any variation from 100% recovery was probably related to difficulties in generating the atmosphere containing the analyte at a given concentration rather than a true bias in the method. The Bartlett's test for homogeneity of variances and an outlier test (9.7.) were applied to this data. The sampling and analysis data passed the Bartlett's test, indicating the CVs could be pooled for all sets of generated samples. One data point in the third set (2 × PEL, n=5) was rejected as an outlier. 4. Collection Efficiency Procedure: The collection efficiency (CE) of MFGBs
containing 0.1% sulfamic acid was assessed. A chlorine concentration of
approximately 2 ppm was generated and samples were collected in series
using the MFGBs. A flow rate of 1 L/min and a Results: The results are shown in Table 3. The CE of the single bubbler was determined to be 1.00; therefore, a recovery correction or sampling train is not necessary. 5. Breakthrough Procedure: Breakthrough is defined as the time the effluent concentration in a second bubbler (containing 0.1% sulfamic acid) connected in series reaches 5% of the concentration of the test gas mixture. A test for breakthrough was conducted at about 2 ppm and at a 1 L/min sample collection flow rate. A sample set consisting of two bubblers in series was used to collect samples for each time interval listed: 15, 30, 60, 120, 180, and 240 min. Results: No breakthrough occurred at this flow rate, during these sampling times, or at the concentration tested. The results are given in Table 4. 6. Storage Stability Procedure: A study was conducted to assess whether
chlorine samples collected at the 1 ppm PEL could be successfully stored
in the 0.1% sulfamic acid collection solution. After sample collection
using MFGBs, samples were transferred into 20-mL vials, capped with
Results: Samples analyzed after 30 days were found to be within 3% of those analyzed immediately. Thus, storage does not represent a source of bias that would need to be corrected in the method. Storage stability data are presented in Table 5. 7. Independent Method (Analytical) An independent volumetric method (9.8.) involving a thiosulfate titration was used to determine the concentration of chlorine used for spiking. Chlorine gas was generated at a theoretical concentration which would give a chlorine concentration of 21.70 µg/mL in a specified volume of sulfamic acid. This value was calculated using the equation given in Appendix A. The gas was collected in 0.1% sulfamic acid solution which was then used as a chlorine stock solution for spiked samples (Section 2.). All other samples were taken using the generation system. Analyses of the stock solution were performed using the RCE and the thiosulfate titration methods. The following results were obtained:
The average value of 20.69 µg/ml from both methods was used as the stock solution concentration for the spiked samples mentioned in Section 2. 8. Conclusions This sampling and analytical method has been shown to be precise and
accurate at exposures near the OSHA PEL of 1 ppm when using
The development and evaluation of this method took place when the OSHA
PEL for chlorine was a Ceiling value 9. References
9.2. Takeuari, J. et al.: Measurement of Chlorine in the Atmosphere. Osen Kenkyu (Air Pollution Research) 9(2): 210 (1974). 9.3. Orion Research, Inc.: Residual Chlorine Electrode, Model 9970 Instruction Manual. Cambridge, MA: Orion Research, Inc., 1976. 9.4. Occupational Safety and Health Administration Analytical
Laboratory: OSHA Analytical Methods Manual
9.5. Rando, R.J., and Y.Y. Hammad: A Diffusive Sampler for
Gaseous Chlorine Utilizing an Aqueous Sulfamic Acid Collection Medium
and Specific Ion Electrode Analysis. Appl. Occup. Environ. Hyg.
5(10): 9.6. Analytical Instrument Development, Inc.: Model 350 Standards Generator Operation and Service Manual. Avondale, PA: Analytical Instrument Development, Inc., 1977. 9.7. 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. 9.8. American Society for Testing and Materials: Standard
Recommended Practices for Apparatus, Reagents, and Safety Precautions
for Chemical Analysis of Metals (Annual Book of ASTM Standards,
Part 12,
Calculation of Generated Concentrations from Permeation Tubes (9.6.) The calculation of chlorine concentration in the generation system was obtained using the following equation:
Where:
The permeation or diffusion rate (R) for commercial permeation or diffusion tubes is usually given by the manufacturer or can be determined by weight loss over an extended period. The constant (k) is the reciprocal density and is calculated as follows:
Note: T and P are the temperature and pressure at which f is measured and not necessarily the temperature and pressure at which the chamber oven is operating.
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