Page:NIOSH Manual of Analytical Methods - 6011.pdf/4

 CHLORINE AND BROMINE: METHOD 6011, Issue 2, dated 15 August 1994 - Page 3 of 5 SAMPLE PREPARATION:

5.

6. 7. 8.

NOTE: Silver halides are photosensitive. Protect from light during transfer and desorption. Under very dim or red light, open cassette and transfer the silver filter with forceps to amber bottle. Add 3 mL 6 m M Na 2S2O 3 and cap. NOTE: Prefilter may be analyzed for particulate halides, or discarded. Allow samples to stand a minimum of 10 min with occasional swirling. NOTE: Once desorbed, samples are no longer photosensitive. Uncap the sample bottles and add 7 mL deionized water for a total solution volume of 10 mL. Pour sample into 10-mL plastic syringe for manual injection or into autosampler vials.

CALIBRATION AND QUALITY CONTROL: 9.

10.

Calibrate daily with at least six working standards covering the range of 0.2 to 15 µg bromide and/or 0.05 to 5 µg chloride per mL of sample. a. Add known aliquots of calibration stock solution to deionized water in 10-mL volumetric flasks and dilute to the mark with deionized water. b. Prepare fresh working standards biweekly. c. Analyze working standards together with samples and blanks (steps 11 through 13). d. Prepare a calibration graph (peak height vs. µg of anion per sample). Analyze three quality control spikes, three analyst spikes and media blanks to ensure that calibration graph is in control.

MEASUREMENT: 11.

12. 13.

Set ion chromatograph according to manufacturer's instructions and to conditions given on page 6011-1. NOTE: Excessive amounts of Ag + and Ag(S 2O 3)23- deteriorate column preformance. Use a metal free column (MFC-1) prior to the chromatographic columns and recondition the column every 100 to 150 analyses (See APPENDIX B). Inject 50-µL sample aliquot manually or with autosampler. For manual operation, inject 2 to 3 mL of sample from syringe to ensure complete rinse of the sample loop. Measure peak height. If sample peak height exceeds linear calibration range, dilute with deionized water, reanalyze, and apply the appropriate dilution factor in the calculations.

CALCULATIONS: 14. 15.

From the calibration graph, determine the mass of Br - or Cl - in each sample, W (µg), and in the average blank, B (µg). Calculate the concentration, C (mg/m 3), of Br 2 or Cl 2 in the air volume sampled, V (L):

EVALUATION OF METHOD: The method was evaluated by sampling generated atmospheres of Br 2 and Cl 2 at both high (80%) and low (20%) relative humidities [1]. Samples were taken at four concentration levels ranging from 0.007 to 1.42 mg/m 3 for Br 2 and 0.354 to 6.77 mg/m 3 for Cl 2. Overall recovery for Br 2 was 98.8% with total overall precision, SˆrT, of 6.8%. Overall recovery for Cl 2 was 98.6% with total overall precision, SˆrT, of 6.7%. Samples for Cl 2 were stable at least 30 days at 25 °C (103 ± 4% Recovery) and up to 60 days at 5 °C (101 ± 3% Recovery). The Br 2 samples were stable up to 60 days at 25 °C (99.2 ± 10.1% Recovery). NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94