National Institute for Occupational Safety and Health

“ Calibrate daily with at least six working standards. a. Add known aliquots of sulfate calibration stock solution to eluent in 50-mL volumetric flasks and dilute to the mark to produce solutions containing 1 to 20 μg/mL SO 24-. b. Prepare sulfite standards in the same manner over the same range. c. Store working standards in tightly-capped polyethylene bottles. Prepare fresh working standards daily. d. Analyze working standards with samples and blanks (steps 8 through 10) . Prepare a calibration graph for each anion [peak height (mm or μS) vs. μg sulfite or sulfate] . ”

“ In subsequent sampling of an atmosphere containing ca. 10 ppm SO 2 at 1 L/min for 30 min, two treated filters were placed in series following a cellulose ester membrane filter. Recoveries were: 0.667 mg SO 2 from the first treated filter, 0.02 mg SO 2 from the second treated filter, and less than 0.003 mg SO 2 in the backup impinger containing 0.3 N H2O 2 [11] . Cellulose ester filters spiked with 0.2 mg H 2SO 4 gave the following recoveries: 83.5% using H2O extraction, 98.5% using hot H 2O extraction, and 82.5% using 0.01 M HCl for extraction. ”

“ SAMPLE PREPARATION: 5. Put the two filters from the sampler into separate, clean vials. Discard the backup pads. Add 10.0 mL eluent to each vial and let stand, with occasional vigorous shaking, for 30 min. NIOSH Manual of Analytical Methods (NMAM) , Fourth Edition, 8/15/94 SULFUR DIOXIDE: METHOD 6004, Issue 2, dated 15 August 1994 - Page 3 of 4 NOTE: The SO 2 collected on the treated (back) filter is present as sulfite, which oxidizes in air slowly (over several weeks) to sulfate. ”