National Institute for Occupational Safety and Health

“ Transfer the front and back sections of sulfuric acid-treated silica gel to separate 80-mL vials. Discard glass wool plugs. Analyze the two sections separately. NOTE: Firm tapping of the tube may be necessary to effect complete transfer of the sulfuric acid-treated silica gel. Add 20 mL of ammonia-free deionized water to each vial. Cap and shake vigorously. Desorption is complete in 45 minutes. Adjust the pH of each sample to 5.0 to 6.5 with sodium hydroxide. NOTE: Analyses should be completed within one day after the ammonia is desorbed. ”

“ This method is based on the sampling procedure of Method S347 [2] , the automated analytical procedure of EPA Method 350.1 [3] , and Standard Methods 417G [4] . NIOSH Method 6701 [5] was less sensitive, employing a passive li quid sorbent badge for collection followed by ion chromatography. NIOSH Method P&CAM 205 [6] used impinger collection and Nessler's reagent for manual colorimetric analysis. OSHA has both impinger collection with ion specific electrode analys is (ID-164) [7] and sulfuric acid-impregnated beaded carbon collection followed by ion chromatography analysis (ID-188) [8] . ”

“ NOTE: Sodium nitroprusside solution is lightsensitive. Store in and use from a brown bottle. 13. Calibration stock solution (100 mg NH 3/L) : Dissolve 0.3144 g anhydrous ammonium chloride, NH 4Cl, dried at 105 °C, in deionized water, and dilute to 1 L. Add 1 mL chloroform as a preservative.
1. Sampler: a. Prefilter (to remove particulate interferences) : 37-mm cellulose ester membrane filter (0.8-μm pore size) supported by stainless steel screen in two piece cassette filter holder. b. Sulfuric acid-treated silica gel sampling tubes. ”