Page:NIOSH Manual of Analytical Methods - 2542.pdf/2

 MERCAPTANS, METHYL-, ETHYL-, and n-BUTYL-: METHOD 2542, Issue 1, dated 15 August 1994 - Page 2 of 4

REAGENTS:

EQUIPMENT:

1.	Methyl mercaptan gas,* lecture bottle, 99.5+%. 2.	Ethyl mercaptan,* 99+%. 3.	n-Butyl mercaptan,* 99+%. 4.	Mercuric acetate, ACS reagent grade. 5.	Hydrochloric acid, ACS reagent grade. 6.	1,2-Dichloroethane, ACS reagent grade. 7.	Methyl mercaptan calibration stock solution, 0.394 mg/mL. Pipet 5.0 mL methylene chloride into a vial and attach PTFE-lined cap. Add 1.0 mL pure methyl mercaptan gas (measured at 25 °C, 1 atm) to the liquid using gas-tight syringe. 8.	Ethyl mercaptan calibration stock solution, 2.52 mg/mL. Dissovle 30 µL ethyl mercaptan in methylene chloride in a 10-mL volumetric flask and dilute to the mark. 9.	n-Butyl mercaptan calibration stock solution, 3.34 mg/mL. Dissolve 40 µL n-butyl mercaptan in methylene chloride in a 10-mL volumetric flask and dilute to the mark. 10.	Helium, purified. 11.	Hydrogen, prepurified. 12.	Air, filtered, compressed.

1.	Sampler: glass fiber filters impregnated with mercuric acetate. The filters are prepared by immersing 37-mm Gelman Metrigard (or equivalent) glass fiber filters with acrylic binder in 5% (w/v) aqueous solution of mercuric acetate, dried in the air, and then assembled in two-piece filter cassettes without backup pads. The filters exhibit yellowish color, but it does not affect their collection efficiency. 2.	Personal sampling pump, 0.10 to 0.20 mL/min, with flexible polyethylene or PTFE tubing. 3.	Gas chromatograph with a flame photometric detector, capillary column, integrator. 4.	Vials, glass, 2-mL and 5-mL, PTFE-lined crimp caps. 5.	Syringes, 10-, 50, and 250-µL. 6.	Volumetric flasks, 10-mL. 7.	Pipets, 5- and 20-mL glass, delivery, with pipet bulb. 8.	Separatory funnel, 30-mL.

SPECIAL PRECAUTIONS: Store methyl-, ethyl-, and n-butyl-mercaptans separately from flammable and oxidizing materials [5,6]. The analytes are highly flammable and irritating to the eyes. Work in a hood. SAMPLING: 1.	Calibrate each personal sampling pump with a representative sampler in line. 2.	Remove the plugs from the filter cassette immediately before sampling. Connect the cassette to the sampling pump with flexible tubing. Air being sampled should not pass through any hose or tubing before entering filter cassette. 3.	Sample at an accurately known flow rate between 0.1 and to 0.2 L/min for a total sample size of 10 to 150 L. 4.	Replace the plugs in the filter cassette immediately after sampling. Store protected from light. SAMPLE PREPARATION: 5.	Add 20 mL of 25% (v/v) hydrochloric acid and 5 mL of 1,2-dichloroethane to a 30-mL separatory funnel. Fold sample filter and insert into the neck of a separatory funnel, without allowing the filter to become wet. While seating the stopper, push filter into funnel. 6.	Shake funnel for 2 min without venting. 7.	Let stand at least 5 min, until the phases completely separate. Then drain the 1,2-dichloroethane into a vial and seal with a PTFE-lined cap.
 * See SPECIAL PRECAUTIONS.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition