Page:NIOSH Manual of Analytical Methods - 2525.pdf/2

 n-BUTYL MERCAPTAN: METHOD 2525, Issue 2, dated 15 May, 1996 - Page 2 of 3 EQUIPMENT:

REAGENTS: 1. 2. 3. 4. 5. 6. 7. 8.

Acetone, chromatographic quality. n-Hexane, reagent grade. n-Butyl mercaptan.* Nitrogen, purified. Hydrogen, prepurified. Oxygen, purified. Air, filtered, compressed. Calibration stock solution, 13.47 mg/mL. Add 160 µL of pure n-butyl mercaptan to acetone and dilute to 10 mL. Prepare in duplicate.


 * See SPECIAL PRECAUTIONS.

1. Sampler: glass tube, 8.5 cm long, 6-mm OD, 4-mm ID, flame-sealed ends with plasticcaps containing two sections of 60/80 mesh Chromosorb 104 (front = 150 mg; back = 75 mg) separated by a 2-mm urethane foam plug. A silylated glass wool plug precedes the front section and a 3-mm urethane foam plug follows the back section. Pressure drop across the tube at 0.025 L/min airflow must be less than 3.4 kPa (25 mm Hg). The sampling tubes are commercially available (SKC, Inc. Cat. # 226-109). 2. Personal sampling pump, 0.01 to 0.05 L/min, with flexible connecting tubing. 3. Gas chromatograph, flame photometric detector with sulfur filter, integrator, and column (page 2525-1). 4. Vials, glass, 2-mL, PTFE-lined crimp caps. 5. Syringes, 10-µL (readable to 0.1 µL) and 50-µL. 6. Flasks, volumetric, 10-mL. 7. Pipet, 1.0-mL. 8. File, triangular.

SPECIAL PRECAUTIONS: Store n-butyl mercaptan away from oxidizing and flammable materials [3,4]. The analyte is highly flammable and irritating to the eyes and mucous membranes. Work in a hood.

SAMPLING: 1. 2. 3. 4.

Calibrate each personal sampling pump with a representative sampler in line. Break the ends of the sampler immediately before sampling. Attach sampler to personal sampling pump with flexible tubing. Sample at an accurately known flow rate between 0.01 and 0.05 L/min for a total sample size of 1 to 4 L. Cap the samplers and pack securely for shipment.

SAMPLE PREPARATION: 5. 6. 7.

Place the front and back sorbent sections of the sampler tube in separate vials. Discard the glass wool and foam plugs. Add 1.0 mL acetone to each vial. Attach cap to each vial. Allow to stand 15 min with occasional agitation.

CALIBRATION AND QUALITY CONTROL: 8.

9.

Calibrate daily with at least six working standards covering the range 0.3 to 20 µg/mL. a. Add known amounts of calibration stock solution to acetone in 10-mL volumetric flasks and dilute to the mark. b. Analyze together with samples and blanks (steps 11 and 12). c. Prepare calibration graph (peak area squared vs. µgn-butyl mercaptan). Determine desorption efficiency (DE) at least once for the batch of Chromosorb 104 used for sampling in the calibration range (step 8). Prepare three tubes at each of five levels plus three media blanks. a. Remove and discard back sorbent section of a media blank sampler. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 5/15/96