Page:NIOSH Manual of Analytical Methods - 3506.pdf/2

 ACETIC ANHYDRIDE: METHOD 3506, Issue 2, dated 15 August 1994 - Page 2 of 4 REAGENTS: 1.

2.

3.

4. 5.

6. 7.

EQUIPMENT:

Hydroxylamine hydrochloride solution. Dilute 200 g (NH 3OH)Cl to 1 L with distilled water in a volumetric flask. Refrigerate in a lightprotected container. Discard after two weeks. Sodium hydroxide solution. Dissolve 200 g in distilled water. Cool and bring to volume in a 1-L volumetric flask with distilled water. Store in a polyethylene bottle. Absorbing solution (needed for sampler). Mix equal volumes of the hydroxylamine hydrochloride and sodium hydroxide solutions just prior to use. Do not use after 2 h. HCl:water, 1:1 (v/v). Mix equal volumes of conc. HCl and distilled water. Ferric chloride solution. Dissolve 100 g FeCl 3·6H 2O in a 1-L volumetric flask with 1:1 (v/v) HCl:water. Dilute to volume with this mixture. Acetone. Acetic anhydride calibration stock solution. Pipet 10 mL acetic anhydride* into a 100-mL volumetric flask. Make to volume with acetone. The solution must be used within 2 h of preparation.

1. Sampler: bubbler, standard midget glass, stem containing fritted end with porosity ca. 170 to 220 mm maximum pore diameter with hard, non-reactive stopper (PTFE or glass). 2. Personal sampling pump, 0.2 to 1 L/min, with flexible connecting tubing. 3. Splashover tube: glass tube, 5 cm long, 8mm OD, 6-mm ID, loosely packed with glass wool. 4. Spectrophotometer reading at 540 nm with 5-cm matched cuvettes. 5. Flasks, volumetric, 1-L and 50- and 100-mL. 6. Pipets, graduated, 1-, 5- and 10-mL. 7. Micropipets, 10- to 100-µL. 8. Ice bath.

See Special Precautions

SPECIAL PRECAUTIONS: Acetic anhydride is readily combustible (flash point = 54 °C) and both the liquid and vapor produce irritation and necrosis of tissues. It may produce allergic sensitization of the skin [4].

SAMPLING: 1. Calibrate the personal sampling pump with a representative sampler in line. 2. Connect a splashover tube between the bubbler and the sampling pump with short pieces of flexible tubing. Do not allow the air being sampled to pass through any tubing or other equipment before entering the bubbler. 3. Pour 10 mL of absorbing solution into bubbler. NOTE: Absorbing solution must be prepared just prior to use (see REAGENTS, 3). 4. Sample at an accurately known flow rate between 0.2 and 1 L/min for a sample size of 25 to 100 L. Change sampler every 2 hrs so that the absorbing solution is fresh. 5. After sampling, remove the bubbler stem and tap gently against the inside of the bubbler tube. Wash the stem with 1 to 2 mL absorbing solution and add the wash to the bubbler. 6. Seal the bubbler tightly with a hard, non-reactive stopper and transport the samples by hand. Alternatively, transfer contents of each bubbler to a glass vial, rinsing bubbler with 1 to 2 mL absorbing solution. Cap the vial securely for shipment.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94