Page:NIOSH Manual of Analytical Methods - 3507-1.pdf/2

 ACETALDEHYDE: METHOD 5512, Issue 2, dated 15 August 1993 - Page 2 of 4 REAGENTS: 1. 2. 3. 4.

5. 6. 7. 8.

9.

10.

11.

EQUIPMENT:

Acetaldehyde.* Citric acid. Disodium hydrogen phosphate (Na 2HPO 4). Girard T reagent [(carboxymethyl)trimethylammonium chloride hydrazide] recrystallized from 95% ethanol. Water, distilled, deionized (DD). Ethanol, 95%. Sodium dihydrogen phosphate monohydrate (NaH 2PO 4·H 2O). Girard T solution: 5.39 g citric acid, 6.63 g Na 2HPO 4, and 16.77 g Girard T reagent diluted to 500 mL with DD water. Store in annealed flask in the dark. Use within two weeks. HPLC mobile phase: 0.22 M Na 2HPO 4·H 2O, 0.019 M NaH 2PO 4·H 2O in 20% ethanol. Dissolve and dilute 31.2 g Na 2HPO 4 and 26.2 g NaH 2PO 4·H 2O to 1 L with DD water. Filter through 5-µm PTFE filter and degas prior to use. Bubble helium through the solution to prevent bacterial growth. Calibration stock solution, 4.32 mg/mL acetaldehyde in 0.2 M Girard T solution. Weight 216 mg freshly-distilled acetaldehyde into 50-mL volumetric flask containing 49 mL Girard T solution. Make to volume with Girard T solution. Use within one day. Helium.

2.

3.



Heat in an oxidizing atmosphere at 580 °C.

See SPECIAL PRECAUTIONS. SPECIAL PRECAUTIONS: Acetaldehyde is extremely volatile and a fire hazard. Cool containers of acetaldehyde to ice bath temperature to reduce pressure buildup and open in an exhaust hood only.

SAMPLING: 1.

1. Sampler: bubbler, glass, midget, with fritted glass stems, annealed,* with PTFE stoppers for shipping. 2. Personal sampling pump, 0.1 to 0.5 L/min, with trap made from midget bubbler with stem broken off and inert, flexible connecting tubing. 3. High pressure liquid chromatograph, with 245nm UV detector, integrator, and column (page 3507-1) with 50-µL injection loop or autosampler. 4. Syringe, 2-mL, Luer-lock. 5. Distillation apparatus for preparation of high purity acetaldehyde. 6. Flasks, volumetric, 1-L; 10-, 50-, and 100-mL; and 500-mL, annealed.* 7. Pipets, 0.02- to 1-mL; 5-, 10-, and 15-mL. 8. Marker, glass. 9. Cylinder, graduated, 250-mL. 10. Filter, 5-µm, PTFE, 37-mm, with holder for liquid filtration. 11. Balance, readable to 0.1 mg.

Calibrate each personal sampling pump with a representative sampler and trap in line. Add exactly 15 mL Girard T solution to each bubbler using a 15-mL pipet. Mark the initial liquid level in the bubbler with a glass marker. Make impinger-to-trap and trap-to-sampling pump connections with flexible inert tubing. Sample at an accurately known flow rate between 0.1 and 0.5 L/min for a total sample size of 6 to 60 L. NOTE: Higher flow rates will cause frothing of the collection medium. If amount of liquid condensed in the trap is greater than 1 mL, collection efficiency of bubbler may be reduced and sample may be invalid.

SAMPLE PREPARATION: 4.

5.

Tap bubbler stem lightly against bubbler body to drain contents into the body. If necessary, bring samples up to the 15-mL mark with distilled water. Swirl bubbler to mix contents well. Do not add solution collected in the trap to the sample. Transfer a 5-mL aliquot to a 100-mL flask and bring to volume with HPLC mobile phase. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/93