Page:NIOSH Manual of Analytical Methods - 3500.pdf/2
FORMALDEHYDE: METHOD 3500, Issue 2, dated 15 August 1994 - Page 2 of 5 EQUIPMENT:
REAGENTS: 1. Chromotropic acid, 1%. Dilute 0.10 g 4,5dihydroxy-2,7-naphthalene disulfonic acid disodium salt to 10 mL with distilled water. Filter. Store in brown bottle. Prepare fresh weekly. 2. Sulfuric acid (H 2SO 4), 96%.* 3. Formaldehyde stock solution, 1 mg/mL (See APPENDIX). 4. Formalin solution, 37%.* 5. Distilled, deionized water. 6. Sulfuric acid, 0.02 N, aqueous. 7. Sodium hydroxide, 0.01 N, aqueous. 8. Sodium sulfite, 1.13 M, aqueous. Prepare fresh immediately before use. 9. Sodium bisulfite (NaHSO 3), 1%. Dissolve 1 g in distilled water. Dilute to 100 mL. Prepare fresh weekly. 10. Magnesium sulfate.
See SPECIAL PRECAUTIONS.
1. Sampler: 37-mm filter cassette with 37-mm polytetrafluoroethylene (PTFE) membrane filter, 1- to 3-µm pore size supported by stainless steel screen or O-ring followed by two midget impingers; inert, flexible tubing for cassette-to-impinger connection. 2. Personal sampling pump, 0.2 to 1 L/min, with flexible connecting tubing. 3. Bottles, screw-cap low-density polyethylene (Nalgene CPE or equivalent), 50-mL. NOTE: Do not use bottles with "polycone" liners (see step 4) 4. Spectrophotometer, visible, 580 nm, with cuvettes, 1-cm. 5. Volumetric pipettes, 0.1-, 0.5-, 1-, 4-, 5-, 6and 10-mL; 1-, 2- and 5-m, graduated in 0.1mL units, with pipet bulb. 6. Volumetric flasks, 10- and 100-mL, and 1-L. 7. Burets, 50-mL. 8. pH meter. 9. Flasks, glass-stoppered, 25-mL. 10. Graduated cylinder, 25-mL. 11. Waterbath at 95 °C. 12. Magnetic stirrer. 13. Beaker, 50-mL.
SPECIAL PRECAUTIONS: Sulfuric acid is extremely corrosive; handle while wearing acid-resistant gloves, apron and full face shield with goggles. Formaldehyde is viewed as a potential carcinogen [9,10] and should be handled in a hood.
SAMPLING: 1. 2.
3. 4.
Calibrate each personal sampling pump with a representative sampler in line. Fill the two impingers for each sample with 20 mL, 1% sodium bisulfite solution. Make cassette-to-impinger and impinger-to-sampling pump connections with flexible, inert tubing. Insert a second filter/cassette assembly in line between the sampler and sampling pump to trap any liquid which might splash over from the impingers during sampling. NOTE: The PTFE filter is necessary when sampling is to be conducted in a dusty environment, which could contribute either a positive or negative interferences to the method [1]. The use of dual impingers in series is recommended to ensure efficient collection of formaldehyde. Sample at an accurately known flow rate between 0.2 and 1 L/min for a total sample size of 1 to 100 L. Transfer the contents of the impingers to separate low-density polyethylene bottles for shipping. Note: Sample contamination may occur if glass scintillation vials with "polycone" plastic lined caps are used [11].
SAMPLE PREPARATION: 5.
Transfer each impinger solution to a clean, dry 25-mL graduated cylinder. Record volume of solution from front impinger, V f (mL) and backup impinger, V b (mL). NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94