National Institute for Occupational Safety and Health

“ Calibrate daily with at least six working standards. a. Prepare a calibration stock solution by dilution of 1 mL of 1 mg/mL formaldehyde stock solution to 100 mL 1% sodium bisulfite solution. b. Pipet, e.g., 0.1, 0.3, 0.5, 0.7, 1.0, and 2.0 mL calibration stock solution into 25-mL glassstoppered flasks. c. Add 1% sodium bisulfite solution to bring the volume of each working standard to 4 mL. Also prepare a reagent blank. ”

“ 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] . ”

“ Analyze together with samples and blanks (steps 5 through 9, and steps 11 and 12) . e. Prepare calibration graph (absorbance vs. μg formaldehyde/mL) .
MEASUREMENT: 11. 12.
Set spectrophotometer according to manufacturer's recommendations and to conditions given on p. 3500-1. Fill 1-cm cuvette with sample. Read sample absorbance at 580 nm. ”