National Institute for Occupational Safety and Health

“ Calibrate each personal sampling pump with a representative sampler in line. Sample at an accurately known flow rate between 1 and 4 L/min for a total sample size of 30 to 180 L. NOTE: This method will collect hydroquinone aerosol only. The equilibrium vapor pressure is equivalent to 0.11 mg/m 3 at 25 °C and may be a significant factor at elevated temperatures. Immediately after sampling, transfer the filter (do not include backup pad) with tweezers to a 60-mL ointment jar. Add 10 mL 1% acetic acid. Process field blanks similarly. Ship the filters in the ointment jars. ”

“ Add known amounts of calibration stock solution to 1% acetic acid in 25-mL volumetric flasks and dilute to the mark. b. Analyze together with samples and blanks (steps 9 and 10) . c. Prepare calibration graph (peak area vs. mg hydroquinone) . Check recovery with at least three spiked media blanks per sample set. a. Add aliquot of calibration stock solution with a microliter syringe directly to a representative filter. Transfer filter to 60-mL ointment jar, add 10 mL 1% acetic acid, and allow to stand overnight. b. Prepare and analyze together with working standards (steps 5, 6, 9 and 10) . ”

“ Average collection efficiency was 100% at 4 mg/m 3. No loss of hydroquinone was seen from filters spiked with 720 μg hydroquinone, and then used to sample 180 L clean air, indicating the hydroquinone vapor pressure is not significant at these conditions. At elevated temperature, however, contribution from vapor may be significant. Storage studies were conducted by storing exposed filters in 1% acetic acid at ambient temperature for seven days. ”