HYDROQUINONE: METHOD 5004, Issue 2, dated 15 August 1994 - Page 2 of 3 REAGENTS: 1. 2. 3. 4.
5.
EQUIPMENT:
Hydroquinone, reagent grade. Distilled water. Acetic acid, glacial. Acetic acid, 1%. Dilute 10 mL acetic acid to 1 L with distilled water. NOTE: This solution is needed at the sampling site for field treatment of samples. Calibration stock solution, 3.6 mg/mL. Dissolve 0.0900 g hydroquinone in 25 mL 1% acetic acid. Prepare fresh daily, in duplicate.
1. Sampler: 37-mm cassette containing 0.8-µm cellulose ester membrane filter and cellulose backup pad. 2. Personal sampling pump, 1 to 4 L/min, with flexible connecting tubing. 3. High pressure liquid chromatograph with UV detector at 290 nm, integrator and column (page 5004-1). 4. Jars, 60-mL, ointment, low form, with PTFE film gaskets and screw caps. 5. Syringe, 100-µL, or autosampler for sample injection. 6. Microliter syringes for standard preparation. 7. Volumetic flasks, 10- and 25-mL, and 1-L.
SPECIAL PRECAUTIONS: None. SAMPLING: 1. 2.
3. 4.
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.
SAMPLE PREPARATION: 5. 6.
Transfer the sample solution from the ointment jar to a 25-mL volumetric flask. Rinse the ointment jar twice with 5 mL 1% acetic acid. Add the washings to the volumetric flask. Make up to volume with 1% acetic acid.
CALIBRATION AND QUALITY CONTROL: 7.
8.
Calibrate daily with at least six working standards over the range 0.01 to 0.8 mg hydroquinone per sample. a. 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). c. Calculate recovery [(mg recovered - mg blank)/mg added)]. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
