National Institute for Occupational Safety and Health

“ Sample at an accurately know flow rate between 1 and 4 L/min for a sample size of 200 to 1000 L. Do not exceed a total loading of 2 mg on the filter. SAMPLE PREPARATION:
Transfer filter with tweezers to jar. Add 5.0 mL methanol. Cap the jar. Swirl to wet filter thoroughly. CALIBRATION AND QUALITY CONTROL:
Calibrate daily with at least six working standards covering the range 4 to 120 μg Warfarin per sample. Add aliquots (2 to 60 μL) of calibration stock solution to 5 mL methanol in ointment jars. Analyze the working standards together with the samples and blanks (steps 7 and 8) . ”

“ The working range is 0.05 to 0.5 mg/m3 for a 400-L air sample.
INTERFERENCES: No interferences have been studied.
OTHER METHODS: This is P&CAM 313 [2] ⁠ in a new format. Analytical methods for Warfarin in some rodenticides [3] and in drugs [4] are available; these are spectrophotometric methods for bulk materials.
REAGENTS: Warfarin, 99%.* Methanol, HPLC grade.* Water, HPLC grade. Phosphoric acid, 85%.* Calibration stock solution, 2 mg/mL.* Dissolve 20.0 mg Warfarin in 10 mL methanol. Mobile phase component, 0.0025 N phosphoric acid. Dissolve 0.06 mL 85% phosphoric acid in 1 L water. ”

“ Sampler: 37-mm diameter PTFE membrane filter, 1-μm pore size, and cellulose backup pad in two-piece filter holder held together with tape or shrinkable band. Personal sampling pump, 1 to 4 L/min, with flexible connecting tubing. ”