National Institute for Occupational Safety and Health, NIOSH Manual of Analytical Methods… (1994)
“ SAMPLE PREPARATION: NOTE: Process the samples, blanks, recovery spikes, and working standards in small groups (e.g., two to four) to maintain consistent timing for all analyses. Include a reagent blank in each small group for use in the reference cell of the spectrophotometer. 4. Add 20 mL methanolic 0.1 M KOH to the vial containing the filter. 5. Place the vial on a shaker for 5 min. 6. Transfer 2 mL sample solution to another vial. Start reagent blank at this step. NOTE: For filter samples containing >1 g Carbaryl, dilute the sample solution with methanolic 0.1 M KOH prior to this step. 7. ”
