National Institute for Occupational Safety and Health

“ Set spectrophotometer according to manufacturer's instructions. Set zero with dimethyl phthalate vs. air. Read sample absorbance at 565 nm vs. air when a stable value is obtained. NOTE: See SPECIAL PRECAUTIONS for procedure for disposal of waste MEKP solutions.
CALCULATIONS: 14. 15.
Determine the mass, μg, of MEKP in the 5-mL aliquot of sample, W, and the average media blank, B, from the calibration graph. Calculate the concentration, C, of MEKP in the air volume sampled, V (L) :
NOTE: Correct for the average media blank, B, only if it exceeds twice the reagent blank (y-intercept) . ”

“ Dilute to the mark with DMP. These working standards contain ca. 5, 10, 25, and 50 mg MEKP/mL (25, 50, 125, and 250 μg MEKP per 5-mL aliquot) . b. Process the working standards together with samples, field blanks, media blanks, and reagent blanks (steps 7 through 10 and 12 and 13) during the same time period using the same batch of reagents. c. Prepare calibration graph (absorbance vs. μg MEKP) . Extrapolate to zero concentration (y-intercept) . Any sample whose absorbance is less than twice the "blank" should be reported as less than that level (about 25 μg MEKP per 5-mL aliquot) . ”

“ Dilute to 100 mL. NOTE: This solution is light-sensitive. Prepare immediately before using. 9. Color reagent. Mix 30 mL 0.25% DPC solution with 20 mL glacial acetic acid. 10. Methyl ethyl ketone peroxide (MEKP) , 60%, technical grade, in dimethyl phthalate. Standardize as in APPENDIX. 11. Calibration stock solution.* Pipet ca. 10 μL of 60% MEKP into a 50-mL pre-weighed volumetric flask. Accurately weigh the flask plus MEKP; dilute to the mark with dimethyl phthalate. Wrap flask in Al foil. Prepare in duplicate. 12. Sodium thiosulfate solution, 0.1 N, standardized. ”