Page:NIOSH Manual of Analytical Methods - 3508.pdf/3

 METHYL ETHYL KETONE PEROXIDE: METHOD 3508, Issue 2, dated 15 August 1994 - Page 3 of 5 8. 9. 10.

Pipet 5.0 mL color reagent into the test tubes. Stopper and invert several times to mix. Loosen the stoppers and heat the test tubes in a waterbath at 85 ± 5 °C for 15 min. Cool in a waterbath at 25 ± 5 °C for exactly 5 min.

CALIBRATION AND QUALITY CONTROL: 11.

Calibrate daily with at least six working standards in duplicate. a. Pipet, e.g., 1.0, 2.0, 5.0, and 10.0 mL calibration stock solution to 25-mL silanized volumetric flasks, fitted with glass stoppers. 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). Perform a volumetric dilution to extend the range upward.

MEASUREMENT: 12. 13.

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).

EVALUATION OF METHOD: This method is based on P&CAM 331 which was issued on August 29, 1980 [1] and was studied using technical grade MEKP containing 58.7% MEKP [2]. A two-level factorial experiment was run to study the effect of three different parameters on the color produced in the reaction between MEKP and DPC. A reaction bath temperature of 85 °C and reaction time of 15 min were determined to be optimum. Samples containing 204 µg MEKP per 5 mL stored in the freezer for 21 days showed 10% loss of MEKP. MEKP standard solutions were tested for interference with acetone, methyl ethyl ketone, cyclohexanone, and 3-methyl-2-butanone. All these ketones, except acetone, exhibited positive interference. Stability of MEKP solutions was tested using various substances which could be likely co-contaminants. At freezer temperatures, samples containing styrene were stable for a week.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94