Page:NIOSH Manual of Analytical Methods - 3508.pdf/5

 METHYL ETHYL KETONE PEROXIDE: METHOD 3508, Issue 2, dated 15 August 1994 - Page 5 of 5 APPENDIX: 1. STANDARDIZATION OF 60% MEKP STOCK SOLUTION a. Weigh to nearest mg, 1 g 60% MEKP in a 100-mL volumetric flask. Dilute to the mark with isopropyl alcohol and cover flask with foil. b. Place ca. 25 mL isopropyl alcohol in a 250-mL iodine flask. Add 5 mL glacial acetic acid then add 10 mL 20% sodium iodide solution to the flask. c. Pipet exactly 10.0 mL MEKP-isopropyl alcohol solution (from step 1.a above) into the flask, cover and let stand in the dark for 15 min. d. Add 10 mL distilled water to the flask immediately before titrating. e. Titrate with 0.1 N sodium thiosulfate from a yellow to colorless end point. Record the volume in mL used. Titrate a blank containing all reagents except MEKP in exactly the same way. f. Calculate the weight % MEKP:

where:

C s = percent MEKP as the cyclic dimer Vs = volume of 0.1 N Na 2S2O 3 used to titrate the sample (mL) Vb = volume of 0.1 N Na 2S2O 3 used to titrate the blank (mL) W = weight of commercial MEKP used (g) 4.405 = constant containing the milliequivalent weight of MEKP (as the cyclic dimer) and various dilution factors.

2. STANDARDIZATION OF SODIUM THIOSULFATE, 0.1 N (or use commercially available standard) a. Prepare the following solutions: (1) Potassium dichromate, 0.1000 N. Dissolve 4.904 g anhydrous K 2Cr2O 7, primary standard grade, in distilled water; dilute to 1 L. (2) Starch indicator. Prepare a thin paste of 1 g soluble starch in a few mL distilled water. Bring 200 mL distilled water to a boil, remove from heat and stir in the starch paste. Prepare fresh before use. (3) Sodium thiosulfate solution. Dissolve 25 g Na 2S2O 3 ⋅ 5H 2O in freshly boiled, cooled distilled water; dilute to 1 L. Add 5 mL CHCl 3 as preservative. Age 2 weeks before standardizing. b. Place 80 mL distilled, deionized water in 150-mL beaker, stirred with magnetic stirrer. Add 1 mL conc. H 2SO 4, 10.0 mL 0.1000 N K2Cr2O 7 and ca. 1 g KI. Allow to stand in dark for 6 min. Titrate with sodium thiosulfate solution. Upon approaching end point (brown changing to yellowish green), add 1 mL starch indicator solution and continue titrating to the end point (blue to light green). Calculate the normality, N, of the sodium thiosulfate solution:

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