TETRAMETHYL THIOUREA: METHOD 3505, Issue 2, dated 15 August 1994 - Page 3 of 4 b. c.
Analyze together with the samples and blanks (steps 6 through 8). Prepare calibration graph (absorbance vs. µg TMTU).
MEASUREMENT: 6.
7. 8.
Complexation. NOTE: Perform this step at the same time for both working standards and samples. Color degradation occurs at the rate of ca. 2% in 3 h. a. Pipet 1.5 mL dilute complexing reagent into each test tube or vial. b. Allow to stand for at least 30 min with occasional shaking to ensure full color development. NOTE: The color of the complex varies with increasing concentration from yellow to light green to turquoise. Very high concentrations have Prussian blue color; dilute these with distilled water before analysis and use the appropriate dilution factor in calculations. Transfer the solution to a clean 5-cm cuvette. Remove droplets from cuvette windows with lens paper. Measure absorbance at 590 nm vs. reference cell containing 15 mL distilled water and 1.5 mL dilute complexing reagent. NOTE 1: Sensitivity is ca. 0.006 absorbance unit/µg. NOTE 2: Scan the absorbance of the bulk sample (several mg of bulk sample dissolved in 15 mL water and treated as in steps 6 through 8) in the range 350 to 700 nm. Compare to spectrum of TMTU to detect possible interferences.
CALCULATIONS: 9. 10.
Determine the mass of TMTU (µg) for the sample (M) and average media blank (B). Calculate the concentration of TMTU, C, in the air volume sampled, V (L):
EVALUATION OF METHOD: The method was tested with 35 standards in the range 15 to 150 µg per sample with an average Sr of 2% [1,2]. All calibration graphs indicated a minimum linear correlation coefficient of 0.9999 [2]. TMTU spiked on VM-1 (PVC) filter samples could not be recovered with water or methanol in waterbath temperatures up to 60 °C because it reacted with the filter material [2]. The method was also used on 42 field samples collected in midget impingers in a survey [2]. The amounts of TMTU found ranged from 9 to 302 µg per sample.
REFERENCES: [1] [2] [3]
NIOSH Manual of Analytical Methods, 2nd. ed., V. 4, P&CAM 282, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 78-175 (1978). Palassis, J. Sampling and Analytical Determination of Airborne Tetramethyl and Ethylene Thiourea, Am. Ind. Hyg. Assoc. J., 41, 91-97 (1980). Registry of Toxic Effects of Chemical Substances, V. 3, U.S. Department of Health and Human Services, Publ. (NIOSH) 83-107 (1983).
METHOD WRITTEN BY: John Palassis, NIOSH/DTMD. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
