# Tetramethyl Thiourea (3505)

​TETRAMETHYL THIOUREA
(CH3)2NC(=S)N(CH3)2
MW: 132.23
METHOD: 3505, Issue 2
3505
CAS: 2782-91-4
EVALUATION: PARTIAL
OSHA : no standard NIOSH: no recommended exposure limit ACGIH: no standard
RTECS: YU2750000 Issue 1: 15 May 1985 Issue 2: 15 August 1994
PROPERTIES: solid; MP 78 °C; BP 245 °C
SYNONYMS: 1,1,3,3-tetramethyl-2-thiourea; TMTU
SAMPLING SAMPLER:
IMPINGER (water)
MEASUREMENT TECHNIQUE:
VISIBLE ABSORPTION SPECTROPHOTOMETRY
ANALYTE:
tetramethyl thiourea-pentacyanoamineferrate coordination complex
WAVELENGTH:
590 nm
CALIBRATION:
solutions of tetramethyl thioureapentacyandamine ferrate coordination complex in water
RANGE:
15 to 150 µg per sample
FLOW RATE: 0.2 to 1 L/min VOL-MIN: -MAX:
50 L @ 0.3 mg/m 3 250 L
SHIPMENT:
ship impinger contents in vial
SAMPLE STABILITY:
unknown
BLANKS:
2 to 10 field blanks per set
BULK SAMPLE:
required; high-volume air or settled dust
ESTIMATED LOD: 3 µg per sample [1] PRECISION (Sr):
0.02 @ 15 to 150 µg per sample [1,2]
ACCURACY RANGE STUDIED:
generated atmospheres not studied
BIAS:
unknown
ˆ ): not determined OVERALL PRECISION (S rT ACCURACY:
not determined
APPLICABILITY: The working range is 0.15 to 10 mg/m 3 for a 100-L air sample. Tetramethyl thiourea is used in the manufacture of adhesives and polychloroprene rubber. The method was also applied to ethylene thiourea [1].
INTERFERENCES: Compounds containing a thione (C=S) group will complex with the pentacyanoamineferrate reagent and may interfere with the analyte absorbance band at 590 nm. Other compounds that absorb at 590 nm may interfere.
OTHER METHODS: This method was originally designated P&CAM 282 [1], which it replaces.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94 ​TETRAMETHYL THIOUREA: METHOD 3505, Issue 2, dated 15 August 1994 - Page 2 of 4 REAGENTS:
EQUIPMENT:
1. Bromine, Br 2, ACS reagent grade.* 2. Disodium pentacyanonitrosyl ferrate dihydrate (sodium nitroferricyanide; sodium nitroprusside), Na 2Fe(CN) 5NO·2H 2O, ACS reagent grade. 3. Hydroxylamine hydrochloride, NH 2OH·HCl, ACS reagent grade. 4. Sodium bicarbonate, NaHCO 3. 5. Water, distilled or deionized. 6. Complexing reagent (see APPENDIX). 7. Dilute complexing reagent. Mix one volume complexing reagent with two volumes water. Prepare fresh daily. 8. Tetramethyl thiourea (TMTU), reagent grade.* 9. TMTU stock solution, 1000 µg/mL.* Dilute 0.250 g TMTU to 250 mL with distilled water. 10. Calibration stock solution, 20 µg/mL. Dilute 5 mL TMTU stock solution to 250 mL with distilled water.
See SPECIAL PRECAUTIONS.
1. Sampler: glass midget impinger with 15 mL water. 2. Personal sampling pump, 0.2 to 1 L/min, with flexible connecting tubing and splashover protection (empty impinger or glass wool in tube between sampler and pump). 3. Spectrophotometer to operate at 590 nm with matched glass cuvettes, 5-cm optical path length. 4. Analytical balance, 0.1 mg. 5. Mortar and pestle. 6. Test tubes, 20-mL, calibrated at 15.0 mL. 7. Vials, glass, 20-mL, with PTFE-lined screw caps. 8. Beaker, 50-mL. 9. Pipets, adjustable (0.1- to 5-mL), with disposable tips. 10. Volumetric flasks, 25- and 250-mL. 11. Tweezers. 12. Microspatula. 13. Rubber suction bulb. 14. Weighing paper. 15. Filter funnel, stand and filter paper.
SPECIAL PRECAUTIONS: Bromine is very corrosive and causes severe burns; vapors are extremely irritating and toxic. Wear gloves and handle only in a hood. Tetramethyl thiourea is an animal teratogen and carcinogen [3]. Avoid inhalation, ingestion or skin contact. Keep TMTU in a bottle labelled "animal carcinogen" and place the bottle in a resealable thick-walled plastic bag in locked storage.
SAMPLING: 1. 2. 3.
Calibrate each personal sampling pump with a representative sampler in line. Sample at an accurately known flow rate between 0.2 and 1 L/min for a total sample size of 50 to 250 L. Transfer the sample solution to a 20-mL vial for shipment. Collect a high-volume air sample or rafter dust sample. Ship in a glass vial in a separate container.
SAMPLE PREPARATION: 4.
Transfer contents of the vial to a test tube. Add water to the 15-mL mark.
CALIBRATION AND QUALITY CONTROL: 5.
Calibrate daily with at least six working standards over the range 3 to 150 µg TMTU per sample. a. Pipet 0- to 10-mL aliquots of calibration stock solution into clean vials. Bring the total volume to 15 mL with distilled water.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94 ​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 ​TETRAMETHYL THIOUREA: METHOD 3505, Issue 2, dated 15 August 1994 - Page 4 of 4 APPENDIX: PREPARATION OF COMPLEXING REAGENT 1. Weigh 0.500 g Na 2Fe(CN) 5NO·2H 2O in a 50-mL beaker. Dissolve in 10 mL distilled water. 2. Grind together 0.500 g NH 2OH·HCl and 1.00 g NaHCO 3 in a mortar. 3. In a hood, add the ground mixture to the solution from step 1 above. When bubbling ceases, add 0.10 mL bromine. When reaction stops, add ca. 10 mL distilled water. Filter. Rinse beaker with 4 mL distilled water and filter. Transfer filtrate to a 25-mL volumetric flask and dilute with distilled water to the mark. Refrigerate.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94