Page:NIOSH Manual of Analytical Methods - 3505.pdf/2

 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