Page:NIOSH Manual of Analytical Methods - 5006.pdf/2

CARBARYL: METHOD 5006, Issue 2, dated 15 August 1994 - Page 2 of 4 EQUIPMENT:

REAGENTS: 1. 2. 3. 4.

5. 6.

7.

Carbaryl, reagent grade.* Methanol, absolute.* Methylene chloride, distilled in glass.* 0.1 M KOH in absolute methanol. Dissolve 0.1 mole (5.612 g) in 10 mL methanol in a 1-L volumetric flask; dilute to mark with methanol. Glacial acetic acid.* p-Nitrobenzenediazoniumtetrafluoroborate. Dissolve 25 mg in 5 mL methanol. Add 20 mL glacial acetic acid. Prepare just before use. Keep in an ice bath (4 °C) during use. Discard if the solution becomes deep yellow. Calibration stock solution, 2 mg/mL.* Dissolve an accurately weighed 20-mg portion of Carbaryl in methylene chloride to make 10 mL solution.

See SPECIAL PRECAUTIONS.

1. Sampler: 37-mm filter cassette with 37-mm Type A/E glass fiber filter (Gelman Sciences, or equivalent). NOTE: The filter must be free of organic binders. 2. Personal sampling pump, 1 to 3 L/min, with flexible connecting tubing. 3. Spectrophotometer capable of measuring at 475 nm with matched glass cuvettes (1-cm path length). 4. Vials, scintillation, 25-mL, with PTFE-lined screw caps. 5. Tweezers. 6. Syringe, Luer-Lok glass, 10-mL, with 13-mm stainless steel filter holder and PTFE filters. 7. Shaker, mechanical wrist-action. 8. Flasks, volumetric, 10-mL and 1 L. 9. Pipets, 1-, 2-, 17- and 20-mL with pipet bulb. 10. Syringes or micropipets, 10-, 25- and 50-µL. 11. Timer, 5- and 20-min. 12. Ice bath.

SPECIAL PRECAUTIONS: Carbaryl is a cholinesterase inhibitor; use precautions to prevent skin contamination [5,6]. Methylene chloride is toxic; use only in a hood. Methylene chloride is a suspect human carcinogen. Methanol is flammable and toxic (flash point = 11 °C); use only in a hood. Glacial acetic acid is corrosive; handle only with gloves and facial splash protection.

SAMPLING: 1. 2. 3.

Calibrate each personal sampling pump with a representative sampler in line. Sample at an accurately known flow rate between 1 and 3 L/min for a sample size of 20 to 400 L. Within 1 h after sampling, remove the filter carefully to prevent sample loss and place it in a vial. Handle filter only with tweezers.

SAMPLE PREPARATION: NOTE: Process the samples, blanks, recovery spikes, and working standards in small groups (e.g., two to four) to maintain consistent timing for all analyses. Include a reagent blank in each small group for use in the reference cell of the spectrophotometer. 4. Add 20 mL methanolic 0.1 M KOH to the vial containing the filter. 5. Place the vial on a shaker for 5 min. 6. Transfer 2 mL sample solution to another vial. Start reagent blank at this step. NOTE: For filter samples containing >1 g Carbaryl, dilute the sample solution with methanolic 0.1 M KOH prior to this step. 7. Add 17.0 mL glacial acetic acid to the 2 mL of sample solution and cover vial with a PTFE-lined screw cap. Mix by swirling. 8. Add 1 mL p-nitrobenzenediazonium tetrafluoroborate solution. Mix by swirling. Start a 20-min timer for each vial at this point. 9. Use a syringe fitted with a PTFE in-line filter to transfer the solution from the sample vial to the cuvette. Proceed directly to step 15 after exactly 20 min from step 8. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94