Page:NIOSH Manual of Analytical Methods - 6002.pdf/3

 PHOSPHINE: METHOD 6002, Issue 2, dated 15 August 1994 - Page 3 of 4 SAMPLE PREPARATION: 5. 6.

Place front and back sorbent sections in separate 50-mL beakers. Add 10 mL of acidic permanganate solution to each beaker. Place in a water bath maintained at 65 to 70 C for 90 min. 7. Decant the acidic permanganate solution into a 10-mL volumetric flask, and dilute to volume with distilled water. 8. Wash the silica gel twice with 3 mL portions of distilled water and decant the contents into another 10-mL volumetric flask containing 1 mL of ferrous solution. Dilute to volume with distilled water. 9. Add the contents of both 10-mL volumetric flasks (extract and washings) to a 125-mL separatory funnel. 10. Add 7.5 mL of molybdate reagent and 25 mL of toluene-isobutanol solvent to the funnel. Shake funnel for 60 seconds. Let the separatory funnel stand for 60 seconds to allow the aqueous and nonaqueous layers to separate. Discard the lower (aqueous) layer. 11. Pipet 10 mL of the nonaqueous layer into a 25-mL volumetric flask containing 10 mL of the alcoholic sulfuric acid solution.

CALIBRATION AND QUALITY CONTROL: 12. Calibrate daily with at least six working standards. a. Add 10 mL of acidic permanganate solution and 1 mL of ferrous reagent to a 125-mL separatory funnel. b. Add 2 to 400 µL of the standard phosphate solution to cover the range 0.1 to 10 µg of PH 3. Add 8 to 9 mL of water to make the total volume of the solution (permanganate solution, ferrous solution, phosphate solution and water) equal to 20 mL. Prepare at least six calibration standards and a blank containing no phosphate. c. Add 7.5 mL of molybdate reagent and 25 mL of toluene-isobutanol solvent to the funnel. Shake funnel for 60 seconds. Let the separatory funnel stand for 60 seconds to allow the aqueous and nonaqueous layers to separate. Discard the lower (aqueous) layer. (step 10) d. Pipet 10 mL of the nonaqueous layer into a 25-mL volumetric flask containing 10 mL of the alcoholic sulfuric acid solution. (step 11) e. Analyze with samples and blanks (steps 15 through 18). f. Prepare a calibration graph (absorbance versus µg of PH 3 added). 13. Determine desorption efficiency (DE) at least once for each lot of sorbent used for sampling in the range of interest. Prepare three tubes at each of five levels plus three media blanks. a. Remove and discard back sorbent section of a media blank sampler. b. Inject a known amount (20 to 400 µL) of standard phosphate solution directly onto front sorbent section with a microliter syringe. c. Cap the tube. Allow to stand overnight. d. Desorb (steps 6 through 8) and analyze with working standards (steps 15 through 18). e. Prepare a graph of DE vs. µg recovered. 14. Analyze three quality control blind spikes and three analyst spikes to ensure that the calibration graph and DE graph are in control.

MEASUREMENTS 15. Turn on the spectrophotometer and allow sufficient time for warmup. Adjust the wavelength to 625 nm and set the zero and 100% transmittance scale using 5-cm cells filled with distilled water. Check these settings prior to making any measurement to check on instrument drift. NOTE: Steps 16 through 18 must be performed within one minute. 16. Add 0.5 mL (25 drops) of stannous chloride reagent and dilute to volume using alcoholic sulfuric acid solution. Mix thoroughly. 17. Transfer the sample into a 5-cm cell and stopper immediately. 18. Measure the absorbance or transmittance using water as a blank.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition