Page:NIOSH Manual of Analytical Methods - 7703.pdf/3

 CHROMIUM, HEXAVALENT by portable VIS: METHOD 7703, Issue 1, dated 15 March 2003 - page 3 of 5 SAMPLING: 1. Calibrate each personal sampling pump with a representative sampler in line. 2. Sam ple at a n ac curately kn own flow ra te in the rang e of 1 to 4 L/m in for a sam ple size of 10 0 to 1000 L. Do not exceed 2 mg of particulate loading on the filter. Label the filter cassette. 3. Don a fresh pair of disposable plastic or latex gloves (to prevent sam ple contam ination). 4. W ith P TFE -coated forceps, rem ove filters from cassette s after of com pletion of s am pling, and place in separate plastic 15-mL centrifuge tubes for subsequent sample preparation. Discard cellulose backup pads and gloves.

SAMPLE PREPARATION: 5. Add 10 mL of extraction solution (weak buffer) to each 15-mL centrifuge tube containing the filter sample. Ensure that the filter is covered by the extraction solution. If necessary, push the filter down with a clean glass or plastic rod to imm erse the entire filter. Cap and label the tubes. 6. Place sample tubes in the ultrasonic bath (sonicator). The water level in the bath should be higher than the liquid level in the centrifuge tube. Sonicate for 30 minutes. NOTE: Num erous centrifuge tubes containing sample filters can be subjected to sonication at one time, depen ding upo n the size of the ultrasonic ba th. Ensure that the ba th is wa rm (but < 40 oC). 7. Set up the solid phase extraction manifold. a. Pla ce disposable solid phase extractio n (S PE ) cartridges in each port, and place scintillation vials beneath the cartridges. Label the cartridges. b. Attach the vacuum pum p to the SPE m anifold. c. To condition SPE cartridges, pipet 3 mL of methanol into each cartridge, and evacuate. Then pipet 3 m L of e xtrac tion so lution into eac h ca rtridge, and evacua te. Re pea t. 8. Extract Cr[VI] from sam ple solution. a. Pipet 3 to 5 mL of each ultrasonicated sample solution from the centrifuge tubes into the disposa ble SPE cartridge. D ispose o f the pipet tip. b. Adjust the vacuum to obtain an extraction rate of about one drop per second (approximately 8" Hg; no more than 10" Hg). Manually tighten cartridges by twisting, if necessary, to slow down the rate of liquid dripping. NOT E 1: For sam ples in the which the expected Cr[VI] concentration is high, sma ller aliquots (1 to 2 mL) should be dispensed into the SPE cartridges to prevent breakthrough. High con cen tration o f Cr[VI] can be ass ess ed visually by its ora nge color. NOT E 2: For samples having low Cr[VI] concentration, additional 3 to 5 mL aliquots of ultrasonicated sam ple solution can be loaded onto SP E c artridges (ste p 8.a.). In th is m ann er, the cartridge c an b e us ed to prec onc entra te Cr[VI]. c. W hen it appe ars the solution has pas sed throu gh a ll the cartridges, increas e the vacuum to ensure that all solution passes through the cartridges. This step selectively binds Cr[VI] to the stationary phase of each cartridge. d. To remove residue of Cr[III] and other potential interferences, turn the vacuum down (by turning counterclockwise) to 0" Hg. Add 1 mL distilled or deionized water to each cartridge, adjust vacuum to 1 drop p er se con d (~8 " Hg), then redu ce to 0" wh en c om pleted . e. Rem ove the scintillation vials beneath the cartridges and discard. NOTE: Th is solution conta ins un wan ted fra ctions that shou ld con tain no Cr[V I]. 9. Place clean, labeled scintillation vials beneath correct cartridges in the SPE manifold. a. Add 9 mL of the elution solution (elution buffer) to each cartridge to elute Cr[VI], and repeat steps 8.b. through 8.d. b. Rem ove the scintillation vials, and cap them. Dispose of the used SPE cartridges. NOTE: The scintillation vials now contain extracted and isolated Cr[VI], which is ready for subsequent analysis. 10. Uncap each scintillation vial conta ining extracted and isolated Cr[VI], an d add 100 µL H cl. 11. Add 2 m L DPC com plexation s olution, reca p vials, a nd m ix thoroug hly. Allow to s tand for at lea st 5 m in for com plete c olor developm ent.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition