CHROMIUM, HEXAVALENT by portable VIS: METHOD 7703, Issue 1, dated 15 March 2003 - page 2 of 5 EQUIPMENT:
REAGENTS: 1. 2. 3. 4. 5. 6. 7. 8.
Am monium sulfate, reagent grade. Am monium hydroxide, reagent grade. W ater, distilled or deionized. Hydrochloric acid (37%), reagent grade. Aceton itrile, reage nt gra de.* 1,5-Diphenylcarbizide (DPC), reagent grade. Methanol, reagent grade. Extraction solution (extraction buffer): 0.05 M (NH 4) 2SO 4 / 0.05 M NH4OH, 1 L, aqueous in distilled or deionized water. NOTE: Modification of method by using carbonate buffer (e.g., sodium carbonate) is required for extraction of insoluble Cr[VI]. 9. Elution solution (elution buffer): 0.5 M (NH 4) 2SO 4 / 0.1 M NH 4OH, 250 m L, in distilled or deionized water. 10. Cr(VI) stand ard (as p otas sium chro m ate),* 1000 µg/mL. 11. Ca libration s tock solution, 100 µg /m L: Dilute 100 0 µg /m L Cr(VI) s tand ard 1 :10 w ith extraction buffer. (Solution is stable for a m onth .) 12. Diphenylcarbazide complexation solution (20 mM): Measure 0.48 g DPC powder and place in a 100-mL volumetric flask. Add ~80 m L of a ceto nitrile and dissolve the DPC . Bring up to the mark with additional aceto nitrile and m ix thoroughly.
- See SPECIAL PRECAUTIONS
1. Sam plers: 5-µm pore size polyvinylchloride (PVC), 0.8-µm pore size mixed cellulose ester (MCE), or 1.0-µm polytetrafluoroethylene (PTFE) filters, 37-m m diam ete r, with backu p pads, in polystyrene cassette filter holder, 2- or 3-piece. NOTE: MCE filters, and some PVC filters, promote reduction of Cr[VI] on a timescale of a few days. However, either filter type is acceptable for field use if the samples are to be analyzed within 24 h of co llection. 2. Personal sa m pling pum p, 1 to 4 L/m in, with flexible connecting tubing. 3. Ultrasonic bath (sonicator), 100 W minimum power. 4. Solid phase e xtrac tion m anifold, 12- o r 24-port. 5. Portable vacuum pum p with pressure metering valve. 6. Portable visible spec troph otom eter, s am ple pa th length 1 cm with Quartz cuvette(s). 7. Strong anion exchange solid phase extraction (SP E) cartridges, 10-m L, disp osa ble; loaded with 500 or 1000 mg quaternary amine bonded silica, capacity ~1 meq/g. 8. Pipettors, m ech anical, ass orted volum es (e .g., 1 to 10 mL) with disposable tips. 9. Micropipettors, mechanical, assorted volumes (e.g., 10 to 100 µL) with disposable tips. 10. Centrifuge tubes, plastic, 15-mL, with screw caps. 11. Scintillation vials, 20-mL, glass, with PTFE-lined screw caps. 12. Assorted beakers (and possibly Erlenmeyer flasks), various volumes. 13. Volumetric flasks, 25-, 100-, 250-, and 1000-mL. 14. Forceps, PTFE-coated. 15. Glass or plastic rods. 16. Disposable gloves, plastic or latex. 17. Laboratory wipes. 18. Portable power ge nerator (if necessary). NOTE: If no power supply is available at the field site, electric power can be provided by means of a portable, gasoline (or othe r) genera tor.
SPECIAL PRECAUTIONS: Hexavalent chro m ium is a hum an re spiratory carcinogen [10]. Efforts m ust be m ade to pre vent aerosolizin g chrom ate -contain ing com pounds and solution s. A ll sam ple preparation should be carried out in a well-ventilated area (vacuum hood preferable); forced ventilation should be used if n o hood is available. Ac eto nitrile solution s are flam m able m ust be handled carefully, i.e., wearing of im perm eable gloves, a nd avoidance of vapors. T o the exte nt possible, solution s should be prepared in the laboratory before taking them to the field.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition
