CH RO MIUM , HEX AVA LEN T: Me thod 7605, Issue 1 dated 15 M arch 200 3 - Page 2 o f 5 REAGENTS:
EQUIPMENT:
1. Sulfuric ac id, con c. (98 % w/w).* 2. Am m onium hydroxide, conc. (28 %).* 3. Am monium sulfate monohydrate, reagent grade. 4. Sodium carbonate, anhydrous. 5. Sodium hydroxide, reag ent grade .* 6. Me than ol, HP LC grad e.* 7. 1,5-Diphenylcarbazide, reagent grade. 8. Potassium dichromate or potassium chromate.* Dry at 100 °C and store in a desiccator. 9. Post-C olum n Derivatizing Reage nt: Diphenylcarbazide solution. Dissolve 500 mg 1,5-diphenylcarbazide in 100 mL HPLC-grade methanol. W hile stirring, add 500 mL water containing 28 mL of conc. sulfuric acid. Dilute to a final volume of one liter with water. This reagent is stable for 4 - 5 days. Prepare in one-liter quantities as needed. 10. Cr(VI) standard, 1000 :g/mL. Dissolve 2.829 g po tass ium dichrom ate in d eionized water to m ak e one liter, or use com m ercially ava ilable solution. NOT E: 3.731 g K 2CrO 4 can also be used. 11. Calibration stock solution, 1.0 :g/m L. Dilute 1000 :g/m L Cr(VI) s tand ard 1 :100 0 with deionized water. 12. Filter extraction solution, 2% NaOH-3% Na 2CO 3. Dissolve 20 g NaOH and 30 g Na 2CO 3 in deionized water to mak e one liter of solution. 13. Eluent (mobile phase); 250 mM amm onium sulfate/200 mM amm onium hydroxide. Dissolve 33 g am m onium sulfate in approximately 500 mL distilled water and add 6.5 m L co nc. am m onium hydroxide. Dilute to one liter with distilled water and mix. 14. Nitrogen, pre-purified.
1. Sam pler: polyvinyl chloride (PVC) filter, 5.0-:m pore size , 37-m m diam ete r in polystyrene cas sette filter holder. NOTE: Som e PVC filters promote reduction of Cr(VI). Check each lot of filters for recovery of Cr(VI) standard. 2. Personal sa m pling pum p, 1 to 4 L/m in, with flexible connecting tubing. 3. Vials, scintillation, 20-mL glass, PTFE-lined screw cap.** 4. Forceps, nonmetallic. 5. Gloves, polypropylene or latex. 6. Liquid chromatography apparatus consisting of au tosa m pler; pu m p; NG1 (Dionex Corp.) or equivalent guard column; HPIC-AS7, 4 x 250-mm (Dionex Corp.) separator column (or equivalent); post-column rea gent delivery system, 2.2-m PEEK™ tubing m ixing/re action loop w ith 1 m in a wa ter ba th at 32 °C ± 3 °C ; and UV detector. 7. Filtration apparatus, PTFE luer-lock filter (Gelman IC Acrodisc or equivalent)/syringe. 8. Bea kers , borosilicate, 50 -m L.** 9. W atch glass.** 10. Volum etric flasks , 25-, 100-, and 10 00-m L.** 11. Oven at 107°C, not to exceed 115°C. NOTE: H ot plate can be used. A n ultrasonic bath can be used instead of oven or hot plate. 12. Micropipettes, 10-:L to 0.5-mL. 13. Pipettes, T D 5-m L.** 14. Bagge d refrigera nt.
- Clean all glassware with 1:1 HNO 3:H 2O and
rinse thoroughly before use.
- See SPECIAL PRECAUTIONS
SPECIAL PRECAUTIONS: Many chrom ate com pounds are suspected hum an carcinogens [8]. All sample preparation should be performed in a hood. Concentrated acids and bases are toxic and corrosive. W hen working with concentrated acids and bases, wear protective clothing. Amm onium hydroxide is a respiratory irritant. Methanol is flamm able and toxic.
SAMPLING: 1. Calibrate the 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 1 to 4 L/m in for a sam ple size of 1 to 400 L. Do not excee d 1 m g total dust loading on the filter.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition
