Page:NIOSH Manual of Analytical Methods - 9101.pdf/1

 CHROMIUM, Hexavalent, in Settled Dust Samples

Cr(VI)

MW: 52.00

METHOD: 9101, Issue 1

PURPOSE:

CAS: 18540-29-9

9101

RTECS: GB6262000

EVALUATION: Not Applicable

Issue 1: 15 May 1996

Estimation of soluble hexavalent chromium content of settled dust.

LIMIT OF DETECTION: 1 µg Cr(VI) per sample FIELD EQUIPMENT: 1. Chromate (Diphenylcarbazide reagent) test kit (Chemetrics Chromate Kit, or equivalent) 2. Sulfuric acid, 20% w/v (included in test kit) 3. Extraction solution, 2% NaOH/3% Na2CO3 in deionized water 4. Deionized water 5. Centrifuge tubes, 15-mL, graduated, clear plastic with screw-caps, disposable 6. Spatula, ~0.1 cm3 capacity 7. pH paper PROCEDURE: 1. Place 1 spatula full of dust (approximately 0.1 cm3; the size of a small pea) to be tested in a 15-mL clear plastic centrifuge tube. Add extraction solution up to the 2-mL mark. Cap the tube and shake vigorously. 2. Allow the tube to stand for 10 minutes, or longer, with occasional shaking. NOTE: Gently heating the tube in hot water will increase the sensitivity of the test. 3. Uncap the centrifuge tube and add deionized water to the 7-mL mark. Mix and allow the residue to settle. 4. Decant or pipet approximately 3 mL of the supernatant liquid into a second tube. NOTE: The sample may be filtered, if excessively turbid. 5. Add 9 drops of 20% sulfuric acid (3 drops /mL of decanted liquid), cap the tube, and invert to mix the contents. 6. Check the pH of the liquid with pH paper. If necessary, add 20% sulfuric acid dropwise to bring to pH <1. 7. Follow the instructions for color development. NOTE: For more accurate determination of total hexavalent chromium in the dust, send a sample to the laboratory for analysis by Method 7600 or 7604.

METHOD WRITTEN BY:Mark Millson, MRSB/DPSE, and Peter Eller, QASA/DPSE

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 5/15/96