CHROMIUM, HEXAVALENT
Cr(VI)
MW: 52.00 (Cr); 99.99 (CrO3)
METHOD: 7600, Issue 2
7600
CAS: 18540-29-9
EVALUATION: FULL
OSHA : 0.1 mg/m 3 (as CrO 3) NIOSH: 0.001 mg/m 3/10 h; carcinogen ACGIH: 0.050 mg/m 3 (as Cr, soluble); some insoluble chromates are human carcinogens
RTECS: GB6262000 Issue 1: 15 May 1989 Issue 2: 15 August 1994
PROPERTIES: oxidizing agent
SYNONYMS: vary depending upon the compound
SAMPLING
MEASUREMENT
SAMPLER:
FILTER (5.0-µm PVC membrane)
TECHNIQUE:
VISIBLE ABSORPTION SPECTROPHOTOMETRY
FLOW RATE:
1 to 4 L/min
ANALYTE:
CrO 42--diphenylcarbazide complex
VOL-MIN: -MAX:
8 L @ 0.025 mg/m 3 400 L
EXTRACTION SOLUTION:
0.5 N H 2SO 4 or 2% NaOH3% Na 2CO 3 (see steps 4 and 5)
SHIPMENT:
routine WAVELENGTH:
540 nm; 5-cm path length
CALIBRATION:
standard solutions of K 2CrO 4 in 0.5 N H 2SO 4
RANGE:
0.2 to 7 µg per sample
ESTIMATED LOD:
0.05 µg per sample
PRECISION (Sr):
0.029 @ 0.3 to 1.2 µg per sample [3]
SAMPLE STABILITY:
analyze within 2 weeks [1]
FIELD BLANKS:
2 to 10 field blanks per set
ACCURACY RANGE STUDIED:
0.05 to 0.2 mg/m 3 [2] (22-L samples)
BIAS:
- 5.48%
ˆ ): 0.084 [2] OVERALL PRECISION (S rT ACCURACY:
± 18.58%
APPLICABILITY: The working range is 0.001 to 5 mg/m 3 for a 200-L air sample. This method may be used for the determination of soluble Cr(VI) (using 0.5 N H 2SO 4 as extraction solution or insoluble Cr(VI) (using 2% NaOH - 3% Na 2CO 3) [3].
INTERFERENCES: Possible interferences are iron, copper, nickel, and vanadium; 10 µg of any of these causes an absorbance equivalent to about 0.02 µg Cr(VI) due to formation of colored complexes. Interference due to reducing agents (e.g., Fe, Fe ++ ) is minimized by alkaline extraction (step 5).
OTHER METHODS: This method combines and replaces P&CAM 169 [1], S317 [2] and P&CAM 319 [3]; the Cr(VI) criteria document [4] contains a method similar to P&CAM 169. Method 7604 is also specific for hexavalent chromium, using ion chromatography for measurement.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
