CHROMIUM, HEXAVALENT, by Field-Portable Spectrophotometry Cr[VI]
MW: 52.00 (Cr) 99.99 (CrO3 )
METHOD: 7703, Issue 1
CAS: 18540-29-9
EVALUATION: FULL
OSHA : C 0.1 mg/m3 (as CrO3 ) NIOSH: 0.001 mg/m3 /10 h (carcinogen) ACGIH: 0.050 mg/m3 (water-soluble compounds); 0.010 mg/m3 (insoluble compounds)
PROPERTIES:
7703
RTECS: GB6262000 Issue 1: 15 March 2003
oxidizing agent
SYNONYMS: vary depending on the compound; chromate commonly used SAMPLING SAMPLER:
FILTER (5.0-µm PVC membrane [1,2]; 0.8-µm MCE or 1.0-µm PTFE acceptable for field analysis [3]).
FLOW RATE:
1 to 4 L/min
VOL-MIN: -MAX:
10 L (2 L/min for 5 min) 1200 L (2 L/min for 600 min)
SHIPMENT:
refrigerant pack at 4 ± 2 o C (optional)
SAMPLE STABILITY:
BLANKS:
MEASUREMENT TECHNIQUE:
FIELD-PORTABLE VISIBLE SPECTROPHOTOMETRY
ANALYTE:
Cr[VI] - diphenylcarbazone complex
EXTRACTION:
10 mL 0.05 M (NH4 )2 SO4 / 0.05 M NH4 OH (pH = 8 + 0.5), ultrasonic extraction 30 min
Cr[VI] ISOLATION:
Strong anion exchange solid phase extraction
analyze within 24 hours; if applicable, keep samples at 4 ± 2 o C.
ELUTION SOLUTION:
0.5 M (NH4 )2 SO4 / 0.1 M NH4 OH
One per twenty field samples, minimum of 2 per set.
WAVELENGTH:
540 nm, 1-cm path length
CALIBRATION:
standard solutions of K2 CrO4 in 0.5 M (NH4 )2 SO4 / 0.1 M NH4 OH
RANGE:
1 to 400 µg per sample
ACCURACY RANGE STUDIED:
0.045 to 1146 µg/m3 (~20 to ~200-L samples) [3, 4]
BIAS:
-1.00% [3]
ESTIMATED LOD: 0.08 µg Cr[VI] per sample [3] PRECISION ( ÿ r ): OVERALL PRECISION ( Ö r T ):
0.080
ACCURACY:
+ 15.7%
0.035 @ 3 to 400 µg per sample [3]
APPLICABILITY: The working range is (at least) 0.05 to 1000 µg/m3 for a 200 to 500-L air sample. This method may be used for the determination of soluble forms of Cr[VI]. Insoluble Cr[VI] requires modification of the method using ultrasonic extraction with carbonate buffer. INTERFERENCES: Interferences from reducing agents such as Fe2 + are minimized to the extent possible by the alkaline ultrasonic and solid phase extraction procedures. Interferences from other metal cations are eliminated by solid phase extraction [5]. Some reduction can occur on the filter during sampling, and is usually due to the presence of Fe2 + , organic material, and/ or acidic conditions [6]. Reduction of Cr[VI] can occur over time on any filter type, and is especially problematic on MCE filters [7]. However, the use of MCE and PTFE filters has been found to be acceptable for field use, where performance has been found to be equivalent to that of PVC filters [3]. During ultrasonic extraction, oxidation of Cr[III] in solution to Cr[VI] is prevented by the use of an ammonium buffer [8]. OTHER METHODS: This method is designed to be used in the field, but can also be utilized in the fixed-site laboratory. It is an alternative to laboratory methods such as NIOSH method 7605 or OSHA method ID-215 (hot plate digestion and ion chromatography). NIOSH method 7600 is a similar procedure, but no separation step is used. A field method not involving a Cr[VI] isolation step, MDHS method 61, has been promulgated by the British Health and Safety Executive [9].
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition
