Page:NIOSH Manual of Analytical Methods - 7703.pdf/1

 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