MONITORING AND LABORATORY DIVISION
STANDARD OPERATING PROCEDURE

S.O.P. No. MLD 039 - Extraction and Analysis of Hexavalent Chromium by Ion Chromatography

SCOPE

The California Air Resources Board identified hexavalent chromium (Cr+6) as a toxic air contaminant in January 1986.  Chromium is a natural constituent of the earth's crust and is present in several oxidation states. Trivalent chromium (Cr+3) is naturally occurring, environmentally pervasive and a trace element in man and animals.  Hexavalent chromium is anthropogenic from a number of commercial industrial sources.  Hexavalent chromium readily penetrates biological membranes and has been identified as an industrial toxic and cancer causing substance.  Hexavalent chromium is a known inhalation irritant and associated with respiratory cancer.  Hexavalent chromium exposure is primarily associated with the chrome plating and anodizing process and emissions from chromate treated cooling towers.

Hexavalent chromium has been measured in the air at sites in many populated areas of California.  Cellulose filters are exposed to ambient air using a XonTech 920 Toxic Air Sampler.  Samples are taken every 12 days year round.  The analytical procedure for the analysis of hexavalent chromium from exposed filters is described in this document NLB-SOP Method MLD 039.

SUMMARY OF METHOD

MLD Method 039 covers the determination of Cr+6 from bicarbonate impregnated ashless cellulose filters exposed to ambient air and submitted to the laboratory by the site operators.  The filters are extracted in deionized water via sonication for three hours.  The extract is analyzed by ion chromatography using a system comprised of a guard column, an analytical column, a post-column derivatization module, and a UV-VIS detector.  In the analysis procedure, hexavalent chromium exists as chromate due to the near neutral pH of the eluant. After separation through the column, the Cr+6 forms a complex with the diphenylcarbohydrazide (DPC) which can be detected at 520 mm.  The peak analysis is determined using Dionex Peaknet chromatography software version 5.1.