Determination of Hexavalent Chromium in Industrial Hygiene Samples Using Ultrasonic Extraction and Flow Injection Analysis

Abstract

A simple, fast, and sensitive method was developed for the determination of hexavalent chromium (CrVI) in workplace samples. Ultrasonic extraction in alkaline solutions with 0.05 M (NH₄)₂SO₄–0.05 M NH₃ provided good extraction efficiency of CrVI from the sample and allowed the retention of CrVI on an ion-exchange resin (95%). The CrVI in the sample solution was then separated as an anion from trivalent chromium [CrIII] and other cations by elution from the anion-exchange resin with 0.5 M (NH₄)₂SO₄ in 0.1 M NH₃ (pH 8) buffer solution. The eluate was then acidified with hydrochloric acid and complexed with 1,5-diphenylcarbazide reagent prior to flow injection analysis. By analyzing samples with and without oxidation of CrIII to CrVI using CeIV, the method can measure CrVI and total Cr. For optimizing the separation and determination procedure, preliminary trials conducted with two certified reference materials (CRMs 013–050 and NIST 1633a) and three spiked samples (ammonia buffer solution, cellulose ester filters and acid washed sand) indicated that the recovery of CrVI was quantitative (>90%) with this method. The limit of detection for FIA–UV/VIS determination of the Cr–diphenylcarbazone complex was in the sub-nanogram range (0.11 ng). The technique was also applied successfully to a workplace coal fly ash sample that was collected from a power plant and paint chips that were collected from a heating gas pipe and a university building. The principal advantages of this method are its simplicity, sensitivity, speed and potential portability for field analysis.