Field method for the determination of hexavalent chromium by ultrasonication and strong anion exchange solid phase extraction

A simple, fast, sensitive, and economical held method was developed and evaluated for the determination of hexavalent chromium (Cr-VI) in environmental and workplace air samples. By means of ultrasonic extraction in combination with a strong anion-exchange solid-phase extraction (SAE-SPE) technique, the filtration, isolation, and determination of Cr-VI in the presence of trivalent chromium (Cr-III) and potential interferents was achieved. The method entails (1) ultrasonication in basic ammonium buffer solution to extract Cr-VI from environmental matrixes; (2) SAE-SPE to separate Cr-VI from Cr-III and interferences; (3) elution/acidification of the eluate; (4) complexation of chromium with 1,5-diphenylcarbazide; and (5) spectrophotometric determination of the colored chromium-diphenylcarbazone complex. Several critical parameters were optimized in order to effect the extraction of both soluble (K2CrO4) and insoluble (PbCrO4) forms of Cr-VI without inducing Cr-III oxidation or Cr-VI reduction. The method allowed for the dissolution and purification of Cr-VI from environmental and workplace air sample matrixes for up to 24 samples simultaneously in less than 90 min (including ultrasonication). The results demonstrated that the method was simple, fast, quantitative, and sufficiently sensitive for the determination of occupational exposures of Cr-VI. The method is applicable for on-site monitoring of Cr-VI in environmental and industrial hygiene samples.