Development and evaluation of a method for hexavalent chromium in ambient air using IC-ICP-MS

The challenge to quantify ambient airborne Cr(VI) comes from three interrelated issues: sensitivity, selectivity, and stability. In this study, we developed a sensitive and reliable method to measure Cr(VI) in ambient air by optimizing each step involved in measurement. The enriched isotope was employed to determine the recovery and inter-conversion between Cr species (valences) during sampling, sample storage and chemical analysis. Specifically, ambient particles were collected on a 47-mm mixed cellulose ester (MCE) filter that was pre-cleaned by HNO 3 (10% v/v) and pre-treated with NaHCO 3 (2 g L −1). 53Cr(VI) and 50Cr(III) isotopes (4 ng each) were spiked on the filter either before or after sampling. Samples were subsequently sonicated in 5 mL HNO 3 (pH 4) solution at 60 °C for 40 min, and separated and analyzed for Cr(VI) and Cr(III) by IC-ICP-MS. The method detection limit was 0.08 ng m −3 and the percent difference was