Thermospray methods for rapid, sensitive, and nonchromatographic speciation of chromium oxidation states

A sensitive technique for speciation and quantification of Cr(III) and Cr(V T) has been developed using thermospray (TSP) sample introduction with indu ctively coupled plasma atomic emission spectrometry (ICPAES). For unacidifi ed solutions, the sensitivity for Cr(III) was found to be lower than that f or Cr(VI), The sensitivity for Cr(III) was further depressed to a negligibl e level by adjusting sample and thermospray operating parameters. The low s ensitivity for Cr(III) was thought to result from the precipitation of that species to form Cr(OH)(3), which deposited within the vaporizer. For acidi c solutions (1% v/v HNO3), the sensitivities for both species were essentia lly identical. On the basis of these results, methods for speciation of Cr( III) and Cr(VI) were developed, With samples buffered to pH 4.4, Cr(VI) cou ld be selectively determined, With acidic sample aliquots (1% v/v HNO3), th e total chromium concentration could also be determined, and the Cr(III) co ncentration could be calculated by difference. Parameters affecting Cr(III) sensitivity, such as control temperature, pH, and pump how rate, were stud ied in addition to optimal TSP-ICPAES parameters. The limits of detection ( LODs) for Cr(VI) and for total Cr were 0.47 and 0.61 mu g/L with standard d eviations of 1.5% and 2.0%, respectively. Good accuracy and precision of th e method were demonstrated for analysis of spiked tap water and lake water samples. Mobile phase ion-pairing chromatography with ICPAES detection prov ided comparable results for moderately high concentration samples. Accuracy of measurements for Cr(VI) was within 1% of the certified value for NIST s tandard reference material 2109.