Determination of Cr(VI) and Cr(III) species in parenteral solutions using a nanostructured material packed-microcolumn and electrothermal atomic absorption spectrometry

A sequential on-line preconcentration and separation system for Cr(VI) and Cr(III) species determination was developed in this work. For this purpose, a microcolumn filled with nanostructured alpha-alumina was used for on-line retention of Cr species in a flow-injection system. The method involves the selective elution of Cr(VI) with concentrated ammonia and Cr(III) with 1mol L(-1) nitric acid for sequential injection into an electrothermal atomic absorption spectrometer (ETAAS). Analytical parameters including pH, eluent type, flow rates of sample and eluent, interfering effects, etc., were optimized. The preconcentration factors for Cr(VI) and Cr(III) were 41 and 18, respectively. The limit of detection (LOD) was 1.9 ng L(-1) for Cr(VI) and 6.1 ng L(-1) for Cr(III). The calibration graph was linear with a correlation coefficient of 0.999. The relative standard deviation (RSD) was 8.6% for Cr(VI) and 6.1% for Cr(III) (c = 10 microg L(-1), n=10, sample volume = 25 mL). Verification of the accuracy was carried out by analysis of a standard reference material (NIST SRM 1643e "Trace elements in natural water") with a reported Cr content of 20.40+/-0.24 microg L(-1). Using the proposed methodology the total Cr content, computed as sum of Cr(III) and Cr(VI), in this SRM was 20.26+/-0.96 microg L(-1). The method was successfully applied to the determination of Cr(VI) and Cr(III) species in parenteral solutions. Concentration of Cr(III) species was found to be in the range of 0.29-3.62 microg L(-1), while Cr(VI) species was not detected in the samples under study.