Separation and determination of Cr(iii) and Cr(vi) in aqueous solution using laser-induced breakdown spectroscopy coupled with resin substrate preconcentration

The direct determination of analytes in aqueous solution using laser-induced breakdown spectroscopy (LIBS) has several difficulties, including low spectral signal, poor stability, and rapid quenching of the plasma. In this study, chelate resin and anion exchange resin were used to adsorb the chromium ions Cr(iii) and Cr(vi) from the liquid onto a solid substrate, thus avoiding the drawbacks of liquid analysis with LIBS. Cr(iii) and Cr(vi) were separated by selective adsorption on these two distinct resins. The following analytical parameters were optimized: flow rate of sample solution for preconcentration on the resins, laser pulse energy, and integral delay time of the ICCD detector. Calibration curves displayed excellent linearity, with correlation coefficients of 0.994 for Cr(iii) and 0.993 for Cr(vi). The analytical limits of detection (LODs) were 0.088 mg L-1 for Cr(iii) and 0.27 mg L-1 for Cr(vi), and were lower than those in most previous studies. The relative uncertainty of Cr(iii) in single and mixed solutions ranged from 2.50% to 4.25% and 4.75% to 14.0%, respectively, and that of Cr(vi) ranged from 2.88% to 7.67% and 11.5% to 13.9%, respectively. Recovery from natural spring water was 92.50-99.86% for Cr(iii) and 97.70-98.75% for Cr(vi). Recovery from sewage wastewater using this method was 99.80% for Cr(iii) and 107.6% for Cr(vi). These results show that this method can be successfully applied to the determination and separation of chromium ions in aqueous solution.