Feasibility of measuring Cr(III) and Cr(VI) in water by laser-induced breakdown spectroscopy using ceramics as the solid support

Laser-induced breakdown spectroscopy (LIBS) is a multi-elemental technique with multiple advantages. However, direct determination in liquid samples is not an easy task since laser water interaction can affect the precision and accuracy of the method and cause loss of sensitivity. To enable LIBS application in liquid sample analysis, some strategies such as liquid-to-solid transfer have been used. This work proposes the quantification of chromium in water samples by LIBS using ceramic as the solid support. Results showed that the ceramic selectively adsorbs Cr(III) species at pH 7 and quantification of Cr(VI) species by LIBS was also possible after reduction of this species to Cr(III) using Fe(II) as the reducing agent. Instrumental parameters were optimized, and the best conditions found included a 65 pm spot size, 430 accumulated pulses with 20 mJ pulse(-1), and 0.75 ms of delay time. Calibration was carried out with synthetic calibration standards prepared by adsorption of increasing concentrations of chromium in ceramic. Tap water samples spiked with 0.9 mg L-1 of Cr(III) and 0.1 mg L-1 of Cr(VI) were analysed by the proposed method and recoveries of 105 +/- 2% and 103 +/- 3% were obtained for Cr(III) and Cr(VI), respectively.