Determination of Cd, Cr and Pb in phosphate fertilizers by laser-induced breakdown spectroscopy

A validated method for quantitative determination of Cd, Cr, and Pb in phosphate fertilizers by laser-induced breakdown spectroscopy (LIBS) is presented. Laboratory samples were comminuted and homogenized by cryogenic or planetary ball milling, pressed into pellets and analyzed by LIBS. The experimental setup was designed by using a Q-switched Nd:YAG at 1064nm with 10Hz repetition rate, and the intensity signals from Cd II 214.441nm, Cr II 267.716nm and Pb II 220.353nm emission lines were measured by using a spectrometer furnished with an intensified charge-coupled device. LIBS parameters (laser fluence, lens-to-sample distance, delay time, integration time gate, number of sites and number of laser pulses per site) were chosen after univariate experiments with a pellet of NIST SRM 695 (Trace Elements in Multi-Nutrient Fertilizer). Calibration and validation were carried out with 30 fertilizer samples from single superphosphate, triple superphosphate, monoammonium phosphate, and NPK mixtures. Good results were obtained by using 30 pulses of 50Jcm−2 (750μm spot size), 2.0μs delay time and 5.0μs integration time gate. No significant differences between Cd, Cr, and Pb mass fractions determined by the proposed LIBS method and by ICP OES after microwave-assisted acid digestion (AOAC 2006.03 Official Method) were found at 95% confidence level. The limits of detection of 1mgkg−1 Cd, 2mgkg−1 Cr and 15mgkg−1 Pb and the precision (coefficients of variation of results ranging from 2% to 15%) indicate that the proposed LIBS method can be recommended for the determination of these analytes in phosphate fertilizers. •First LIBS application for quantitative Cd, Cr and Pb determination in fertilizers.•LIBS method was validated for analysis of phosphate fertilizers pressed pellets.•LIBS sample throughput is remarkably better than already existing methods.