Calibration strategies to overcome matrix effects in laser-induced breakdown spectroscopy: Direct calcium and phosphorus determination in solid mineral supplements

Abstract

Several calibration strategies were evaluated for Ca and P determination in mineral supplements for cattle using direct solids analysis by laser-induced breakdown spectroscopy (LIBS). Matrix-matching calibration (MMC), internal standardization (IS), multi-energy calibration (MEC) and a new calibration strategy named one-point gravimetric standard addition (OP GSA) were evaluated in order to correct for matrix effects normally observed in measurements by LIBS. The MEC and OP GSA were the calibrations strategies that led to better recoveries for Ca (86–109% MEC and 72–117% OP GSA) and for P (80–108% MEC and 82–111% OP GSA). Applying both strategies only two calibration standards were used and the presence of the sample itself in the calibration standards contributes for correcting for matrix effects. For MEC several atomic emission wavelengths with different sensitivities were used to determine the analyte concentration in the sample and also to identify spectral interferences that showed up as outliers points in the calibration curve. However, for OP GSA, only one atomic emission wavelength is used to build the calibration curve, simplifying data handling when compared to the MEC method. A statistical evaluation using student's t-test showed that there is no significant difference at 95% confidence level between the value determined and the reference value (reference material or ICP OES data) when using MEC or OP GSA calibrations. Both MEC and OP GSA can be used for direct determination of Ca and P in mineral supplements for cattle allowing proper quality control in order to support the Brazilian Regulation Normative Instruction No. 12, 2004.