Multi-energy calibration (MEC) applied to laser-induced breakdown spectroscopy (LIBS)

Abstract

In this study, the multi-energy calibration (MEC) method is applied to solid sample analysis by laser-induced breakdown spectroscopy (LIBS). The MEC method uses only two calibration standards and several atomic emission wavelengths with different sensitivities to determine the analyte concentration in the sample. Both calibration mixtures are prepared using the same amount of sample, which contributes to minimizing matrix effects. The MEC-LIBS method was used to determine Ca, Cu, Fe, Mn and Zn in complex-matrix samples of cattle mineral supplements with an adequate sample throughput (15 samples per h). The limits of detection (LODs) calculated for these elements in the solid sample were 11 g kg⁻¹, 45, 188, 53 and 44 mg kg⁻¹, respectively. For Cu, Mn and Zn, these LODs were approximately 10, 10, and 20 times lower than the minimum level required in a commercial product by the Brazilian legislation. The method's accuracy was evaluated by analyzing five reference materials (RM) of cattle mineral supplements, and by comparing values determined in six commercial samples with results from ICP-OES determinations. No statistically significant difference was observed between MEC-LIBS and RM or ICP-OES-determined values at the 95% confidence level (Student’s t-test, n = 3). LIBS is an inherently atomic-emission-rich technique, which suffers from severe matrix effects. MEC is an efficient matrix-matching method, for which the larger the number of analytical signal sources for an analyte the more precise the results. Therefore, MEC is a highly compatible, complementary approach to LIBS calibration.