Two-step procedure for trace element analysis in food via calibration-free laser-induced breakdown spectroscopy

Abstract

Elemental analyses via calibration-free laser-induced breakdown spectroscopy (LIBS) usually suffer low sensitivity due to continuum emission generated by the plasma in local thermodynamic equilibrium. Here we propose a two-step measurement procedure that enables improved sensitivity of calibration-free LIBS. The method consists of recording two emission spectra with different delays between the laser pulse and the detector gate. The short delay is used to probe the plasma in conditions of full local thermodynamic equilibrium in order to measure major and minor element concentrations. To evaluate the concentrations of trace elements, a second measurement with improved limits of detection is performed with a larger gate delay. In that condition, the partial equilibrium state of the plasma enables the quantification of minor and trace elements. Demonstrated via analyses of lyophilized seafood samples, the presented method is suitable for all types of food, and more general for organic materials and all materials that include elements such as carbon, oxygen, nitrogen and hydrogen, for which the equilibrium state is hardly achieved.