Despite the intrinsic elemental analysis capability and lack of sample preparation requirements, laser-induced breakdown spectroscopy (LIBS) has not been extensively used for real world applications, e.g. quality assurance and process monitoring. Specifically, variability in sample, system and experimental parameters in LIBS studies present a substantive hurdle for robust classification, even when standard multivariate chemometric techniques are used for analysis. Considering pharmaceutical sample investigation as an example, we propose the use of support vector machines (SVM) as a non-linear classification method over conventional linear techniques such as soft independent modeling of class analogy (SIMCA) and partial least-squares discriminant analysis (PLS-DA) for discrimination based on LIBS measurements. Using over-the-counter pharmaceutical samples, we demonstrate that application of SVM enables statistically significant improvements in prospective classification accuracy (sensitivity), due to its ability to address variability in LIBS sample ablation and plasma self-absorption behavior. Furthermore, our results reveal that SVM provides nearly 10% improvement in correct allocation rate and a concomitant reduction in misclassification rates of 75% (cf. PLS-DA) and 80% (cf. SIMCA)-when measurements from samples not included in the training set are incorporated in the test data – highlighting its robustness. While further studies on a wider matrix of sample types performed using different LIBS systems is needed to fully characterize the capability of SVM to provide superior predictions, we anticipate that the improved sensitivity and robustness observed here will facilitate application of the proposed LIBS-SVM toolbox for screening drugs and detecting counterfeit samples as well as in related areas of forensic and biological sample analysis.

Optimization of temporal window for Calibration-Free Laser Induced Breakdown Spectroscopy (CF-LIBS) using single transition of the constituent elements.

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Laser-induced copper plasma is investigated experimentally and theoretically. Laser-induced plasma on the surface of the copper sample is generated by focusing a nanosecond (∼7 ns) laser pulse. The experiment is performed in the ambient atmosphere at three different focal positions (lens to sample distances). The main objective of this work is to investigate the effect of the focal position on the radiation decay constant of the plasma. Experimental data are used for estimating the plasma temperature, electron density, ablated mass, and radiation decay constant. It is shown that these parameters essentially depend on the focal position with respect to the sample surface. The theory of relaxation of radiation is considered for the kinetic evolution of the plasma. The results of the theory are compared with the obtained experimental data.

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