Analysis of time‐resolved laser‐induced breakdown spectra by mean field‐independent components analysis (MFICA) and multivariate curve resolution–alternating least squares (MCR‐ALS)

Abstract

Laser‐induced breakdown spectroscopy (LIBS) is an analytical technique allowing the determination of elemental concentrations in a variety of matrices in the solid, liquid, and gaseous phases. Because of the inherent complexity of the signal and to the high dimensionality of experimental data, chemometrics has been more and more applied in LIBS to perform samples identification or quantitative measurements. But multivariate methods can also be used for the description and physical interpretation of the plasma, particularly to exploit the temporal dimension of the LIBS signal, which is usually neglected in spectrochemical measurements. In this work, time‐resolved spectra of a pure aluminum sample were treated with 2 methods, mean field‐independent components analysis and multivariate curve resolution–alternating least squares, applying non‐negativity constraints for scores and components in both cases. Results obtained were compared with reference univariate measurements of the emission of the species of interest (ions, neutral atoms, and molecules). The interpretation of scores and components provided a physical description of phenomena that take place between species in the plasma, like ionic recombination and molecules formation. Overall, mean field‐independent components analysis and multivariate curve resolution–alternating least squares yield equivalent solutions with our dataset. This new approach is very promising for the treatment of time‐resolved data obtained by LIBS.

Dielectrophoretically Modulated Optical Spectroscopy of Colloidal Nanoparticle Solutions in Microfluidic Channels

“…[46] The second important demonstration in this work is the disentanglement of the extinction spectra of two differently sized gold NPs mixed in the same sample by DEP-modulated spectroscopy. The spectrotemporal data generated through DEP modulation of the NP concentration in the spectroscopic observation volume can be submitted to chemometric multicomponent analysis, [31,32] as demonstrated in the Supporting Information. This offers promising prospects for the in situ analysis of more complex NP samples, such as those encountered during the intermediate steps in the construction of DNA-programmed supercrystals.…”

“…This demonstration of the analysis of a predefined two-component sample is deliberately simple, in order to illustrate the capability of DEP-modulated spectroscopy to perform in situ multicomponent analysis. The data in the form of spectrotemporal matrices generated in these measurements is suitable for analysis using multivariate chemometric methods, [31,32] and further work is being undertaken to exploit this possibility. This is illustrated in Section S7 in the Supporting Information.…”

“…Such multivariate spectrotemporal data are amenable to chemometric analysis that can extract the spectral responses of several subpopulations present in a mixture. [31,32] The DEP-modulated spectroscopy described in this paper is illustrated in Figure 1. It employs a device consisting of a microfluidic channel engraved in an elastomer positioned on top of a substrate of fused silica.…”

“…Such multivariate spectrotemporal data are amenable to chemometric analysis that can extract the spectral responses of several subpopulations present in a mixture. [ 31,32 ]…”

Multiway Calibration Strategies in Laser-Induced Breakdown Spectroscopy: A Proposal

“…Despite their application in several types of data, the use of these algorithms is still quite restricted in LIBS data analysis, − and no study in the literature has reported the modeling of LIBS data by multiway algorithms to achieve the second-order advantage. Thus, this study was focused on the application of the PARAFAC and U-PLS/RBL algorithms to LIBS data to obtain the second-order advantage in two case studies: (i) a reference material of printed circuit board (PCB) from electronic waste and (ii) human mineral supplement samples.…”