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In this work, a solid phase microextraction procedure, denoted as Thin Film Microextraction (TFME), was combined with Laser-induced Breakdown Spectroscopy for the detection of several analytes in aqueous solutions (Cu, Cr, Ni and Pb). The adsorbent films, consisting of a thin layer of graphene oxide deposited on glass substrates, were generated by using the electrospray deposition technique (ESD). Several parameters affecting the quality and shape of the films resulting from the ESD process were studied, and the morphology and adsorption capacity of the films were evaluated. The generated films were used for extraction of the target analytes from aqueous solutions and, after extraction, the analytes-enriched adsorbents were analysed by LIBS without the need of any desorption or elution step. In order to assess the analytical capability of the TFME-LIBS procedure, different analytical figures of merit of the proposed TFME-LIBS methodology were evaluated. The obtained limits of detection were 14 μg kg−1 for Pb and 15 μg kg−1 for the rest of the tested analytes. Measurement repeatability was better than 4% RSD at low concentration level (20 μg kg−1) but deteriorated by increasing the concentration level at 100 μg kg−1, with %RSD ranging from 3.6% (Cr) to 24% (Pb). Method trueness, evaluated from the analysis of a real sample of bottled water, led to recovery values in the range 85%–106%. This work was supported by the Spanish Ministry of Economy and Competitiveness [CTQ2016-79991-R], the Regional Government of Valencia (Spain) [PROMETEO/2013/038 and PROMETEO/2018/087]; and the University of Alicante [UAUSTI17-04 and UAUSTI18-04]. L. Ripoll is grateful to the Ministry of Economy and Competitiveness for her PhD fellowship (FPI-MICINN (BES-2012-058759)).

Graphical abstract, Highlights • Characterization of LIP by the Columnar Density Saha-Boltzmann (CD-SB) plot. • Use of strongly self-absorbed lines to calculate the plasma temperature. • Temporal evolution of the plasma temperature by CD-SB plot. • CD-SB plot as a promising method to obtain plasma temperature at later times. • CD-SB plot does not require the calibration of the detection system., In exploiting the analytical capabilities of plasma-based spectroscopy method, the evaluation of plasma parameters, particularly the plasma temperature, is a crucial step. In this work, a modified Saha-Boltzmann plot, which uses the columnar densities of atomic and ionic ground levels, is utilized to calculate the plasma temperature in a laser-induced plasma from an aluminum alloy target. The columnar densities are here calculated by quantifying the self-absorption of resonance lines. It is demonstrated that this is a promising method for accurate determination of plasma temperature. To validate the capability of this technique, plasma emission is measured at different gate delay times. For each delay, excitation temperature is calculated both by the conventional Saha-Boltzmann plot (by using the excited states) and by exploiting the new Columnar Density Saha–Boltzmann (CD-SB) plot. The results suggest that at later times of the plasma evolution, the CD-SB plot can be more suitable for the determination of plasma temperature than conventional Saha-Boltzmann plot. These findings provide a new approach for physical characterization of plasmas and give access to a wealth of information about the state of plasma.

An analytical methodology based in the combination of Thin Film Microextraction with Laser-induced Breakdown Spectroscopy (TFME-LIBS) was investigated, for the first time, for detection of Cu, Cr, Ni and Pb in aqueous solutions. In this methodology, the analytes were extracted in a thin film of adsorbent material deposited on a solid support, which was introduced in the sample to analyse. After extraction, the analytes retained in the adsorbent were analysed by LIBS. In order to obtain adsorbent films useful for the microextraction step, two different experimental procedures for film generation, denoted as Drop Casting Deposition and Mould Deposition, were evaluated. In both cases, graphene oxide was used as adsorbent material. The mould deposition procedure was found to produce more homogeneous graphene oxide layers, leading to more uniform distribution of the adsorbed analytes on the graphene oxide surface. Experimental parameters affecting the TFME procedure, such as the adsorbent amount and extraction time, were studied. Under optimum microextraction conditions, the analytical figures of merit of the proposed TFME-LIBS method were evaluated, leading to limits of detection ranging from 41 μg kg−1 and 52 μg kg−1. Method trueness, evaluated from the analysis of a real sample of bottle water, led to recovery values about 70%, indicating the existence of strong matrix effects probably due to the presence of major cations in the bottle water. After 50% dilution of the sample with deionized water, recoveries values improved to 100%–108%. This work was supported by the Spanish Ministry of Economy and Competitiveness [CTQ2016-79991-R], the Regional Government of Valencia (Spain) [PROMETEO/2013/038 and PROMETEO/2018/087]; and the University of Alicante [UAUSTI17-04 and UAUSTI18-04]. L. Ripoll is grateful to the Ministry of Economy and Competitiveness for her PhD fellowship (FPI-MICINN (BES-2012-058759)).

In this chapter we will discuss fundamental concepts and applications of self-calibrated methods for quantitative analysis by laser-induced breakdown spectrometry (LIBS). The hypotheses at the basis of the classical calibration-free (CF)-LIBS method (Ciucci et al., 1999) [8] will be critically revised and the evolution of the technique in the last two decades will be discussed, distinguishing between minor improvements or, in most cases, simple implementations of the technique and new approaches that are effectively different from the classical approach. In particular, among the alternative calibration-free methods discussed, particular attention will be given to the Monte Carlo LIBS method and the recently proposed extended C-sigma methods, which are particularly promising alternatives to standard CF-LIBS. At the end of the chapter, a very short review of the main applications of the CF-LIBS methods will be presented, with particular attention to applications where the availability of matrix-matched standards, needed for building uni- or multivariate calibration curves, are scarce (health, environment, space research, etc.).

The introduction of multivariate calibration curve approach in Laser-Induced Breakdown Spectroscopy (LIBS) quantitative analysis has led to a general improvement of the LIBS analytical performances, since a multivariate approach allows to exploit the redundancy of elemental information that are typically present in a LIBS spectrum. Software packages implementing multivariate methods are available in the most diffused commercial and open source analytical programs; in most of the cases, the multivariate algorithms are robust against noise and operate in unsupervised mode. The reverse of the coin of the availability and ease of use of such packages is the (perceived) difficulty in assessing the reliability of the results obtained which often leads to the consideration of the multivariate algorithms as ‘black boxes’ whose inner mechanism is supposed to remain hidden to the user. In this paper, we will discuss the dangers of a ‘black box’ approach in LIBS multivariate analysis, and will discuss how to overcome them using the chemical-physical knowledge that is at the base of any LIBS quantitative analysis.

In this work, the possibility of using Laser-Induced Breakdown Spectrometry (LIBS) combined with liquid–liquid microextraction techniques is evaluated as a simple and fast method for trace elemental analysis. Two different strategies for LIBS analysis of manganese contained in microdroplets of extraction solvent (Triton X-114) are studied: (i) analysis by direct laser irradiation of microdroplets; and (ii) analysis by laser irradiation of microdroplets dried on metallic substrates (surface-enhanced LIBS — SENLIBS). Experiments were carried out using synthetic samples with different concentrations of manganese in a 10% w/w Triton X-114 matrix. The analysis by direct laser irradiation of microdroplets showed low precision, sensitivity and poor linearity across the concentration range evaluated (R2 < 0.95). On the other hand, the SENLIBS method of analysis improved the sensitivity, the precision and the linearity of the calibration curve with respect to the direct analysis of microdroplets. In comparison with experimental results obtained by direct analysis, SENLIBS also allowed several replicate measurements to be carried out in a single microdroplet. The limit of detection obtained was 6 μg g− 1 of Mn. This research has been supported by the Spanish Government (project no. CTQ2008-06730-C02-01), the regional Government of Valencia (project nos. ACOMP/2009/144 and COMP/2010/047) and the University of Alicante (project no. INV09-39).