1. IntroductionLaser-induced breakdown spectroscopy (LIBS) has become anattractive and popular technique in the field of chemical analysis.In addition to the positive characteristics of solid sampling techniques,LIBS allows simultaneous multi-element determinationand in situ analysis, since portable instruments are available. Forall these reasons, LIBS has been considered a possible future ‘superstar’of spectrometric techniques [1]. Despite all its advantages,LIBS has some limitations: sensitivity and precision are poor sincea very low sample mass size is commonly used (<10 lg). A strongmatrix interference caused by the complex nature of the laser–sample interaction processes is observed, which depends uponboth the laser characteristics, the sample material properties andplasma–particle interaction processes [2]. For these reasons, quantitativeanalysis is not an easy task and has been considered the‘‘Achilles heel’’ of the LIBS technique. Efforts have been made toallow the application of LIBS for quantitative purposes.One of the most important and difficult issues in LIBS analysis isthe calibration; this is due to the non-availability of appropriatesolid standards and strong matrix effects. Calibration-freelaser-induced breakdown spectrometry (CF-LIBS) has beendeveloped to overcome the matrix interference. This approachtakes the matrix into account as a part of the analytical problemand quantification is performed considering the intensity of emissionlines based on plasma properties, such as electronic densityand temperature. It has been successfully applied in the analysisof metallic alloys [3] and other applications are still underinvestigation.Another possibility is the use of matrix-certified referencematerials (CRMs). There are more than 22,000 commercially availableCRMs; however, materials of the same matrix containing differentconcentrations of the same analyte are practicallynon-existent. Moreover, most of them are not homogeneous forthe sample mass size commonly practiced in LIBS analysis [4,5].In considering this difficulty, many authors have proposed newstrategies for method calibration. Godoi et al. [6] proposed theuse of polymers spiked with Ba, Cd, Cr and Pb for the analysis oftoys, while Carvalho et al. [7] proposed the use of pharmaceuticaltablets mixed with a cellulose binder in different proportions toperform the method calibration. To measure some elements inwood samples, Chen et al. [8] spiked some wood pieces with ametallic ions’ solution, and Trevizan et al. [9] used CRMs ofvarious matrices such as peach leaves, soy, rice and corn flakes,among others to calibrate the LIBS method for measurement ofmicronutrients in plant samples. An interesting strategy for calibrationproposed by Gomes et al. [10] involves the dilution of the
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