Calibration-Free Laser-Induced Breakdown Spectroscopy (CF-LIBS) has been proposed several years ago as an approach for quantitative analysis of Laser-Induced Breakdown Spectroscopy spectra. Recently developed refinement of the spectral processing method is described in the present work. Accurate quantitative results have been demonstrated for several metallic alloys. However, the degree of accuracy that can be achieved with Calibration-Free Laser-Induced Breakdown Spectroscopy analysis of generic samples still needs to be thoroughly investigated. The authors have undertaken a systematic study of errors and biasing factors affecting the calculation in the Calibration-Free Laser-Induced Breakdown Spectroscopy spectra processing. These factors may be classified in three main groups: 1) experimental aberrations (intensity fluctuations and inaccuracy in the correction for spectral efficiency of a detection system), 2) inaccuracy in theoretical parameters used for calculations (Stark broadening coefficients and partition functions) and 3) plasma non-ideality (departure from thermal equilibrium, spatial and temporal inhomogeneities, optical thickness, etc.). In this study, the effects of experimental aberrations and accuracy of spectral data were investigated, assuming that the analytical plasma is ideal. Departure of the plasma conditions from ideality will be the object of future work. The current study was based on numerical simulation. Two kinds of metallic alloys, iron-based and aluminum-based, were studied. The relative weight of the error contributions was found to depend on the sample composition. For the here-investigated samples, the experimental aberrations contribute to the overall uncertainty on the quantitative results more than theoretical parameters. The described simulation method can be applied to the Calibration-Free Laser-Induced Breakdown Spectroscopy analysis of any other kind of sample.
The analytical methods mass spectrometry, UV/Vis, IR, Raman, Fluorometry, XRD, Mössbauer, and NMR used to elucidate chemical structure are evaluated regarding their capabilities to be used as primary analytical techniques in quantitative measurements, considering the criteria in the CCQM definition of primary methods. This includes a review of the respective measurement equations, the evaluation of the measurement uncertainty, and a discussion of evidence for the highest metrological level, as obtained from intercomparisons in contest with other methods. It is shown that only few methods fulfill the CCQM criteria. Quantitative NMR spectroscopy is one of them and may be considered as a potential primary method as recommended by CCQM because of being free of empirical factors in the uncertainty budget.
Quality assurance according to ISO or EN norms entails a periodical check of critical instrumental parameters. Not yet all commercial software purchased with instruments supports the related measurements and their fast evaluation. EDXTOOLS consist of a programme library which complements the existing software for electron excited energy dispersive X-ray spectrometry (EDS) in this respect. EDXTOOLS can be used to check the detection efficiency by the evaluation of the L/K intensity ratio in a copper or nickel spectrum or by the calculation of the thickness of absorbing detector layers from experiments, which can be performed on any scanning electron microscope. Moreover, measured spectra can be modified by the transmission curve of absorbing media to estimate their influence on the result of quantitative analysis. EDXTOOLS allow the determination of the signal to background ratio from an Fe-55 spectrum and the fitting of measured FWHM's of K-lines to find the resolution curve DE = Ö{DE 2el + DE 2det}. They are completed by the possibility of calculating EDX spectra for the K-lines of light elements and to compare the resulting spectra for different formulae, physical data tables, and detector parameters chosen for the calculation. EDXTOOLS are written in MATLAB®, a wide spread interpreter language. This has the advantage that the programmes are readable text files. A user can check each computational step and modify it. The installation of MATLAB® and its optimization toolbox is necessary to work with EDXTOOLS.