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The effects of changing solvent composition on the LOD of TLS detection in gradient elution HPLC have been studied from the perspective of thermo-optical properties of the solvent. Hyphenated gradient high-performance liquid chromatography (HPLC)-thermal lens spectrometry (TLS), was used to separate and detect 13 carotenoid compounds and two chlorophylls. Utilization of mixing coils into the system reduces the inhomogeneities during eluent changes and therefore enables the application of thermal lens detection in the gradient HPLC method. For gradient chromatographic conditions in which the thermo-optical properties and related enhancement factor change as much as 50% over 10 min, the LODs for the TLS detector were enhanced by as much as three times in comparison with UV-Vis detection. For the isocratic part of the chromatogram, up to a tenfold improvement of LODs was achieved with TLS detection.

Biofuels are common addition or substitute for fossil fuels, applied as an atempt to decrease the impact of transport on the environment. Because of a large variety of already known biofuels and intensive research in the ield, there is a high demand for analytical techniques for their quantiication in fuels. Liquid scintillation counting (LSC) is one of the ideal candidates for this kind of measurements because the measured substance is radiocarbon found in all biofuels. This chapter describes the fundamental feature of LSC measurements and possible sample preparation steps. One of the methods (direct LSC method) is highlighted. One of the method's advantages is simple sample preparation, thus suitability for every LSC laboratory. Calibration and validation results of three types of biocomponents, i.e., bioethanol, synthetic biodiesel [hydrogen-ated vegetable oil (HVO)], and conventional biodiesel [faty acid methyl esters (FAME)], are presented. All results show that the described method is suitable for routine analysis of various biocomponents.

The Kubelka-Munk theory is applied to the thickness-dependent diffuse reflectance of black-painted samples in the mid-IR. The calculated absorption and scattering coefficients are wavenumber-dependent. The reflectance of the nonideal backing also shows spectral features, which is attributed to the reflections from the boundary surface between the scattering medium and the substrate. The spectral dependence of scattering penetration depth is caused by the scattering and absorption processes. At some wavenumbers, the diffuse reflectance is independent of layer thickness, because of particular values of the parameters of the applied theory. The application of the Kubelka-Munk function is discussed.

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