The paper is written as an introductory review, presenting summary of current knowledge about chemometric fingerprinting in the context of TLC, due to a rather small interest in the literature about joining TLC and chemometrics. The paper shortly covers the most important aspects of the chemometric fingerprinting in general, creating the TLC fingerprints, denoising, baseline removal, warping/registering, and chemometric processing itself. References being good candidates as a starting point are given for each topic and processing step. 1. Introduction Exactly 40 years ago, in 1971, Swante Wold used the term “chemometrics” for the first time in his grant application. These 40 years of continuous development of computer abilities and analytical chemistry methods made chemometrics accessible to any interested scientist. The chemometric techniques allow the researcher to compare and explore complex and multivariate data by a proper projection methods [1]. The chemometric exploration of chromatographic data is a well-established topic in the case of HPLC equipped with different detection techniques [2–4]. The application of this approach is very wide, from ion chromatography of mineral waters [5], through oil spills [6], metabolic profiling [7], different kinds of food [8], petroleum oils [9], and ending in pharmaceutical and herbal investigations [10–16]. Although such approach needs some chemometric (mathematical) knowledge, it is more and more often preferred because of the lack of the need of identifying every peak or, at least significant peaks. The chromatogram is treated not as the set of any peaks, but as an unique multivariate signal. Therefore, there is an increasing interest in chemometric chromatographical fingerprinting. Although thin-layer chromatography is a well-established technique and its pharmaceutical and herbal applications are very wide (see e.g., books of Macek [17] and Waksmundzka-Hajnos et al. [18]), the fingerprinting is done here mainly in a nonchemometric way. The most often used approach relies on identifying peaks and comparing their height, area, or intensity. There is still lack of comprehensive fingerprinting TLC approaches based on the full chemometric processing of collected data. The reason for this cannot be definitely justified; it is most probably caused by narrow specializing of thin-layer chromatographers, some fear of chemometrics, and lack of cooperation between TLC chromatographers and chemometricians. Therefore, the purpose of this paper is to review and summarize all possibilities in TLC fingerprinting and
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