High performance thin layer chromatography

Abstract

One of the first points made in most analytical chemistry texts is the distinction between the qualitative and quantitative aspects of chemical analysis. However, the problems of detecting, identifying, and determining the amounts of sample constituents are not always the initial issue of concern. Often some form of preliminary separation must take place. Increasingly, the principles of chromatography are being introduced in many undergraduate science courses. This paper will attempt to clarify where in the scheme of modern chromatography high performance thin layer chromatography fits, and why in some situations it is a viable alternative to gas and high performance liquid chromatography.Until the middle of this century, the separation of a sample into its various components was accomplished in painfully slow ways, such as paper or column chromatography. This is definitely not the situation today. Beginning with the advent of practical gas chromatography in the 1950's, high efficiency in sample separation became commonplace. After the pioneering work of Justus Kirchner and Egon Stahl, thin layer chromatography (TLC) became important for the separation of samples not amenable to analysis by gas chromatography. The rapid growth of TLC was slowed during the 1970's with the corresponding rise in popularity of high pressure liquid chromatography (HPLC). Although both HPLC and TLC are capable of separating the same type of compounds, HPLC is considerably more efficient. Further, capacity factors in HPLC are more reproducible than R{ values in TLC. However, recent improvements in TLC have removed many of its limitations, and in some situations, it actually gives better results than HPLC. To emphasize the fact that TLC may be a legitimate alternative to HPLC, the relatively new term high performance thin layer chromatography (HPTLC) has been introduced.Just what is high performance thin layer chromatography (1-4)1 How is it different from classical TLC? To what extent does HPTLC keep the advantages of classical TLC, such as minimal sample clean up, flexibility in solvent selection and sample detection, high sample through put, and low analysis costs?Many of the recent improvements in TLC may be placed under the heading of high performance thin layer chromatography, as a means of emphasizing improved efficiency and precision. Zlatkis and Kaiser (J) define HPTLC as a combination of improvements in several aspects of TLC. These improvements include optimized plate coating materials, a new method of developing the mobile phase, the ways in which samples are applied to the plate, and a novel procedure for conditioning the TLC plate. A more concise definition of high performance is given by Jupille (2). It was pointed out that for a given chromatographic system resolution of sample components are dependent upon selectivity and efficiency.