A New Miniaturized Planar Chromatography

Abstract

Planar chromatography or thin-layer chromatography (TLC) is one of the oldest and most versatile techniques within the huge family of modern separation science methods. Without doubt, the main advantage of TLC is its simplicity. Fast and efficient fractionation and/or separation of multicomponent mixtures can be performed using just small strip of filter paper (working as the stationary phase) and few milliliters of water or water-organic solvent (acting as the mobile phase) poured into a glass jar operating as the chromatographic chamber. But even this equipment may be reduced if we replace the container with mobile phase by a small glass capillary or syringe tip filled with the liquid phase (Fig. 1). Under such conditions the movement of a given eluent through the paper is entirely driven by capillary forces. Therefore, no pump or any different pressure gradient device is required for the chromatographic run, which may be also performed in two dimensions. It should be noted that contrary to its column counterpart, a number of individual samples may be analyzed simultaneously. TLC allows parallel separations limited only by the plate width along the start line direction. If the components of interest are colored the eye can act as surprisingly sensitive detector. Colorless substances can be simply detected via a number of selective (like ninhydrin) or non-selective (e.g. iodine vapor) visualization reagents. Planar chromatography based on common filter paper provides probably the simplest and cheapest experimental setup for an effective separation of selected optical isomers, e.g., amino acids, considering the fact that native cellulose (operating as the chromatographic stationary phase) has chiral properties. Interestingly, in its simplest form, circular micro-planar chromatography has been reported as a fast optimization and mobile phase selection tool for complex sample separation [1]. In general, planar chromatography has enormous educational potential for demonstration and teaching of separation science principles, including all aspects of qualitative and quantitative analysis [2]. During my postgraduate education I was really lucky to start my experience with chromatography working under supervision of Professor Henryk Lamparczyk, who prematurely passed away at the end of 2012. He was an enthusiast for solving any complex research problems via the simplest possible, methodological approach. Therefore, in his laboratory, despite GC and HPLC machines, he applied planar chromatography extensively as a fast experimental data acquisition tool. Such TLC-generated retention data sets were often used for further chemometric calculations and physicochemical investigations. He successfully supervised and mentored a number of important research projects concerning temperature effects in planar chromatography, focusing on the thermodynamic study of macrocycles and their interaction with n-alcohols and the separation of bile acids using temperature-controlled TLC. Based on planar chromatographic data, he clearly demonstrated, that the general behavior of the solute molecules in chromatographic systems can be explained on the basis of solutephase reversible interactions like electrostatic (van der Waals) forces and stereoselective molecular fitting to stationary and mobile phases. Lamparczyk successfully proposed an electrostatic retention index system common to GC, HPLC and TLC based on the experimental data Published in the topical collection Miniaturized and New Featured Planar Chromatography and Related Techniques with guest editor Pawel K. Zarzycki.