Paper and Thin Layer Chromatography TLC

3 Paper and thin layer chromatography (TLC) J.Chem.Educ.,75(1999)640). 

In these microscale techniques, a strip of filter paper or a glass or plastic plate act as the stationary phase. The plate is coated with a thin layer of silica gel or similar material. The paper or plate, suspended in a glass tank containing a solution of the analyte mixture in a suitable solvent, is adequate. The components of the mixture and the solvent ascend the paper or the coating of the plate by capillary action. Their separation depends on their Rf values defined by  

Rf = (distance to the zone centre/distance to solvent front) (2.72), 

---

Paper and thin layer chromatography (TLC) are essentially analytical techniques that can also be used semi-preparatively. The paper or thin layer material serves as the solid phase and the mobile phase is the solvent, or mnning buffer, which is transported along the stationary phase by capillary forces. We discuss here only thin layer chromatography (Grinberg 1990 Touchstone 1992) which has superseded paper chromatography in almost all applications. 

In general, methods are classified according to the isolation technique and the detection system. Most methods for the isolation/separation of organomer-cury compounds have been based on solvent extraction, differential reduction, difference calculations between total and ionic mercury, derivatization, or with paper- and thin-layer chromatography (TLC). The most common approaches to organomercury separation and detection are schematically presented in Figure 1. 

One of the bluest drawbacks to paper and thin-layer chromatography (TLC) methods of determining RCP is the resolving power of the methods. Most methods commonly used will only resolve one component and so two or three methods may be needed to identify all the major contaminants in a product. Time can also be a limiting factor with some methods taking 20-30 min to develop, or even longer. 

Unlike paper and thin-layer chromatography (TLC Chapters 5 and 6) techniques in which very little new work has been published since the 1970 s, supercritical fluid chromatography (SFC) is a rapidly expanding area. 

Quite an evolution has resulted in the past SO-plus years, dating back to fire bioassay and gravimetric procedures, colorimetry, and paper- and thin-layer chromatography (TLC)-based methods of the 1940s and SOs, which were quite tedious in terms of hands-on time commitments (Figure 1). The Schecter-Haller... 

Paper and thin-layer chromatography (TLC) was applied in early analytical studies to increase selectivity in the analysis of ascorbic acid and other similar chemical compounds. Nowadays these methods have little if any qualitative or quantitative use. However, TLC has proven to have some advantages in the analysis of vitamin C compounds, especially in pharmaceuticals, which often consist of a... 

Paper chromatography (PC) and thin layer chromatography (TLC) have been used since the 1940s. Preparative PC on Whatman 3 paper, analytical PC on Whatman 1 paper, and analytical TLC on microcrystalline cellulose, silica gel, or polyamide have been applied with a variety of solvents and the behaviors of anthocyanins have been similar in all media. Two-dimensional TLC allows the separation of several compounds and has been nsed to clarify the anthocyanin compositions of different commodities. ... 

Paper chromatography and thin-layer chromatography (TLC) constitute the planar methods mentioned above. Paper chromatography makes use of a sheet of paper having the consistency of filter paper (cellulose) for the stationary phase. Since such paper is hydrophilic, the stationary phase is actually a thin film of water unintentionally adsorbed on the surface of the paper. Thus, paper chromatography represents a form of partition chromatography only. The mobile phase is always a liquid. 

There are two popular LC techniques in which the stationary bed is supported on a planar surface rather than in a column paper chromatography (PC) and thin-layer chromatography (TLC). PC preceded TLC by some 10 to 15 years, and a large number of excellent separations were devised for it. But beginning about 1956, it was found that TLC could also be used for most of these separations and that it was faster, more reproducible, more versatile, and more convenient. As a result, most laboratories have abandoned the use of PC with its large cumbersome glass chambers. Those who have not, continue to use PC because they feel that the original PC methods are superior or because of the lower cost of PC. 

Zweig (1968) has reviewed some of the recent methods in column chromatography, gel-filtration, and gel-permeation chromatography, and paper and thin-layer chromatographies. He has listed several papers dealing with forensic and toxicological TLC analyses. 

Paper chromatography was in use over 50 years ago for fractionation and quantitative analysis of nucleotides in nucleic acid hydrolysates. Techniques for paper and thin-layer chromatography were developed over 30 years ago for the analysis of phosphosaccharide mixtures. [40] Thin-layer chromatography (TLC) has now generally replaced paper chromatography for the analysis of organo-phosphorus mixtures. It is usually faster and more sensitive than the latter. 

Analysis of nicotinic acid, nicotinamide, and its metabolites in biological materials, i.e., blood, plasma, urine, and tissues, is important in studies on biochemical pathways (Hengen and deVries, 1985). Finder et al. (1971) described several paper and thin-layer chromatographic systems useful for the differentiation of nucleotides in tissues derived from nicotinamide and nicotinic acid. Hengen and deVries (1985) provided a table summarizing the Rp values of nicotinic acid, nicotinamide, and various intermediates of NAD+ and NADP-I- synthesis for both paper and thin-layer chromatography. Haworth and Walmsley (1972) used two-dimensional TLC on silica gel for the identification of tryptophan metabolites in urine and resolved 32 compounds including nicotinic acid and nicotinamide. Kala et al. (1978) used silica gel TLC to examine urine for nicotinic acid and its metabolites after administration of nicotinyl alcohol. They... 

Shibata and Shimono (1992) reviewed the analytical techniques used to study nicotinic acid and nicotinamide. They noted that TLC is generally not used for the separation of these compounds because of low sensitivity and low resolution. The method of choice for these compounds is HPLC and GC. However, TLC is still useful for the separation of labeled compounds. Shibata and Shimono (1992) presented a table showing the values of nicotinic acid and nicotinamide and their metabolites using both paper and thin-layer chromatography. The table considers separations of these compounds using various stationary and mobile phases. 

Paris and Theallet were able to separate 23 antibiotics which were described in the French Pharmacopia into seven groups utilizing paper chromatography (PC) and thin-layer chromatography (TLC), as well as electrophoresis. The groups were as... 

---