Thin-layer chromatography factor analysis

Formation, factors affecting concentrations, legal limits and occurrence of polycyclic aromatic hydrocarbons in smoked meat products and smoke flavor additives are briefly reviewed by Simko. The most widely employed techniques such as thin-layer chromatography (TLC), gas chromatography (GC), and high-performance liquid chromatography (HPLC) are evaluated. Moreover, sample preparation, pre-separation procedures, separation and detection systems being used for the determination have been evaluated with emphasis on the latest developments in applied food analysis and... 

A radiopharmaceutical has adequate radiochemical purity when the fraction in the form of the wanted chemical form is high enough to meet specifications. Radiolysis (degradation due to own radiation) and the usual factors that affect stability (light, oxidation, reduction, pH shifts), may cause incomplete or slow labelling, degradation and create radiochemical impurities. Thin layer chromatography is the most widely used technique for the analysis of radiochemical purity. HPLC techniques may also be used, for instance for the assessment of the radiochemical purity of PET radiopharmaceuticals. 

Over the last two decades, HPLC has to a large extent superseded the classical modes of open column, thin-layer or paper chromatography previously used for natural product separation and has become an integral part of natural product analysis and preparative isolation. This can be attributed to various factors, including (1) availability of numerous chromatographic modes, robust high-resolution chromatographic materials and... 

The problem resolves itself into three stages. Firstly, the additives must be extracted from the extraction liquid in the form of an extract which is suitable for subsequent analysis. Frequently, extraction with diethyl ether or another low boiling organic solvent will achieve the required separation, certainly in the case of the aqueous and simple hydrocarbon polymer extractants. In addition to isolating the additives in the form of a suitable extract, this process will achieve a useful concentration factor of up to 100 fold in the level of additives present in the extract. Secondly, it is usually necessary to separate in this extract the additive or additives which it is required to determine from those for which analysis is not required, in order to avoid any analytical interference effects. Techniques such as thin-layer or column chromatography are particularly useful in this respect and are discussed in further detail next. 

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