High-performance liquid chromatography preparative purposes

High performance liquid chromatography (HPLC) has been by far the most important method for separating chlorophylls. Open column chromatography and thin layer chromatography are still used for clean-up procedures to isolate and separate carotenoids and other lipids from chlorophylls and for preparative applications, but both are losing importance for analytical purposes due to their low resolution and have been replaced by more effective techniques like solid phase, supercritical fluid extraction and counter current chromatography. The whole analysis should be as brief as possible, since each additional step is a potential source of epimers and allomers. 

Resolution of a-substituled aldehydes. The SASP hydrazones of a-substituted aldehydes can be resolved by high-performance liquid chromatography. The separahility factors are sufficient for analytical and preparative purposes. The (S,S)-isomer elutes consistently before the (S,R)-isomer. Both isomers can be cleaved to the enantiomerically pure aldehydes by ozonolysis or acid hydrolysis, with resolution yields of 35-70%. 

Thin-layer chromatography (TLC) is mainly applied in micropreparative taxoids separation [2-4]. Silica gel 6OF254 preparative plates are usually applied for this purpose. The problem of taxoids separation involves not only their similar chemical structure (e.g., paclitaxel versus cephalomannine) but also, due to different coextracted compounds usually encountered in crude yew extracts (polar compounds such as phenolics and nonpolar ones such as chlorophylls and biflavones), the separation is very difficult. The common band of paclitaxel and cephalomannine was satisfactorily resolved from an extraneous fraction in isocratic elution with ethyl acetate as a polar modifier [4] and n-heptane-dichloromethane as the solvent mixture and it was of suitable purity for high-performance liquid chromatography (HPLC) quantitative determination. 

Trace enrichment is a sample precleaning procedure which is performed prior to a sample analysis. The purpose of any sample preparation procedure is twofold. First, such a procedure must selectively collect and concentrate the components of interest. Second, the method should eliminate any other components that would either interfere with the analysis or would contaminate an analytical gas chromatography (GC) or high-performance liquid chromatography (HPLC) column to shorten its useful analytical life. 

Column separation of proteins and peptides is used for both preparative and analytical purposes. Generally, in the former case low- or medium-pressure systems are preferred, whereas in the latter, high-performance-liquid-chromatography (HPLC) is the method of choice. These systems are coupled with a spectrophotometric detector normally set at wavelengths 280 and (around) 220 nm for proteins and peptides, respectively. Coupling of HPLC with mass spectrometry allows structural identification of compounds after the separation. 

Batch column chromatographs have long been used for conventional preparative purposes. In spite of the great separating efficiency of high-performance liquid chromatography (HPLC) and its applicability to a wide range of compounds, little... 

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