Preparative layer chromatography classical

As explained in Chapter 1, classical preparative layer chromatography (PLC) involves flow of the mobile phase by capillary action. The method uses relatively basic equipment and is not expensive. 

Classical preparative layer chromatography (PLC) is designed for the isolation of 10 to 1000 mg quantities of material. The practice of PLC and analytical TLC is similar in most respects, except that thicker layers are employed for the former. Most preparative applications have been carried out on 20 X 20 cm silica gel or alumina plates with a layer thickness of 1-5 mm and fluorescent indicator to facilitate nondestructive detection. 

Circular development of TLC plate, 27 Classical preparative layer chromatography (CPLC), 307,308-317 applicability of, 317... 

Preparative-layer chromatography (PLC) can be used for the fractionation and/or isolation of compounds in amounts up to 1000 mg. According to the elution mode, it can be classified into classical PLC (i.e., conventional capillary-flow) and forced-flow PLC (e.g., OPLC and RPC). The main differences between analytical TLC/ HPTLC plates and preparative PLC plates are the layer thickness, mean particle size, and particle size distribution. In TLC and HPTLC, layer thickness is typically 0.2 or 0.25 mm. Mean particle size is about 12 jam in TLC and 5 jam in HPTLC, and the particle size distribution is up to 20 jam for TLC and about 10 jam for HPTLC. Consequently, HPTLC offers better resolution and lower limit of detections (LODs) than conventional TLC [17]. 

High-performance thin-layer chromatography (HPTLC) presents better resolution, sensitivity, and precision than classical TLC, and allows determination of the analytes with sufficient accuracy (e.g., determination of preservatives in creams and lotions) besides this, sample preparation may be simple. However, due to the high versatility of other techniques, this is probably the less commonly used of the chromatographic techniques in this area. 

This entry describes the classical and modem sample preparation methods that have been used prior to qualitative and quantitative analysis by thin-layer chromatography (TLC) and high-performance (HP) TLC. Extraction and cleanup methods that are covered include classical methods such as liquid-liquid extraction (LLE) and Soxhlet extraction, as well as modern methods such as solid-phase extraction (SPE), pressurized liquid extraction (PLE), and supercritical fluid extraction (SEE). Modern methods have not been as widely apphed in TLC as for other modes of chromatography, e.g., column high-performance liquid chromatography (HPLC). 

The purpose of this chapter is to present an overview of all important aspects of thin-layer chromatography (TLC). It will briefly review information and references on topics covered in the following chapters in Part I and will refer readers to these specific chapters. It will treat in more detail topics not covered further in separate chapters, such as sampling and sample preparation and the more classical procedures of TLC. A suggested source of additional basic, practical information on the practice and applications of TLC is the primer written by Fried and Sherma (1). 

Precoated layers. See Sorbents and precoated layers Preparative layer (planar) chromatography (PLC), 20, 38-39, 307-340 classical PLC, 307,308-317 comparison of varions PLC techniques, 335-336 lipids and, 699... 

The traditional procedures are similiar to analytical methods with the major differences being the use of thicker sorbent layers. These procedures are generally faster and more convenient than classical column chromatography [6,49]. Preparative scale TLC usually has decreased analyte resolution compared to analytical TLC. 

Flavonols and flavones are present in many food products and medicinal plants and show relevant antioxidant activity in vitro. In this chapter, classical analytical methods sueh as thin layer ehromatography and two-dimensional paper chromatography together with modem methodologies such as HPLC-MS-MS are reported. Preparative ehromatography methods are also reviewed as well as spectroseopie methods used for flavonoid characterization and identification, including UV spectrophotometry and MS spectrometry. Chemical and enzymatic methods used in flavonoid identification are also reviewed. 

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... 

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