Applications of TLC in Pharmaceutical Analysis

The technique of thin-layer chromatography (TLC) has been used extensively in the domain of pharmaceutical analysis for a variety of specific and useful applications, for example  

The various applications of TLC as cited above would be discussed in the sections that follow  

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As a number of drugs are used for the medication of more than one health problem, the analysis of various pharmacological drug classes will not be given however,. some applications of TLC in pharmaceutical analysis will be given in detail where certain advantages are given by TLC [1211. 

With respect to applicability and significance of TLC in pharmaceutical analysis, the methods used in Pharmacopoeias can be separated from those used in industrial pharmaceutical analysis. 

Analytical information and data were presented on the TLC analysis of the most widely prescribed human and animal drugs as well as illicit drugs. In addition, applications of quantitative TLC in pharmaceutical analysis were described. " Biennial reviews of TLC typically contain more than 75 references that describe applications to drug and pharmaceutical analysis. ... 

An important application of TLC is to serve as a pilot method for HPLC, the most widely used analytical method for pharmaceutical analysis. If the stationary phases are similar, TLC can predict solute retention behavior and suitability of a particular mobile phase through correlation of log k in HPLC and Rf data in TLC. Particularly useful is detection of compounds that migrate minimally in the mobile phase and can contaminate the HPLC column during subsequent nms. 

TLC is generally less sensitive and gives worse separation than HPLC. However, it predominates over HPLC in at least two aspects It allows for the analysis of many samples at the same time, and it requires limited sample pretreatment. These features are very important in the analysis of antibiotics, which usually concerns controlling their level in many complicated matrices such as blood, urine, dietary products, and pharmaceuticals. Thus, TLC can be a very useful screening method preceding HPLC analysis. Nevertheless, there are also many examples of analytical applications of TLC, which can achieve selectivity and sensitivity comparable with those characteristic of HPLC. The future of the analytical option in antibiotic analysis is connected with progress in detection and the development of FFPC methods. 

The most important tasks of capillary action planar chromatography in pharmaceutical analysis are summarized in Table 2. In general, it can be stated that although HPLC has superseded TLC in many application areas, TLC both in instrumentalized or in noninstrumentalized forms have remained as standard methods for solving many difficult analytical problems. 

In comparison with the literature on other methods, e.g., HPLC or in other fields of pharmaceutical analysis, there are few reports on the application of TLC to steroid separation. The practical examples which follow serve to demonstrate the newest developments in the field of steroid analysis. 

Major applications of modern TLC comprise various sample types biomedical, pharmaceutical, forensic, clinical, biological, environmental and industrial (product uniformity, impurity determination, surfactants, synthetic dyes) the technique is also frequently used in food science (some 10% of published papers) [446], Although polymer/additive analysis takes up a small share, it is apparent from deformulation schemes presented in Chapter 2 that (HP)TLC plays an appreciable role in industrial problem solving even though this is not reflected in a flood of scientific papers. TLC is not only useful for polymer additive extracts but in particular for direct separations based on dissolutions. 

Therefore, the application of skill and wisdom may give rise to a fairly wide spectrum of possible layers, employed in conjunction with a vast combination of solvent systems permits and affords an almost infinite variation of separating power that really makes TLC such a versatile and useful technique in the domain of pharmaceutical analysis. 

Taylor and co-workers further demonstrated the value of open-access LC/MS systems for generating a widened scope of pharmaceutical analysis applications, including (1) characterization of synthetic intermediates and target compounds (2) reaction monitoring (3) reaction optimization (4) analysis of preparative HPLC fractions and (5) analysis of thin layer chromatography (TLC) plate spots. The availability of these methods led to the increased use of LC/MS for structural analysis. The short analysis time and reliable structure confirmation resulted in the use of LC/MS as a first choice for structure characterization for synthetic chemistry applications, as well as an expanded, and perhaps, integrated role of sample generator and analyst. 

Two-dimensional planar chromatography (2D-TLC) is frequently used in combination with autoradiography or digital autoradiography (DAR) in studies on metabolism. Examples of 2D-TLC-DAR will be given in the analysis of pharmaceutical products. Other applications generally use either different types of development, or utilise different interactions for separation, or different stationary phases, such as elution-displacement absorption-partition normal phase-reversed phase ion exchange-normal phase. 

Sample extraction and cleanup procedures for TLC are similar to those for gas chromatography (GC) and HPLC. If the analyte concentration is sufficiently high, pharmaceutical dosage forms can often be simply dissolved in a solvent that will completely solubilize the analyte and leave excipients or extraneous compounds undissolved to yield a test solution that can be directly spotted for TLC analysis. Grinding of the sample and application of heat and/or sonication may be required to assure solubility of the analyte, as well as filtration or centrifugation to remove undissolved excipients. If the analyte is present in low concentration in a complex sample, solvent extraction, cleanup (purification), and concentration procedures usually precede TLC in order to maximize the analyte and minimize interfering extraneous components in the... 

Analytical TLC differs from PLC in that larger weights and volumes of samples are applied as a band across the entire layer width to thicker (0.5-2 mm) and sometimes larger layers, the purpose of which is the isolation and purification of 10-1000 mg of sample for further analysis. Multiple development of the plate is commonly used, and the separated substances are detected by a non-destructive method (e.g., under UV light and iodine vapors), and recovered by extraction from scraped layer material. PLC can be used to isolate sufficient pure drug compounds for confirmation by spectrometry in cases where analytical TLC is not adequate for identification. Examples of pharmaceutical applications of PLC include a new sesquiterpene trimer and phenylpropanoid glycosides. ... 

Because of the biological and pharmaceutical interest in phenothiazine derivatives, these compounds have been used in a variety of analytical studies and applications. For a number of years, several analytical methods have been proposed by various groups for the determination of phenothiazine and its derivatives in pharmaceutical formulations and biological fluids, including thin-layer chromatography (TLC) [51-54], high-performance liquid chromatography (HPLC) [55-58], spectrofluorimetry, either direct or with derivatization [59-64], flow-injection analysis (FIA) [10,65-73] and other techniques [11,74-76]. 

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