Scanning densitometry

Manual devices for sample application are inappropriate if scanning densitometry is to be used for detection. First of all, the starting position of each spot must be known precisely. This f is most easily achieved with mechanical devices operating to a precise grid mechanism. The sample must be applied to the layer without disturbing the surface, something that is near iaqposslble r... 

Karuna, R. and Sashidhar, R. B., Use of ion-exchange chromatography coupled with TLC-laser scanning densitometry for the quantitation of fumonisin Bl,... 

Modern TLC is thus an effective tool for separation of complex solutions into their components. Analysis can be qualitative or quantitative. When the composition or the analysed solution is known approximately, identification of the substance contained in a particular spot by its positional coordinates is frequently adequate. HPTLC provides the means not only for flexible screening procedures but also for demanding quantitative determinations. HPTLC features highly sensitive scanning densitometry and video technology for rapid chromatogram evaluation and documentation. 

Thin-layer chromatography is employed in many areas of QC and routine monitoring of product quality [458]. Fluorescence scanning, densitometry or videodensitometry are used for quantification. Not all polymer additives are amenable to TLC analysis. Some fatty acid amides are virtually insoluble in organic solvents and cannot be isolated by thin-layer or column chromatography. 

The greatest strength of 2D planar methods is that they distribute components widely over a 2D space of high peak capacity. Multidimensional TLC development has the advantages of requiring simple equipment is compatible with scanning densitometry for solute identification and quantitation and enables exploitation of the spot reconcentration mechanism. 

An example of release testing by TLC is shown in Fig. 13.24. In this example, two more polar bands are observed, one that is quantitated at <0.1% and another at 0.3%. Quantitations are based on visual estimation using the standards on the plate. Alternatively, scanning densitometry can be utilized to obtain a more definitive quantitation of impurities. 

A number of compounds have been quantified by tic or high performance thin-layer chromatography (hptlc) using absorption or fluorescence scanning densitometry. 

J. C. Spell and J. T. Stewart, Quantitative analysis of chloroprocaine and its major impurity 4-amino-2-chlorobenzoic acid in drug substance and injection dosage form by HPTLC and scanning densitometry, JP C, 8 12 (1995). 

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