Preparation of TLC-Plates

Preparation of TLC Plates The Plate Spotter Spotting the Plates Developing a Plate Visualization Interpretation Multiple Spotting Preparative TLC... 

FIG. 3 Preparation of TLC plates by dipping. The two microscope slides are grasped at one end, dipped into the silica gel slurry, removed and separated, and dried and activated by heating. 

In the first edition of Stahl s laboratory handbook Durmschicht-Chromatographie published in 1962, equipment for coating glass plates is illustrated, and detailed procedures for the preparation of TLC plates are described. Even today, TLC sorbents for a manual coating operation are produced in an only shghtly modified form, especially where labor costs are small and time is a minor consideration. The layers obtained often show good selectivity, but do not achieve the separation efficiency obtained by precoated layers and seldom lead to reproducible results. 

FIGURE 1 Illustration of preparation of TLC plates and use of the HTLE 7000 electrophoresis apparatus. 

Such an apparatus is most time-saving when more than 100 TLC-plates are required daily. The experience gained in the film industry will have to be turned to account for mass preparation of TLC-plates or sheets, and preference given to a combination of conveyor belt and spraying procedure. 

Many types of TLC equipment are commercially available and may serve a variety of purposes. Quantities of samples ranging from milligrams (for preparative work) to nanograms may be separated and detected depending on the size of TLC plate, the type and... 

Taylor, Johnson, and Raso 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 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. 

The universal TLC facilities are utilized plates, adsorbents, microcapillaries, or micropipettes for sample application, development tanks, detection spray reagents, devices for spraying, and densitometers for quantification. Plates are either commercially precoated or handmade. Silica gel G (G, for gypsum as a binding substance), silica gel H (no binding substance) and, rarely, alumina and kieselguhr, form the thin-layer stationary phases. Complete sets of devices necessary for the preparation of handmade plates are commercially available. After the silica gel slurry is spread on the plates, they are left to dry in the air for at least 24 hr and shortly in an oven at 110°C. The plates are then ready for either direct use or for modification of the layer. From the great variety of precoated plates, which are commercially available and preferred nowadays, silica gel plates and plates with layers... 

Specific surface area of silica gel used to prepare a TLC plate can differ from the packing material in the column... 

It is possible to add other chemicals to the slurry when preparing a TLC plate. These might be added to adjust the pH of the layer, to aid in the separation or detection of various compounds. These are not used routinely, so should be purchased as needed to insure they are not degraded in any manner. 

Fell (1996) has provided useful information on analytical techniques and approaches for the separation of ecdysteroids by TLC. He noted that ecdysteroid separation can be achieved on silica gel TLC plates, HPTLC plates, RP-TLC and RP-HPTLC plates. Plates with a fluorescent indicator (F254) allow for ecdysteroid detection visually by UVC (fluorescence quenching). Paraffin-coated plates can be used (by developing plates in dichloromethane containing 5 to 7.5% paraffin oil) to improve the separation and recovery of ecdysteroids. For details on the preparation of these plates, see Fell (1996). For a practical approach to the analysis of ecdysteroids by TLC including methods of sample preparation, choice of chromatographic systems (i.e., combination of plates and solvent systems) and methods of detection, see Fell (1996). 

For research and routine work, we prepared a data-evaluation package named QTLC-pack. It was suitable for quantitative evaluation of TLC plates with a computerized scanner. The advantage of this software package was its very sophisticated integration algorithm, INTAL, which was the... 

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