Automated multiple-development

The basis of automated multiple development (AMD) is the use of different modes of multiple development in whieh the mobile phase eomposition (5j and Sy values) is ehanged after eaeh, or several, of the development steps. Figure 8.11 illustrates the prineiple of AMD employing a negative solvent-strength gradient (deereasing 5-p values). 

K. Burger, Online coupling HPLC-AMD (automated multiple development) , Awa/ytw 18 1113-1116(1990). 

E. Menziani, B. Tosi, A. Bonora, P. Reschiglian and G. Eodi, Automated multiple development high-performance thin-layer chromatographic analysis of natural phenolic compounds , 7. Chromatogr. 511 396-401 (1990). 

M. T. Belay and C. E. Poole, Determination of vanillin and related flavor compounds in natural vanilla exti acts and vanilla-flavored foods by thin layer chromatography and automated multiple development , Chromatographia 37 365-373(1993). 

Fig. 2 The steps in the process of thin-layer chromatography that have been instrumentalized and automated to a large degree in the recent past. PMD = Programmed Multiple Development, AMD = Automated Multiple Development, DC-Mat or ADC = Automatic Development Chamber.

Raith and Neubert [57] have developed a method for the profihng of human stratum comeum ceramides. The method enables the investigation of the role of ceramides in maintaining the barrier function of stratum comeum. TLC using automated multiple development was modified for semipreparative purposes. The fractionation of complex lipid extracts using this method ensured specific, sensitive, and... 

Figure 7.13 Separation of a test eixture using automated multiple development with a universal mobile phase gradient from acetonitrile through dlchloromethane to carbon disulfide on a silica gel HPTLC plate. The chromatogram was scanned at different wavelengths to enhance the chromatographic information.

Figure 7.18 Apparatus for automated multiple development. (Courtesy of Camag Scientific, Inc.)... 

Two-dimensional separations in planar chromatography are rather trivial to perform. All unidimensional multiple development techniques employ successive repeated development of the layer in the same direction, with removal of the mobile phase between developments. The main variants are multiple chromatography and incremental multiple development. The basis for automated multiple development (AMD) is the automation of unidimensional, incremental, multiple development with a reverse solvent strength gradient [998]. 2D TLC finds limited use, and is mainly a qualitative technique. 

Automated multiple development (chamber) (2) Atmospheric mass detector (3) Advanced method development... 

Automated Multiple Development System (AMD2) is a handy device that automatically develops the plates, dries them, and holds the plate in a clean environment for the analyst to document the findings. Several mobile phases can be mixed and preconditioning programs exist to expose the plate to specified solvents prior to development. Upon completion of the development of the plate, the solvent is evacuated and the plate is dried for the predetermined amount of time. The advantage to this system is the user can tend to other tasks without watching the plates develop. The disadvantage is that sample application still needs to occur separate from this unit. An example of this device is shown in Fig. 13.14. 

Fig. 13.14. Taken from CAMAG website, an Automated Multiple Development System (AMD2).

Automated multiple development (AMD) has been successfully applied for the separation of compounds from plant extracts. AMD is a technique using the concentration gradient to separate substances differing... 

The thickness of the sorbent layer for analytical purposes lies between 50 and 100 (un (extra thin films for automated multiple development, AMD, are described in Section 11.1), 200 [un for HPTLC plates and 250 pm for the normal TLC plates. The layer thickness on aluminum foil is 200 pm, while layers that can be used for preparative work can be up to 2 mm thick. 

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