Unidimensional multiple development

A detailed description of the versatility of multiple development techniques in one dimension has been given by Szabady and Nyiredy (18). These authors compared conventional TLC with unidimensional (UMD) and incremental (IMD) multiple development methods by chromatographing furocoumarin isomers on silica using chloroform as the monocomponent mobile phase. The development distance for all three methods was 70 mm, while the number of development steps for both of the "D techniques was five. Comparison of the effects of UMD and IMD on zone-centre separation and on chromatographic zone width reveals that UMD increases zone-centre separation more effectively in the lower Rf range, while IMD results in narrower spots (Figure 8.8). 

Unidimensional multiple development consists in repeated developments of the same plate with the solvent for the same distance and in the same direction. After each... 

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. 

Unidimensional multiple development provides a complementary approach to forced flow for minimizing zone broadening.All unidimensional multiple development techniques employ successive repeated development of... 

In all techniques of multiple development, the plate is repeatedly developed in the same direction, with intermittent evaporation of the mobile phase between the consecutive developments (Fig. 2b). If the layer is developed many times to the same distance with the same eluent, the technique is called unidimensional multiple chromatography. A variation of this technique, called incremental multiple development, consists in the stepwise change of the development distance that is the shortest in the first step and is then increased, usually by a constant increment (equal dis-... 

Amino-modified high-performance TLC (HPTLC) silica gel layers (NH2 F254S HPTLC) was used for identification of 13 amphetamine derivatives by unidimensional multiple development (UDM) in the 2-D TLC mode. The mobile phases used were ethanol-triethylamine-n-hex-ane (15 9 76, v/v) and acetone-triethylamine-n-hexane (23 9 68, v/v) in the first and the second directions, respectively. Because 1-D HP-TLC was not effective, UDM with the same solvent system and development distance and with two development steps was investigated. The resolution of separation was higher in the low hRf compared to that predicted by the UDM theory. 

E. Multiple (manual) In multiple (manual) development, following a single development in the ascending mode, the chromatogram is removed from the chamber, air-dried and then placed in the same solvent and redeveloped in the same direction. This process, which may be repeated numerous times, increases the resolution of components with Rp values below 0.5. The theory of unidimensional multiple development has been reviewed by Perry et al. [47]. 

Unidimensional multiple development enhances the separation of compounds with low (< 0.2), very similar R p values. The same solvent is used to repeatedly develop the paper in the same direction, with complete drying of the solvent between runs... 

When the paper is impregnated with an organic liquid, the drying period is shortened to remove only the volatile mobile phase. The theory of unidimensional multiple development has been described [48], and the method has been used to analyze steroids [49] and amino acids [50] among other classes of compounds. Fractional chromatography is a special variation of multiple development in which a solvent of increasing polarity is employed for each subsequent development [51]. 

Other method development approaches used in TLC include unidimensional multiple development [127] and multi-modal separation techniques [127], where TLC, in normal phase mode is used in conjunction with reversed-phase liquid column chromatography [131] or GC [131] to provide additional information in separations. This complementary strategy can prove very inportant even for well... 

Multiple development techniques [unidimensional multiple development (UMD) and incremental multiple development (IMD)] were also used to separate the components of a reference solution of amino acids in blood plasma on cellulose plates eluted with acetonitrile-water (8 2 y/y)P ... 

Poole, S.K. Poole, C.F. The influence of the solvent entry position on resolution in unidimensional multiple development thin layer chromatography. J. Planar Chromatogr. 

The Revalue is the fundamental parameter in planar chromatography to describe the position of a spot on a developed chromatogram. values in linear, circular, and anticircular chromatography were defined. Correlations between these types of R were evidenced for conversion of linear R values in circular and anticircular and unidimensional multiple development. Definition of thermodynamic and relative Revalues were also reported and discussed. In addition, the importance of Rm value, which has a linear relationship with structural elements of the solute and can be used to characterize molecular hydrophobicity in reversed planar chromatography, was evidenced. 

Unidimensional multiple development is the repeated development of a plate over the same distance with an eluent of constant composition after careful drying between development steps. 

Although the different types of multiple development (38) are also rarely used for preparative purposes, the advantage of the method may be undestood. The location of the compounds to be separated, and hence the ARf values, can be influenced by the number of developments using the unidimensional multiple development (UMD) technique. UMD means the repeated development of the chromatographic layer over the same development distance with a mobile phase of constant composition. Perry et al. reported (39) that using UMD, if the Rf after the first development is /iyi the values of the multiply developed solute can be predicted by use of the equation ... 

Multiple unidimensional development (MUD) is the simplest approach for enhancement of the separation capacity in TLC [2]. In this approach, the TLC plate is developed for a selected distance, then the plate is withdrawn from the developing chamber and the adsorbed solvent is evaporated before repeating the development process. MUD is a very versatile strategy for the separation of complex mixtures. The main feature of MUD is that it leads to an increase in the spot reconcentration mechanism. There is an optimum number of developments that provide maximum separation. 

Multiple (unidimensional) development. This term is generally used to signify two or more development cycles. The development could be carried... 

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