K.L. Busch in J. Sherma and B. Fried (Eds) Handbook of TLC, Marcel Dekker, 2003, pp. 239–277. H. Luftmann , Anal. Bioanal. Chem. 378 (2004) 964
Chromatogr. 1996 9 84 91 K.L. Busch . In: J. Sherma and B. Fried (Eds) Handbook of TLC
A new mode of development for TLC, multidimensional relay development, developed on the basis of half-way and relay development, is described in this paper. The new method provides more space for further separation of spots and is suitable for invisible samples. Multidimensional relay development using the half-way development device transfers unseparated spots to a new thin layer plate on the basis of the first separation, then re-develops this new plate. Such development and transfer can be performed repeatedly. The process is very simple and effective. If the number of transfers is sufficient, substantial improvement to the TLC separation is possible. A mixture of 13 dyes was used to evaluate the technique and the results obtained were satisfactory.
The computer-assisted simulation program DryLab has been used to simulate TLC separations. The simulations were based on data from preliminary TLC separations. For DryLab data entry R F values from TLC were converted to retention times, the development distance on the plate was used as column length, and the plate thickness was used as the column diameter. To achieve reasonably accurate simulations it was found necessary to run three preliminary runs in which differences between organic modifier concentration in two adjacent runs was more than 5%. The possibility of predicting HPLC separation on the basis of TLC separations was also studied. It was found that the method can be transferred from TLC to HPLC and that DryLab can be used to predict HPLC separation on the basis of the information obtained from TLC experiments. To produce a reasonably accurate HPLC simulation on the basis of TLC data, however, a relatively large number of preliminary experiments is required.
An improved method of two-dimensional development in thin-layer chromatography is described. The innovative feature is that before the second development the thin layer on the glass plate is divided into several zones and these zones are developed with different mobile phases, instead of with the same mobile phase, as in traditional two-dimensional TLC. The operating procedure and the device are described in detail, as are means of avoiding interference. A mixture of ten dyes was used to evaluate the technique and the results obtained were satisfactory.
We have compared the profiles of toxigenic molds and their mycotoxins after collection of dust from work-place buildings by simple use of adhesive tape. After cultivation of the molds on a variety of agars, and selected molds in appropriate liquid media, mycelia, conidia, spores, and culture filtrates were collected, extracted with methanol, and the extracts were concentrated. The extracts were investigated by TLC on silica gel plates with chloroform-xylene-acetone, 6 + 3 + 1 ( v/v ), as mobile phase and, usually, UV detection. After theoretical simulation, and optimization of several systems, these conditions were selected because they furnished better separations and were highly reproducible, thus enabling comparison of results. The results obtained revealed it was possible to identify differences among species of toxigenic molds and most of the mycotoxins present in work places by use of TLC. Our results were indicative of differences among offices, student laboratories, instrumental laboratories, sterile or partly sterile rooms, and lecture rooms. After standardization, methods similar to this can be offered as kits for detection of mycotoxins in work places.
The Eurachem/Citac Guide on measurement uncertainty establishes general rules for evaluating and expressing measurement uncertainty across a broad spectrum of measurements and presents a special calculation procedure called the ‘error-budget approach’. In this work the error-budget model has been tested using the quantitative HPTLC determination of sodium glutamate in a food product as an example. The TLC procedure was divided into stages, each of which was evaluated. The cause-and-effect diagram was constructed and possible sources of uncertainty were listed. We found that the dominant sources of uncertainty were sample preparation, chromatographic separation, secondary chromatography, stability of instrumentation, inhomogeneous illumination, distribution of compound molecules in the stationary phase, and the relative position of spots and scanning slit, among others. The uncertainty estimated by means of the error-budget method was less than one fifth of the value obtained from the validation study. The contribution from sources selected and processed according to the Citac guide is so small that it can be neglected.
TLC and HPLC methods have been developed for analysis of eight dyes, 9-phenylxanthene derivatives, four of which are new unsaturated ether esters. The methods developed are suitable for monitoring synthesis of the dyes, for analysis of their purity when used for coloring foods and cosmetics, and for studying their photostability, etc.
A quick and simple TLC method has been established for distinguishing among benzalkonium salts differing in the length of the side alkyl chain. The method could be used not only for determination of benzalkonium salts but also for distinguishing among other long-chain quaternary salts, for example tetraalkylammonium, pyridinium, quinolinium, and isoquinolinium compounds, used as micellar catalysts or as disinfectants.
A method for optimization of a TLC separation based on use of a genetic algorithm is described. The procedure was tested by optimization of the reversed-phase HPTLC separation of a mixture of six pesticides and satisfactory optimum results were obtained. The performance of the genetic algorithm was tested by measurement of the number of generations, the population size, the mutation probability, and the crossover probability. Three separation criteria ( MRF , R * and R **) were examined as fitness functions. The genetic algorithm was compared with the simplex method.