Thin-layer chromatography analyte concentration

In conclusion, synthetic dyes can be determined in solid foods and in nonalcoholic beverages and from their concentrated formulas by spectrometric methods or by several separation techniques such as TEC, HPLC, HPLC coupled with diode array or UV-Vis spectrometry, MECK, MEECK, voltammetry, and CE. ° Many analytical approaches have been used for simultaneous determinations of synthetic food additives thin layer chromatography, " " derivative spectrophotometry, adsorptive voltammetry, differential pulse polarography, and flow-through sensors for the specific determination of Sunset Yellow and its Sudan 1 subsidiary in food, " but they are generally suitable only for analyzing few-component mixtures. 

Similar effects were observed by Stigter e< al. (185) with silica and aluminum chloride. The assumption of hydrolytic adsorption is supported by an observed increase of conductivity upon addition of silica to aluminum chloride solutions. Kautsky and Wesslau (240) observed hydrolytic adsorption of Th + ions. The reaction scheme given above is a simplification since, in reality, solutions of basic iron or aluminum salts contain polynuclear complexes. The size of the aggregates depends on pH and concentration. Chromatographic separation of various metal ions on silica gel columns was first described by Schwab and Jockers (241). The role of hydrolytic adsorption in column chromatography on silica gel was stressed by Umland and Kirchner (242). The use of this technique in analytical separations was investigated in detail by Kohlschiitter and collaborators (243-246). An application to thin-layer chromatography was described by Seiler (247). 

Analytical thin layer chromatography (TLC) was conducted on pre-coated TLC plates, silica gel 60 F254, layer thickness 0.25 mm, manufactured by E. Merck and Co., Darmstadt, Germany. Silica Gel for flash column chromatography was obtained from Silicycle Chemical Division Silica Gel, 60 (particle size 0.040 - 0.063 mm) 230-240 mesh ASTM. All columns were prepared, loaded, and fractions collected according to the specification of Still.37 Ethyl acetate used for chromatography was dried over 4 A molecular sieves for at least 24 hours prior to use. Hexanes are the mixed hydrocarbon fraction (bp 60-70 °C), principally n-hexanes, which was purified as follows the commercial solvent was stirred concentrated sulfuric acid for at least 24 hours, decanted, stirred over anhydrous sodium carbonate for 6 hours, decanted, then distilled. 

The abuse of cannabis cannot be detected by thin-layer Chromatography or by conventional gas Chromatography because the concentrations of cannabinoids in urine are too low. Immunoassay, applied to either blood or urine, is the best method (see B. Law et ah, J. analyt. Toxicol., 1984, <5, 14-... 

In addition, it should be noted that results from these analyses of mushroom extracts indicated the presence of a previously unknown alkaloid, which I have named aeruginascin. The molecular stmcture of this substance must be similar to those of psilocybin and baeocystin. It is a compound that is soluble only in polar solvents, such as water, methanol and acetic acid. The levels of concentration of aemginascin found in the fmiting bodies is comparable to those of the other two alkaloids. The compound is characteristic of the Inocybe species, so that the analytical results of mushrooms extracts using thin-layer chromatography constitute a kind of fingerprint identification of Inocybe aeruginascem. 

Screening tests for the trichothecene mycotoxins are generally simple and rapid but, with the exception of the immunochemical methods, are nonspecific. A number of bioassay systems have been used for the identification of trichothecene mycotoxins.73 Although most of these systems are very simple, they are not specific, their sensitivity is generally relatively low compared to other methods, and they require that the laboratory maintain vertebrates, invertebrates, plants, or cell cultures. Thin-layer chromatography (TLC) is one of the simplest and earliest analytical methods developed for myco-toxin analysis. Detection limits for trichothecene mycotoxins by TLC is 0.2 to 5 ppm (0.2 to 5 pg/ mL). Therefore, extracts from biomedical samples would have to be concentrated 10- to 1,000-fold to screen for trichothecene mycotoxins. 

The technical compound EPN was supplied by Promochem, West Germany. The purity of the sample was tested by thin layer chromatography. Stock solution was prepared by dissolving the required amount of EPN in dimethylformamide (DMF) as a solvent and making up with the supporting electrolytes to get the desired concentration. All the supporting electrolytes used in this work were of analytical grade. 

All sample types are amenable to SPE with suitable handling solids, liquids, semisolids, etc. Solid-phase extraction is extensively used in sample preparation, as it offers a fast, safe, and convenient means for subsequent analysis by chromatographic techniques [HPLC, thin-layer chromatography (TLC), GC, etc.]. The major benefit is that it requires less solvent than conventional LLE methods. Impurities are removed and the analytes are concentrated, leading to a higher sensitivity in subsequent analysis. The SPE process can be carried out either online or off-line. 

TLC is a sensitive technique, and it is important to think small with respect to sample size. The highest resolution will always be obtained with the smallest sample commensurate with the ability to visualize the analyte. This is also one of the prerequisites for reproducibility, especially if densitometry is to be used for quantitation (see Chap. 13.8). Zones that are too concentrated re.sult in integrated curve areas that behave in a nonlinear way on regression plots. Depending on the nature of the analyte, sample. sizes as small as picogram amounts are not uncommon, especially in high-performance thin layer chromatography (HPTLC). This is especially true in the analysis of fluorescent substances. Thus, for ultimate sensitivity it is sometimes desirable that a fluorescent derivative of the analyte be prepared. 

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