By use of pH 6.0 acetate buffer a mixture of Chelidonium majus L. alkaloids has been separated, on a classical silica column, into two groups, tertiary and quaternary alkaloids. The relationships between RF and the concentration of methanol in the acetate buffer suggested it was possible, by gradient elution in which the concentration of methanol in the pH 6.0 aqueous acetate buffer was increased, to separate the quaternary alkaloids further into fractions containing 2 or 3 alkaloids. These fractions were then separated by micropreparative zonal thin-layer chromatography. Sanguinarine and chelerithrine of high purity were obtained.
A computer-driven office scanner has been modified to enable measurement of the fluorescence of aflatoxins on thin-layer chromatography (TLC) plates. The main modifications were substitution of the light tube with a black light tube and inclusion of a filter. The strategy behind this modification, and its problems, are discussed. The modified scanner can be used to determine aflatoxins at low nanogram levels, which, when used in combination with an appropriate TLC method, enables monitoring of the compounds in food and feed at the levels stipulated in European legislation.
The chromatographic behavior of calixarene, 4-tert-butylcalixarene tribenzoate, 4-tert-butylcalixarene, and pyrene have been studied. Chromatography was performed on K-60 and RP-18 wettable with water TLC and HPTLC plates under isothermal conditions (303 K). Methanol, ethanol, and acetonitrile and their binary mixtures with water were used as mobile phases. The ranges of mobile-phase compositions in which retardation factor (RF) values were equal to zero were wider for alcohol–water mixtures than for acetonitrile–water mixtures. Plots of RM against the mole fraction of acetonitrile in water (0.19 ≤ XS ≤ 1.00) were linear for all the solutes investigated. The best separation of the calixarenes was obtained by use acetonitrile–water mobile phases and RP18W plates.
Levels of formaldehyde, formed within the cells of plants, animals, and man, are related to the physiological state of an organism. We have previously reported the possibility of determining the formaldehyde content of human teeth in some physiological states, and it was established that the level of HCHO in carietic teeth is higher than in healthy teeth. The aim of the work described in this paper was the OPLC determination of HCHO levels in teeth suffering from eight different rare pathological disorders. It was shown that significantly different levels of formaldehyde were present in teeth in different pathological states. The highest HCHO content was observed in teeth with acute inflammatory changes. The lowest level was found in teeth with no inflammatory changes.
A new TLC procedure has been developed for the purification, separation, and isolation of paclitaxel and cephalomannine from yew twigs. Preliminary purification of the taxoid fraction from non-polar ballast (chlorophylls and waxes) and highly polar components is possible by use of an alumina column and stepwise gradient elution with dichloromethane–ethyl acetate containing different proportions of methanol. The application of zonal TLC on silica with dichloromethane–dioxane–acetone–methanol as mobile phase enables enrichment of the paclitaxel- and cephalomannine-containing fraction. Isolation from the fraction containing paclitaxel and cephalomannine was achieved by TLC on silanized silica gel with methanol–water as mobile phase.
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.
Reversed-phase TLC of aromatic hydrocarbons with different functional groups has been performed on RP18 of high and low coverage density, and on silanized silica, with binary mobile phases comprising mixtures of methanol, acetonitrile, or tetrahydrofuran with water. Comparison of the RM values obtained revealed distinctly diverse selectivity among the systems investigated. For all the stationary phases investigated the selectivity obtained with tetrahydrofuran-containing mobile phases was very different from those containing acetonitrile and methanol. With methanol- and acetonitrile-containing mobile phases and high coverage-density RP18 plates similar selectivity was obtained for solutes with proton-donor and proton-acceptor properties; the same mobile phases resulted in greater selectivity differences when used with lower coverage-density (RP18W) or silanized silica plates. The use of different modifiers can be advantageous for optimization of TLC separations with binary and ternary mobile phases, especially when tetrahydrofuran is used in place of methanol or acetonitrile, or vice versa.
TLC is an ideal technique for quantitative analysis of an ethanolamine compound, 2-(methylamino)ethanol. A semi-quantitative TLC method has been developed that can be used to determine the level of 2-(methylamino)ethanol in the pyridyl compound 2-(N-methyl-N-2-pyridylamino)ethanol. The method was reliable and a good alternative to gas chromatographic analysis; the latter was shown to be problematic because of the non-linear response to 2-(methylamino)ethanol. TLC detection was performed after derivatization with p-benzoquinone reagent. The chemistry of the derivatization reaction was studied and was found to be influenced by the solvent used to dissolve the reagent. Some recommendations are made on the use of p-benzoquinone.
The use of p-benzoquinone as a derivatization reagent for amines was also studied and compared with use of an established amine-specific reagent, Fast Black K Salt. It was found that p-benzoquinone is a useful and sensitive derivatization reagent for some primary and secondary amino compounds.
A new, simple, accurate, and rapid high-performance thin-layer chromatographic method has been developed for the determination of fleroxacin, sparfloxacin, and cinoxacin in tablets. HPTLC was performed on silica gel 60 F254 plates in horizontal chambers with dichloromethane–isopropyl alcohol–25% NH3, 4 + 5 + 2, as mobile phase. Detection and quantification were achieved by means of videodensitometry at λ = 254 nm. The range of linearity was 0.08–0.48 μg μL–1 for all the drugs analyzed. The sensitivity of detection was 10 ng spot–1 for cinoxacin and 100 ng spot–1 for sparfloxacin and fleroxacin. The relative standard deviations were <5.3%. The recovery of the three antibiotics from tablets ranged from 96 to 105%.