Physico-Chemical Properties of the Most Suitable Spray Reagent for Fluorescence Enhancement in Thin-Layer Chromatography

Enhancement of fluorescence in thin-layer chromatography induced by the interaction between n-alkanes and an organic cation

Fluorescence enhancement of a broad variety of solutes has been used extensively in TLC although no thorough explanation has been proposed. In this work, we try to understand it and explore new applications to which it can be put. In this way, alkanes can be quantitatively determined by fluorescence scanning densitometry using silica gel plates impregnated with berberine sulfate. Molecular simulation and analysis of molecular orbitals allows this phenomenon to be explained in this case and lays the groundwork to explain fluorescence enhancements produced by other molecules. A ion-molecule interaction between alkanes and berberine sulfate is responsible for the enhancement of fluorescence produced by alkanes. Computational results suggest that the surrounding alkane molecules provide an apolar environment to the berberine cation, thus enhancing the intensity of the fluorescence signal. This proposed explanation has been tested by extending the fluorescence determination to other compounds. These include biologically interesting saturated and unsaturated fatty acids, steroids and derivatives, prostaglandins, ceramides, galactocerebrosides, as well as terpenes, and polypropylene glycols. In addition, according to the proposed explanation, the properties required for alternative impregnants to berberine are discussed.

Progress in densitometry for quantitation in planar chromatography

The principal methods for obtaining quantitative information from separations performed by planar chromatographic techniques are reviewed. Recent advances in obtaining structural information for sample identification of separated components are also discussed. Reasonable expectations concerning future developments in densitometry are made.

Use of enhancers in the HPTLC fluorescence analysis of thiols

Several thiols of biological and pharmacological interest, including glutathione, coenzyme A, acetylcysteine and captopril were derivatized with the fluorogenic reagents SBD-F and ABD-F and analysed by high-performance thin-layer chromatography (HPTLC)-fluorodensitometry on silica gel 60 plates, using isopropyl ether-methanol-water-acetic acid (9:8:2:1, v/v/v/v) as the developing solvent. The luminescence was considerably increased when several types of enhancers were applied as dipping reagents: Triton X-100, liquid paraffin and cyclodextrins; thus the detectability of the thiol fluorophores was improved. The influence of enhancer concentration, method of application, sample concentration, drying conditions and measuring time after plate dipping were investigated. The greatest enhancement was achieved using a 40% (v/v) solution of Triton X-100 in toluene as a dipping reagent for the determination of SBD-acetylcysteine; more than a 10-fold increase of the fluorescence signal was obtained, allowing low picogram detection limits.