Thin-layer chromatography spraying/dipping

Fig. 1 Schematic representation of a mass spectrometer depicting its main components and the different modes used. Abbreviations DIP direct insertion probe DEP direct exposure probe GC gas chromatography LC liquid chromatography CE capillary chromatography TEC thin-layer chromatography FEE field-flow fractionation APCI atmospheric pressure ionization El electron impact Cl chemical ionization FAB fast-atom bombardment PD plasma desorption MALDI matrix-assisted laser desorption ionization ED laser desorption TSP thermospray ESI electron spray ionization HSI hypherthermal surface ionization Q quadropole QQQ triple quadropole TOE time-of-fiight FTMS Fourier transform mass spectrometer IT ion trap EM electrom multiplier PM photomultiplier ICR ion cyclotron resonance.

Opiates can be identified by thin-layer chromatography (TLC) with many different combinations of mobile-phase solvent systems and detection reagents. A solvent system prepared with ethyl ace-tate-methanol-ammonium hydroxide (85 10 5) is commonly used to resolve heroin, codeine, acetylco-deine, morphine, and acetylmorphine. After development, opiates can be visualized by spraying or dipping the chromatogram in Dragendorff, iodoplatinate, or Marquis reagent. 

Reagents used for the visualisation of amino acids on the dried chromatogram may be applied either by spraying or dipping. Those commonly used produce intensely coloured bands with approximately 20 nmol of each amino acid for paper chromatography and 5 nmol for thin-layer separations, although smaller amounts can be detected. 

A variety of procedures are available for staining paper and thin-layer plates with fluorescamine after chromatography or electrophoresis. Spraying thin-layer plates with a solution of triethylamine, both before and after spraying with fluorescamine, stabilizes the fluorescent spots (Felix and Jimenez, 1974). A sensitivity of 10 pmol was achieved for peptides by dipping thin-layer chromatograms into a solution of fluorescamine in acetone-hexane (1 4) (Nakamura and Pisano, 1976). Somewhat poorer sensitivity for peptides was found with o-phthalaldehyde, and these fluorophors decomposed after several hours (Mendez and Gavilanes, 1976). Peptides prelabeled with fluorescamine have also been resolved on thin-layer plates (Imai et aU 1974). 

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