BACKGROUND MASS SIGNALS IN TLC/HPTLC–ESI-MS AND PRACTICAL ADVICES FOR USE OF THE TLC-MS INTERFACE

Abstract

Among the different thin-layer and high-performance thin-layer chromatography mass spectrometry (TLC/HPTLC-MS) approaches, the elution head-based TLC-MS Interface is increasingly used due to its good detectability, reliability, and versatility in its application. The influence of different solvents, either used for prewashing or chromatography, on the mass signal background was studied. It was shown that the use of acidic solvents can cause intense background signals (acid sodium clusters) and ion suppression in the analyte mass spectra. Using a mixture of methanol–water 3:1 (v/v) for plate prewashing, background mass signals could be reduced to a minimum for both ionization modes. The TLC/HPTLC-MS background mass signals obtained from different plates with the green manganese activated zinc silicate fluorescence indicator F₂₅₄, and without, did not show substantial differences. As sodium is ubiquitary in solvent, tubing, glassware, adsorbent, and so forth, the sodium adduct was often formed and observed, whereby the extent of formation was different depending on the plate type. Recommendations for plate handling for use in TLC/HPTLC-MS are provided, as well as practical advices with regard to integration of the inline filter, various sorts of pressure increase, and leakage using the TLC-MS Interface.

Keywords:

• acidic mobile phase
• adsorbent
• cluster
• contamination
• high-performance thin-layer chromatography
• impurities
• ion suppression
• mass spectra
• solvent
• TLC-MS Interface

ACKNOWLEDGMENT

Thanks to Eva Müller and Katja Schreihans for partial recording of the plate background spectra during their voluntary study and to Merck (Darmstadt, Germany) and CAMAG (Berlin, Germany) for support regarding plate material and instrumentation.

Notes

Eluted with methanol by TLC-MS Interface; assignments preliminary.

Intensities given can vary up to ±10%, chlorine adducts obtained due to system background.

Intensities given can vary up to ±10%.

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