Comparison of high-performance thin-layer with overpressured layer chromatography combined with direct bioautography...

Bioactive polyacetylenes in tansy (Tanacetum vulgare L.) root extract were separated by overpressured layer chromatography (OPLC) with better resolutions than achievable by capillary flow high-performance thin-layer chromatography (HPTLC). OPLC enabled a longer development distance in a shorter time (16 cm, 7 min) in comparison to conventional HPTLC (7 cm, 16 min). OPLC separations on HPTLC plates with spherical particles resulted in higher resolutions than on such with irregular particles. A slight distortion of zones sometimes occurred that could be eliminated by sonication of the mobile phase through removal of the dissolved air. However, zone distortion did not diminish the meaning of the qualitative outcome. The combination of OPLC with direct bioautography and direct analysis in real time-high resolution mass spectrometry (DART-HRMS) led to the determination of the individual polyacetylenes responsible for the diverse effects. In each recorded mass spectrum, the basepeak was the respective protonated molecule. The assignments confirmed the results of a previous study, however, compounds TR5a (tetradeca-2,4,6-triine-8-en-12-one) and TR5b (trans-2-(2,4-hexadiynylidene)-1,6-dioxaspiro[4,5]dec-3-ene) that were not separable by HPTLC were partially separated by OPLC. Thus, it was proven that TR5b was not an oxidation product of TR5a and thus not formed as artefact during the HPTLC-DART-HRMS analysis, but originally present in the sample.