Sharp-bounded zones link to the effect in planar chromatography-bioassay-mass spectrometry

• Sharp-bounded zones were obtained for HPTLC-direct bioautography.
• Non-target analysis of single effective compounds in complex mixtures.
• Simultaneous detection of six different (xeno)estrogens.
• LODs reached 0.25 pg/zone for 17β-estradiol and 2 pg/zone for 17α-ethinylestradiol.
• Direct elution of (xeno)estrogens via the TLC-MS Interface into the MS.

The traditional direct bioautography workflow was substantially altered to yield narrow, sharp-bounded effective zones. For the first time, microorganisms quantitatively detected the single effective compounds in complex samples, separated in parallel on a planar chromatogram. This novel effect-directed workflow was demonstrated and optimized for the discovery of endocrine disrupting compounds (EDCs) reacting with the human estrogen receptor down to the femtogram-per-zone range, like 250 fg/zone for 17β-estradiol (E2). For application volumes of up to 0.5 mL, estrogen-effective compounds could directly be detected in complex samples at the ultratrace level (ng/kg-range). Sharp-bounded, estrogen-effective zones discovered were further characterized by direct elution into the mass spectrometer. HPTLC-ESI-MS mass spectra of (xeno)estrogens were shown for the first time. Owed to the substantially improved zone resolution, compound assignment was reliable and a comparison of the receptor affinities was conducted for six (xeno)estrogens. Also, long-term cell cultivation of the genetically modified yeast was demonstrated on the HPTLC plate. The optimized HPTLC-pYES workflow was proven for real food samples, exemplarily shown for beer. The general applicability of generating sharp-bounded zones was successfully proven by transfer of the fundamentally improved workflow to the Bacillus subtilis bioassay used for discovery of antibiotics in plant extracts. This new era of quantitative direct bioautography in combination with mass spectrometry will accelerate the scientific understanding in a wide application field via the streamlined access to fast and reliable information on effective components in complex samples.