New coupling of planar chromatography with direct analysis in real time mass spectrometry

The coupling of planar chromatography with direct analysis in real time time-of-flight mass spectrometry (DART-TOF-MS) was shown for the first time. Cutting the plate within a track led to substance zones positioned on the plate edge which were directly introduced into the DART gas stream. Mass signals were obtained instantaneously within seconds. Detectability was shown in the very low ng-range per zone on the example of isopropylthioxanthone. The coupling was perfectly suited for identification and qualitative purposes, but it was initially critical for quantification of results. Analytical response (R2 0.8202) and repeatability were strongly dependent from proper manual positioning of the HPTLC plate into the electronic or vibronic excited-state gas stream of the ion source. This drawback was overcome by using stable isotope-labeled standards shown on the example of caffeine. This way, analytical response (R2 0.9892) and repeatability (RSD < +/- 5.4%, n=6) were improved to a high extent. Spatial resolution by an in-house-built plate holder system was shown to be better than 3 mm. The decay of the signal was observed. The efficacy of this new coupling was compared to a plunger-based extraction device for HPTLC/electrospray ionisation-MS. The latter device showed detectability down to the pg-range, e.g. the limit of quantification for isopropylthioxanthone was found to be 100 pg. Repeatability was comparable (RSD +/- 6.7%), however, without the need of internal standard correction. Analytical response was slightly better and showed a determination coefficient R2 of 0.9983. Similar data were obtained for caffeine as well. Spatial resolution was 2 mm or 4 mm depending on the plunger head used. The comparison showed that HPTLC/DART-TOF-MS is a useful coupling method regarding qualitative aspects and it has the potential to cope also with the difficulties of quantification if isotope-labeled standards were used or if a plate holder system is employed as initially shown.     

Analytical strategy for rapid identification and quantification of lubricant additives in mineral oil by high-performance thin-layer chromatography with UV absorption and fluorescence detection combined with mass spectrometry and infrared spectroscopy

A simple strategy for identification and quantification of lubricant additives in mineral oil was demonstrated by high-performance thin-layer chromatography with UV absorption and fluorescence detection using various coupling options, e.g., with attenuated total reflectance infrared (ATR-IR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, electrospray ionization mass spectrometry (ESI-MS), and direct analysis in real-time mass spectrometry (DART-MS). For the additives zinc bis(O,O'-diisobutyl dithiophosphate), zinc bis(O,O'-didodecyl dithiophosphate), and Anglamol 99, 2 chromatographic systems were developed, i.e., a reversed-phase (RP) system on RP2 plates using an acetonitrile-based mobile phase and a normal-phase system on silica gel 60 plates using a toluene-based gradient. Densitometry was performed by absorption measurement at 220 nm. Repeatabilities (relative standard deviation, n = 6) between 2.2 and 5.5% and correlation coefficients >0.9973 were highly satisfactory for the analysis of these additives in the mineral oil. Primuline reagent was used to improve the detection limit of the lipophilic additives by a factor of 2, followed by fluorescence measurement at UV 366/>400 nm. For rapid identification by ATR-IR and FTIR, the respective additive zones on the plate were online extracted by an interface called ChromeXtract, concentrated, and directly applied for measurements in the wave number range of 4000-400 cm(-1). Identification was confirmed by online ESI-MS within a minute using ChromeXtract and by DART-MS within seconds.     

Hyphenations in planar chromatography

This review is focused on planar chromatography and especially on its most important subcategory high-performance thin-layer chromatography (HPTLC). The image-giving format of the open, planar stationary phase and the post-chromatographic evaporation of the mobile phase ease the performance of various kinds of hyphenations and even super-hyphenations. Examples in the field of natural product search, food and lipid analysis are demonstrated, which point out the hyphenation with effect-directed analysis (EDA) and mass spectrometry and illustrate the efficiency gain. Depending on the task at hand, hyphenations can readily be selected as required to reach the relevant information about the sample, and at the same time, information is obtained for many samples in parallel. The flexibility and the unrivalled features through the planar format valuably assist separation scientists.     

Literatur

Analytical and Bioanalytical Chemistry -     

Ein Beitrag zur Frage der Überschreitungserscheinungen

Zusammenfassung Es war vielfach angenommen worden, daß die spontane Krystallisation unterkühlter Schmelzen und übersättigter Lösungen in Temperaturgebieten, wo nicht immer Erstarrung eintritt, gar nicht als solche aufzufassen sei, sondern nur durch unlösliche Partikel hervorgerufen werden könne. Als Stütze für diese Annahme war die Tatsache angeführt worden, daß verschiedene Proben der gleichen unterkühlten Schmelze unter identischen Bedingungen zu ganz verschiedenen Zeiten erstarren und sich also nicht gleichartig verhalten. Es wurde nun in dieser Arbeit versucht, festzustellen, ob diese Ungleichartigkeit nicht nur scheinbar sei und nur durch den Zufall hervorgerufen werde.Tatsächlich hat sich gezeigt, daß bei längerer Beobachtung einer sehr großen Anzahl Proben weitaus die meisten sich gleichartig verhalten, obzwar sie zu ganz verschiedenen Zeiten auskrystallisieren und daß nur bei einem sehr kleinen Bruchteil die erwähnten Verunreinigungen mitzuwirken scheinen.Es ist mir eine angenehme Pflicht, Herrn Prof. Rothmund für sein reges Interesse an dieser Arbeit und seine liebenswürdige Förderung meinen herzlichsten Dank abzustatten.     

Zur Kenntnis der Pyridanthron- und Anthrakumarin-Synthesen II

Ohne Zusammenfassung     

HPTLC Coupled with Bioluminescence and Mass Spectrometry for Bioactivity-Based Analysis of Secondary Metabolites in Marine Sponges

JPC – Journal of Planar Chromatography – Modern TLC - Rapid analysis by coupling HPTLC with bioluminescence and mass spectrometry enables very fast response to bioactive substances in...