Ondřej Peš

Off-line coupling of microcolumn separations to desorption mass spectrometry.

The presented review provides comprehensive and detailed characteristics on microcolumn separation techniques off-line coupled to mass spectrometry. Major attention is paid to the classification of junctions between the separation column and the deposition needle and to the process by which the liquid is transferred onto the target. Both contact and non-contact deposition techniques are covered. In order to emphasize the significance of the topic of off-line separations, current commercially available devices have been compared in terms of their potential utilization in analytical chemistry with a summarization of applications used over the past few years.

Off-line coupling of capillary electrophoresis to substrate-assisted laser desorption inductively coupled plasma mass spectrometry.

A novel off-line coupling of capillary electrophoresis (CE) and inductively coupled plasma mass spectrometry (ICPMS) is reported here. The coupling interface is based on the connection of a separation capillary to a deposition capillary via a liquid junction maintaining high separation efficiency and sample utilization due to the self-focusing effect and lack of pressure-induced flow in comparison with nebulizer-like interfaces. The separation is recorded in the form of droplets of CE effluent on a suitable substrate--a poly(ethylene terephthalate) glycol (PETG) sample plate placed inside a partially evacuated chamber. Substrate-assisted laser desorption (SALD) is used to vaporize the sample fractions and to enable further transfer to the ICPMS. The mechanism of SALD is examined using model samples deposited on a variety of substrates. The highest response is obtained for a PETG substrate; sample desorption due to ablation of PETG is found to outweigh direct ablation of sample. Detection limits are given for several metal elements. Finally, a rapid (2.5-min), high-resolution separation of Cr(III)/Cr(VI) species injected in subpicomolar quantity is shown.

Substrate-assisted laser desorption inductively-coupled plasma mass spectrometry for determination of copper in myeloid leukemia cells

This work presents a detailed characterization of substrate-assisted laser desorption inductively coupled plasma mass spectrometry (SALD ICP-MS), a new approach in the determination of trace elements in submicrolitre volumes. SALD ICP-MS allows quantitative analysis of metals in liquid samples with defined volumes deposited onto an absorbing substrate due to complete sample desorption at relatively low laser power density. Analysis of model samples of Cu(II) showed a constant signal over a wide range of laser power density, an independence of signal on desorption modes and a wide linear dynamic range. SALD ICP-MS with its limit of detection for copper below 26 fg in submicrolitre samples was successfully applied to investigate cytotoxic effects of disulfiram in human myeloid leukemia cells U937 depending on intracellular levels of copper.

Seasonal variation in alkaloid composition and antiproliferative activity of Stylophorum lasiocarpum (Oliv.) Fedde

Stylophorum lasiocarpum (Oliv.) Fedde (Papaveraceae) belongs to traditional Chinese medicine herbs but there was minimal information on the content of alkaloids in this plant. Extracts from the aerial part and roots were examined by liquid chromatography with UV and mass spectrometric detection, with nineteen alkaloids identified. Changes in alkaloid content over the entire vegetation period of a one- and two-year old plant were studied. The protoberberine alkaloids, coptisine and stylopine, were found to be the main substances in extracts of the aerial part irrespective of the plant’s age and time of harvest. Variable amounts of protopine, sanguinarine, chelerythrine, chelirubine, macarpine, chelilutine and berberine were also recorded in the aerial part. The roots contained significantly larger quantities of all alkaloids than the aerial part with the levels of most alkaloids varying from May to October, peaking in the middle of the vegetation period. Coptisine was the dominant alkaloid in all samples. The antiproliferative activities of the root extract and of seven individual alkaloids were tested on A375 human malignant melanoma cells. The significant dose-dependent toxicity of the root extract was attributed largely to the quaternary benzo[c]phenanthridine alkaloids, macarpine and sanguinarine.

Modulatory Effects of Eschscholzia californica Alkaloids on Recombinant GABAA Receptors

The California poppy (Eschscholzia californica Cham.) contains a variety of natural compounds including several alkaloids found exclusively in this plant. Because of the sedative, anxiolytic, and analgesic effects, this herb is currently sold in pharmacies in many countries. However, our understanding of these biological effects at the molecular level is still lacking. Alkaloids detected in E. californica could be hypothesized to act at GABAA receptors, which are widely expressed in the brain mainly at the inhibitory interneurons. Electrophysiological studies on a recombinant α 1 β 2 γ 2 GABAA receptor showed no effect of N-methyllaurotetanine at concentrations lower than 30 μM. However, (S)-reticuline behaved as positive allosteric modulator at the α 3, α 5, and α 6 isoforms of GABAA receptors. The depressant properties of aerial parts of E. californica are assigned to chloride-current modulation by (S)-reticuline at the α 3 β 2 γ 2 and α 5 β 2 γ 2 GABAA receptors. Interestingly, α 1, α 3, and α 5 were not significantly affected by (R)-reticuline, 1,2-tetrahydroreticuline, codeine, and morphine—suspected (S)-reticuline metabolites in the rodent brain.