Analyzing small samples with high efficiency: capillary batch injection–capillary electrophoresis–mass spectrometry

We present an experimental approach to conducting fast capillary electrophoresis-mass spectrometry (CE-MS) measurements of very small samples in the nanoliter range. This is achieved by injecting sample very efficiently into a CE-MS system. Injection efficiency represents the ratio of injected sample to the amount of sample needed for carrying out the injection process (v/v). In order to increase this injection efficiency from typical values of 10(-3) to 10(-7), the concept of capillary batch injection is used to build an automated, small-footprint injection device for CE-MS. This device is capable of running true multi-sample measurement series, using minimal sample volumes and delivering an injection efficiency of up to 100?%. It is compatible with both aqueous and non-aqueous background electrolytes. As an additional benefit, CE-MS separations of a catecholamine model system in capillaries of 15?cm length under conditions of high electric field strength could be accomplished in 20?s with high separation efficiency. This report details design and specifications of the injection device and shows optimal parameter choices for injections with both high injection efficiency and high separation efficiency. Furthermore, a procedure is presented to coat the tip of a fused silica capillary with a silicone elastomer which acts as a seal between two capillaries.     

Electron spin density distribution in the special pair triplet of Rhodobacter sphaeroides R26 revealed by magnetic field dependence of the solid-state photo-CIDNP effect

Photo-CIDNP (photochemically induced dynamic nuclear polarization) can be observed in frozen and quinone-blocked photosynthetic reaction centers (RCs) as modification of magic-angle spinning (MAS) NMR signal intensity under illumination. Studying the carotenoidless mutant strain R26 of Rhodobacter sphaeroides, we demonstrate by experiment and theory that contributions to the nuclear spin polarization from the three-spin mixing and differential decay mechanism can be separated from polarization generated by the radical pair mechanism, which is partially maintained due to differential relaxation (DR) in the singlet and triplet branch. At a magnetic field of 1.4 T, the latter contribution leads to dramatic signal enhancement of about 80,000 and dominates over the two other mechanisms. The DR mechanism encodes information on the spin density distribution in the donor triplet state. Relative peak intensities in the photo-CIDNP spectra provide a critical test for triplet spin densities computed for different model chemistries and conformations. The unpaired electrons are distributed almost evenly over the two moieties of the special pair of bacteriochlorophylls, with only slight excess in the L branch.     

Chromatography of esculin from stems and bark ofAesculus hippocastanum L. for consecutive vegetative periods

Chromatographia - Coumarin glucosides, esculin and fraxin, were determined in several older and younger layers of stems ofAesculus hippocastanum L. by three methods (TLC-densitometry,...     

Analysis of illicit drugs by nonaqueous capillary electrophoresis and electrochemical detection

Nonaqueous capillary electrophoresis (NACE) was applied to the determination of illicit drugs. The complete separation of amphetamine, methamphetamine, 3,4-methylene dioxy amphetamine (MDA), 3,4-methylene dioxy methamphetamine (MDMA), mescaline, cocaine and benzoylecgonine was obtained using an acetonitrile based buffer solution containing 10 mM sodium acetate and 1 M acetic acid. Electrochemical detection using a Pt microdisk electrode set to a potential of +1.8 V was found to be selective for MDA, MDMA and mescaline. The detection limits for these compounds were in the low ng/mL range which is between 2 and 3 orders of magnitude lower compared to UV-detection.     

Improvement of separation in zonal preparative thin-layer chromatography by gradient elution

Summary Complex extracts of the plants Azulan and Hemorigen were separated by zonal micropreparative thin-layer chromatography in sandwich chambers of the ES and DS type which permitted zonal application of large volumes of sample, without auxiliary equipment. Application from the edge of the layer, in the frontal chromatography mode, markedly improved the separation efficiency and capacity owing to displacement effects which narrow the initially broad zones. Further improvement of separation efficiency and purity of fractions, revealed by densitometry, was observed using stepwise gradient elution. This was confirmed by extraction of some of the separated fractions from the layer and rechromatography; the composition of these fractions were generally simpler than for the corresponding isocratic chromatograms.     

Thin-layer chromatography and densitometry of anthocyanins in the petals of red poppy during development of the flowers

Summary The variation in anthocyanins content of the petals of red poppy (Papaver, Rhoeas) during development of the flower from the closed bud stage have been investigated. Six-stage gradient thin-layer chromatography of the polyzonalstepwise type was used, starting from ethyl acetate, the last eluent fraction being isopropanol-water-acetic acid (65323). Silica Si 60 was used as adsorbent. The densitograms were recorded at 465 nm; they show gradually increasing peaks of red anthocyanins in the petals of closed buds, partly opened buds and fully developed flower and changes in the proportions of several anthocyanins, with various R_F values, during the growth of the flower.Editor's note: see also J. P. Goiffon, M. Brun and M.-J. Bourrier, J. Chromatogr.517, 101 (1991)     

HPTLC-densitometric method of determination of oleanolic acid in the Lamii albi flos

HPTLC combined with densitometric method was used to determine the content of oleanolic acid in acetone extract from the Lamii albi flos L. The plant extract was separated on Si 60 HPTLC plates and determined with the use of two densitometric methods: measurement of fluorescence and absorbance. The content of oleanolic acid was statistically calculated. In a measurement of absorbance in 1 g of the dry Lamii albi flos L. 1458 microg of oleanolic acid was determined (0.147%). In a fluorescence method in 1 g of the plant material 1516 microg of oleanolic acid was determined (0.149%).     

Particular concentration profiles at the electrode with respect to interferometric investigations

The variations of concentration profiles at the working electrode as a consequence of Fick's law and the electroneutrality maintaining rule as considered. The conclusion is drawn that the cause of reversed or twofold interference fringe shifts may be, among others, the effect of the superposition of the concentration gradients of particular species. The calculations are illustrated by original interferograms.