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51.
A capillary electrophoresis method with direct ultraviolet detection was developed for the analysis of organotin species. Despite the fact that direct detection of organotin compounds by ultraviolet absorption is difficult because most organotins possess poor chromophoric properties, the application of low wavelength (=200 nm) and mixed organic-aqueous media enabled a significant enhancement in sensitivity. A mixed organic-aqueous system (10% methanol/40% acetonitrile/50% H2O) containing acetic acid and tetrabutylammonium perchlorate formed the basis for rapid, efficient and sensitive determinations of organotin cations such as tripropyltin, tributyltin, triphenyltin and diphenyltin. The concentration limits of detection (LOD) for the four organotin compounds were in the range of 0.4–14 M, comparable to that obtained with the most sensitive indirect UV method reported until now, and took advantage of a stable baseline, a symmetric peak shape and an absence of disturbing system peaks. The relative standard deviations (n=7) for the relative peak time and peak area were 0.44–0.77 and 4.8–5.8%, respectively. In addition to sensitivity enhancements, the use of organic-aqueous systems instead of pure aqueous media resulted in improved selectivity and efficiency of separations. 相似文献
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Frank-Michael Matysik L. Nyholm Karin E. Markides 《Fresenius' Journal of Analytical Chemistry》1999,363(3):231-235
End-column electrochemical detection based on either the use of a 25 μm microdisk electrode or a 0.5 mm macrodisk electrode
has been compared with respect to performance and influence on non-aqueous capillary electrophoretic separations. Despite
the much higher coulometric efficiency obtained with the larger disk electrode, the microdisk electrode configuration offers
comparable limits of detection (LOD) for the neutral and positively charged ferrocene compounds employed in conjunction with
a non-aqueous acetonitrile-based buffer. The LODs for ferrocene were found to be 4.0 × 10–8 M and 6.7 × 10–8 M for the microdisk and macrodisk detector, respectively. In addition, both detector arrangements showed different relative
responses for neutral and positively charged analytes. The macroelectrode-based detector introduced additional zone broadening
while this was not found to be the case with the microelectrode arrangement. Using the microelectrode detector, the band broadening
in an electro-osmotically driven flow system was compared to that in a gravity flow-based system. It was demonstrated that
the zone broadening under gravity flow conditions was approximately twice as large as under electro-osmotic flow conditions
for a typical set of experimental parameters.
Received: 1 June 1998 / Revised: 20 August 1998 / Accepted: 24 August 1998 相似文献
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Summary A modified Niederwieser chamber for stepwise gradient elution, consisting of a PTFE capillary to store the series of eluents and a horizontal glass sandwich chamber with a glass distributor was used for the chromatographic separation of complex plant extracts (Seboren, Hemorigen and Pectosol) used in therapy. Densitograms demonstrate markedly improved separations of the extracts in comparison to isocratic elution.Produced by Polish Reagents, Melgiewska 18, 20-234 Lublin, Poland 相似文献
59.
G. Matysik 《Chromatographia》1996,43(5-6):301-303
Summary A mixture of 13 DABS-amino acids has been chromatographed on high-performance silica gel layers developed with eluents containing increasing concentrations of ethyl acetate in heptane + chloroform, using a modification of stepwise multiple development MGD described in a earlier paper. Densitograms were obtained at 485 nm. The MGD method was very efficient, separating all 13 DABS-amino acids, and rapid, owing to the use of a non-aqueous mobile phase. 相似文献
60.
The relationship RM=f (log % S; S- modifier) of several flavonoids and their sugar derivatives was examined by using chromatographic systems chosen by preliminary experiments. The dependence for flavonoid aglycones was flat in the whole mobile phase concentration. Two types of the RM=f (log % S) plots, related to the size of sugar molecule, were found. For glycosides with smaller sugar moiety (arabinose or glucose) the plot was almost parallel, while plots of derivatives with larger sugar moiety (rutose) were convergent. After plotting the relationship RM=f (log % S), even if standards are not available, it is possible to qualify the examined compound as containing single or complex sugar moiety. For all mentioned above compounds the RM=f (log %S) values were given. Silica gel Si60 was used as polar adsorbent. Mobile phase composition was determined in preliminary experiments; it was composed of two solvents: methanol in ethyl acetate in increasing concentration of methanol: 5 – 20%. 相似文献