Showing papers by "Jörg Peter Kutter published in 1998"

Solvent-Programmed Microchip Open-Channel Electrochromatography

Abstract: Open-channel electrochromatography in combination with solvent programming is demonstrated using a microchip device. Channel walls were coated with octadecylsilanes at ambient temperatures, yielding stationary phases for chromatographic separations of neutral dyes. The electroosmotic flow after coating was sufficient to ensure transport of all species and on-chip mixing of isocratic and gradient elution conditions with acetonitrile−buffer mixtures. Chips having different channel depths between 10.2 and 2.9 μm were evaluated for performance, and van Deemter plots were established. Channel depths of about 5 μm were found to be a good compromise between efficiency and ease of operation. Isocratic and gradient elution conditions were easily established and manipulated by computer-controlled application of voltages to the terminals of the microchip. Linear gradients with different slopes, start times, duration times, and start percentages of organic modifier proved to be powerful tools to tune selectivity and ...

Determination of metal cations in microchip electrophoresis using on‐chip complexation and sample stacking

Abstract: A method for the determination of metal cations in aqueous solution using a monolithically integrated microfabricated (microchip) device which allows sample stacking, electrophoretic separation, and postcolumn derivatization is described. The metal cations are detected by UV laser-induced fluorescence following complexation with 8-hydroxyquinoline-5-sulfonic acid. To make use of electrokinetic stacking phenomena, the sample is added to a reservoir containing a low-conductivity buffer and is then introduced into a main separation channel using a gated injection scheme. The complexing agent is added downstream from the injection cross. For two model compounds, magnesium and calcium, detection limits were 0.5 and 18 ppb, respectively. The reproducibility for multiple injections was 1.5% relative standard deviation. © 1998 John Wiley & Sons, Inc. J Micro Sep 10: 313–319, 1998

Influence of Counter Pressure on Separation Performance in SDS‐MEKC

Abstract: The influence of a hydrostatic counter pressure on basic mobility equations in MEKC was analyzed theoretically and investigated experimentally. Taking into account the influence of counter pressure, the modified mobility equations predict a decreased migration time ratio t0/tMC, which was confirmed by results obtained in SDS-MEKC separation of a homologous series of n-alkyl phenyl ketones. As a result, the migration time window could be enlarged in a simple way without having to change the chemistry of the system. Although counter pressures reduce peak efficiency in MEKC by disturbing the plug profile, the concomitant enlargement of the migration time window compensates for this effect. Especially for later migrating compounds, peak resolution could be enhanced at moderate counter pressures. The overall peak capacities within the whole migration window increases slightly when applying counter pressures up to 10 mbar.

Rapid Electrophoretic and Chromatographic Analysis on Microchips

Abstract: Rapid, high-performance electrokinetically-driven separations are easily incorporated into microfabricated devices. The first example is an electrophoretic separation of a binary mixture that was completed in less than 1 millisecond. A separation field strength of 53 kV cm-1 was used (8.6 kV applied to the microchip), and the separation was monitored 200 μm downstream from the injection valve. The second separation technique described is solventprogrammed open-channel electrochromatography. Using a microchip with its channel walls coated with a C-18 stationary phase and applying a five second, linear gradient, a sample of coumarin dyes was resolved in just under 20 seconds.