In microchip capillary electrophoresis most frequently electrokinetic sample injection is utilized, which does not allow
pressure driven sample handling and is sensitive for pressure drops due to different reservoir levels. For efficient field
tests a multitude of samples have to be processed with the least amount of external equipment. We present the use of a
hydrogel plug to separate the sample from clean buffer to enable independent sample change and buffer refreshment. In-situ
polymerization of the gel does away with complex membrane fabrication techniques. The sample is
electrokinetically injected through the gel and subsequently separated by a voltage between the second gel inlet and the
buffer outlet. By blocking of disturbing flows by the gel barrier a well-defined ion plug is obtained. After each
experiment, the sample and the separation channel can be flushed independently, allowing for a continuous operation
mode in order to process multiple samples.
We present a new method for the direct injection of liquid sample into a capillary electrophoresis (CE) device. Instead of
a double-T injection mechanism, a single inlet provided with a membrane filter is used. From a reservoir on top of this
inlet, the liquid directly enters the separation channel through the membrane. The driving force is a short electrical pulse.
This avoids an additional sample channel, so that the chip needs only three microfluidic connects and no mechanical
sample pumping is demanded. The high injection reproducibility and the comparatively simple setup open up the way for
mobile application of soil analysis.