Novel variable volume injector for performing sample introduction in a miniaturised isotachophoresis device.

A microdevice design furnished with a novel sample injector, capable of delivering variable volume samples, for miniaturised isotachophoretic separations is presented. Micromachining by direct milling was used to realise two flow channel network designs on poly(methyl methacrylate) chips. Both designs comprised a wide bore sample channel interfaced, via a short connection channel, to a narrow bore separation channel. Superior injection performance was observed with a connection channel angled at 45 degrees to the separation channel compared to a device using a channel angled at 90 degrees. Automated delivery of electrolytes to the microdevice was demonstrated with both hydrostatic pumping and syringe pumps; both gave reproducible sample injection. A range of different sampling strategies were investigated. Isotachophoretic separations of model analytes (metal ions and an anionic dye) demonstrated the potential of the device. Separations of ten metal cations were achieved in under 475 s.

Integrated moulded polymer electrodes for performing conductivity detection on isotachophoresis microdevices.

The feasibility of using integrated injection moulded polymer electrodes as drive and detection electrodes for performing miniaturised isotachophoresis (ITP) separations with conductivity detection has been demonstrated. Injection moulded electrodes were produced from three different grades of carbon-filled polymer. Two of the electrode designs were found to be suitable for performing on-chip conductivity detection. The high-voltage characteristics of the microdevices were found to be suitable for performing ITP, with a power dissipation up to 1.4 W m(-1) being achieved. Three model separations are presented to demonstrate the separation capability of the miniaturised injection moulded devices. Three anionic dyes, two inorganic anions and a mixture of eight alkaline earth, transition and lanthanide metal cations were analysed.

Determination of metal cations on miniaturised planar polymeric separation devices using isotachophoresis with integrated conductivity detection.

The feasibility of using miniaturised planar polymeric separation devices for the isotachophoretic separation of metal cations was demonstrated. Devices were produced in silicone rubber using a cast moulding fabrication technique. Detection was performed using an integrated single electrode conductivity detector, a design which offers simple fabrication and high resolution. The electrical characteristics of the devices were found to be suitable for performing electroseparations with a power dissipation of up to 1.5 W m-1 being achieved. The separation of a sample containing a mixture of the four metal ions lithium, lanthanum, dysprosium and ytterbium was reproducibly achieved using miniaturised devices. A comparison with a capillary scale separation of the same mixture was made. The miniaturised separations were achieved in under 600 s, which is less than half the time taken for the capillary scale separations.