Conductivity detection and quantitation of isotachophoretic analytes on a planar chip with on-line coupled separation channels

A polp(methylmethacrylate) chip, provided with two separation channels in t he column-coupling (CC) arrangement and on-column conductivity detection se nsors and intended, mainly, to isotachophoresis (ITP) and ITP-capillary zon e electrophoresis (CZE) separations was developed recently. The present wor k was aimed at assessing its performance relevant to the detection and quan titation of the ITP analytes. Hydrodynamic (HDF) and electroosmotic (EOF) h ows of the solution in the separation compartment of the CC chip were suppr essed and electrophoresis was a dominant transport process in the ITP separ ations with model analytes carried out in this context. When the surfaces o f the detection electrodes of the conductivity sensors on the chip were app ropriately cleaned qualitative indices of the test analytes [relative step heights (RSHs)], provided by a particular detection sensor, agreed within 1 % (expressed via RSDs of the RSH values). Their long-term reproducibilities for one sensor, as estimated from 70 ITP runs repeated in 5 days, were 2% or less. Sensor-to-sensor and chip-to-chip fluctuations of the RSH values f or the test analytes were 2.5% or less. In addition? experimentally obtaine d RSH values agreed well with those predicted by the calculations based on the ITP steady-state model. Reproducibilities of the migration velocities a ttainable on the CC chips with suppressed EOF and HDF, assessed from the mi gration time measurements of the ITP boundary between well-defined position s on the separation channels of the chips (140 repeated runs on three chips ), ranged from 1.4 to 3.3% for the migration times in the range of 100-200 s. Within-day repeatabilities of the time-based zone lengths for the test a nalytes characterized 2% RSDs, while their day-to-day repeatabilities were less than 5%. Chip-to-chip reproducibilities of the zone lengths, assessed from the data obtained on three chips for 100 ITP runs, were 5-8%. (C) 2001 Elsevier Science B.V All rights reserved.