Electrophoretic injection bias in a microchip valving scheme

The pinched injection strategy, implemented on microfabricated fluidic devi ces (microchips), was investigated for an electrophoretic injection bias. B oth the sample loading and dispensing steps were found to contribute to the injection bias whereby neutral species were injected preferentially to ani onic species. In the sample loading step, neutral species filled a larger v olume in the cross intersection than anionic species. Similarly, in the dis pensing step, a larger volume of neutral analyte was injected than anionic analyte. Up to a 27% difference in injected volumes was observed. Fluoresce ntly labeled amino acids were used as model analytes.