Valving characteristics on microfluidic devices were controlled through manipulation of the electric field strengths during both the sample loading and dispensing steps. Three sample loading profiles for the constant volume valve (pinched injection) in conjunction with four dispensing schemes were investigated to study valving performance. The sample confinement profiles for the sample loading step consisted of a weakly pinched sample, a medium pinched sample, and a strongly pinched sample. Four dispensing schemes varied the electric field strengths in the sample and sample waste channels relative to the analysis channel to control the volume of the sample dispensed from the valve. The axial extent of the sample plug decreased as the electric field strengths in the sample and sample waste channels were raised relative to the analysis channel. In addition, a trade-off existed between sample plug length and sensitivity.