Patent ID: 7217350

Claim:
A capillary particle electrophoretic mobility distribution determining apparatus comprising: a holder for a capillary cell adapted to contain a dispersion; a light source; a detector adapted to detect light scattered from a detection zone of the capillary; electric field generating electrodes adapted to generate an electric field in the region of the detection zone; a controller adapted to control the electric field applied by the electrodes; a signal processor adapted to process the signals detected in use by the detector to determine a velocity mobility distribution; and in which the controller is adapted to apply an electric field at a first relatively low frequency and at least a second relatively high frequency, the first frequency being low enough that better velocity distribution resolution is achieved in use than could be achieved at the second frequency, and the second frequency being high enough that the measured velocity distribution is substantially unaffected by electro-osmotic flow; and in which the processor is adapted in use to modify the particle velocity distribution spectrum obtained at the first frequency by shifting it by an offset amount to remove the electro-osmotic velocity, the offset amount being determined using information from measurements at both the first and second frequencies of field reversal.