Patent ID: 8441638

Claim:
An apparatus to measure the electrophoretic mobility of particles in an aliquot of a sample solution comprising A) a means to create a beam of coherent monochromatic light; B) an optical means to divide said coherent monochromatic light beam into 1. a sample beam that will pass through said sample, and 2. a reference beam; C) a non-conductive sample cell comprised of 1. a chamber to hold said sample aliquot, 2. electrodes, between which a voltage may be applied across said sample aliquot contained therein, and 3. optical windows in said chamber through which a) said sample beam enters said chamber and scatter from particles in said aliquot contained therein, b) said sample beam and a fraction of the light scattered from said particles in said sample aliquot leaves said sample cell; D) an optical means to collect and collimate said sample beam leaving said sample cell unscattered and said fraction of said sample beam light scattered from said particles and leaving said sample cell; E) means to modulate the optical phase of said reference beam relative to the optical phase of said sample beam; F) an optical means in free space to combine said reference beam with said collimated fraction of light scattered from said particles, forming thereby a third coherent beam; G) an array of photo detector elements onto which said third coherent beam is incident, with each said detector element producing time varying signals therefrom; and H) electronic means comprising a trans-impedance amplifier with a resistor in its feedback loop and a band-pass filter to process said time varying signals received from each of said photo detector elements, an analog-to-digital converter to convert said signals into digital representations and transmit said resultant digital signals to a computer containing an algorithm to calculate therefrom said electrophoretic mobility.