Potential-sensing method and apparatus for sensing and characterizing particles by the coulter principle

Abstract

A Coulter apparatus comprises a volumeter assembly containing a conduit through which a particle suspension is caused to pass simultaneously with an electrical current. In preferred embodiments the volumeter assembly comprises at least one traditional Coulter conduit wafer, i.e., a dielectric wafer containing a central circular conduit, and at least two electrically conductive collars. The conductive collars approximate the conduit diameter in thickness, are uninsulated, and are attached to opposite sides of the conduit wafer, the openings being congruent with the Coulter conduit. The Coulter conduit in the dielectric wafer and the openings in the conductive collars collectively form a hydrodynamically smooth conduit, in which the electric and hydrodynamic fields of the Coulter conduit are amended. The electric field is shaped to confine the particle-sensitive zone of the novel volumeter conduit within the conduit's physical boundaries, thereby decreasing the zone's coincidence volume. The hydrodynamic field is caused to develop quasi-laminar flow, thereby increasing the proportion of particles per second transiting the zone's electrically homogeneous areas. The conductive collars are provided with electrical connections and also function as electrodes, used either in a passive mode to allow potential-sensing of particle characteristics or in an active mode in response to such particle characteristics. The volumeter assembly substantially eliminates need to compensate for the effects of particles either transiting the sensitive zone on trajectories near the conduit wall or recursing through the exit portion of the particle-sensitive zone.