Response of the Coulter Counter^® Model ZM to Spheres

Abstract

Most existing theories of the response of electrical sensing zone particle size analysers, for instance of the type Coulter Counter®, predict that a significant deviation from sizing linearity will occur at and above some 40% of the aperture diameter. Practical experience, at least for the only test models available ‐ latex spheres ‐ shows that this is not the case in practice. Linear particle response up to 80% of the aperture diameter has been established, confirming the prediction recently made by Scarlett in a new response theory.

Impedance-Based Flow Cytometry for the Measurement of Microparticles

“…The linear range for accurate particle measurements is between 2% and 60% of the flow cell aperture diameter. 25,26 Thus for the standard 125-mm flow cell chamber, the lower level of accuracy for sizing is $2.5-mm microns. To detect submicron particles, the Quanta flow cytometer has been refitted with smaller (25-or 40-mm diameter) flow cells.…”

The Linearity and Response of Focussed Apertures

“…The instrument component is itself divided into two parts; the amplitude of the voltage pulse height for any given value of i above, and the scaling or label applied to that voltage. The relationship between the current pulse from an aperture at the input to a virtual earth amplifier [2] and the voltage output pulse in the measuring circuit is the "conversion gain" of the amplifier. In the generation of model ZM COULTER COUNTER instruments used by Harfield and Cowan previously, the measured conversion gain, C, was 0.141 Vper p A corresponding to 1.7576 threshold units per p l at unit gain.…”

“…Indeed, Harfield and Cowan [l] showed near theoretical sizing resolution by distinguishing in a focussed aperture system between two latex modes only 1.9% apart in diameter. Harfield et al [2] have shown that conventional unfocussed apertures present a linear response to spheres, and Harfield and Cowan [3] demonstrated a cross-sectional (i. e. two dimensional) model that responded to circles linearly to 77% of the "aperture". This was also the finding of earlier workers such as Thorn [4], and Lloyd [5] who made scaled up models of the aperture.…”

Particle size analysis

“…Harfield et al (20,40) evaluated the response of a Coulter counter using spherical latex particles. Their results showed that particle response was linear when analyzing particles up to 80% of the aperature diameter.…”