Increased Resolution of Size Distributions with the Coulter Counter

Abstract

AbstractThe limiting resolution of Coulter size measurements, the size within which two separate populations can be distinguished, is discussed in relation to the standard aperture.Electronic pulse editing, by comparing pulse height to width, enables small particles to be resolved from baseline instrument noise, but can give incomplete resolution of ultra‐narrow distributions from artefactually produced peaks using the standard aperture. Improvements in the minimum measurable size and in sizing resolution of narrow size ranges are also shown to be possible by improving the signal quality from the Coulter aperture.A novel mathematical approach is described for the derivation of true size spectra for narrow particle size distributions by deconvolution of the composite spectra resulting from the effect of the inhomogeneous electric field in the Coulter aperture. Simple empirical equations are used derived from the location and amplitude of the spurious peaks observed in such composites relative to the genuine peaks.The method is applied to three “industrial” materials (wide size range samples) to determine the likelihood that such size ranges are affected by the spurious or artefactual peaks. A fresh blood sample deconvoluted by this method is shown to be apparently composed of more than one population of cells.