Comparison of techniques improving the resolution of standard Coulter cell sizing systems

Latex spheres with nominal diameters of 1.857, 2.02, 3.5, 5.2 and 9.69 mum were used to compare improvement in Coulter resolution gained (a) by a simple hydrodynamic focusing modification and (b) by Coulter edit and high resolution circuits. Since pulse size profiles of focused 9.69-mum spheres appeared quasimonodisperse [geometric SD (GSD) congruent to 0.016 congruent to (1 + Arithmetic SD/arithmetic mean)], unfocused profiles of these particles approximated the error function resulting from inhomogeneities in the electric and hydrodynamic sensing-zone fields. As expected, this field error function differed systematically with differences in orifice diameters (30, 50, 70 and 100 mum) and length to diameter ratios (0.75 or 1.2), the error being reduced slightly by the edit circuit and considerably by the high resolution circuit. Data on the 1.857- and 2.02-mum spheres (focused GSDs congruent to 1.06) and 3.5- and 5.2-mum spheres (focused GSDs congruent to 1.6) indicated that the field error affected closely similar particles similarly but its influence on the unfocused population means and variances differed in the GSD regions of 1.06 and 1.60.