Effect of ionic strength of buffer on the measurement of erythrocyte electrophoretic mobility

Measurement of the electrophoretic mobility (EM) of biological cells provides information on the electrical properties of the cell surface. Different research groups have used different electrophoretic techniques. It is well known that the osmolality of the buffer used during an experiment exerts a major impact on EM, particularly in biological cells. In previous experiments either high or low ionic strength electrophoresis buffers were used with an arbitrary preference. The aim of this study is to investigate which buffer is more useful for EM measurements, and hence to give greater insight into the results of such experiments.

Blood was drawn from healthy volunteers. Two different buffers were prepared: low ionic and high ionic. Twenty molarity steps were prepared by mixing the buffers in different ratios. Measurements were made using a Zetasizer.

Our data confirmed that the EM fell as ionic strength increased. However, the relationship was biphasic: the first ten points were linear with a steep negative slope and the second set also linear but with a much smaller slope.

EM studies usually have one of two extreme aims: either to compare the inherent surface electrical properties of cells from different sources at the same ionic strength, or to study the influence of different ionic environments on the surface electrical properties of cells from the source. Our data suggest that in the first instance it is better to work at high ionic strength. In the second, low ionic strength is preferable.