Improved reproducibility in capillary electrophoresis through the use of mobility and migration time ratios

Abstract

Fluctuations in solute migration times are an important source of non-reproducibility in the use of capillary electrophoresis (CE) for the analysis of drugs or biological compounds. This work examined the use of mobility ratios ( M) and migration time ratios ( R t ) as a means for obtaining a more reliable description of analyte migration in CE. Replicate injections of amino acids or o-nitrophenol gave a typical within-day precision of ±1% for R t and M (range, 0.5 to 1.5%), but a within-day precision of up to 5% (range, 1.0% to 5.5%) for other measures of solute migration, such as migration times and electrophoretic mobilities. Similar results were noted for the day-to-day variations in these parameters. By using R t values to plot or characterize CE data, it was possible to identify analytes that could not be distinguished from one another based on the use of migration times. Altering the voltage, temperature or current of the CE system produced only small, random variations in M and R t (±1.0% or less), but much larger and systematic changes in the more standard measures of migration. Similar results were obtained when the capillary length or diameter was changed and when various buffer additives were used.