Salt effects in capillary zone electrophoresis - IV. Resolution versus time and the effect of potassium phosphate and its concentration in the high ionic strength separation of sulphonamides

The effects of potassium phosphate buffer and its concentration upon the ca pillary zone electrophoretic separation of 23 sulphonamides and a neutral m arker were examined at pH 7. The resolution between the pairs was improved with the increased concentration of the buffer from 65 mM to 174 mM. Ninete en sulphonamides, a hydrolysis product and several unidentified minor compo nents were baseline resolved in both 101 and 138 mM phosphate buffers. In 1 74 mM buffer all 21 ionised sulphonamides and the other compounds were sepa rated. A simple relationship between the resolution of analyte pairs (R-s) and the square root of the mean analysis time for the pair (root<(t(app))ov er bar>) was derived, but few of the pairs displayed this behaviour. For th e majority of pairs of compounds, Joule heating appeared to cause a maximum in the R-s versus root<(t(app))over bar> relationship, while non-ideality and shifts in ionisation with increasing salt concentration appeared domina nt in other cases. (C) 1999 Elsevier Science B.V. All rights reserved.