When a truck becomes a motorcycle: The impact of sample load on a chiral capillary electrophoresis separation using mixtures of neutral and sulfated cyclodextrins

Chiral capillary electrophoresis (CE) separations are useful for monitoring the presence of a minor isomer at low levels (e.g., <0.5%) in the presence of the major form. In order to quantitate these low levels, it is necessar y to inject large amounts of sample. Separations which appear to have more than enough resolution ("big enough to drive a truck through) for dilute, e qual-concentration mixtures of isomers can become inadequately resolved whe n the necessary amount of sample is injected. This paper addresses some imp ortant considerations in maintaining adequate resolution at high sample loa ds for chiral separations involving a dual-cyclodextrin (CD) system, For hy drophobic compounds, the use of both a neutral and a sulfated CD can be hel pful in achieving a chiral separation. In such a system, the migration time and resolution can be controlled by varying the ratio of neutral to charge d CD concentrations. It is demonstrated here that not only the ratio, but a lso the total CD concentration can significantly affect the separation. In this paper, the impact of the total CD concentration in a dual-CD system (w ith the concentration ratio constant) is examined with respect to peak shap e and resolution. The influences of temperature, capillary diameter, and cu rrent are also considered. The corresponding impact on the amount of sample which can be loaded and successfully separated determines the limit of qua ntitation of the minor isomer. Thus, this information is important in makin g such chiral separations applicable to determinations of low levels of min or isomer in the presence of large amounts of the major form.