ON THE MEASUREMENT OF DEAD-TIME IN MICELLAR LIQUID-CHROMATOGRAPHY

Modelling of the retention of solutes in micellar liquid chromatograph y allows the optimization of the resolution of a mixture of solutes an d the determination of physico-chemical retention parameters. Both tas ks imply the calculation of capacity factors, which are severely affec ted by the value of dead time. However, the determination of the dead time is not easy when a micellar mobile phase is used owing to the wid e and variable perturbations that appear at the heads of the chromatog rams. Four different criteria of determination of a reference time in the chromatograms are proposed and compared. The criteria are applied to mobile phases containing a varying concentration of surfactant and modifier, in order to observe the dependence of the reference time wit h the mobile phase composition. The study of the influence of the erro rs in the dead time on the modelling of the retention indicated that a n accurate dead time is necessary to calculate retention parameters, b ut an excellent prediction of retention times can be achieved with a w ide range of values of dead time.