Optimization of the separation of mono- and dichloroanilines in ion interaction high-performance liquid chromatography

To optimize the ion-interaction chromatographic separation of nine chloroan iline isomers, the effect on retention of six experimental parameters is in vestigated by means of multivariate analysis. The factors considered are th e organic modifier concentration in the mobile phase; the length of the alk yl chain of the alkylammoniumion salts used as the ion-interaction reagents (IIRs); the concentration of IIRs; the pH of the mobile phase, the flaw-ra te and the ionic strength. The use of fractional factorial and star designs allowed one to draw out useful information on the retention mechanism invo lved and to build a model characterized by both descriptive and predictive ability. Concerning descriptions, the results suggest a retention mechanism mainly based on reversed-phase partition, while the main role of the alkyl amine (used as IIR) seems to mask the activity of the residual silanol grou ps on the stationary phase. As a result efficiency is improved. For predict ion purposes, the regression models allow the optimization of the chromatog raphic separation, as regards both resolution and total analysis time. The study allowed one to develop a method able to separate the nine mono- and d ichloroanilines in a total analysis time within 66 min and with detection l imits ranging from 4.0 to 21.0 mu g/l. (C) 1999 Elsevier Science B.V. All r ights reserved.