Journal of Chromatography A, 863 (1999) 1–11 www.elsevier.com / locate / chroma Optimization of the separation of mono- and dichloroanilines in ion interaction high-performance liquid chromatography a a, a b * E. Marengo , M.C. Gennaro ,V. Gianotti , E. Prenesti a ` Dipartimento di Scienze e Tecnologie Avanzate, Universita del Piemonte Orientale Amedeo Avogadro, Corso Borsalino 54-15100, Alessandria, Italy b ` Dipartimento di Chimica Analitica, Universita degli Studi di Torino, Via P . Giuria 5, 10125 Turin, Italy Received 27 July 1999; received in revised form 27 July 1999; accepted 23 August 1999 Abstract To optimize the ion-interaction chromatographic separation of nine chloroaniline isomers, the effect on retention of six experimental parameters is investigated by means of multivariate analysis. The factors considered are the organic modifier concentration in the mobile phase; the length of the alkyl chain of the alkylammoniumion salts used as the ion-interaction reagents (IIRs); the concentration of IIRs; the pH of the mobile phase, the flow-rate and the ionic strength. The use of fractional factorial and star designs allowed one to draw out useful information on the retention mechanism involved 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 alkylamine (used as IIR) seems to mask the activity of the residual silanol groups on the stationary phase. As a result efficiency is improved. For prediction purposes, the regression models allow the optimization of the chromatographic separation, as regards both resolution and total analysis time. The study allowed one to develop a method able to separate the nine mono- and dichloroanilines in a total analysis time within 66 min and with detection limits ranging from 4.0 to 21.0 mg/l.  1999 Elsevier Science B.V. All rights reserved. Keywords: Optimization; Chloroanilines 1. Introduction added to the mobile phase and adsorbed onto the stationary phase surface. The modification makes it According to the most well-established theory, possible the separation on the new stationary phase retention in ion-interaction high-performance liquid of anionic and cationic species and also, since not all chromatography (HPLC) is due to the dynamic the original reversed-phase (RP) sites are modified, formation of an electrical double layer on the also neutral species can be retained, so that ion- reversed stationary phase [1,2]. The double layer is interaction and conventional RP mechanisms can formed when a suitable ion-interaction reagent (IIR), coexist and alternatively predominate, as a function comprising a lipophilic moiety with a polar head, is of the experimental conditions. When working in IIR mode many variables are involved in the retention, such as the chemical *Corresponding author. Tel.: 139-131-283-806; fax: 139-131- properties and the concentration of the ion-inter- 254-410. E-mail address: gennaro@al.unipmn.it (M.C. Gennaro) action reagent, the amount of organic modifier, the 0021-9673 / 99 / $ – see front matter  1999 Elsevier Science B.V. All rights reserved. PII: S0021-9673(99)00914-0