Integrated conductimetric detection: mass distribution in a dynamic sample zone inside a ¯ow injection manifold Francisco J. Andrade, Fernando A. In Äon, Mabel B. Tudino * , Osvaldo E. Troccoli Laboratorio de Ana Âlisis de Trazas, Departamento de Quõ Âmica Inorga Ânica, Analõ Âtica y Quõ Âmica Fõ Âsica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, 1428 Buenos Aires, Argentina Received 23 March 1998; received in revised form 28 July 1998; accepted 29 July 1998 Abstract The insights provided by integrated detection (conductimetric) as a novel approach to follow physical dispersion in continuous-¯ow manifolds are presented. This approach replaces the conventional instantaneous detection and permits to follow the dispersion phenomena, including details of the radial component as the sample plug travels the manifold. Integrated detection permits to look at the radial dispersion in a detailed manner inaccessible to instantaneous detection. The effect of different experimental parameters affecting mass distribution was studied (e.g., ¯ow rate, tube length and diameter, injected sample volume, and reactor type) and their effects on integrated response curves are discussed. A single channel manifold employing aqueous nitric acid as the conducting carrier, and water injected as sample plug, and playing the role of an insulator, provided the physicochemical model for the reported studies. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Integrated conductimetric detection; Physical dispersion; Flow analysis 1. Introduction The relatively small sample volumes commonly used in ¯ow injection analysis (FIA) together with the fact that detection is accomplished in ¯ow-through arrangements, produce signals (peaks) that exhibit a transient character in which the steady state is not reached. The complete characterization and the ade- quate manipulation of the peak pro®le allows the improvement of analytical performance in method development. Therefore, considerable efforts have been dedicated to improve the knowledge of this transient characteristic as well as those factors affect- ing it. This paper provides a different look to the study of dispersion, and adds to the advancement of such a knowledge. According to Ru È zicka and Hansen [1], dispersion is the main issue in ¯ow injection systems as it deter- mines, together with the dynamic characteristics of the detector, the shape and size of the response curve. However, an uniformly acceptable description of dis- persion is currently not available as it has been shown in several reviews [2±4]. Dispersion is a complex phenomenum affecting the analyte while it ``travels'' from the injector to the detector and is related to physical and chemical processes, both kinetic in na- ture, usually discriminated as ``physical dispersion'' and ``chemical dispersion''. This paper will only deal with physical dispersion, that is, the study of mass Analytica Chimica Acta 379 (1999) 99±106 *Corresponding author. Fax: +54-1-576-3360; e-mail: tudino@q3.fcen.uba.ar 0003-2670/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S0003-2670(98)00557-1