Ž . Chemometrics and Intelligent Laboratory Systems 50 2000 263–271 www.elsevier.comrlocaterchemometrics pH-Gradient spectrophotometric data files from flow-injection and continuous flow systems for two- and three-way data analysis Javier Saurina ) , Santiago Hernandez-Cassou, Anna Izquierdo-Ridorsa, Roma Tauler ´ ` Department of Analytical Chemistry, UniÕersity of Barcelona, Diagonal 647, 08028 Barcelona, Spain Received 30 August 1999; received in revised form 30 November 1999; accepted 6 December 1999 Abstract This paper describes a contribution to Chemometrics and Intelligent Laboratory Systems Elsevier’s data base of files. Mixtures of nucleosides and a pharmaceutical preparation composed of cytosine and inosine-5 X -monophosphate are analyzed using three different pH-gradient spectrophotometric flow-injection and continuous flow systems. Results for one of the flow-injection systems and for the continuous-flow system are reported for the first time in this paper. Resolution and quanti- tation of the constituents in the mixtures are given using a multivariate curve resolution method based on a constrained alter- nating least squares optimization. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Acid–base spectrophotometric data; Three-way data analysis; Rank deficiency; Multivariate curve resolution; pH-gradients; Flow systems 1. Introduction Flow-injection analysis and related flow tech- niques with diode-array spectrophotometric detection provide large amounts of data in a very simple and fast way. This work presents data files from three different flow systems: two flow-injection systems referred to as FIA-A and FIA-B, and one conti- nuous-flow system referred to as CCF-A. These three flow systems were designed to generate an on-line pH-gradient in the time domain. The analytes selected in this study were four nu- Ž . cleosides adenosine, cytidine, inosine and uridine Ž and the components of a pharmaceutical drug cyto- ) Corresponding author. Tel.: q 34-93-403-4445; fax: q 34-93- 402-1233. Ž . E-mail address: xavi@zeus.qui.ub.es J. Saurina . X . sine and inosine-5 -monophosphate . Some of these compounds, such as adenosine, cytosine and cytidine have p K values around 4, while uridine, inosine and a inosine-5 X -monophosphate have p K values around 9. a Since the spectra of the corresponding acidic and ba- sic species of the same compound are different, pH variations in the flow system lead to changes in the shape of measured spectra over flow time. The set of time-ordered spectra obtained in the analysis of each sample gave a two-way data matrix. If several sam- ples were simultaneously analyzed, a three-way data set was obtained. Data from FIA-A, FIA-B and CCFA systems were analyzed using a multivariate curve resolution proce- Ž dure based on alternating least squares MCR-ALS . w x method 1–3 . In the present paper, the particular features and modeling strategies to resolve each flow system are outlined. Files giving the results of the 0169-7439r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0169-7439 99 00067-2