Abstract A method for the identification and quantifica- tion of cross-reacting analytes using competitive immuno- chemical assays is described. The method uses informa- tion both of antibodies with and without significant inhi- bition caused by a sample. Maximum concentrations of all possible analytes were estimated for all antibodies not showing a significant inhibition. These maximum concen- trations could be used to exclude certain analytes from the further identification process. A minimum variance method was used for the identification of analytes from the data given by antibodies showing significant inhibition. All samples were measured in a parallel affinity sensor array (PASA). The PASA system allows the parallel perfor- mance of numerous individual immunochemical assays. Triazines were used as a model substance class. Samples containing either atrazine, terbuthylazine, simazine or deethylatrazine at different concentration levels were gen- erated and analyzed in the PASA system. 11 out of 13 samples were correctly identified, 2 samples could not be identified without doubt, no wrong identification was ob- served. Samples of atrazine, terbuthylazine and simazine at a concentration level of 0.1 μg/L, the EU maximum ad- missible concentration for individual pesticides, and of deethylatrazine at 0.3 μg/L could be quantified. 1 Introduction Immunochemical sensors are a promising tool in environ- mental analysis. They are often used as fast high-through- put screening methods. Most immunochemical sensors show a characteristic lack in selectivity towards cross-re- acting analytes. Therefore, with many immunochemical sensors the identification and quantification of a single compound is not possible and only sum parameters of structurally related compounds can be obtained. Many efforts have been made to overcome the problem of cross-reactivities by means of pattern recognition [1, 2]. Therefore, immunoarrays of different antibodies di- rected to the same class of analytes have been constructed on conventional microtiter plates [3, 4]. A drawback of these arrays is that the number of immunoassays that have to be performed successively increases with the number of antibodies forming the array. Hence, additional infor- mation on a sample is contrary to analysis time and costs. In order to improve immunoarray performance, auto- mated immunosensors with multianalyte ability have been developed [5, 6]. Nevertheless, the described sensor sys- tems suffer from a lack of scalability concerning the num- ber of antibodies forming the array. In order to overcome these problems, we have devel- oped a parallel affinity sensor array (PASA) for the deter- mination of cross-reacting analytes, applying a direct as- say format. Previous results have shown the high scalabil- ity of the PASA system [7]. Therefore, a PASA is ideally suited to carry out parallel, automated immunochemical assays. This paper focuses on the application of the PASA system on the identification and quantification of triazines as a model substance class. We present an improved approach for the identification and quantification of cross-reacting analytes with im- munochemical methods. The method is not dependent on the origin of the experimental data and can be applied to measurements performed on microtiter plates as well as in automated sensor systems. 2 Materials and methods Reagents MAb 4A54 and MAb K4E7 were purchased from Connex (D- 82152 Martinsried, Germany). MAb 4063-21-1 (21-1) was pro- vided by Dr. Schlaeppi, Novartis (Basel, Switzerland) and MAb AM7B2 by Dr. Karu, Immunochemistry Facility, College of Nat- ural Resources, University of California (Berkeley, USA). All other reagents were of the highest purity available. Michael Winklmair · Andreas J. Schuetz · Michael G. Weller · Reinhard Niessner Immunochemical array for the identification of cross-reacting analytes Fresenius J Anal Chem (1999) 363 : 731–737 © Springer-Verlag 1999 Received: 25 September 1998 / Revised: 30 November 1998 / Accepted: 5 December 1998 CONFERENCE CONTRIBUTION M. Winklmair · A. J. Schuetz · M. G. Weller () · R. Niessner Institute of Hydrochemistry, Technical University of Munich, Marchioninistrasse 17, D-81377 München, Germany e-mail: michael.weller@ch.tum.de