CHLORMEQUAT SELECTIVE ELECTRODES: CONSTRUCTION, EVALUATION AND APPLICATION AT FIA SYSTEMS M. GORETI F. SALES, NUNO F.M.C. LINO and PAULA C.B. PAI ´ GA ABSTRACT A flow injection analysis (FIA) system having a chlormequat selective electrode is proposed. Several electro- des with poly(vinyl chloride) based membranes were constructed for this purpose. Comparative character- ization suggested the use of membrane with chlormequat tetraphenylborate and dibutylphthalate. On a single-line FIA set-up, operating with 1 x 10 -2 mol L -1 ionic strength and 6.3 pH, calibration curves presented slopes of 53.6 ± 0.4 mV decade -1 within 5.0 x 10 -6 and 1.0 x 10 -3 mol L -1 , and squared correlation coeffi- cients > 0.9953. The detection limit was 2.2 x 10 -6 mol L -1 and the repeatability equal to ±0.68 mV (0.7%). A dual-channel FIA manifold was therefore constructed, enabling automatic attainment of previous ionic strength and pH conditions and thus eliminating sample preparation steps. Slopes of 45.5 ± 0.2 mV dec- ade -1 along a concentration range of 8.0 x 10 -6 to 1.0 x 10 -3 mol L -1 with a repeatability ±0.4 mV (0.69%) were obtained. Analyses of real samples were performed, and recovery gave results ranging from 96.6 to 101.1%. Keywords: Chlormequat; Growth regulator; Pesticides; Potentiometry; Ion-selective electrode; FIA INTRODUCTION Plant growth retardants are applied in agronomic and horticultural crops to reduce unwanted longitudinal shoot growth without lowering plant productivity. Most growth retardants act by inhibiting gibberellin biosynthesis. To date, four different types of such inhibitors are known, among which are the onium compounds such as chlormequat chloride (CMQ-Cl), the 2-chlorethyltrimethylammonium [1]. Chlormequat (CMQ) is extensively used in agriculture for its growth regulating properties as it also presents the ability to control ozone damage to wheat by protecting it against yield reduction [2]. Overall, the attainment of better crops is connected to the mode and concentration of its application. This feature is directly associated with the amount of active compound among the commercial preparations and for which they must be accurately controlled. Furthermore, this widespread practice may