A new analytical methodology for the electrochemical detection of the herbicide maleic hydrazide (3,6-dihydroxypyridazine) by flow injection analysis is presented. This method is supported by the novel application of a palladium-dispersed carbon paste electrode as an amperometric sensor for this herbicide. Maleic hydrazide shows anodic electrochemical activity on carbon-based electrodes (glassy carbon or carbon paste electrodes) in all the pH range. This electrochemical activity is enhanced using metal-dispersed carbon paste electrodes, especially at Pddispersed CPE which displays good oxidation signals at 690 mV (0.050 M phosphate buffer pH 7.0), 140 mV lower than at unmodified electrodes. Under the optimized conditions, the electroanalytical performance of Pd-dispersed CPE in flow injection analysis was excellent, with good reproducibility (RSD 3.3%) and a wide linear range (1.9 Â 10 À7 to 1.0 Â 10 À4 mol L À1 ). A detection limit of 1.4 Â 10 À8 mol L À1 (0.14 ng maleic hydrazide) was obtained for a sample loop of 100 mL at a fixed potential of 700 mV in 0.050 M phosphate buffer solution at pH 7.0 and a flow rate of 2.0 mL min
À1. The proposed method was applied for the maleic hydrazide detection in natural drinking water samples.
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