Nickel catecholate complexes, bis(diphenylphosphino)ethanenickelcatecholate [(dppe)NiO(2)C(6)H(3)4-R-1] R-1 = CH3 (1), C(CH3)(3) (2). H (3) and F(4)] were studied using CV and SWV techniques between -1.5 and +1.5 V at 50 mV s(-1) in cathodic and anodic sweeps. Glassy carbon electrode was used with 0.1 M tetrabutylammonium tetrafluroborate (TBATFB) in CH2Cl2. Complexes 1-4 before addition of SO2, showed approximately reversible behaviour (i(pa)/i(pc) approximate to 1 and Delta E approximate to 77-88 mV); oxidation peaks observed between +313 and +524 mV, reduction peaks between +225 and +436 mV, depending on the substituent on the ligand. Detection limit 0.01 ppm, linear range 0.01-20 ppm, sensitivity 0.02 ppm/mV (with SWV) were obtained. The complexes 1 and 2 could be used as voltammetric sensors while complexes 3 and 4 would be suitable as amperometric sensors, for monitoring industrial SO2 emissions. (C) 2009 Elsevier Ltd. All rights reserved.