Abstract

SANTOS, Emília M. G. et al. Determination of gibberellic acid by sequential injection analysis using a potentiometric detector based on Mn(III)-porphyrin with improved characteristics. J. Braz. Chem. Soc. [online]. 2004, vol.15, n.5, pp. 701-707. ISSN 0103-5053.  http://dx.doi.org/10.1590/S0103-50532004000500015.

This work describes the determination of gibberellic acid in growth promoters formulations used in agriculture by sequential injection analysis and potentiometric detection. The potentiometric detectors with improved characteristics used a PVC membrane prepared with Mn(III)tetraphenylporphyrin-Cl as electroactive specie. Different membranes formulated with several ionic additives were compared in order to select the most suitable one concerning slope, response time, reproducibility and selectivity. A membrane containing 6 wt% of manganese tetraphenylporphyrin-Cl [(Mn(TPP)Cl], 27 wt% of PVC, 66 wt% of dibutylphthalate (DBP), as mediator solvent, and 1 wt% of sodium tetraphenylborate, as anionic additive, was chosen for analytical applications. When coupled to a SIA system the tubular electrode presented a linear range between 5×10^-4 mol L^-1 and 8×10^-3 mol L^-1, a slope of -64.5 ± 1.6 mV/dec and lower potentiometric selectivity coefficients (log K^pot) than those obtained with the conventional electrodes. Standard deviation of 0.01 and 0.4 (n= 4) and a sampling rate of 30 samples/hour were obtained in the analysis of real samples.

Keywords : gibberellic acid; ion selective tubular electrode; SIA; metalloporphyrins; agricultural growth promoters.