title: Ion-selective electrodes based on metalloporphyrins for gibberellic acid determination in agricultural products.
abstract: This work describes the construction, evaluation and analytical application of electrodes selective to the gibberellate anion for the determination of gibberellic acid in agricultural products. Several types of PVC membrane electrodes without internal reference solution were prepared using the manganese(III) complex of meso-tetraphenylporphyrin (TPP) as ionophore and dibutyl phthalate (DBP), as plasticizer. The incorporation of lipophilic chemical species as additives, was also carried out aiming the evaluation of the response characteristics of the electrodes. To accomplish the analysis of commercial agricultural products a selective membrane composed of 28.0% (w/w) of PVC, 66.0% (w/w) of plasticizer and 6% (w/w) of ionophore was used, with no additive. This potentiometric unit presented a linear response between 10(-4) and 10(-1) mol L(-1) in gibberellate, a slope of about -69 mV dec(-1) and a reproducibility of about +/-1 mV day(-1). The potentiometric analysis of gibberellic acid in commercial products was carried out by direct potentiometry and the results obtained were compared with those provided by HPLC.
authors.affiliation: CEQUP/Department of Physical Chemistry, Faculty of Pharmacy, Rua Aníbal Cunha 164, 4050-047, Porto, Portugal.
authors.forename: Emília M G
authors.initials: EM
authors.lastname: Santos
authors.forename: Cristina M C M
authors.initials: CM
authors.lastname: Couto
authors.forename: M Conceição B S M
authors.initials: MC
authors.lastname: Montenegro
authors.forename: M Graça P M S
authors.initials: MG
authors.lastname: Neves
authors.forename: Susana L H
authors.initials: SL
authors.lastname: Rebelo
authors.forename: J A S
authors.initials: JA
authors.lastname: Cavaleiro
authors.forename: Boaventura F
authors.initials: BF
authors.lastname: Reis
mesh_terms: D018556:Crops, Agricultural / Q000737:chemistry*; D005875:Gibberellins / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D017736:Ion-Selective Electrodes; D008665:Metalloporphyrins; D015203:Reproducibility of Results
chemical_list: D005875:Gibberellins; D008665:Metalloporphyrins; C007842:gibberellic acid