Ion selective electrodes for penicillin-G based on Mn(III)TPP-Cl and their application in pharmaceutical formulations control by sequential injection analysis

The work describes the construction, evaluation and analytical application of ion selective electrodes sensitive to penicillin-G antibiotics for pharmaceutical products analysis. Different types of polymeric membranes based on PVC (poly(vinyl chloride)) and EVA (ethyl-vinyl-acetate), without internal reference solution, were prepared using 5,10,15,20-tetraphenylporphyrinate (TPP) manganese(III) (Mn(III)TPP-Cl) as electroactive material. Different additives such as tetra- n-octylammoniumbromide (cationic additive) and sodium tetraphenylborate (anionic additive) were incorporated into the membranes to evaluate their influence on electrodes performance. The comparison of the developed detectors was based on general analytical characteristics, selectivity and lifetime. To accomplish the analysis of real samples, two selective membranes composed of 33.0% (w/w) of PVC, 66.0% (w/w) of o-NPOE and 1.0% (w/w) of Mn(III)TPP-Cl (type A) and 33.0% (w/w) of PVC, 66.0% (w/w) of o-NPOE, 1.0% (w/w) of Mn(III)TPP-Cl and 10% mol (relative to the molar concentration of Mn(III)TPP-Cl) of sodium tetraphenylborate (type B) were used. Type A electrode presented a linear response between 2 × 10 −5 and 10 −1 mol l −1 for penicillin-G, a slope of about −59 mV dec −1 and a reproducibility of about ±0.5 mV day −1, while type B exhibited a linear response between 5 × 10 −5 and 10 −1 mol l −1 for penicillin-G, a slope of about −61 mV dec −1 and a reproducibility of about ±0.3 mV day −1. The potentiometric analysis of penicillin-G in pharmaceutical products was carried out by direct potentiometry and the results obtained were compared with those provided by the HPLC reference method. These membranes (type A and type B) were used to prepare tubular electrodes that were coupled to a sequential injection system (SIA) and presented a linear range between 2 × 10 −4 and 1 × 10 −2 mol l −1 and slopes of −59.3 ± 0.8 and −57.3 ± 1.2 mV dec −1, respectively. The tubular electrode constructed using type B membrane (type TB) was used to carry out the potentiometric analysis of penicillin-G in pharmaceutical formulations. The proposed procedure enabled relative errors between 0.1% and 1.2% ( n = 4) and a sampling-rate of about 25 samples per h.