Valproate-Selective Membrane Electrode Based on Gallium(III) Tetraphenylporphyrin

Gallium(III) tetraphenylporphyrin (GaTPP) was found to act as an ionophore for valproate, an agent widely used for anti-epileptic therapy. An electrode constructed using GaTPP and bis(1-butylpentyl)decane-1,10-diyl diglutarate (ETH 469) as a membrane solvent in a poly(vinyl chloride) membrane matrix exhibited a near-Nernstian response to valproate in the concentration range 5×10–5–1×10–2 M with a slope of –55 mV per concentration decade in a buffer solution containing 0.1 M 2-morpholinoethanesulfonic acid (MES)-NaOH (pH 5.5). The lower limit of detection was 20 µM. The electrode displayed the following selectivity sequence: valproate>salicylate> SCN–>benzoate>ClO4–≈F–>NO2–>CH3COO–≈I–>Cl–>NO3–. This electrode was applied to the determination of valproate levels in deproteinized serum samples.