Determination of benzoate in cranberry and lingonberry by using a solid-contact benzoate-selective electrode

Benzoic acid is used as a preservative in processed food, and occasionally in cosmetics and pharmaceuticals, while benzoic acid occurs naturally in, e.g., cranberry and lingonberry. Therefore, the determination of benzoate is of interest for product quality assurance, food safety, and personal health. In this work, a solid-contact benzoate-selective electrode (benzoate-ISE) was developed by utilising poly(3,4-ethylenedioxythiophene) (PEDOT) as solid contact and a solvent polymeric membrane containing a 1,3-bis(carbazolyl)urea derivative as ionophore. The benzoate-ISE was characterised in parallel with an ionophore-free control-ISE by electrochemical impedance spectroscopy and potentiometry. The presence of the ionophore in the membrane improved the selectivity to benzoate. Benzoate-ISEs and control-ISEs were used further to determine the benzoate concentration in cranberry and lingonberry by standard addition. The results obtained with both types of ISEs were compared with those obtained by ion chromatography. The results obtained with benzoate-ISEs were consistent with those obtained with ion chromatography. On the contrary, the control-ISE (without ionophore) gave significantly higher benzoate concentrations, especially in the case of cranberry where the benzoate concentration was low (ca 0.2 g kg^-1) compared to lingonberry (ca 1 g kg^-1). Hence, the benzoate-selectivity of the ionophore was crucial to obtain a benzoate-ISE that was practically applicable for determination of benzoate concentrations in cranberry and lingonberry.