4.1.4. Potentiometric Sensors

Potentiometry is based on the detection of the change in electric potential of an electrode when it comes in contact with a certain analyte [85,86]. These systems contain an indicator electrode and a reference electrode. Often potentiometric sensors are commercially available and they include glass coated and metal oxide electrodes, as well as ion-selective electrodes, which are a group of potentiometric sensors, the most widely used among them being a pH-sensitive glass electrode [87].

The signal is generated by charge separation at the interface between ion-selective membrane and the solution due to selective partitioning of ionic species between these two phases [86].

It is an appropriate technique for many applications because it allows the detection and quantification of various ions in wide ranges of concentrations and commercially available equipment can be used.

Potentiometric sensor for HIS detection in fish and wine samples was already reported, consisting of the incorporation of MIPs in poly(vinylchloride) membranes [88]. The LOD achieved was 1.12 × 10⁻⁶ mol/L. The authors concluded that the use of nanoparticles with high specificity and affinity allowed for label-free detection of histamine in real samples. To detect BAs in water electrodes functionalized with a SAM of 4-mercaptobenzoic acid as an artificial receptor for BAs was used. The carboxylate group can recognize the amine group through hydrogen-bonding or electrostatic interactions. The LOD obtained with this method was 25 mm [89].

A solid-state potentiometric sensor for the determination of TYR was optimized with the main purposed of using TYR alone as a food marker. Through this sensor optimization process, the effect of each factor was evaluated. Among those, interferences of several cationic species were evaluated by measuring the potentiometric selectivity coefficients with the separate solution method. The smaller the value, the better the selectivity to the target ion. These coefficients were found to be small enough, thus proving this potentiometric sensor selectivity towards TYR. Although all the examples of detection of BAs have as a principle the potentiometry, the studies showed different functionalization’s of their electrodes, conducting to different LODs.