SI lab-on-valve analysis of histamine using potentiometric detection for food quality control

In this work the implementation of a histamine ion-selective electrode for fish freshness control is described. The solid-contact electrode is based on a polymeric membrane incorporating, respectively, α-cyclodextrin as an ionophore, 2-fluorophenyl 2-nitrophenyl ether as a plasticiser and potassium tetrakis(p-chlorophenyl) borate as an ionic additive. The conventionally shaped histamine electrode responded to histamine cation in the pH operational range of 3.5–5.5 with a slope of 31.7 ± 1.3 mV dec−1, and with a practical detection limit of (1.6 ± 0.2) × 10−6 mol L−1. The miniaturisation of the above-described electrode enabled its use as a detector in a sequential-injection lab-on-valve system, yet with a useful lifetime shortened from 10 months to approximately 1 month under continuous operation. The optimised flow conditions were achieved for sample injection volumes of 70 μL propelled towards the detection cell at the flow-rate of 12 μL s−1 during 20 s followed by a flow-rate of 15 μL s−1 during 50 s. The potentiometric analysis of histamine in different kinds of fish furnished results similar to those provided by the chromatographic method. The low cost of the analysis, the speed of the method and the use of a smaller volume and non pollutant reagents justify the use of potentiometry as an alternative analytical technique for this food control.