New type magnetite based solid-state composite pH sensor and applications

In this work, epoxy and silicone based pH electrodes were prepared by using sulphated and pure Fe3O4 either synthesized or natural. Potentiometric performance characteristics of the prepared electrodes were tested in steady-state conditions by using a computer-controlled potentiometric system. Sulphated natural Fe3O4/silicon based pH electrode was determined to have the best performance among the prepared electrodes. The best potentiometric response was reached for an electrode composition of 20% (w/w) sulphated natural Fe3O4, 40% (w/w) graphite, and 40% (w/w) silicon. The electrode, exhibiting a linear response in the pH 2-12 range, showed 30.80±5.4 mV/pH potential difference. The response time of the all solid-state composite pH electrode, though increasing a little from acidic to basic region, was 15 sec in average, and life time of this electrode was determined to be longer than one year. Selectivity coefficients of pH electrodes tested against interfering ions (K+, Na+, Li+, NH4+, NO3-, SO42-, and CH3COO-) were calculated by fixed interference method of mixed solution method for the H3O+ ion. The prepared composite electrode showed to work efficiently in the presence of these anions and cations without any interference effect and had high sensitivity against H3O+ ion.Acid-base titrations and direct pH measurements of various commercial milk and soft drink samples were carried out by using sulphated natural Fe3O4/silicon based pH electrode and glass pH electrode, for reference electrode. The results obtained with the composite pH electrode were comparable to those of glass pH electrode.The flow-rate of carrier and injection volume of a FIA system constituted with a flow-through cell that has a few microliter dead volume prepared with composite pH electrode for routine pH determination were optimized. Reproducibility and stability of the electrodes were tested under dynamic conditions. Potentiometric acid-base titrations and pH measurements of various commercial milk and soft drink samples were carried out in the FIA system developed.