Evaluation of a Fe2O3-based graphite-epoxy tubular electrode as pH sensor in flow injection potentiometry

A systematic evaluation of a Fe2O3 graphite-epoxy tubular electrode was inv estigated through pH measurements in a single-channel flow injection system . The tubular electrode was obtained by deposition of a mixture of iron(III ) oxide, graphite powder and epoxy resin into a hole previously made in the injection channel (of a polyuretane resin block). The effect of electrode composition and flow injection parameters (flow rate and injection sample v olume) on the Fe2O3-tubularelectrode response was initially evaluated in qu intuplicate (confidence level of 95%). The best potentiometric response (E/ mV = 178.2 - 26.5 pH; r = 0.9995) was reached in the pH range 2 to 12 with an electrode composition in mass of 30% Fe2O3, 20% graphite and 50% epoxy r esin, injection sample volume of 300 mu L and a flow rate of 3.2 mL min(-1) . The frequency rate was 90 h(-1) and a useful lifetime of at least six mon ths (more than 2000 determinations) was obtained.