Flow injection analysis of sulfite ion with a potentiometric titanium phosphate–epoxy based membrane sensor

A potentiometric sensor based on the use of titanium phosphate (TP) in epoxy matrix membrane is prepared and characterized. The sensor exhibits near-Nernstian response for many anionic species over the concentration range 10−1–10−5 mol l−1. The origin of response is explained on the basis of the conversion of titanium phosphate cation exchanger into hydrated titanium oxide anion exchanger by the effect of the high pH of the epoxy matrix. The sensitivity and selectivity of the sensor for sulfite ions are optimized by conversion of sulfite into gaseous SOx by acidification, and diffusion of the gas through a membrane-based gas dialyzer followed by potentiometric detection of sulfite ions formed within a flowing recipient stream. No interferences are caused by many common anions and acidic gas releasing species except sulfide and nitrite ions. Determination of sulfite ion at levels as low as 10−4 mol l−1 or less in the presence of nitrite and sulfide ions is performed by using a modified carrier buffer stream (10−2 mol l−1 MES, pH 5.0 containing sulfamic acid) and pretreatment with Pb2+. Advantages offered by the proposed gas dialyzer/flow injection system with TP–epoxy membrane based sensor over traditional ion exchange based sensors includes long life time (>8 months), excellent stability and reproducibility (∼1 mV), fast response time (<30 s), wide pH working range (pH 5–9), high sample throughput (∼60 samples h−1), low detection limit (8×10−6 mol l−1) and high thermal stability (up to 80°C).