Hydrogen sulfite optical sensor based on a lipophilic guanidinium ionophore Original Research Article

An optical chemical sensor is described for the sensitive and selective detection of hydrogen sulfite. The optode membrane is constructed by entrapping within a plasticized poly(vinyl chloride) membrane a hydrogen sulfite selective carrier (a lipophilic multicyclic guanidinium ionophore) and a proton chromoionophore (4′,5′-dibromofluorescein octadecyl ester). Due to selective transport of hydrogen sulfite into the membrane by the guanidinium-based ionophore, protons are co-extracted into the polymeric membrane phase leading to a change in the ratio of the protonated and deprotonated form of the chromoionophore, and consequently a change in the absorbance value. The optode membrane shows a reproducible and reversible response toward hydrogen sulfite in the concentration range 0.02 mM–0.1 M in 50 mM MES buffer, pH 5.5. In addition, the optode membrane is more selective toward hydrogen sulfite than other anions, including the more lipophilic anions (e.g., thiocyanate, perchlorate, iodide and nitrate).