BISULFITE ADDITION-REACTION AS THE BASIS FOR A HYDROGENSULFITE BULK OPTODE

The reversible addition of hydrogensulfite to benzaldehydes was employ ed as the basic reaction type for the construction of a new kind of hy drogensulfite sensor. The membrane of the sensor consists of plasticiz ed PVC, electrically neutral, lipophilized benzaldehyde compounds, and abasic chromoionophore. The coextraction of a proton together with th e monovalent analyte ibn into the membrane is accompanied by a change in the absorption spectrum due to protonation of the chromoionophore. Hence, an optical transduction in the visible range is achievable. A m athematical formalism is discussed that accounts for the dependence of the sensor response on the properties of the membrane. The experiment al calibration curve for various hydrogensulfite concentrations in buf fered solution is understood, within experimental precision, in terms of the theoretical model. These so-called bulk optode membranes allowe d the detection of hydrogensulfite within a dynamic range of about thr ee decades, down to 6 mg of HSO3-/L (7.6 x 10(-5) M) depending on the pH of the solution. Sufficient selectivity and reproducibility in addi tion to a response time in the range of minutes make this optode a pro mising system for application in environmental and food analysis. This simple and economical sensor will be built in a sulfur dioxide sensin g arrangement.