Selective pool optode for mercury ion sensing in aqueous solution

A selective pool optode for mercury ion sensing has been developed. The sel ectivity of sensor operation is based on the reagent pool of safranin-iodid e solution trapped behind the Nafion membrane, which is highly permeable to cations and excludes all anions electrostatically. Further selectivity tow ards cations is governed by safranin-iodide reaction, which occurs specific ally in the presence of Hg(II) ions as catalyst. In the absence of Hg(II), no reaction occurs between safranin and iodide. However, when trace of Hg(I I) ions are present the reaction take place within a few minutes and a colo ur change from red to colourless occurs, which can be spectroscopically det ected via optical fibres. This kind of sensor scheme would be suitable for vast number of irreversible reactions and also shows the possibility of opt ode development in cases where the immobilisation of reagent is not suitabl e. Furthermore, for simple measurements the optode can be used as a disposa ble sensor, since it preparation is simple and inexpensive. Since a membran e is employed in the sensor system where the reagent and sample are separat ed, the sensor can be applied for in situ measurements, as sample condition ing (e.g. buffer and ionic strength) would not be necessary. Various experi mental parameters, such as reagent concentration, pH, temperature and volum e have been optimised to obtain high sensitivity and selectivity of measure ments. The optode has a dynamic range 0-50 muM with limit of detection of 5 muM toward Hg(II) ions, with only Ag(T) as the main interferent. (C) 2001 Elsevier Science B.V. Ah rights reserved.