A potential new optical transducer for the detection of Hg(II) in water

The 2-(5-amino-3,4-dicyano-2H-pyrrol-2-ylidene)-1,1,2-tricyanoethanide dye (L') is a specific indicator of Hg(II). It undergoes a colour change from v iolet to blue as a consequence of the formation of the corresponding monopy rrolizinato [HgL] complex. L' was fixed electrostatically on different supp orts by means of anionic exchange. Controlled pore glasses, cross-linked st yrene and cellulose paper were used as supports. L' was also covalently bou nd on controlled pore glass. The immobilisation of L' was carried out and c ontrolled more easily when it was achieved electrostatically rather than co valently. On the other hand, the L'-doped supports resulting from the latte r procedure showed better performance in terms of stability. Two different optode configurations were developed in order to fix the solid support to t he end of a plastic optical fibre bundle. All supports were characterised i n the presence of mercury acetate [Hg(AcO)(2)] aqueous solutions. Particula r attention was given to leakage and stability in the immobilised indicator . In the case of anionic exchange, the best results were obtained using cel lulose paper, but the optode realised was characterised by continuous, alth ough minor, leakage. The covalent immobilisation of the ligand on controlle d pore glass assured good chemical stability, and a detection limit of 0.5 muM was obtained.