CATHODIC STRIPPING VOLTAMMETRIC DETERMINATION AT A HANGING MERCURY DROP ELECTRODE OF THE ENVIRONMENTAL HEAVY-METAL PRECIPITANT TRIMERCAPTO-S-TRIAZINE (TMT)

Trimercapto-s-triazine (TMT) is available commercially for precipitati ng heavy metals in effluents prior to discharge and for recovering sil ver and copper. The TMT content of an effluent for discharge is normal ly monitored down to about 2 ppm by means of its UV absorption at 285 nm. Indirect cathodic-stripping voltammetric methods of determining TM T at sub-ppb levels in standard solutions are reported here. These met hods might prove suitable for the determination of TMT in effluent al levels lower than is currently possible. TMT can be accumulated and de termined indirectly at pH 9.0 as its mercury salt down to sub-ppb leve ls. Accumulation is made at 0 V and the mercury TMT reduction peak is at -0.47 V. Alternatively, by adding nickel(II), TMT can be determined optimally at pH 7.8, using the catalytic nickel peak at -0.73 V and a ccumulating between -0.10 and -0.60 V: at this pH the HgTMT peak at -0 .47 V is small. At slightly higher pH (pH 8.6) the nickel TMT complex can be accumulated directly at -0.40 V, but at this pH, however, a sli ghtly increased sensitivity can be achieved by accumulating TMT as its mercury salt, at -0.1 V in the presence of nickel(II), the nickel TMT complex being formed during the potential sweep on the release of the TMT when the mercury salt is reduced. Unlike many other thiols TMT is not accumulated as its copper(I) salt on addition of copper(II) to th e solution. (C) 1997 Elsevier Science B.V.