1-Pyrrolidine Dicarbodithioate Based Electrodes for Determination of Iron(III) in Lubrication Oil

The lipophillic ammonium salt of 1-pyrrolidine dicarbodithioic acid (PCDT) (1) was introduced as a new selective ionophore for an iron selective electrode. In addition, the effect of immobilization of 18-crown-6 (18CE6) (membrane type-II), on the electrode performance was discussed. The slope of the PCDT-based (I) electrode was (20 mV/decade). The linear concentration range was (10(-5)-10(-1) M) after one day doping. The detection limit for electrode type-(II) was (1.3 x 10(-6)M). For membrane with only 18CE6 (type-III) the linear range and the detection limit were improved (10(-5)-10(-1) M and 3.2 x 10(-6) M, respectively). The pH-range was between 5-11 for type-II, and III electrodes, while it was 7-11 for type-1 electrode. Most of the common cations were tested for the evaluation of the electrode selectivity with correlation to the ionic radii of the tested cations. Among them only Ag(+) and Pb(2+) were the real interference for type-III electrode. Application of using the electrode for the determination of iron in lubrication oil samples was performed with RSD (1.77-2.7\%) and (1.01-2.3\%) for type-II and III electrodes, respectively. The corresponding recovery ranges were (93.0-99.9\%) and (96.3-100\%). The obtained results were compared to those of an atomic absorption spectrophotometric method.