Bismuth-tin-film electrodes for Zn(II), Cd(II), and Pb(II) trace analysis

The focus of this work is the novel development and validation of different in situ formed Bi-Sn-film glassy carbon electrodes (BiSnFEs) with changed BKIII):Sn(II) mass concentration ratios (2:8, 4:6, 6:4, 8:2). These electrodes were formed from solutions with 0.5 mg/L and 1.0 mg/L total Bi(III) and Sn(II) mass concentrations therefore, eight new electrodes were designed. BiSnFEs were compared with pure Bi-film electrodes (BiFEs) and Sn-film electrodes (SnFEs). It was shown that all electrodes tested demonstrated a high degree of selectivity for Zn(II), Cd(II), and Pb(II) determination, with clearly separated stripping peaks. The widest linear concentration range for Zn(II) determination was obtained at 19.6-413.9 pg/L using an electrode with a BKIII):Sn(II) ratio of 0.6:0.4 at 0.5 mg/L total mass concentration. For Cd(II) and Pb(II), the widest linear concentration range was measured using pure SnFE at 0.5 mg/L. Moreover, different BiSnFEs significantly increased the method's sensitivity for Zn(II), Cd(II), and Pb(II) determination compared with pure BiFEs and SnFEs. The lowest LOD values were measured using pure BiFEs; however, the LOD values were also relatively low for certain BiSnFEs. An electrode with a Bi(Ill):Sn(II) ratio of 0.4:0.6 at 0.5 mg/L total mass concentration (Le. a final solution containing 0.2 mg/L Bi(III) and 0.3 mg/L Snap to form an in situ electrode) demonstrated the greatest accuracy and precision for simultaneous analyte ion determination. Therefore, improved analytical performance can be obtained using BiSnFE compared to pure BiFE. This work also reports for the first time the use of the electrochemical impedance spectroscopy technique to analyse SnFEs and BiSnFEs. The latter analysis showed that the electro-analytical system is under kinetic- and diffusion-controlled processes for SnFEs, whereas BiSnFE is under a kinetic-controlled process. A possible interference effect on the Zn(II), Cd(II), and Pb(II) stripping signals was tested for the presence of Fe(II), As(III), Na(I), K(I), Ca(II), Mg(II), Cu(II), Sb(III), and NO3- ions in the analysed solution. Finally, an analysis of tap water was performed using an electrode with a Bi(III):Sn(II) ratio of 0.4:0.6 at 0.5 mg/L total mass concentration.