New, renewable copper (Hg(Cu)FE) and silver (Hg(Ag)FE) based amalgam film electrodes applied for the determination of elemental sulfur using differential pulse cathodic stripping voltammetry are presented. With surface areas adjustable from 1 to 12 mm 2 , both electrodes are characterized by very good surface reproducibility ( 2%) and long-term stability (a few thousand measurement cycles). The mechanical refreshing of the amalgam film takes about 1 -2 seconds. The effects of various factors such as instrumental parameters and the supporting electrolyte composition were optimized. Interferences from sulfides are easily removed by the addition of acid, and bubbling with argon, for Hg(Ag)FE. In the case of Hg(Cu)FE, sulfides did not interfere. The calibration graph is linear within the studied range from 16 ng L À1 to 4.8 mg L À1 for Hg(Cu)FE, and up to 6.4 mg L À1 for Hg(Ag)FE (t acc ¼ 15 s). The correlation coefficients for the two electrodes were at least 0.997. The detection limits for a low concentration of S(0) and t acc ¼ 60 s are as low as 14 ng L À1 for Hg(Cu)FE and 4 ng L À1 for Hg(Ag)FE. The proposed method was successfully applied and validated by studying the recovery of S(0) from spiked river water.
The TiC working electrode was tested as a novel, potential electrode for anodic stripping voltammetric determination of lead(II) ions traces. To demonstrate the practical applicability of the TiC electrode, an underpotential deposition/ dissolution (UPD) phenomena system in electrolyte without removal of oxygen was tested. The electrode was constructed be means of mounting a TiC disk (˘¼ 3.5 mm) in a resin body. Three compositions of TiC were tested differing in stoichiometry, namely TiC 0.6 , TiC 0.8 , and TiC 1.0 . The key problem is the method of electrochemical activation of the TiC electrode. No or improperly activated electrode is not polarized and is unsuitable as a voltammetric sensor. The TiC electrode was used for the determination of Pb 2þ in concentrations ranging from 1 to 100 nM. The instrumental parameters, composition of supporting electrolyte and procedures of the electrode activation were optimized. The repeatability of DP ASV runs in synthetic solutions covering the entire concentration range is better than 3%. The calibration curve is characterized by a correlation coefficient of at least 0.999. The detection limit was 2 nM for an electrodeposition time of 30 s. The method enables determination of Pb 2þ in the presence of, among the others, high excesses of Cd, Cu, In, Sb, Se, and Tl ions as well as surfactants, Triton X-100 and humic acids. The analysis of Pb 2þ in synthetic solutions with and without surfactants, certified reference material and natural water samples have been performed. The voltammetric data were associated with the structural characterization of the electrode surface using scanning electron microscopy (SEM) and X-ray fluorescence spectroscopy (XRF).
In the work the procedure of chromium(VI) determination by catalytic adsorptive stripping voltammetry (CAdSV) with application of fumed silica, is presented. Two variants of the method are proposed: in the first fumed silica is put directly to the electrolytic cell containing tested solution, in the second the silica is shaken with the sample and next centrifuged. The effectiveness of many surface-active substances removal from synthetic solutions as well as natural water samples, is studied. In the experiments the fumed silica (Sigma-Aldrich) of the specific surface area in the range 200 -390 m 2 g À1 was used. Two types of the working electrodes were applied, i.e., hanging mercury drop electrode (HMDE) and cyclic renewable mercury film electrode (Hg(Ag)FE). In the silica presence i) the relative standard deviation (RSD) for 0.1 mg L À1 Cr(VI) is < 2% (HMDE) and < 5% (Hg(Ag)FE), n ¼ 7, ii) the detection limits estimated deposition time 20 s were respectively 14 ng L À1 (HMDE) and 22 ng L À1 (Hg(Ag)FE). The accuracy of the method was tested by studying the recovery of Cr(VI) from spiked natural water samples.
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