Władysław W. Kubiak

The cyclic renewable mercury film silver based electrode for determination of molybdenum(VI) traces using adsorptive stripping voltammetry.

The new cyclic renewable mercury film silver based electrode (Hg(Ag)FE), applied for the determination of molybdenum(VI) traces using differential pulse adsorptive cathodic stripping voltammetry (DP AdSV) is presented. The Hg(Ag)FE electrode is characterized by very good surface reproducibility (<or=2%) and long-term stability (more than 2 thousand measurement cycles). The preparation of the Hg(Ag)FE is very simple and its operation may be controlled automatically. The effects of various factors such as: preconcentration potential and time, pulse height, step potential and supporting electrolyte composition are optimized. The calibration graph is linear from 2 nM (192 ng L(-1)) to 200 nM (19 microg L(-1)) for an accumulation time of 15s, with correlation coefficient of 0.9995. For a Hg(Ag)FE with a surface area of 3.5mm(2) the detection limit for an accumulation time of 60s is as low as 8 ng L(-1). The repeatability of the method at a concentration level of the analyte as low as 2.4 microg L(-1), expressed as R.S.D. is 1.3% (n=7). The proposed method was successfully applied and validated by studying the certified reference material TMRAIN-95 and simultaneous recovering of Mo(VI) from spiked water and sediment samples.

Application of sequential injection analysis to anodic stripping voltammetry

Sequential injection analysis (SIA) technique has been applied to anodic stripping voltammetry (ASV). The sample and reagent volumes can easily be controlled by SIA. The technique also allows plating of the mercury film on-line and therefore substantially reduces generation of mercury containing waste. Repeated sample passage through the detector was used during the deposition step to enhance the sensitivity. The way solution handling is done in SIA allows an easy and effective medium exchange procedure increasing the selectivity of the method. This has been demonstrated by changing the stripping medium and having different complexing agents in the stripping solution. The observed potential shifts of the stripping peaks could theoretically be explained in the cases where the complexation constants are known. Calibration and the standard addition methods are discussed and demonstrated by determining copper in tap water as a method of testing the procedure.

Interferences in a polypyrrole-based amperometric ammonia sensor

The main focus of this article is on the interferences encountered when an amperometric ammonia sensor is used in matrices that are typical in clinical samples. The sensor is tested in presence of such interferences and ways to suppress them by sensor modification are presented. Two modification procedures are evaluated by comparing the stabilities, detection limits and signal-to-noise ratios of such sensors. Further, the issue of the ammonia-sensing mechanism of the polypyrrole electrode is addressed. Evidence is shown that a mobile counterion may be required for proper sensor operation. Such evidence supports the idea that polypyrrole undergoes a reversible redox reaction when ammonia is detected at submillimolar concentrations.

Determination of trace arsenic on hanging copper amalgam drop electrode

Hanging copper amalgam drop electrode has been applied for trace determination of arsenic by cathodic stripping analysis. Detection limit for As(III) as low as 0.33nM (0.02mug/L) at deposition time (240s) could be obtained. For seven successive determinations of As(III) at concentration of 5nM relative standard deviation was 2.5% (n=7). Interferences from selected metals and surfactant substances were examined. Absence of copper ions in sample solution causes easier optimization and makes method less vulnerable on contamination. The developed method was validated by analysis of certified reference materials (CRMs) and applied to arsenic determinations in natural water samples.

The sequential injection system with adsorptive stripping voltammetric detection.

Two sequential injection systems have been developed for adsorptive stripping voltammetric measurement. One is for substances adsorbing at mercury, e.g. riboflavin. In this case, a simple arrangement with only sample aspiration is needed. Reproducibility was 3% and detection limit 0.07 muM. The measuring system was applied to determination of riboflavin in vitamin pills and to study the photodegradation process of riboflavin in aqueous solutions. In the second case, metal ions were determined. They have to be complexed before deposition on the mercury surface. Thus, both the sample and the ligand have to be aspirated in the system. In this case, the reproducibility was approximately 6% and the detection limit <0.1 ppm for cadmium, lead and copper when complexation with oxine was used. Dimethylglyoxime was used in determination of nickel and cobalt and nioxime complexes were used in determination of nickel and copper. With these complexing agents, the reproducibility was the same as with oxine, but the metals could be determined at concentrations lower than 0.01 ppm. Application of two ligands in a SIA system with AdSV detection was also studied. Simultaneous determination of copper, lead, cadmium and cobalt was possible by using oxine and dimethylglyoxime. Copper and nickel were simultaneously determined by using dimethylglyoxime and nioxime.

Flow injection analysis as a tool for studying polymer modified electrodes

Abstract Flow injection analysis with a thin-layer amperometric detector is used for elucidating the transport properties of polymer-coated electrodes. The permeation, selectivity and dynamic properties of films such as cellulose-acetate, Nafion, polypyrrole, polyaniline or polyvinylpyridine are thus explored. The advantages of the flow injection manifold for this task are discussed. Equations are derived to support the discussion.

Voltammetric classification of ciders with PLS-DA.

Voltammograms recorded on the glassy carbon electrode (GCE) may be a chemical fingerprints of food samples, enabled distinguishing the origin of the considered products. In this work the objects of the study was 5 Polish ciders of various brands. For each sample 10 scans were recorded by DPV in the potential range between -0.2 and 1.0 V in Britton-Robinson buffer at pH 2.0. The signals preprocessing realized by baseline correction with 4-th degree polynomial and normalization (in 0 to 1 interval), performed to reduce problems with insufficient signals repeatability associated with mechanical renovation of the electrode surface before each measurement. The PLS-DA classification models were built using the training set and then validated using the samples absent in the learning process. The final multi-class model with optimized complexity enables classification of the ciders with 100% sensitivity and specificity, with the exception of one cider, where specificity was 95% (for validation set).

NEW MULTIPURPOSE ELECTROCHEMICAL ANALYZER FOR SCIENTIFIC AND ROUTINE TASKS

This work presents a modernized and improved analyzer, different versions of which have been developed by our team over the past 30 years. Modern solutions and fully integrated chips have been applied to this device, which is dedicated to measuring low and very low levels of a recorded value. The up-to-date software fulfills the requirements of scientists, routine analysts, teachers, and students in the areas of electrochemical measurements and the interpretation of recorded signals. The proposed multipurpose analyzer ensures full measuring capability and allows the control of different electrochemical sensors, including the controlled growth mercury drop electrode (CGMDE). Various typical and more advanced signal processing procedures are built-in and are easily accessible.

Influence of the Electrolyte on Triton X-100 Adsorption on Fumed Silica

Fumed silica was used for adsorption of Triton X-100 from electrolyte solutions. Influence of such parameters as the kind of fumed silica and its pretreatment, pH, ionic strength and ionic composition of solution on the process of surfactant adsorption has been studied using differential capacity measurements at a controlled growth mercury drop electrode. The kinetics of Triton adsorption on silica have also been studied. It was found that under optimal conditions 0.1% of fumed silica removes completely 5 ppm of Triton X-100 in time shorter than 1 minute.

Potentiometric titration of hydroxide, aluminate and carbonate in sodium aluminate solutions

Abstract An automated potentiometric titration of hydroxide, aluminate and carbonate in sodium aluminate solutions is described. The addition of barium chloride before titration with hydrochloric acid enables the three components to be determined in one run, involving neutralization of hydroxide, protonation of aluminate and dissolution of barium carbonate. The accuracy and precision of the method are satisfactory for a rapid method used for control of aluminum oxide production.