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Voltammetry is one of a few analytical methods, suitable for on-line monitoring of trace metals and is sufficiently sensitive in the low μg/L range for this purpose. The advantages of in-situ use of voltammetry are low cost and no or minimal sample change, since the sample is taken automatically and analysis is performed immediately without a need to collect a sample manually risking contamination and metal loss. Automatic monitoring is essential to record the natural variations of metal concentration in natural or industrial water and registration of accident due to natural or anthropogenic reasons. Remote monitoring of trace metals is of special importance due to their biological role. For that reason extensive research has been carried out internationally to develop suitable monitoring methods. The introduction of the innovative solid silver amalgam and other solid metal electrodes made the use of voltammetry suitable for remote monitoring without the use of toxic electrode materials. An automatic trace metal system (ATMS) in combination with solid silver amalgam electrode has been applied for long time monitoring of zinc and iron in waste water. The system worked automatically with manual maintenance every five days. Sample taking, addition of electrolyte solution, stirring, chemical analysis, electrode cleaning and cell draining were carried out automatically, while electrode polishing, filter changing and calibration were carried out manually every five days. For comparison, verification and to provide a better insight into the complex waste water matrix manual samples have been taken regularly and analyzed with ICP-MS. From data obtained from those two analytical methods a speciation study was performed. The automatic voltammetric system for continuous monitoring of trace metals has been applied in three different locations for monitoring of trace metals in different water samples. River water and drainage water has been used as complex natural water matrixes. A solid silver amalgam electrode has been used as a working electrode. The systems have been fully automated to measure the labile concentration of trace metals for a long time monitoring and store the collected data. Manual maintenance has been performed to calibrate the systems and to clean the working electrodes. Additionally, random samples have been collected manually and analyzed by ICP-MS for the total dissolved metal concentration for data verification and getting better insight into sample matrix. Development of the ATMS has provided an opportunity to monitor earthquake precursor in ground water. A monitoring station has been installed in Husavik, Northern Iceland, for monitoring of trace metals in a ground water. The monitored concentration of metals clearly indicated changes in the ground water prior to the earthquake. The results revealed increased electrolabile concentrations of zinc, iron and copper 7-8 days before the earthquake. The increased concentrations lasted until the occurrence of the earthquake and were possible to monitor by the ATMS. The characterization and application of a Nafion coated solid silver amalgam electrode has been tested for the determination of trace metals by differential pulse anodic stripping voltammetry (DPASV). Effect of model surfactants, commonly presented in natural water sources has also been investigated. It has been found that Nafion coated electrode is useful in surfactant containing samples. The performance of the Nafion coated silver amalgam electrode has been investigated and compared to uncoated silver amalgam electrodes. The modification of the electrode yields higher sensitivity. Moreover, the long time use of Nafion film and practical application has been tested by the use of DPASV in polluted river water sample and has shown to work optimal for 2 weeks. New electrodes made of silver germanium and silver antimony have been tested and found to be suitable for determination of metals by DPASV with very good linearity. This type of electrodes extends potential window to both positive and negative direction. Additionally, very good sensitivity for cadmium has been observed. The practical application has been tested for applying the electrodes in monitoring station to monitor zinc concentration in polluted river water. Moreover, Nafion coating has been applied and has been found to be advantageous considering electrode stability. The aim of this work has been to test silver amalgam and other solid metal electrodes for application in natural and environmental water samples for use in long time online monitoring in field. The papers included in this thesis prove successful applications of these electrodes in different environmental matrixes. The results provide positive evidence about the ability of voltammetry in combination with solid metal electrodes (bare and modified with Nafion) as a working electrodes to be employed in automatic monitoring of trace metals in polluted water with minimal sample pretreatment and minimal maintenance of the system. The use of solid metal electrodes avoids the use of liquid mercury in voltammetric analyses, and offers an environmental friendly alternative suitable for use in field. Due to ease to use, nontoxic fabrication materials, wide cathodic potential window, long time stability, and good sensitivity these electrodes can be applied for continuous online monitoring in various environmental and industrial solutions. They are also easy to modify and this extends the application even further. Several experimental projects at different locations and in different water samples (river-, sea-, ground-, drainage- and waste water) have shown sufficiently long time stability without the need for physical presence for maintenance. These results strongly indicate that further developed and improved method may in future be used as a commercial warning system for environmental pollution accidents.

A new method is presented for the determination of electrochemically labile iron in estuarine and coastal seawater. The method is based on differential pulse anodic stripping voltammetry (DPASV) at a rotating silver-alloy disk electrode. The voltammetric parameters include a plating potential of −1.5 V and an activation potential of −5 V for 10s; the seawater is at the original sample pH. The main finding is the presence of a peak for low nmol L−1 levels of iron at −0.55 V ascribed to elemental iron deposited on the bare silver alloy electrode. The peak increased linearly with the iron concentration between

Electrochemical properties of silver electrodes with 2, 4, 6, 10 and 15% bismuth have systematically been investigated with cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). Increased overpotential towards hydrogen evolution reaction (HER) was found as a result of increasing amount of added bismuth. This was also demonstrated in acid solution where zinc was successfully detected on mixed electrodes, but failed on pure silver electrodes. Formation and decomposition of oxide products formed on the different electrode surfaces were studied by cyclic voltammetry, and in addition to known species found on sliver, also peaks attributed to bismuth were achieved and examined. Zinc, cadmium, and lead were measured in the low μg/L range on the mixed electrodes, and good linearity (r2=0.998) was found for 2 to 10 μg/L. Lead was measured down to 0.1 μg/L. Further it was found in DPASV that the zinc peak significantly shifted towards a more negative value with increasing amount of bismuth in the silver electrodes. The same was also observed for cadmium and lead, but in a less extent. Finally a silver electrode containing 15% bismuth was used for continuous analyses in a polluted river for 6 weeks.

An automated voltammetric system using solid electrodes was investigated for continuous and on-line remote monitoring of heavy metals in natural waters. Both a polluted river impacted by a copper mine, and costal seawater were monitored automatically every 30 minutes for six months. The huge difference in these two locations demonstrates the wide application range for this system. Results have been automatically monitored every thirty minutes for six months, and can be correlated against a range of parameters, e.g., season, flow of water, temperature, pH etc.

Liquid mercury is a unique material for the indicator electrode in voltammetry. One reason for this is the high overvoltage for hydrogen formation, thus extending the actual potential window. Diluted amalgams are important reaction products in voltammetric (polarographic) processes, however liquid amalgams are rarely used directly as electrode material for analytical purposes. Because of the fact that voltammetry is very suitable for field and remote monitoring, issues concerning the use of mercury electrodes in environmental analyses have led to considerable research effort aimed at finding alternative tools with acceptable performance. Solid electrodes are such alternatives. Different types of electrodes are reviewed. In particular, solid amalgam electrodes are very promising, with acceptable low toxicity to be used for field measurements. Solid amalgam electrodes are easy and cheap to construct and are stable over a reasonable time up to several weeks. Assessment of the toxicity risk and the long time stability for remote and unattended monitoring is discussed. The differences between solid dental amalgam electrodes, made by using techniques known from dental clinical practice, and mercury film or mercury layer electrodes on solid substrates are reviewed. In particular the dental technique for constructing solid amalgam electrodes gives advantage because it's fast and inexpensive. Also the technique for making dental amalgam has been explored and optimized over years by dentists, giving advantage when the same technique is used for constructing electrodes. Dental amalgam electrodes has been found to act similar to a silver electrodes, but with high overvoltage towards hydrogen. This make it possible to use the dental amalgam electrode for detection of zinc, cobalt and nickel in additions to other metals like lead, copper, thallium, cadmium, bismuth, iron etc. Also the use for reducible organic compounds is expected to be promising.

Issues concerning the use of mercury electrode in environmental analyses has led to considerable research effort aimed at finding alternative tools with acceptable performance. A renewing silver working electrode is investigated. This system has shown a good response to lead and cadmium. Concentrations as low as 10 µg L−1 have been detected for both ions in 0.1 M HCl solutions. The system shows also little interference from copper. A detection limit of 0.5 µg L−1 is estimated for these systems. The electrode system may be used repeatedly without maintenance over a considerable period of time as a new silver film is formed prior to each scan. The silver electrode has been excited, oscillated with both triangular and sinusoidal audio frequency waves. The results indicate that the reproducibility of the response is increased when the electrode is oscillated sinusoidally. A study of the oscillating frequency has also been carried out. The result shows that the detection sensitivity improved considerably when low frequencies typically in the range 40 to 80 Hz are used. Good detection sensitivity, along with the simplicity of use and maintenance renders this system potentially attractive for use in online and field instruments.

Improvement of the sensitivity in trace analyses of about 300% without any increase in the noise level by use of low frequency sound in stripping voltammetry has been successfully carried out and reported in earlier articles. One problem in the former investigations was that the sound source was placed inside the analytical cell. This is inconvenient and gives a risk for contamination. In this article the sound source has been successfully moved out of the analytical cell. This has been made possible by mounting a loud speaker directly under the analytical cell made of inert plastic material that effectively allows the sound waves to be transferred into the analytic solution. This greatly improves the practical application, and the risk for cell contamination is reduced. The three-electrode system used in the experiments consist of a silver/silver chloride/saturated silver chloride/saturated potassium chloride reference electrode, a platinum wire counter electrode, and a mercury or glassy carbon working electrode. The aim of the present work was to investigate how the sound intensity effected the current signal. It was found that a logarithmic increase of the sound intensity resulted in an exponential increase in the current signal. The use of sound exposure to a glassy carbon electrode is also investigated, and results reported show a 60% increase in the current compared to analyses using magnetic stirrer. The standard deviation was found to be 3% for the sound exposed analyses. The enhancement in sensitivity together with the simplicity of using low frequency sound makes this method potentially attractive for use in on-line instruments.

Improving the sensitivity of voltammetric analysis containing low metal concentrations has been attempted by exposure to low frequency sound. It was found that audible sound in the low frequency range, around 100 Hz was very effective for this purpose, with an increase of the analytical signal up to about 300%, without any significant increase in the corresponding noise level. Ordinary stirring has to be avoided during the voltammetric scanning due to the low reproducibility when stirring takes place. Sound exposure, however, can be performed during the entire measurement, and this explains the increased sensitivity. Further it is concluded that sound exposure close to the resonant frequency, has improvement effects at least comparable to stirring, and thus all mechanical stirring can be avoided. Differential pulse anodic stripping voltammetry with a three-electrode cell system was used with a static mercury drop electrode exposed by low frequency sound, a Pt counter-electrode and a silver/silver chloride/saturated silver chloride/saturated potassium chloride reference electrode. However, it is presumed that other modes of voltammetry than DPASV would show similar behavior when exposed to audible sound. Low frequency sound is assumed to influence the physical conditions in the vicinity of the electrode by diffusion layer thinning, to increase the surface concentration. Moreover, the simplicity of using audible sound, with high reproducibility of the measurements, makes this analytical method potentially attractive.

Glassy carbon electrodes modified with Nafion or poly(3-thiopheneacetate) and subsequently plated with mercury where used for lead speciation studies in buffered (0.1 M Tris, pH 8) sodium chloride (0.6 M) solutions. The complexing agents studied were nitrilotriacetic acid, ethylenediamine, oxalic acid and the well known electrode ‘foulant’ huinic acid. Most measurements were performed with square wave anodic stripping voltammetry. Films of Nafion were spin-coated and heat-cured, and poly(3-thiopheneacetate) films were produced by base hydrolysis of electropolymerized poly(ethyl 3-thiopheneacetate). The results are, to a certain extent, supporting the permselective model which has been suggested for Nafion modified electrodes. However, they d o not allow the conclusions that negative species in general are not sensed by these ionomer coated electrodes, because the negatively charged groups of the ionomers may compete successfully for metal cations with chelating agents forming labile species. The nonlabile, negatively charged lead-NTA, where hardly measurable at the polymer-coated electrodes, and the lead-oxalate complexes were also to a certain extent excluded by the ionomers. The response of the Nafion-coated electrode to the positively charged lead-ethylenediamine complexes was in accordance with the earlier reported permselective properties of the polymer when the literature values of the stability constant were used to calculate the lead species distribution. At the poly(3-thiopheneacetate) film, the response to lead-ethylenediamine complexes were higher than to the lead-oxalate complexes, but not as high as one could have expected if charge dependent permselectivity prevailed. As a means to understand the partition of ligands between bulk solution and polymer film, stability constants for the lead complexes of these were determined at the polymer-coated electrodes as well as at the bare mercury film electrode.

Four different polymer-modified mercury film electrodes (MFEs) on a glassy carbon substrate were tested for their ability to determine lead and cadmium in the presence of surfactants. The polymers used for electrode modification were: Nafion, polyaniline, base-hydrolyzed cellulose acetate, and base-hydrolyzed poly(ethyl 3-thiophene acetate). Triton X-100, sodium dodecyl sulfate, dodecyl pyridinium chloride, and bovine serum albumin were chosen as representatives of surface active compounds. It is shown that polymer-covered electrodes are useful in surfactant-containing media in some instances, but none of them remained unaffected by any of the four surfactants. The cellulose acetate electrodes seem to be less affected by proteins than the bare MFE and other modified electrodes. The Nafion and cellulose acetate-coated electrodes were used for the determination of lead in filtered and acidified, but otherwise untreated, water samples from a sewage treatment plant. The results obtained with the cellulose acetate-coated electrode were in good agreement with those from atomic absorption spectroscopy.

A fast differential pulse polarographic method for the determination of the artificial sweeteners acesulfame-K and saccharin in beverages has been developed. Polarograms of the sweeteners are recorded directly in a supporting electrolyte containing 0.1 M NaCl (5.8 g/L) and 0.004 M tetrabutyl ammonium iodide (1.5 g/L). The pH of the supporting electrolyte is adjusted to 1.9 with concentrated HCl. The results are found to be in good agreement with high performance liquid chromatography (HPLC) results.