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Voltammetric detection of trace metals at mercury-free electrodes


Project Description

Our aim is to develop new analytical methods to detect trace metals that are of environmental or industrial concerns. Metals (e.g. lead, cadmium, iron, copper, arsenic, mercury) are naturally present in air, water and soils; they can be bio-essentials and/or toxic depending on their concentrations, the organisms of interest and on the chemical/physical forms. Although often present at naturally low concentrations, there are concerns that anthropogenic activities may significantly increase environmental concentrations leading to unknown effects (e.g. [1]). In view of only metal toxicity, there is a strong need to monitor their concentration.
Reliable determination of total concentrations is still challenging, due to low concentrations and challenging matrices. While spectroscopic or spectrometric techniques such as ICP-MS are now widely used because of their sensitivity and wide linear range, they have limited capabilities in solution with a high salt content (e.g. seawater, brine), are expensive, require expert knowledge and are bulky-laboratory based techniques.
An alternative to spectroscopy is stripping voltammetry. This electrochemical method has played a preponderant role in the determination of both total concentration and chemical speciation (e.g. [2,3]). It is very sensitive and can be applied to a wide range of metals whilst requiring minimum equipment and being relatively cheap. The method first requires accumulation of the metal of interest onto an inert material before stripping either by oxidation or reduction. For both physical and chemical reasons, mercury has been and is still the material of choice for the inert material, allowing the analysis at low concentrations of a wide range of metals. However, due to growing concerns about mercury toxicity, alternative non-toxic materials that allow the detection of trace metals at environmentally relevant levels are now urgently needed.
The most common alternative material to mercury is bismuth but applications can also be found for gold, silver, lead, antimony or copper, depending on the target metal. New experimental methods are continuously being developed for an ever-growing list of metals and detection limits are decreasing. In Liverpool, we have developed a solid gold electrode and published several methods for the detection of various toxic and bio-essential metals [4-9]; this work contributed to the development and commercialization of the scTRACE Gold by Metrohm AG, an internationally renowned company (https://www.metrohm.com/en) specialized in analytical detection of a wide range of chemical parameters and species, including metals.
This analytically based, method development, project is in collaboration with Metrohm AG. It aims to develop analytical methods for the detection and speciation of specific metals at mercury-free electrodes. The common challenge that all solid electrodes are facing is to avoid memory effects: small changes at the interface electrode/solution can lead to continuous change of the sensor surface leading to a drift in sensitivity or gradual loss due to e.g. progressive passivation. The aim is to develop analytical methods that are sensitive, reliable, robust and sufficiently convivial to be commercialized and used by non-experts. The following strategy will be used for this project:
- Literature review highlighting past studies achieved at mercury-free techniques;
- Design and preliminary testing of possible analytical routes onto Metrohm’s equipment; this can be based on the direct use of the scTRACE Gold or development of new sensors. either in terms of design or sensing material.
- Validation and quality control along Metrohm’s standard application procedures.

You will use electrochemical, microscopic and spectroscopic techniques to characterise the sensor and optimize its analytical performances. Current projects of interest to Metrohm AG include the simultaneous sensitive detection of sub ppb concentrations of Cd and Pb, the detection and speciation of Fe at low levels and/or the detection of chromium, at the scTRACE Gold electrode or other solid electrodes.

Funding Notes

Full funding (fees, stipend, research support budget) is provided by the University of Liverpool. Formal training is offered through partnership between the Universities of Liverpool and Manchester in both subject specific and transferable skills to the entire PhD cohort and at each University through local Faculty training programmes.

References

1. Cobelo-Garcia A, Filella M, Croot P, Frazzoli C, Du Laing G, Ospina-Alvarez N, Rauch S, Salaun P, Schaefer J, Zimmermann S (2015) COST action TD1407: network on technology-critical elements (NOTICE)-from environmental processes to human health threats. Environmental Science and Pollution Research 22 (19):15188-15194. doi:10.1007/s11356-015-5221-0
2. Batley GE, Florence TM (1974) EVALUATION AND COMPARISON OF SOME TECHNIQUES OF ANODIC-STRIPPING VOLTAMMETRY. J Electroanal Chem 55 (1):23-43
3. Omanovic D, Garnier C, Gibbon-Walsh K, Pizeta I (2015) Electroanalysis in environmental monitoring: Tracking trace metals-A mini review. Electrochem Commun 61:78-83. doi:10.1016/j.elecom.2015.10.007
4. Domingos RF, Carreira S, Galceran J, Salaun P, Pinheiro JP (2016) AGNES at vibrated gold microwire electrode for the direct quantification of free copper concentrations. Anal Chim Acta 920:29-36. doi:10.1016/j.aca.2016.03.035
5. Salaun P, Frezard F (2013) Unexpectedly high levels of antimony (III) in the pentavalent antimonial drug Glucantime: insights from a new voltammetric approach. Anal Bioanal Chem 405 (15):5201-5214. doi:10.1007/s00216-013-6947-5
6. Bi Z, Salaun P, van den Berg CMG (2013) Study of Bare and Mercury-Coated Vibrated Carbon, Gold and Silver Microwire Electrodes for the Determination of Lead and Cadmium in Seawater by Anodic Stripping Voltammetry. Electroanalysis 25 (2):357-366. doi:10.1002/elan.201200446
7. Salaün P, Gibbon-Walsh KB, Alves GMS, Soares HMVM, van den Berg CMG (2012) Determination of arsenic and antimony in seawater by voltammetric and chronopotentiometric stripping using a vibrated gold microwire electrode. Anal Chim Acta 746:53-62. doi:10.1016/j.aca.2012.08.013
8. Gibbon-Walsh K, Salaun P, van den Berg CMG (2011) Determination of manganese and zinc in coastal waters by anodic stripping voltammetry with a vibrating gold microwire electrode. Environmental Chemistry 8 (5):475-484. doi:10.1071/en11023
9. Alves GMS, Magalhaes JMCS, Salaün P, van den Berg CMG, Soares HMVM (2011) Simultaneous electrochemical determination of arsenic, copper, lead and mercury in unpolluted fresh waters using a vibrating gold microwire electrode. Anal Chim Acta 703 (1):1-7

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