Browsing by Author "Md Noh, Mohd Fairulnizal"

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    Electrochemical sensors development for toxic heavy metals
    (2005-03) Md Noh, Mohd Fairulnizal; Tothill, Ibtisam E.
    Heavy metals are toxic environmental pollutants and the development and application of decentralised monitoring equipment for their real time monitoring is gaining rapid popularity. Research within this thesis presents the work undertaken to develop single-use sensors for on-site detection of toxic heavy metals in various environmental matrices. The fabricated three-electrode configuration system (graphite carbon/gold-working electrode, carbon-counter electrode and silver/silver chloride - reference electrode) was coupled with square-wave anodic stripping voltammetry (SWASV), constant current stripping chronopotentiometry (CCSCP) or linear sweep voltammetry (LSV) in order to provide a mean of a relatively inexpensive on-site detector for trace levels of lead (II), copper (II), cadmium (II) and arsenic (III). Detections and determinations of these metals were carried out on bare mercury film screen-printed carbon electrode (SPCE), mercury film SPCEs modified with cysteine and bare screen-printed gold electrode (SPGE) using the optimised procedures developed during this investigation. Modifications of mercury film SPCEs with cysteine provided means of increasing the sensitivity of stripping response obtained at the mercury film SPCE. Detection limits of 0.4, 0.7 and 3 jug V1 were estimated for lead (II), cadmium (II) and copper (II) measurements, respectively for 120 s deposition times. For the bare SPGE, which provides mercury-free sensor, detection limits of 2 and 5.8 jig I' 1 were obtained for lead (II) detection using SWASV at 240 s and 120 s deposition times. Cadmium (II) was found to interfere with lead (II) measurement with SPGE. Arsenic (III) was also detected with SPGE and detection limit of 0.7 pg I' 1 was obtained. Other metals such as lead (II), copper (II) and mercury (II) were tested for interference study with As (III) measurements. With the optimised working conditions, the results obtained indicate that the screen-printed electrochemical sensors are sensitive and reproducible for the CCSCP, SWASV and LSV determination of lead (II), copper (II), cadmium (II) and arsenic (III) in the microgram per litre - milligram per litre range. The reproducibility of the measurements, which also contributed to the interest in developing the electrochemical sensing devices for metal ions, was below 15 % for the mercury film SPCE, cysteine modified SPCE, and SPGE. Surface analysis was conducted using Scanning electron microscopy (SEM) in order to study the electrode surface characterisation. The application of the various electrodes to real samples was demonstrated and proved successful for both waste­ water and soil extracted samples including in situ measurements at a contaminated site in Spain and Germany.