Detection of ascorbic acid in clinical samples and foodstuffs

Detection of ascorbic acid in clinical samples and foodstuffs using selectively
catalytic electrode surfaces
Supervisor: Ciara K. O’ Sullivan, Nanobiotechnology & Bioanalysis Group, Universitat Rovira I
Virgili, Tarragona, Spain. E-mail: ciara.osullivan@urv.cat
Ascorbate (vitamin C) is a water-soluble substance present in a wide number of foods, such as
fruits and vegetables. [1]. Due to the presence of ascorbate in the mammalian brain, it has an
important role in bioelectrochemistry, neurochemistry and clinical diagnostics applications. It is
also necessary for the formation of collagen, and has been used for the prevention and
treatment of common cold, metal illness, scurvy and cancer [2-4]. The content of ascorbate in
biological fluids can be used to assess the amount of oxidation stress in human metabolism,
and excessive oxidative stress has been linked to cancer, diabetes mellitus and hepatic disease
[5]. Therefore, the determination of ascorbate contents is particularly important in the
pharmaceutical and food industry at different concentration levels. The direct oxidation of
ascorbate at conventional (carbon or metal) electrodes is irreversible [6, 7], and it is thus difficult
to determine ascorbate directly due to its large overpotential and fouling by oxidation products
[8-11]. So, the development of voltammetric methods for the selective determination of
ascorbate has been a major target of electroanalytical research. Therefore, numerous attempts
have been made to reduce the large overpotentials by using various active mediators
immobilized at the electrode surface for the catalysis of electrooxidation of ascorbate [11-20].
Uric acid (UA) and other oxypurines are the principal final products of purine metabolism in the
human body [21]. Abnormal levels of UA are symptoms of several diseases, including gout,
hyperuricemia, and Lesch-Nyan disease [22]. Thus the determination of the concentration of UA
in human blood or urine is a powerful indicator in diagnosing diseases caused by any alteration
in purine metabolism which leads to raising or lowering the UA level and in controlling it during
the use of chemotherapeutic drugs [23-25]. UA and ascorbate commonly coexist in biological
fluids of humans, mainly in serum, blood and urine. The major obstacle in monitoring UA is
interferences from other electroactive constituents, such as ascorbate, which oxidizes close to
the potential of UA on various types of electrodes [26-28]. Therefore much effort has been
made to develop a simple and rapid method for the simultaneous determination of UA and
ascorbate [29-31].
In a recent work, we have developed a modified electrode for the selective detection of ascorbic
acid in urine and would like to investigate further applications of this work. The student will be
trained in basic bioelectrochemistry and the construction and testing of ascorbic acid sensors.
Additionally, the student will be trained in the use of screen-printing for the production of
electrodes. Following this initial training, work will focus on the application of the sensors to the
detection of ascorbic acid in a wide variety of foodstuffs as well as clinical samples, and the
validation of the sensors using the standard method of analysis of titration with 2,6dichloroindophenol. The effect of interferents will be evaluated and the sensors tested for shelflife stability and reproducibility. It is anticipated that a publication will arise from this short
project.
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