Amperometric determination of selected persistent organic pollutants and heavy metals using horseradish peroxidase biosensor.
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Date
2010
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Abstract
Persistent organic pollutants and heavy metals are released into the environment through
different anthropogenic processes. They are of concern because they tend to bioaccumulate in the
food chain and show adverse health effects ranging from acute to chronic toxicity. These
pollutants need therefore to be monitored to conserve the environment. Conventionally, samples
are sent to a laboratory for analysis by standard techniques such as chromatography and
spectroscopy. Although these conventional techniques display high accuracy and low detection
limits, they are expensive, require the use of highly trained personnel and tedious sample
preparation. In comparison, electrochemical methods such as biosensors are sensitive, low cost
and simple to operate. In this thesis, the determination of selected persistent organic pollutants
(polybrominated diphenyl ethers, polybrominated biphenyls and polychlorinated biphenyls) and
heavy metals (Cd, Pb and Cu) was achieved by the use of amperometric inhibition biosensor
based on horseradish peroxidase (HRP) immobilized on the surface of platinum-polyaniline
modified electrode.
Polyaniline (PANI) film was electrochemically deposited on the platinum electrode
surface. The film was characterized by cyclic voltammetry and spectrometric techniques. The CV
results proved that the PANI was electroactive and exhibited a fast reversible electrochemistry.
Characteristic Ultraviolet–Visible and Fourier Transform Infrared features of the polymer film
were identified. They revealed that PANI film synthesized in this study is the conductive
emeraldine salt.
Horseradish peroxidase based biosensor was constructed by electrostatic attachment of
the enzyme onto Pt-PANI electrode surface. Spectrometric and cyclic voltammetric results
indicated that the immobilized HRP retained its bioelectrocatalytic activity towards the reduction
of hydrogen peroxide. The Pt/PANI/HRP biosensor showed a linear response over a
concentration range of 0.05 to 3.17 mM with a detection limit of 36.8 nM. Apparent Michaelis-
Menten constant (
app
M K ) was calculated as 1.04 mM. This implied that the HRP biosensor had a
high affinity for H2O2. Furthermore, the fabricated biosensor showed high sensitivity, good
reproducibility, repeatability and long-term stability.
The Pt/PANI/HRP biosensor was applied to the determination of selected persistent
organic pollutants and heavy metals. The latter was found to inhibit the HRP enzyme’s activity.
The percentage inhibition of the investigated persistent organic pollutants decreases in the following order: 2,2´4,4´,6-pentabrominated diphenyl ether> 2-brominated biphenyl> 2-chlorinated biphenyl> 2,2´,4,5,5´-pentachlorinated biphenyl> 2,4,4´-trichlorinated biphenyl. In the case of heavy metals, the degree of inhibition of heavy metals was highest for Cd2+, followed by Cu2+ and then Pb2+. Kinetic study for the amperometric response to H2O2, recorded in the absence and presence of persistent organic pollutants and heavy metals revealed that for polybrominated diphenyl ethers, the inhibition process corresponded to a competitive type whereas for polybrominated biphenyls, polychlorinated biphenyls and heavy metals, it corresponded to the on-competitive type. The biosensor exhibited high sensitivity towards the determination of the metals and persistent organic pollutants as pollutants in real water samples, namely tap water and landfill leachate samples.
Description
Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2010.
Keywords
Persistent pollutants., Biosensors., Heavy metals., Peroxidase., Organic solvents., Theses--Chemistry.