Measuring mercury ion concentration with a carbon nano tube paste electrode using the cyclic voltammetry method

Mercury sources, contaminations, mercury cycle, detection and treatment techniques: A review

Mercury is considered a toxic pollutant harmful to our human health and the environment. Mercury is highly persistent, volatile and bioaccumulated and enters into the food chain, destroying our ecosystem. The levels of mercury in the water bodies as well as in the atmosphere are affected by anthropogenic and natural activities. In this review, the mercury species as well as the mercury contamination towards water, soil and air are discussed in detail. In addition to that, the sources of mercury and the mercury cycle in the aquatic system are also discussed. The determination of mercury with various methods such as with modified electrodes and nanomaterials was elaborated in brief. The treatment in the removal of mercury such as adsorption, electrooxidation and photocatalysis were explained with recent ideologies and among them, adsorption was considered one of the efficient techniques in terms of cost and mercury removal.

Carbon paste electrodes in the new millennium

In this review (with 500 refs), both electrochemistry and electroanalysis with carbon paste-based electrodes, sensors, and detectors are of interest, when attention is focused on the research activities in the years of new millennium. Concerned are all important aspects of the field, from fundamental investigations with carbon paste as the electrode material, via laboratory examination of the first electrode prototypes, basic and advanced studies of various electrode processes and other phenomena, up to practical applications to the determination of inorganic ions, complexes, and molecules. The latter is presented in a series of extensive tables, offering a nearly complete survey of methods published within the period of 2001–2008. Finally, the latest trends and outstanding achievements are also outlined and future prospects given.

A Highly Selective Luminescent Sensor for Detecting Mercuric Ions in Water

A chemoluminescent sensor utilizing the substrate 2,6-pyridinedicarboxaldehydebis(o-hydroxyphenylimine) (S1) was developed for low-concentration detection of mercuric ions in aqueous solutions. The sensor selectively detects mercury in the presence of sodium, calcium, magnesium, and iron ions. A strong binding was observed between the mercuric ions and the substrate at a pH range of 6.5–7.5, which makes the substrate a distinctive luminescence sensor for detecting mercury at ambient conditions. The sensor shows a linear response towards Hg2+ in the concentration range 5.0 × 10–5 to 2.5 × 10–8 M with a limit of detection of 5.0 × 10–8 M. The sensor can also detect zinc ions at a pH of 10 or higher. The results indicate that this sensor has a promising future for the detection of mercury in real environmental water samples.

Diagnosis of human hepatitis B virus in non-treated blood by the bovine IgG DNA-linked carbon nanotube biosensor

OBJECTIVES

To identify an effective bioassay for human hepatitis B virus (HBV) using voltammetric sensor.

STUDY DESIGN

Electrode was prepared with bovine IgG immobilized onto a DNA-linked carbon nanotube electrode (BIDCE). Analytical BIDCE conditions were optimized through square wave (SW) stripping and cyclic voltammetry (CV).

RESULTS

Optimum parameters of 75 Hz SW frequency, 0.1 V SW amplitude, -1.3 V SW accumulation potential, 100 s accumulation time, and 3.0 mV SW increment potential were obtained. Within working ranges of 0.035-0.242 mg/mL anti-bovine IgG, the relative standard deviation of 0.2 mL HBV was observed to be 0.04 (n=4).

CONCLUSIONS

Diagnostic application was performed through direct assay of HBV in non-treated human blood.

Administering Pesticide Assays in In Vivo-Implanted Biosensors

An analytical pesticide assay of O-ethyl-O-4-(nitrophenyl)phenyl phosphonothioate (EPN) was carried out using the following: a carbon nanotube paste electrode, a mercury-immobilized carbon nanotube paste electrode, a glassy carbon electrode, a metal–gold electrode, and a DNA-immobilized carbon nanotube paste electrode (DPE), which is two-fold more sensitive than other sensors. The DPE was optimized using cyclic and square wave stripping voltammetry. Linear working ranges approached 5–55 mg L–1 EPN and the nano-range of 10–210 ng L–1 in a 0.1 mol L–1 NH4H2PO4 electrolyte solution, with a speedy analytical time of 30-s stripping. The detection limit was 2.57 ng L–1 (7.94 × 10–12 mol L–1), and the precision was 0.102% relative standard deviation (n = 15) at the 10.0 mg L–1 EPN spike. This indicates that the method is more sensitive than common voltammetric methods. This method was applied to fruit samples using patch- and needle-type electrodes, specifically on the skin tissues of an orange and an apple. Moreover, the implanted electrode was interfaced with a fish brain cell at the electrochemical workstation. Results showed that the aforementioned method can be used to conduct a pesticide assay in neuro-treated and non-treated cell systems.

Stripping analysis of mercury(II) ionic solutions under magneto-hydrodynamic convection

Inorganic mercury(II) ions are ubiquitous contaminants of world water systems and thus their determination and removal from the environment are important. The effects of magnetic field on the stripping analysis of mercury(II) ionic solutions have been experimentally investigated. During the stripping analysis, a potential difference is applied across the working and reference electrodes positioned in the working sample and a current density transmits through the electrolyte solution. When the electrochemical cell is exposed to a magnetic field, provided by a permanent magnet, the interaction between the current density and the magnetic field induces Lorentz forces, which, in turn, induce fluid motion. The induced magneto-hydrodynamic (MHD) convection enhances the ionic mass transport during the deposition and stripping steps, which leads to larger anodic current during the stripping step, thus obtaining higher detection sensitivity during the determination of the mercury(II) ions. The Hg2+ ionic solutions with concentrations ranging from 1 nM to 1 microM in the presence and absence of supporting electrolyte, 30 mM nitric acid (HNO 3) and 0.1 M potassium nitrate (KNO 3), under various magnetic flux densities (B=0,0.27,0.53, and 0.71 T) were measured with a linear sweep stripping voltammetry (LSSV) technique. The experimental results demonstrated that the stripping signals of the Hg2+ ions are enhanced, respectively, more than 10 and 30% in the absence and presence of the supporting electrolyte under a magnetic flux density B=0.71 T as compared to the cases in the absence of the magnetic field with all other identical conditions.