Electrochemical detection environmental analysis

Despite the potential for direct aqueous injection of water samples into reverse phase systems, there are very few cases where this is possible due to the low detection levels normally required for environmental analysis. Using direct aqueous injection and coulometric electrochemical detection, the analysis of phenol and chlorophenols and 2-mercaptobenzothiazole have been achieved at trace levels (methods with limits of detection for phenol 0.034 ngp and 0.8 pgl for mercaptobenzothiazole have been achieved). There is a potential for the use of direct aqueous injection for the analysis of phenol in effluents using fluorescence detection which would be expected to detect down to low mg T. Direct aqueous injection has been used in an automated system similar to that shown in Figure 11.1. The trace enrichment cartridge was replaced by a large sample loop (50 pi) and a coulometric electrochemical detector used instead of the UV detector. 

There is an increasing interest in the development of electrochemical sensors and microsensors for detecting and monitoring NO or N02, due to their importance in clinical and environmental analysis. It has been suggested that transition metal electrocatalysts active for NO or N02 coordination and reduction could be exploited for the development of metal-complex film electrodes for N02 and NO sensing. However, most of the sensory devices reported so... 

Craffeo AP, Riggin RM. 1978. The application of electrochemical detection to the HPLC analysis of nonvolatile pollutants. In Proceedings 4th joint conference on Sensory Environmental Pollution, 637-639. 

Nitrite and nitrate may also be determined by HPLC using anion-exchange columns with either UV absorption or electrochemical detection. These methods are generally used for environmental samples and urine where fewer interfering compounds exist. The more extensive sample preparation and analysis time have limited its use for biological samples. 

However, it should be mentioned that there is a flexible hand-held electrochemical instrument on the market, which can be programmed to be used in a variety of voltammetric/amperometric modes in the field [209]. Although the majority of biosensor applications described in this review were for single analyte detection, it is very likely that future directions will involve development of biosensor arrays for multi-analyte determinations. One example of this approach has been described in an earlier section, where five OPs could be monitored with an array of biosensors based on mutant forms of AChE from D. melanogaster [187]. This array has considerable potential for monitoring the quality of food, such as wheat and fruit. Developments and applications of biosensors in the area of food analysis are expected to grow as consumer demand for improved quality and safety increases. Another area where biosensor developments are likely to increase significantly is in the field of environmental analysis, particularly with respect to the defence of public... 

The analysis of trace substances in environmental science, pharmaceutical and food industries is a challenge since many of these applications demand a continuous monitoring mode. The use of immunosensors based on AuNPs in these applications should also be appropriate. Although there are many recent developments in the immunosensor field, which have potential impacts [36], nevertheless there are few papers concerning environmental analysis with electrochemical detection based on AuNPs. The application of some developed clinical immunosensors can also be extended to the environmental field. 

Electrochemical immunosensors have been widely used for environmental analysis in amperometric, potentiometric, and conductimetric configurations. Amperometric immunosensors measure the current generated by oxidation or reduction of redox substances at the electrode surface, which is held at an appropriate electrical potential. Wilmer et al. measured concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D) in water by using an amperometric immunosensor with a limit of detection of 0.1 Jtg L-1 (Wilmer et al., 1997). Some examples of new developments are the disposable screen-printed electrodes for the detection of polycyclic aromatic hydrocarbons (PAHs)... 

Electrochemical analysis methods assure, generally, the most reliable analytical information because of the simplicity of the sampling process which includes (1) sample dissolution in water or in organic solvents and (2) the possibility of measuring directly and continuously the activity of the species present in the solutions. The preconcentration step is not necessary, because of the sensitivities and limits of detection that characterize the electrochemical methods. The determined species are not necessary to be converted to other measurable species. The electrochemical methods can be successfully used for in vivo monitoring. Spectrometric analysis methods, on the other hand, nearly always require a complex sampling process because of the presence of interfering species. Therapy is necessary to adopt the best separation techniques that can assure, for each analytical method, the most reliable analytical information. Nondestructive techniques are used especially for environmental analysis, and surface analysis assures the best reliability of the analytical information. 

M. Chicharro, A. Zapardiel, E. Bermejo and A. Sanchez, Multiresidue analysis of pesticides in environmental waters by capillary electrophoresis using simultaneous UV and electrochemical detection. Electroanalysis, 16, 311-318, 2004. 

Hybrid techniques such as HPLC-EC or electrochemical detection in combination with flow injection analysis (FIA) will foreseeably play a much more important role in the environmental analysis. 

Such a variety of compounds requires the application of the full panoply of analytical techniques including ELISA, LC, LC-MS, GC-MS (negative and positive ion), GC-MS-MS. Newer methods may include online SPE systems combined with MS or UV or electrochemical detection systems. One important consideration is that analysis of a particular EDC should also include its degradation and/or metabolic products because these too may remain active. So for alkyl phenols the concurrent measurement of the appropriate alkyl phenol ethoxylates and alkyl phenoxycarboxylic acids is environmentally important and a significant analytical challenge. 

EcDs are used for quantitation of compounds which can be easily oxidized or reduced by an applied potential. The standard reduction potential at the electrode is measured and transformed into a detector signal. The number of compounds which can be electrochemically detected is, however, considerably smaller than the number of optically detectable compounds by UV, RI, and FL. To become oxidized or reduced, a compound must possess electrochemically active groups. EcDs are mainly used in clinical, food, and environmental analysis. 

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