Electrochemical detection methods

As a universal method for the detection of ionic species, conductometric detection has the highest significance in ion chromatography. The fundamental 

Handbook cflon Otmmatography, Fourth Edition. Joachim Weiss. 

Handbook of Ion Chromatography, Third, Completely Revised and Enlarged Edition. Joachim Weiss Copyright 2004 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 3-527-28701-9 

---

The anti-DNA antibody has been used as a marker molecule of Systemic Lupus Erthematosus (SLE) which is a severe autoimmune disease. Enzyme immunoassay is the most reliable, widely used method of assay however, the electrochemical detection method reported here should be interesting for the purpose of a rapid and convenient diagnostic tool of SLE. 

V- Much effort has been expended in the development of more sensitive methods for the analysis and detection of catecholamines. They have been analyzed as the dansyl derivatives (376) or after precolumn derivati-zation with o-phthalaldehyde (377, 378). Postcolumn derivatization followed by fluorometric analysis have been described in which the fluoro-phore was formed with o-phthalaldehyde (379) or with 9,10-dimethoxyanthracene-2-sulfonate as the ion-pair (380). Several laboratories have shown the sensitivity and specificity in electrochemical detection methods (381 -383). 

Despite being relatively new technology, aptamers have a tremendous potential and can be envisioned to rival antibodies and other traditional recognition elements for molecular detection and recognition, due to their inherent affinity, selectivity, and ease of synthesis. In addition, the combination of aptasensors with electrochemical detection methods has the added advantage of further cost reduction and miniaturization of such systems. 

Semiconductor NPs, such as CdS, are commonly used as labels for optical detection of bioanalytes due to their inherent fluorescent properties. Several reviews on semiconductor NPs as fluorescent labels for biosensors are currently available in the literature.53 However, since these fluorescent labels are beyond the scope of this chapter, only semiconductor NPs that involve electrochemical detection methods (stripping voltammetry or photoelectrochemical detection) will be discussed. 

Two analytical methods for priority pollutants specified by the USEPA (38) use HPLC separation and fluorescence or electrochemical detection. Method 605, 40 CFR Part 136, determines benzidine and 3,3-dichlorobenzidine by amperometric detection at +0.80 V, versus a silver/silver chloride reference electrode, at a glassy carbon electrode. Separation is achieved with a 1 1 (v/v) mixture of acetonitrile and a pH 4.7 acetate buffer (1 M) under isocratic conditions on an ethyl-bonded reversed-phase column. Lower limits of detection are reported to be 0.05 /xg/L for benzidine and 0.1 /xg/L for 3,3-dichlorobenzidine. Method 610, 40 CFR Part 136, determines 16 PAHs by either GC or HPLC. The HPLC method is required when all 16 PAHs need to be individually determined. The GC method, which uses a packed column, cannot adequately individually resolve all 16 PAHs. The method specifies gradient elution of the PAHs from a reversed-phase analytical column and fluorescence detection with an excitation wavelength of 280 nm and an emission wavelength of 389 nm for all but three PAHs naphthalene, acenaphthylene, and acenaphthene. As a result of weak fluorescence, these three PAHs are detected with greater sensitivity by UV-absorption detection at 254 nm. Thus, the method requires that fluores-... 

Many specific and highly sensitive fluorometric and electrochemical detection methods for various analytes are available. The combination of such detection schemes with a DS-based collection system provides a combination of sensitive and affordable instrumentation for atmospheric measurements. A step-by-step construction and operation manual for a DS-based fluorometric H202 analyzer is available (94). With a change in the reagents, the calibration source, and the conditions of the fluorometric measurement, such an instrument is readily reconfigured for a different analyte. The 1992 fabrication cost of a complete DS instrument that utilizes fluorometric detection and includes a thermostated calibration source from commercially available components is approximately 12,000. 

Isosorbide dinitrate can be determined by reversed-phase h.p.l.c. (Ci8-phase) using48 methanol as the mobile phase and detection at 218 nm for other methods, see Refs. 47 -49a. Among other organic nitrates, isosorbide dinitrate can be selectively detected by h.p.l.c. by first using a photolysis step, followed by an electrochemical detection method.30,31... 

Acworth IN, Bogdanov MB, McCabe DR, Beal MF (1999) Estimation of hydroxyl free radical levels in vivo based on liquid chromatography with electrochemical detection. Methods Enzymol... 

Kotani, A., Kusu, F., Takamura, K. 2002. New electrochemical detection method in high-performance liquid chromatography for determining free fatty acids. Anal. Chim. Acta. 465, 199-206. 

DNA is fixed directly on the graphite-epoxy composite (GEC) substrate by dry-adsorption [18-20]. Hybridization was confirmed through biotinylated target DNA and HRP-SA conjugate interaction. It is possible to measure very low concentrations of target DNA with the electrochemical detection method. 

In the last decade, a large amount of effort has been devoted to the development of detection methods which are compatible for use in combination with DNA sensor array platforms and are sufficiently sensitive to detect single point mutations using minute amounts of sample [164,166]. Electrochemical detection methods are a particularly interesting alternative to the methods described above due to their simplicity and low cost. 

Milhury, P.E. Analysis of complex mixtures of flavonoids and polyphenols hy high-performance hquid chromatography electrochemical detection methods. Methods Enzy-mol. 2001, 335, 15-26. 

Sensitive Optical Detectors. More sensitive optical techniques that have been used with CE include fluorescence, refractive index, chemiluminescence, Raman spectrophotometry, and circular dichroism. The most sensitive optical detection method used in CE is laser-induced fluorescence (LIE), which is capable of detection limits in the 10 to 10" mol (or better) range. This detection mode is easily accomplished with analytes that are either easily labeled with a fluorescent substrate (e.g., intercalators for double-stranded DNA) or are naturally fluorescent (e.g., proteins or peptides containing tryptophan). CE systems have also been interfaced with mass spectrometers, and electrochemical detection methods have been developed, although such detectors must be isolated electrically from the electrophoretic voltages. 

An electrochemical detection method has been applied to the analysis of some isoquinoline... 

Whelpton reported the analysis of physostigmlne in plasma using a silica gel column with the mobile phase methanol - 1 M ammonium nitrate (pH 8.6)(9 1) in combination with an electrochemical detection method. 

White developed an electrochemical detection method for the HPLC, also suitable for the... 

This kind of amperometry is the most widely used electrochemical detection method in liquid chromatography. A constant DC potential is continuously applied to the electrodes of the detector cell. The theory of amperometry with constant working potential does not differ from the theory of hydrodynamic voltammetry, even though the applied potential remains constant. 

These results emphasize the advantages of merging electrochemical detection methods with adjusted design and process of MEMS, which result in fast response... 

Biochemical process, which intends to prodnce a measurable signal, has immense benefit while utilizing enzymatic activity. Since enzymes form continu-onsly, and each enzyme reacts with many snbstrate molecules successively, this enzymatic mechanism serves as an intrinsic amplifier consequently the signal is produced faster, more sensitively, and increasing with time [14]. Combining enzymatic system with electrochemical detection methods enables measurements in tnrbid solutions and under anaerobic conditions [9]. 

There are about 20 laboratory based ASTM standard test methods available for the determination of sulfur in various petroleum products and lubricant samples [6]. These utilize diverse analytical techniques and have applicability range sparming from m% to low mg/kg levels. However, at the very low end of sulfur analysis there are only three or four test methods which can adequately determine sulfur in such fuels. These lab-based standard test methods include ASTM D 2622 - wavelength dispersive X-ray fluorescence, D 3120 - oxidative microcoulometry, D 5453 - combustion UV-fluorescence, and D 6920 - oxidative combustion electrochemical detection methods. Without a doubt, the most widely used two methods out of these in oil industry laboratories are D 2622 and D 5453. Studies have shown that at truly ultra-low levels of sulfur only D 5453 can deliver accurate and precise results. This conclusion has... 

---