Electrochemical array

Figure 16.5 Schematic of the electrochemical array cell. CE, counter-electrode compartment WE, working electrode compartment RE, reference electrode compartment GS, glass sinter GS/GI, gas inlet with glass sinter.

Because process mixtures are complex, specialized detectors may substitute for separation efficiency. One specialized detector is the array amperometric detector, which allows selective detection of electrochemically active compounds.23 Electrochemical array detectors are discussed in greater detail in Chapter 5. Many pharmaceutical compounds are chiral, so a detector capable of determining optical purity would be extremely useful in monitoring synthetic reactions. A double-beam circular dichroism detector using a laser as the source was used for the selective detection of chiral cobalt compounds.24 The double-beam, single-source construction reduces the limitations of flicker noise. Chemiluminescence of an ozonized mixture was used as the principle for a sulfur-selective detector used to analyze pesticides, proteins, and blood thiols from rat plasma.25 Chemiluminescence using bis (2,4, 6-trichlorophenyl) oxalate was used for the selective detection of catalytically reduced nitrated polycyclic aromatic hydrocarbons from diesel exhaust.26... 

Microcoulometric titration is used as the detection mode in some commercial sulfur-specific analysers. Sulfur in PP and waxes (range from 0.6 to 6 ppm S) were determined by means of an oxidative coulometric procedure [537]. The coulometric electrochemical array detector was used for determining a variety of synthetic phenolic antioxidants (PG, THBP, TBHQ, NDGA, BHA, OG, Ionox 100, BHT, DG) in food and oils [538],... 

Ferruzzi, M.G., Sander L.C., Rock C.L., and Schwartz S.J. 1998. Carotenoid determination in biological microsamples using liquid chromatography with a coulometric electrochemical array detector. Anal. Biochem. 256 74-81. 

DR McCabe, IN Acworth. Determination of synthetic phenolic antioxidants in food using gradient HPLC with electrochemical array detection. Am Lab News 30(13) 18B, 18D, 16, 1998. 

Hensley, K., Maidt, M. L., Pye, Q. N., Stewart, C. A., Wack, M., Tabatabaie, T., and Floyd, R. A. (1997). Quantitation of protein-bound 3-nitrotyrosine and 3,4-dihydroxy-phenylalanine by high-performance liquid chromatography with electrochemical array detection. Anal. Biochem. 251 187-195. 

Gavin PF, Ewing AG. Characterization of electrochemical array detection for continuous channel electrophoretic separations in micrometer and submicrometer channels. Anal Chem 1997 69 3838-3845. 

Often, low levels of carotenoids in biological samples provide significant challenges in quantification by HPLC-PDA alone. Electrochemical detection (ECD) has been successful in quantifying low concentrations of carotenoids (MacCrehan and Schonberger, 1987 Finckh et ah, 1995 Yamashita and Yamamoto, 1997). More information about ECD can be found in Chapter 2. ECD has also been successful in quantifying carotenoid isomers in foods, plasma, prostate tissue, cervical tissue, and buccal mucosal cells (Ferruzzi et ah, 1998,2001 Allen et ah, 2003 Unlu et ah, 2007). Electrochemical array detection for all-irans - 3-carotene has been reported to be 10 fmol on column, which is approximately 100-1000 times more sensitive than UVA is detectors (Ferruzzi et ah, 1998). 

Puspitasari-Nienaber, N.L. Ferruzzi, M.G. Schwartz, S.J. 2002. Simultaneous detection of tocopherols, carotenoids, and chlorophylls in vegetable oils by direct injection C30 RP-HPLC with coulometric electrochemical array detection. J. Am. Oil Chem. Soc. 79 633 640. 

Use of the Electrochemical Array to Confirm Compound Identity Courtesy of the Analyst. 

The Separation of 30 Neuroactive Substances Monitored by an Electrochemical Array Courtesy of the Analyst. 

It is seen that for certain applications the electrochemical array detector can be extremely useful. Nevertheless, in order to use the detector, the solutes must be amenable to electrochemical reaction and capable of being separated using a mobile phase that will conduct an ion current... 

Some phenols are readily oxidized or reduced, which allows detection by electrochemical detectors (ECD). However, when using single-electrode ECD, the peak identification is only based on retention times (RT). To enhance the selectivity of this technique, it is essential to use dual electrode or electrochemical array detectors, both of which would give more information based on the shape of the voltammograms of the eluting compounds. 

Campas, M. Katakis, I., Electrochemically arrayed and addressed DNA multi-sensor platforms, Sens. Actuator B-Chem. 2006,114, 897-902... 

Fig. 12.4 HT-29 colon cancer cells response to BA, AN-7, and AN-9. Amperometiic response curves for monitoring of alkaline phosphatase activity using the electrochemical array chip. The HT-29 colon cancer cells were exposed to the differentiation agents Butyric acid (2.5 mM), AN-7 and AN-9 (50 pM). The HT-29 cells with the substrate PAPP were placed into the 100 nL volume electrochemical chambers on the chip. Current was measured using the amperometric technique at 220 mV...

Fig. 12.5 Amperometiic response curves for monitoring of alkaline phosphatase activity using the electrochemical array chip. We show the deposited cells with PAPP (left) and the output as a function of time on the right correspondingly...

Jensen, G.C., Krause, C.E., Sotzing, G.A., Rusling, J.F. Inkjet-printed gold nanoparticle electrochemical arrays on plastic. Application to immunodetection of a cancer biomarker protein. Phys. Chem. Chem. Phys. 13, 4888 894 (2011)... 

Gavin, P.F. Ewing, A.G. Characterization of Electrochemical Array Detection for Continuous Channel Electrophoretic Separations in Micrometer and Submicrometer Channels. Anal. Chem. 1997 69, 3838-3845. 

Laschi, S., Centi, S. and Mascini, M. (2011) Electrochemical arrays coupled with magnetic separators for immunochemistry. Bioanal. Rev., 3,11-25. 

Quantitative Determination of Pigments by HPLC and Coulometric Electrochemical Array Detection... 

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