Flow-Injection Analysis with Electrochemical Detection

Instituto de Qulmica, Universidade de Sdo Paulo, Av. Prof. Linen Prestes, 748, CEP05508-000, Sdo Paulo, SP, Brazil 

Edited by Alberto Escarpa, Marfa Cristina Gonzalez and Miguel Angel Ldpez. 2015 John Wiley Sons, Ltd. Published 2015 by John Wiley Sons, Ltd. 

Traditional methods such as high-performance liquid chromatography (HPLC), gas chromatography (GC), HPLC, or GC coupled to tandem mass spectrometry are widely used for the identification and quantification of nutrients (fats, carbohydrates, proteins, water, mineral elements, and vitamins), additives, or contaminants (afiatoxin, pesticides, pathogens, antimicrobial agents, growth promoters, additives, etc.), which can be found in foods [2-4], 

FIA is a well-established technique based on the injection of a sample plug into a continuously flowing carrier stream [9]. BIA was described as noncontinuous flowing injection technique due the step of sample introduction [15]. However, the detection is performed 

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Fig. 31. The determination of ethylamine by flow-injection analysis with electrochemical detection. Chronoampero-gram with repeated 20 pi injections of 0.25 mM ethylamine in 0.1 M carbonate buffer, pH 10, to a flowing (0.5 mL min-1) carbonate buffer solution. Reprinted with permission from [146], Copyright (1997) American Chemical Society.

Neumayr, M. Friedrich, O. Sontag, G. Pittner, F. Flow-injection analysis with electrochemical detection for determination of salicychc acid in pharmaceutical preparations. Anal. Chim. Acta 1993, 273, 469-475. 

Phenol can also be determined by flow injection analysis with electrochemical detection (FI AEC). In FI AEC the sample is injected directly into... 

T. R. Lindstrom, The Determination of Mercury at Trace Levels by Flow Injection Analysis with Electrochemical Detection. Diss. Abstr. Int. B, 41 (1981) 3021. 

T. Toyoda, S. S. Kuan, and G. G. Guilbault, Determination of Lactate Dehydrogenase Isoenzyme (LD-1) Using Flow Injection Analysis with Electrochemical Detection after Immunochemical Separation. Anal. Lett., 18 (1985) 345. 

Note HRP Horseradish peroxidase TMB Tetramethylbenzidine ACV Alternating-current voltammetry amole le-18 moles DPV DifTerential pulse voltammetry E Detection limit for unconjugated enzyme E Detection limit for conjugated (Ab/Ag) enzyme FIA-EC Flow-injection analysis with electrochemical detection CC Classy carbon LC-EC Liquid chromatography with electrochemical detection P Detection limit for final enzymatic product P Detection limit for standards of P RDE Rotating disk electrode SPE Screen-printed electrode SQV Square-wave voltammetry zmole le-21 moles. 

Source Adapted from C. A. Wijayawardhana, H. B. Halsall, W. R. Heineman, in Encyclopedia of Electrochemislry (Vol. 8) (Eds. A. J. Bard, P. Stratmann), Wiley-VCH, New Yoric, submitted. ALP alkaline phosphatase C competitive assay E enzime FIA-EC flow-injection analysis with electrochemical detection GC glassy carbc He heterogeneous Ho homc eneous LC-EC liquid chromatography with electrochemical detection N non-enzyme PAPP 4-amin< henyl phosphate PP j enyl j osjdiate RDE rotating disk electrode S sandwich assay SECM scanning electrochemical microscopy. 

Five types of amperometric detection have been applied for enzyme-based ECIA. They are flow-injection analysis with electrochemical detection (FIAEC), liquid chromatography with electrochemical detection (LCEC), amperometric detection with interdigitated array electrodes (IDA), rotating disk electrode (RDE) amper-ometry, and scanning electrochemical microscopy (SECM). Of these, the two conventional types, FIAEC and LCEC, shall be discussed in this section, leaving the discussion of the other types to Section V on miniaturized immunoassays. 

Flow-Injection Analysis with Electrochemical Detection... 

Figure 3 shows a schematic of the FIA system and details the thin-layer transducer cell, which contains the poly(3-methylthiophene) anion sensor electrode(s). Electrochemical detection in the amperometric mode was employed for the FIA/EC (flow injection analysis with electrochemical detection) studies. A typical potential used was +1.00 volts vs. Ag/AgCl reference electrode. The FIA-EC system consisted of an Altex lOOA double reciprocation pump and a Rheodyne injector (Cotai, CA) with either a 20 or 50 microliter sample loop. Constant potentials were applied using the herein described DWEP, which is software controlled. The electronically transduced signals are converted from analog to digital by use of A/D and D/A converter circuits. The option exists to automatically save the data on the computer or print the results as the experiment progresses. 

We have developed a new voltammetric method using a quinone reagent [5]. Based on the voltammetry of quinone and acids, we assembled an electrochemical detector for measuring acid concentration at a given potential. The flow injection analysis with electrochemical detection (FIA-ECD) method we developed is preferable, as it is a simpler, more sensitive, and rapid method for acid determination. This chapter assesses this method for determining the acid content in foods and beverages. 

Abbreviations FIA-ECD, flow injection analysis with electrochemical detection PTFE, polytetra-fluoroethylene PEEK, polyetheretherketone. 

Takamura, K., T. Fuse, and F. Kusu. 1995. Determination of free fatty acid content in fats and oils by flow injection analysis with electrochemical detection. Anal. Sci. ll 979-982. 

Takamura, K., S. Ohtsuki, and F. Kusu. 2001. Development of a new amperometric sensor for probing the total acid of beverages. Anal. Sci. 17(Suppl.) i737-i739. Takahashi, K., A. Kotani, S. Ohtsuki, and F. Kusu. 2004. Flow-injection analysis with electrochemical detection for determining the titratable acidity of a pH adjuster for foods. Bunseki Kagaku 53 271-274. 

In another approach the electrocatalytic activity of lead oxide was enhanced with fluoride doping. The F-doped lead oxide-modified electrode leads to the fabricatirai of an electrochemical detection system for flow injection analysis to detect the chemical oxygen demand (COD) in water samples. The combination of flow injection analysis with electrochemical detection of COD results in the development of a low-cost, rapid, and easily automated detection system with minimum reagent consumption. The basic principle of the F-doped lead oxide electrode is the generation of hydroxyl radicals which are subsequently utilized for the oxidation of COD pollutants in order to determine the COD value. It is a multistep process at first, hydroxyl radicals will be produced at the surface of the F-PbOa electrode by the anodic discharge of water ... 

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