Detector in flow injection analysis

Liu, W. Z. and Zuo, A. L. Construction and application of all-solid-state aconitine electrochemical detector in flow injection analysis. Yaoxue Xuebao 27(4) 294-298, 1992. 

A.S. Tauliq, AM.S. Abulkibash, Differential electrolytic potentiometric detector in flow injection analysis for cyanide determination, J. Flow Injection Anal. 24 (2007) 9 12. 

RK Force, GR Harrison. Surface-enhanced Raman spectroscopy at a silver electrode as a detector in flow injection analysis. Anal Chem 60 1987-1989, 1988. 

Granger, M. C., J. Xu, J. W. Strojek, and G. M. Swain. 1999. Polycrystalline diamond electrodes Basic properties and applications as amperometric detectors in flow injection analysis and liquid chromatography. Anal. Ghim. Acta... 

Abulkibash, A. M. S., M. E. Koken, M. M. Khaled, and S. M. Sultan. 2000. Differential electrolytic potentiometry, a detector in flow injection analysis for oxidation-reduction reactions. Talanta 52 1139-1142. 

Cano, M., B. Palenzuela, and R. Rodriguez-Amaro. 2006. A PVC/TTF-TCNQ composite electrode for use as a detector in flow injection analysis. Electroanalysis 18 1727-1729. 

Among polymer coated electrodes which have been the object of active investigations during this last decade, particular attention has been paid to the conductive polypyrrole films, obtained by electrooxidation of pyrrole in acetonitrile. Such electrodes have been used to study the electrochemical behaviours of the quinone-hydroquinone redox couple " and tetrathiafulvalene , The controlled release of ferrocyanide from polypyrrole by reduction of the polymer has been demonstrated . As an application, electroinactive anions can be determined using a polypyrrole modified electrochemical detector in flow-injection analysis. Pyrrole can be polymerized from aqueous solutions. Enlarging the modification field, the polymerization step may be preceded by a chemical reaction between pyrrole and another substrate . 

Two examples of dual-channel manifolds for use In flow Injection analysis where R1 and R2 are reagent reservoirs P Is the pump S Is the sample I Is the Injector B Is a bypass loop W Is waste C Is the mixing and reaction coll and D Is the detector. 

The 1/16" x 0.02" i.d. transfer line also functioned as a sample dilution device in other applications, a stainless steel column packed with glass beads has been found to be useful for dilution. This simple dynamic dilution technique has been used extensively in flow injection analysis.3 A refractive index detector is typically used to measure the sample transfer time. As shown in Figure 4, approximately 5 minutes is required to transfer the sample plug to the Rheodyne valve. As the apex of the sample band passes though the Rheodyne valve, the valve is activated and 1 pi injected onto the liquid chromatographic column. The sample transfer time was checked periodically over 1 year of operation and found to be stable. 

Because of its advantages (high sensitivity and selectivity, low cost and miniaturization) amperometric detection has been frequently used in flow injection analysis (FIA) and RP-HPLC. However, it has been established that the peak area (detector response) considerably depends on the flow rate. A general approach has been proposed to predict the effect of flow rate on the peak area in FIA and RP-HPLC. The general form of the correlation describing the flow in a parallel plate cell with short rectangular electrodes is... 

Sometimes it is not necessary to use the selectivity of a chromatographic technique. Sensitive analysis can sometimes be achieved with selective detection in flow injection analysis (FIA). Whilst some of the detectors described below may be appropriate in themselves in favourable cases, in most cases more sophisticated detection regimes are necessary, such as post-injection derivatisation of the analyte. Strategies involving some of the derivatisation methods outlined in Section 4.9.2 may be considered. 

In flow injection analysis, a sample is injected into a moving liquid stream to which various reagents can be added. After a suitable time, the reacted sample reaches a detector, which is usually a spectrophotometric cell. Flow injection is widely used in medical and pharmaceutical analysis, water analysis, and industrial process control. 

Potentiometric electrodes of all types In flow-injection analysis (FIA) glass, ion-selective, amperometric electrodes, etc., can all theoretically be used in a detector cell to quantify some chemical substance. 

The presence of artefacts in the analytical path, such as mixing chambers, tubing connections, de-bubblers and other chamber-like components, can also affect sample dispersion in flow injection analysis. The effects of a mixing chamber and the detector inner volume are discussed in 3.1.2.2 and 6.3.2, respectively. The presence of devices for liquid—liquid extraction and gas diffusion (or dialysis) alters dispersion, and is dealt with in Chapter 8. 

Amperometry is when voltammetry is used at a fixed potential and the current alone is followed. This current is proportional to the concentration of a species in a stirred or flowing solution. It is, therefore, a very suitable detection method for use in flow injection analysis systems and in chromatographic separations its use as a detector for separation techniques is discussed in that section. The current is the result of the electrochemical oxidation or reduction of the analyte after application of a potential pulse across the working and auxiliary electrodes. 

H. Ma and H. Yan, An Amperometric Detector for Flow Injection Analysis [in Chinese]. Yigi Yibiao Xuebao, 4 (1983) 44. 

Various analytical methods now employ amperometric measurements as part of their procedures. In particular, amperometric titrations have been widely used for the analysis of various substances in samples ranging from water to radioactive materials. Also, amperometric sensors, such as the dissolved oxygen probe and various amperometric biosensors, are widely used for clinical, environmental, and industrial monitoring. Furthermore, amperometric detectors have gained considerable use since the 1970s in high-performance liquid chromatographic determination of various substances and in flow injection analysis. 

Wujian Miao illustrated a time line of various events in the development of ECL till 2002 (Fig. 1.3) [1]. As the time went on, this field attracted bulk of people to do research on ECL basic theory, emitters, mechanisms, applications, etc. Hence, advancements in the area of ECL increased exponentially over more than 45 years. After a long journey of almost half a century, ECL has now grown to be an incredibly potent analytical technique and been extensively used in many areas, such as criminology, forensic, environment, biomedical, biowarfare agent detection immunoassay [3], etc. This technique has also been effectively employed as a detector of flow injection analysis (FIA), high-performance liquid chromatography (HPLC), capillary electrophoresis (CE), and micro total analysis (pTAS) [13]. 

A pentaerythritol-based dendrimer modified with bis-terpyridyl Ru(II) was shown to be effective as a catalyst for the electrochemical oxidation of methionine (L-Met) and cystine (L-Cys) in aqueous solution or the mixed solvent AN-water (12% AN) [100]. In this case, the dendrimer was mixed with carhon powder and, using a sol-gel hinder, the carhon electrode doped with the [Ru(tpy)2] " -functionalized dendrimer was prepared. The oxidation peak of [Ru(tpy)2] was enhanced by the addition of L-Met, indicating the electro-catalytic effect of the dendrimer. Using the composite electrode doped with the dendrimer as an amperometric detector for flow-injection analysis, a linear calibration curve was obtained over the range 1-lOpM of L-Met in phosphate buffer (pH 7.0). A similar cahbration curve was obtained for L-Cys over the range 1-10 pM in phosphate buffer (pH 2.3). 

In flow injection analysis (FIA), this solution invariably detracts from throughput while in SIA, the loss can be minimized by stopping the flow at the reaction coil, located behind the switching valve, and starting processing of the next sample. When the second sample reaches the reaction coil, it will push the first, which by then will have reacted to an adequate extent, to the detector. 

Because of their stability against chemical dissolution and their effective promotion of oxidations of biochemical compounds, catalysts comprising inorganic polymers and other maCTomolecules that contain platinum-group metal centers will be the focus of the present report. The applications primarily will be as amperometric detectors in HPLC and in flow-injection analysis, in which case both surface-modified electrodes and doped CCEs are suitable. Specifically addressed will be the use of sol-gel processing as a means of immobilizing catalysts in composites. 

This approach will not be practical for some time to come. The fundamental properties of surfactants (micelle formation, enrichment at interfaces) mean that the activity of a surfactant will usually differ from its absolute concentration (1). Just as serious is the technical problem that current surfactant-selective electrodes suffer from response which varies with their past and recent history they are also sensitive to the concentration of nonsurfactant ions. The result is that quantitative applications use electrodes not in direct measurements relating potential to concentration, but as indicators of the end point of a titration. In this latter application, it is not important that the electrode potential be exactly reproducible, but only that the potential change sharply as the surfactant concentration changes. For the titration of an anionic surfactant with a cationic surfactant, the electrode used for end point detection can be chosen to respond to either surfactant. Because of the drift in electrode potential, titrations must be conducted to an inflection in the titration curve rather than to a specific millivolt value. Details of the potentiometric titration methods can be found earlier in this chapter. The electrodes have also been demonstrated as detectors for flow injection analysis. 

Another device is based on optical equipment which measures the drop size of a liquid stream exiting a capillary into air. In the presence of a surfactant, the drop size is smaller. This was demonstrated for sodium dodecylsulfate, and it was shown that the effect was accentuated by the presence of an ion pairing reagent such as tetrabutylammo-nium ion. The instrument is proposed as a detector for flow injection analysis or HPLC... 

Flow injection analysis (FIA) was developed in the mid-1970s as a highly efficient technique for the automated analyses of samples. °> Unlike the centrifugal analyzer described earlier in this chapter, in which samples are simultaneously analyzed in batches of limited size, FIA allows for the rapid, sequential analysis of an unlimited number of samples. FIA is one member of a class of techniques called continuous-flow analyzers, in which samples are introduced sequentially at regular intervals into a liquid carrier stream that transports the samples to the detector. ... 

A graph showing the detector s response as a function of time in a flow injection analysis. 

A sensitive method for the flow injection analysis of Cu + is based on its ability to catalyze the oxidation of di-2-pyridyl ketone hydrazone (DPKH) by atmospheric oxygen. The product of the reaction is fluorescent and can be used to generate a signal when using a fluorometer as a detector. The yield of the reaction is at a maximum when the solution is made basic with NaOH. The fluorescence, however, is greatest in the presence of HCl. Sketch an FIA manifold that will be appropriate for this analysis. 

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