Flow-injection analysis technique

Johnson and Petty [129] reduced nitrate to nitrite with copperised cadmium, which was then determined as an azo dye. The method is automated by means of flow injection analysis technique. More than 75 determinations can be made per hour. The detection limit is 0.1 xmol/l, and precision is better than 1% at concentrations greater than 10 xmol/l. 

J. F. Tyson, Flow Injection Analysis Techniques for Atomic-Absorption Spectrometry. A Review. Analyst, 110 (1985) 419. 

C. C. Y. Chan, Semiautomated Method for Determination of Selenium in Geological Materials Using a Flow Injection Analysis Technique. Anal. Chem., 57 (1985) 1482. 

X. Wang and Z. Fang, Determination of Trace Amounts of Selenium in Environmental Samples by Hydride Generation—Atomic Absorption Spectrometry Combined with Flow Injection Analysis Technique. Kexue Tongbao, 31 (1986) 791. 

The peroxide method has proven to be the most useful for this purpose, owing to the high acidity of the medium in which the reaction is conducted. Interferences are observed only in the presence of V, Mo, or F, but these species are not normally present in U.S.P. grade titanium dioxide. In the spectrophotometric assay method, the absorption maximum at 410 nm is used to determine the titanium concentration after the oxide is dissolved [39]. The spectrophotometric endpoint of the peroxide method has been combined with flow injection analysis techniques to yield an automated procedure [40]. 

Methods of monitoring aldehydes in food and pharmaceutical samples have also been reported. A semiautomatic method by a stopped-flow flow injection analysis technique was successful in identifying the presence of furfural and 5-hydroxymethyl-2-furfuraldehyde in several commercial pharmaceutical preparations and food samples [398], The analysis is based on the reaction of the aldehydes with 2-thiobarbituric acid, with determination of the derivatives. 

One of the methods involves injection of small volumes of solutions into the stream of carrier liquid percolating through the adsorbent in the calorimetric cell and is designed for the determination of the heats of adsorption of irreversibly adsorbed solutes at increasing degrees of surface coverage. This technique is based essentially on flow injection analysis techniques, but it is confined to strong interactions between small amounts of active components of fluid mixtures and adsorbents and has been named Flow Injection Adsorption Thermodynamics. The downstream detector determines the concentration of that part of the injected solute in the effluent from the cell which is not retained by the adsorbent. The heat effect... 

D. Lannuzel, J. de Jong, V. Schoemann, A. Trevena, J.-L. Tison, and L. Chou. Development of a sampling and flow injection analysis technique for iron determination in the sea ice environment. Analytica Chimica Acta 556 476-483, 2006. 

Flow Injection Analysis Technique and Spectrophotometric Methods... 

There are many potential advantages to kinetic methods of analysis, perhaps the most important of which is the ability to use chemical reactions that are slow to reach equilibrium. In this chapter we examine three techniques that rely on measurements made while the analytical system is under kinetic rather than thermodynamic control chemical kinetic techniques, in which the rate of a chemical reaction is measured radiochemical techniques, in which a radioactive element s rate of nuclear decay is measured and flow injection analysis, in which the analyte is injected into a continuously flowing carrier stream, where its mixing and reaction with reagents in the stream are controlled by the kinetic processes of convection and diffusion. 

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. ... 

Finally, FIA is an attractive technique with respect to demands on time, cost, and equipment. When employed for automated analyses, FIA provides for very high sampling rates. Most analyses can be operated with sampling rates of 20-120 samples/h, but rates as high as 1700 samples/h have been realized. Because the volume of the flow injection manifold is small, typically less than 2 mb, consumption of reagents is substantially less than with conventional methods. This can lead to a significant decrease in the cost per analysis. Flow injection analysis requires additional equipment, beyond that used for similar conventional methods of analysis, which adds to the expense of the analysis. On the other hand, flow injection analyzers can be assembled from equipment already available in many laboratories. 

Since 1970, new analytical techniques, eg, ion chromatography, have been developed, and others, eg, atomic absorption and emission, have been improved (1—5). Detection limits for many chemicals have been dramatically lowered. Many wet chemical methods have been automated and are controlled by microprocessors which allow greater data output in a shorter time. Perhaps the best known continuous-flow analy2er for water analysis is the Autoanaly2er system manufactured by Technicon Instmments Corp. (Tarrytown, N.Y.) (6). Isolation of samples is maintained by pumping air bubbles into the flow line. Recently, flow-injection analysis has also become popular, and a theoretical comparison of it with the segmented flow analy2er has been made (7—9). 

Enzyme linked electrochemical techniques can be carried out in two basic manners. In the first approach the enzyme is immobilized at the electrode. A second approach is to use a hydrodynamic technique, such as flow injection analysis (FIAEC) or liquid chromatography (LCEC), with the enzyme reaction being either off-line or on-line in a reactor prior to the amperometric detector. Hydrodynamic techniques provide a convenient and efficient method for transporting and mixing the substrate and enzyme, subsequent transport of product to the electrode, and rapid sample turnaround. The kinetics of the enzyme system can also be readily studied using hydrodynamic techniques. Immobilizing the enzyme at the electrode provides a simple system which is amenable to in vivo analysis. 

The determination of lead in blood is the most widespread clinical use of ASV The technique is attractive because it is rapid, simple and reproducible A recent advance is to couple ASV to flow injection analysis in order to automate the process so that smaller samples and shorter analysis time can be achieved Lead is also routinely determined in bonemeal meant for human consumption by ASV Both lead and cadmium are determined in agricultural crops by ASV... 

Sample preparation, injection, calibration, and data collection, must be automated for process analysis. Methods used for flow injection analysis (FLA) are also useful for reliable sampling for process LC systems.1 Dynamic dilution is a technique that is used extensively in FIA.13 In this technique, sample from a loop or slot of a valve is diluted as it is transferred to a HPLC injection valve for analysis. As the diluted sample plug passes through the HPLC valve it is switched and the sample is injected onto the HPLC column for separation. The sample transfer time typically is determined with a refractive index detector and valve switching, which can be controlled by an integrator or computer. The transfer time is very reproducible. Calibration is typically done by external standardization using normalization by response factor. Internal standardization has also been used. To detect upsets or for process optimization, absolute numbers are not always needed. An alternative to... 

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. 

In the laboratory, electroanalysis is used for two main purposes, either for direct measurement of a physico-chemical property that is informative with respect to the identity and/or amount of the analyte, or for detecting the course of conversion of the analyte or indicating the separate appearance of analyte components, which is informative with respect to their identity and amount. In the former instance we are dealing with conductometry, voltammetry and coulometry and in the latter with various titrations and mostly separational flow techniques such as chromatography and flow injection analysis. 

Flow injection analysis (FIA) (Ruzicka and Hansen), since 1975 In continuous flow, stopped flow or with merging zones (FIA scanning or intermittent pumping) Adapted voltammetric electrodes Membranes for Partial dialysis Membrane amperometry (Clark) Differential techniques (Donnan) Computerization, including microprocessors Special measuring requirements in plant control (to avoid voltage leakage, etc., Section 5.5)... 

Flow injection analysis (F1A). In this technique, introduced by Ruzicka and Hansen, a small amount of sample is injected into a liquid flow (see Fig. 5.16), which apart from being automated is normally continuous, but can include the use of stopped-flow, merging zones extraction techniques in addition to FIA scanning and methods based on intermittent pumping89. The principles of FIA and the versions just mentioned will now be briefly discussed on the basis of the excellent review of Ruzicka and Hansen89 in order to understand the appli-cational possibilities of electrochemical detection in this technique. 

Vinas et al. [47] determined penicillamine routinely by using batch procedures and FIA. A capsule was dissolved in water, diluted to 250 mL, and a suitable portion of the solution treated with 1 mM Co(II) solution (2.5 mL) and 2 M ammonium acetate (2.5 mL). The mixture was diluted to 25 mL and the absorbance of the yellow complex was determined at 360 nm. Calibration graphs were linear for 0.02-0.3 mM of penicillamine. The method was modified for flow injection analysis using peak-height or peak-width methods, but in both cases the flow rates were maintained at 3.3 mL/min. For the peak-height technique, calibration graphs were linear for 0.1-2 mM, and the sampling frequency was 150 samples per hour. For the peak-width method, the response was linear for 50 pM to 0.1 M, and this method was particularly useful for routine determinations. 

Flow injection analysis is another technique that has been applied to the determination of nitrate and nitrite in seawater. Anderson [ 126] used flow injection analysis to automate the determination of nitrate and nitrite in seawater. The detection limit of his method was 0.1 imol/l. However, the sampling rate was only 30 per hour which is low for flow injection analysis. Reactions seldom go to completion in a determination by flow injection analysis [127,128] because of the short residence time of the sample in the reaction manifold. Anderson selected a relatively long residence time so that the extent of formation of the azo dye was adequate to give a detection limit of 0.1 pmol/l. This reduced the sampling rate because only one sample is present at a time in the post-injector column in flow injection analysis. Any increase in reaction time causes a corresponding increase in the time needed to analyse one sample. 

This technique differs from flow injection analysis in the sense that whereas in the latter technique the sample plug is injected into a flowing stream of reagent, in the former technique plugs of reagent are injected into a continuous stream of the sample. Under these conditions the amount of sample in the zone of the reagent will increase as the dispersion increases. The sample will become well... 

FLOW INJECTION ANALYSIS VERSUS SEGMENTED FLOW ANALYSIS AND SEPARATION TECHNIQUES... 

A more recent development is a technique known as flow injection analysis, in which a discrete volume of a liquid sample is injected into a carrier stream. Reagents required for the development of the analytical property of the analyte, e g. colour developing reagents for spectrophotometry, are already present in the stream. The stream then flows straight to the detector and the technique depends upon the controlled and reproducible dispersion of the sample as it passes through the reaction zone. Thus the reaction does not necessarily need to develop to completion,... 

Flow injection analysis is a fast-developing technique with many potentialities. Particular attractions are the relative simplicity of operation and automation, together with sample throughputs which may exceed 100 per hour. Thus routine monitoring of process streams and pollution control are obvious areas for application. 

Tandem mass spectrometric methods have demonstrated superb specificity because of their ability to isolate analytes selectively in the presence of endogenous interferences. Attempts to further increase sample throughput led to the idea of using LC/MS/MS without the LC. Traditional chromatographic separations were replaced with flow injection analysis (FLA) or nanoelectrospray infusion techniques. The MS-based columnless methods attracted a lot of attention because of their inherent fast cycle times and no need for LC method development. 

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