Flow-injection

We will only be dealing with segmented-flow methodology in manual, but there are sure to be equivalent FIA methods available. 

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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. ... 

Schematic diagram of a simple flow injection analyzer showing the principal units.

Effect of dispersion on a sample s flow profile at different times during a flow injection analysis (a) at injection and when the dispersion is due to (b) convection ... 

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

Example of a single-channel manifold for use in flow injection analysis where R1 is a reagent reservoir P is the pump S is the sample I is the injector B is a bypass loop ... 

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. 

Separation Modules Incorporating a separation module in the flow injection manifold allows separations, such as dialysis, gaseous diffusion, and liquid-liquid extraction, to be included in a flow injection analysis. Such separations are never complete, but are reproducible if the operating conditions are carefully controlled. 

Separation module for a flow Injection analysis using a semipermeable membrane for dialysis and gaseous diffusion. 

Separation module for a flow injection analysis using a liquid-liquid extraction (inset shows the equilibrium reaction). 

Source Adapted from Valcarcel, M., Luque de Castro, M. D. Flow-Injection Analysis Principles am ... 

In a quantitative flow injection analysis a calibration curve is determined by injecting standard samples containing known concentrations of analyte. The format of the caK-bration curve, such as absorbance versus concentration, is determined by the method of detection. CaKbration curves for standard spectroscopic and electrochemical methods were discussed in Chapters 10 and 11 and are not considered further in this chapter. 

Flow injection analysis has been applied to a wide variety of samples, including environmental, clinical, agricultural, industrial, and pharmaceutical samples. The majority of analyses to date involve environmental and clinical samples, which is the focus of this section. 

Flow injection analysis has also found numerous applications in the analysis of clinical samples, using both enzymatic and nonenzymatic methods. A list of selected examples is given in Table 13.3. 

The accuracy and precision of FIA are comparable to that obtained by conventional methods of analysis. The precision of a flow injection analysis is influenced by variables that are not encountered in conventional methods, including the stability of the flow rate and the reproducibility of the sample s injection. In addition, results from FIA may be more susceptible to temperature variations. These variables, therefore, must be carefully controlled. 

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. 

Kinetic methods of analysis are based on the rate at which a chemical or physical process involving the analyte occurs. Three types of kinetic methods are discussed in this chapter chemical kinetic methods, radiochemical methods, and flow injection analysis. 

The following experiments may he used to illustrate the application of kinetic methods of analysis. Experiments are divided into two groups those based on chemical kinetics and those using flow injection analysis. Each suggested experiment includes a brief description. 

The following set of experiments provide examples of the application of flow injection analysis or the characterization of the behavior of a flow injection analysis system. 

Carroll, M. K. Tyson, J. F. An Experiment Using Time-Based Detection in Flow Injection Analysis, /. Chem. Educ. 1993, 70, A210-A216. 

Most flow injection analyses use peak height as the analytical signal. When there is insufficient time for reagents to merge with the sample, the result is a split-peak, or doublet, due to reaction at the sample s leading and trailing edges. This experiment describes how the difference between the peak times can be used for quantitative work. 

Hansen, E. H. Ruzicka, J. The Principles of Flow Injection Analysis as Demonstrated by Three Lab Exercises, /. Chem. Educ. 1979, 56, 677-680. 

McKelvie, I. D. Cardwell, T. J. Cattrall, R. W. A Microconduit Flow Injection Analysis Demonstration Using a 35-mm Slide Projector, /. Chem. Educ. 1990, 67, 262-263. Directions are provided for constructing a small-scale FIA system that can be used to demonstrate the features of flow injection analysis. For another example see Grudpan, K. Thanasarn, T. Overhead Projector Injection Analysis, Anal. Proc. 1993, 30, 10-12. 

Meyerhoff, M. E. Kovach, P. M. An Ion-Selective Electrode/Flow Injection Analysis Experiment ... 

This experiment describes the adaptation of the bicinchoninic acid (BCA) protein assay to a flow injection analysis. The assay is based on the reduction of Cu + to Cu+ by the protein, followed by the reaction of Cu+ with bicinchoninic acid to form a purple complex that absorbs at 562 nm. Directions are provided for the analysis of bovine serum albumin and rabbit immunoglobulin G, and suggestions are provided for additional analyses. 

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. 

The concentration of chloride in sea water can be determined by a flow injection analysis. The analysis of a set of calibration standards gives the results in the following table. 

A f.OO-mL sample of sea water is placed in a 500-mL volumetric flask and diluted to volume with distilled water. When injected into the flow injection analyzer, an absorbance of 0.3f7 is measured. What is the concentration of Ck in the sample ... 

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