Analysis flow injection

Flow injection (FI) is a powerful front-end sampling accessory for ICP-MS that can be used for preparation, pretreatment, and delivery of the sample. Originally described by Ruzicka and Hansen, FI involves the introduction of a discrete sample 

FIGURE 17.5 Schematic of an FI system used for the process of microsampling. 

Some of the many online procedures that are applicable to Fl-ICP-MS include the following  

FI coupled to ICP-MS has shown itself to be very diverse and flexible in meeting the demands presented by complex samples, as indicated in the foregoing references. However, one of the most interesting areas of research is in the direct analysis of seawater by FI-ICP-MS. Traditionally, seawater has been very difficult to analyze by ICP-MS because of two major problems. First, the high NaCl content will block the sampler cone orifice over time unless a 10-20-fold dilution is made of the sample. This is not such a major problem with coastal waters, because the levels are 

FIGURE 17.6 3D plot of intensity versus mass in the time domain for the determination of a group of elements in a transient peak. (Courtesy of PerkinEhner, Inc., 2003-2012. All rights reserved. With permission.) 

Flow injection analysis as introduced by the work of Ruzicka [129] has been used extensively in combination with atomic absorption spectrometry, the aim being to  

In a flow injection system the sample flow and a reagent flow are continuously brought together so as to allow a chemical reaction to take place. This reaction produces a gaseous compound, which has to be separated off as in hydride generation, or forms a complex, which can be adsorbed onto a solid phase to be isolated and preconcentrated. In the latter case, elution with a suitable solvent is carried out and the analytes are led on-line into the AAS system. 

With graphite furnace atomic absorption only an off-line determination is possible or by a semi-automated coupling, which adapts the analysis cycle with respect to the frequency and time required for a determination to the flow-rates in the system. 

Flow injection analysis (FIA) is based on the injection of a defined volume of liquid sample into a moving stream of a suitable liquid. It was developed to overcome the disadvantages of batch assay and continuous-flow analysis forms of chemical analysis and as a means of automating wet chemical reactions. In batch assays, the sample is mixed 

NIR = near infrared spectroscopy, IR = infrared spectroscopy, UV= ultraviolet spectroscopy, Raman = Raman spectroscopy, FBRM = focused beam reflectance measurement, 

A schematic diagram of a working FIA system is shown in Fignre 9.9. FIA can be nsed with many types of detector incinding electrochemical, e.g. pH probes, ISEs and condnc-tivity, and spectroscopic, e.g. UV-Vis, infrared and flnorescence. Diode array detectors allow the monitoring of many components simnltaneonsly, and conpled with chemometrics can be a very fast and information-rich technique. The detector itself should have a small cell volume to avoid undue dispersion. 

The information obtained depends on the information required by the analyst and the analyte under investigation. It can be qualitative or quantitative. The reagents employed 

Kinetic discrimination and kinetic enhancement are two procedures that can be used in conjunction with wet chemical FIA. Kinetic discrimination works well when it is known that there are differences in the rate of reaction between the reagent and the analyte of interest and the rates of reaction between the reagent and the interferents in the sample. If, for example, the analyte reacts more quickly with the reagent than the interferents, then the timing for measuring of the signal by the detector can be set so as to exploit this. Kinetic enhancement is when the direction of the reaction is manipulated to favour measurement of the analyte of interest with improved signal-to-noise. 

The simplest flow injection analyzer (Fig. 2.4a) consists of a pump, which is used to propel the carrier stream through a narrow tube an injection port, by means of which a well-defined volume of a sample solution is injected into the carrier stream in a reproducible manner and a microreactor in which the sample zone disperses and reacts with the components of the carrier stream, forming a species that is sensed by a flowthrough detector and recorded. A typical recorder output has the form 

It follows from the preceding discussion that FIA is based on a combination of three principles sample injection, controlled dispersion of the injected sample zone, and reproducible timing of its movement from the 

When recorded, the transient signal observed by a detector during the passage of the dispersed sample zone has the form of a peak, the height 

width W, or area A of which contains the analytical information (Fig. 2Ab). 

Flow injection analysis (FIA) was first introduced by Ruzicka and Hansen in 1975. FIA is a technique for the manipulation of the sample and reagent streams in instrumental analysis. The purpose of flow injection is to have sample preparation and injection take place automatically in a closed system. The flow injection technique combines the principles of flow and batch type processing and it consists of a set of components which can be used in various combinations. 

In AAS, FIA has been applied to hydride generation and cold vapour techniques, microsampling for flame atomic absorption, analysis of concentrated solutions, addition of buffers and matrix modifiers, dilution by mixing or dispersion, calibration methods, online separation of the matrix and analyte enrichment, and indirect AAS determinations. 

AAS determinations can be fully automated by using a FIA system. For example, by a Perkin Elmer FIAS-200 system up to about 180 determinations can be performed per hour. The FIA system is also economical, since sample and reagent consumption are minimal. 

The term flow injection anaiysis (FIA) describes an automated continuous analytical method in which an aliquot of sample is injected into a continuously flowing carrier stream. The carrier stream usually contains one or more reagents that react with the sample. A transient signal is monitored as the analyte or its reaction product flows past a detector. We have just described CVAAS, where a reduction reaction occurs and the analyte must be swept in a carrier stream into the optical path. This results in a transient signal. All of the components for a FIA are present—sample, reagent. 

An FIA system consists of four basic parts a pump or pumps for regulation of flow, an injection valve to insert sample volumes accurately and reproducibly into the carrier stream, a manifold, and a flow-through detector. A manifold is the term used for the tubing, fittings, mixing coils, and other apparatus used to carry out the desired reactions. The flow-through detector in AAS is the atomizer/ detector combination in the spectrometer. 

FIA techniques for AAS are described in detail in the reference by Tyson. In addition to automated CVAAS and HGAAS, FIA has been used to automate online dilution for the preparation of calibration curves, online matrix matching of solutions, online preconcentration and extraction for GFAAS, automated digestion of samples, and much more. Commercial FIA systems are available for most AAS instruments. 

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. 

FIGURE 2.5 A flow injection system for the potentiometric determination of ammonium in Kjeldahl plant digests used in Brazil in 1976. The flow setup is supported by LEGO blocks and includes a needleless syringes for manual sample injection, an air-gap ammonium electrode (in white), a model 8511 Polymetron peristaltic pump and a model 64 Radiometer pH meter (recorder not shown). For experimental details, see Ref. [43], 

FIGURE 2.6 A flow injection system for the potentiometric determination of nitrate in natural waters. For experimental details see Ref. [52], 

The classical 10-article series [16—18,43—49] discussing in detail theoretical, methodological and practical aspects of flow injection analysis, as well as emphasising its potential, limitations, applications and trends, was published during the 1970 s. Concomitantly, other early contributions from different countries appeared in the literature [50], and those prepared by the research team headed by M. Valcarcel in Spain [51] should be highlighted. 

One can then infer that flow injection analysis relies on three cornerstone features sample injection, controlled dispersion and reproducible timing [50]. A typical flow injection analyser and the related recorder output are shown in Fig. 2.7. 

FIGURE 2.7 How diagram of a typical flow injection analyser and the associated recorder tracing. S = sample C — sample/ wash carrier stream R = reagent Rc = coiled reactor D — detector arrows = sites where pumping is applied. 

The term flow injection (FI) analysis describes the technique of injecting small volumes or plugs of sample into an unsegmented carrier stream. There have been 

For many years, flow injection analysis has been used for automated spectrophotometric determination of anionics. Although UV absorbance at 224 nm has been reported for FLA of LAS (68), FIA is normally based upon the more robust methylene blue visible spectrophotometric method (69-71). Other cationic dyes may be used in place of methylene blue (72,73). The methylene blue method requires a two-phase system, a feature which is a continuing target of optimization experiments. Most commercial systems rely on gravity 

A number of other FIA approaches for anionic determination have been proposed, although it is doubtful that they are much used. For example, determination of high concentrations of LAS can be performed based on the solvatochromism of p-diphenylaminoa-zobenzene sulfonate (80). Another method for automated analysis of anionic surfactants involves flow injection analysis with continuous formation and extraction of the ion pair with copper(II)-l,10-phenanthroline. The extract is introduced into an atomic absorption spectrophotometer for determination of the copper (81). Cationics can be determined similarly, using adduct formation with tetrathiocyanatocobaltate(II) (82). The last system is tolerant of interference by ethoxylated nonionic surfactants, since potassium ion is not added. 

FIA of anionics without a phase separation may be based on the quenching effect of surfactants on the fluorescence intensity of 8-anilino-l-naphthalenesulfonic acid coupled with bovine serum albumin (83). Another method of avoiding a phase separation is to use a surfactant-selective electrode. Since interference is a problem, the surfactant-selective electrode approach is best coupled with online concentration with a reversed-phase column. Such a system has been demonstrated for trace analysis of sodium dodecylsulfate (84). 

The ion-pair extraction and colorimetric determination of cationics described in Chapter 12 has been automated using flow injection analysis. Orange n is a suitable anionic dye. A fluorocarbon membrane permits the separation of the organic from the aqueous phase for color measurement. Addition of methanol to the chloroform/water system aids in the efficiency of the extraction, so that nearly identical molar responses are obtained for a variety of cationic surfactants. As in the manual method, use of a neutral pH allows determination of only quatemaiy surfactants, while an acid pH permits determination of both quats and fatty amines (85,86). A flow injection method based on tetrabro-mophenolphthalein ethyl ester eliminates interference from amines by measuring the absorbance at 45 C, at which temperature the ion associates with amines are colorless (87). The amine interference may also be eliminated by conducting the determination at high pH (88). 

Other spectrophotometric methods have been proposed for FIA of ionic surfactants based on the change in absorbance of an anionic dye in the presence of a cationic surfactant, which change is attenuated by the presence of an anionic surfactant in the system 

Modern-day instruments are so sophisticated that they actually possess automated features whether they perform an analysis automatically or not. For example, they may monitor sample chamber temperature and by feedback to a regulator maintain it constant (important in enzyme reactions). 

FIA is like HPLC without a column. It is low pressure, and there is no separation. The injected sample mixes and reacts with the flowing stream. A transient signal (peak) is recorded. 

Continuous-flow analyzers, (a) Single channel (batch.) ( ) Multichannel. 

A key feature of FIA is that since all conditions are reproduced, dispersion is very controlled and reproducible. That is, all samples are sequentially processed in exactly the same way during passage through the analytical chaimel, or, in other words, what happens to one sample happens in exactly the same way to any other sample. 

single line B, two-line with a single confluence point C, reagent premixed into a single line D, two-line with a single confluence point and reagent premix E, three-hne with two confluence points. 

In this chapter, we first discuss flow injection analysis (ITA), a recent and important type of continuous flow method. We next consider microfluidic systems, which are miniaturized types of continuous flow units. We then describe several types of discrete automatic systems, several of which are based on laboratory robotics. 

How injection methods were first described l)y Ruzicka and Hansen in Denmark and Stewart and coworkers in the United Slates in the mid-1970s.- Flow injection 

Infei ivni Analvu. Ri ci di e. NJ World Sciontitic Fubliihina ( , n. K.irlfvri and ( I- fniecri.in Anjl sn.. 4 Pracu al (luuir. 

FIGURE 33-2 Flow injection determination of chioride (a) flow diagram (b) recorder traces for standards containing 5 to 75 ppm chloride ion (left) and fast scan of two of the standards to demonstrate the low analyte carryover (less than t %(from run to run (right). Note that the point marked X% corresponds to where the response would just begin for a sample injected at time. SV (From J. Ruzicka and E. H. Hansen, Flow Iniectlon Methods, 2nd ed., p. 16, New York Wiley, 1988. Reprinted by permission of John Wiley Sons, Inc.) 

From the reaclor coil, the solution passes into a (low-through photometer equipped with a 480-nm interference filler, 

The flexibility of the apparatus stems directly from the avoidance of air segmentation, and for systems without mixing chambers. There are, in addition to the mechanical benefits, some interesting chemical possibilities. 

The physical dispersion of a plug of sample in a liquid flowing through a pipe was thoroughly discussed by Taylor in 1953 41). His theory, although modified in some 

Determination of trace elements or anions. (i) Direct injection of sample into carrier stream of 

Inlet system for pH meters, aas etc. Kinetic determination of mixtures of metal ions or enzymes etc. 

Tube lengths and the rotation speed of the peristaltic pump are dictated by the reaction time. Thus, if a long time is required for kinetic reasons, then a long piece of tubing is inserted—usually in coiled form—in order to increase residence times of the sample and reagents in the reactor. 

Another difference between SFA and FIA, is that unlike SFA which operates under turbulent flow regime, FIA works in laminar flow, which reduces the likelihood of carryover between successive 

Schematic depiction of a typicai FiA system. IV injection valve. RC reaction coil. 

Manual injection valve typically used in FIA. (For color version of this figure, the reader is referred to the online version of this book.) 

Practical Guide to ICP-MS A Tutorial for Beginners, Second Edition 

Microsampling for improved stability with heavy matrices  

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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. ... 

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. 

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. 

The following resources provide additional information on the theory and application of flow injection analysis. 

Duarte and colleagues used a factorial design to optimize a flow injection analysis method for determining penicillin potentiometricallyd Three factors were studied—reactor length, carrier flow rate, and sample volume, with the high and low values summarized in the following table. 

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