Flow injection analysis sample volume

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. 

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. 

Another interesting development, in which continuous flow was combined with discrete sample titration, is continuous flow titration by means of flow injection analysis (FIA) according to Ruzicka and co-workers70. Fig. 5.16 shows a schematic diagram of flow injection titration, where P is a peristaltic pump, S the sample injected into the carrier stream of diluent (flow-rate fA), G a gradient chamber of volume V, R the coil into which the titrant is pumped (flow-rate fB), D the detector and W waste. 

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 based on the introduction of a defined volume of sample into a carrier (or reagent) stream. This results in a sample plug bracketed by carrier (Fig. 1 (a)). 

In this technique, which was developed in the 1970s, microlitre volumes of liquid sample are injected, at intervals, into a continuously flowing carrier stream which is not air-segmented. Various reagent streams are introduced as required and controlled mixing of reagents and sample occurs. The fact that flow injection analysis does not involve air-segmented streams makes it possible to include such separation steps as solvent extraction and gas diffusion. 

Flow injection analysis is based on the injection of a liquid sample into a continuously flowing liquid carrier stream, where it is usually made to react to give reaction products that may be detected. FIA offers the possibility in an on-line manifold of sample handling including separation, preconcentration, masking and color reaction, and even microwave dissolution, all of which can be readily automated. The most common advantages of FIA include reduced manpower cost of laboratory operations, increased sample throughput, improved precision of results, reduced sample volumes, and the elimination of many interferences. Fully automated flow injection analysers are based on spectrophotometric detection but are readily adapted as sample preparation units for atomic spectrometric techniques. Flow injection as a sample introduction technique has been discussed previously, whereas here its full potential is briefly surveyed. In addition to a few books on FIA [168,169], several critical reviews of FIA methods for FAAS, GF AAS, and ICP-AES methods have been published [170,171]. 

Dialysis units provided highly efficient means for increasing selectivity in a dynamic system by placement in front of a lithium-selective electrode constructed by incorporating 14-crown-4 ether 3-dodecyl-3 -methyl-1,5,8,12-tetraoxacyclotetradecane into a PVC membrane that was in turn positioned in a microconduit circuit by deposition on platinum, silver or copper wires. The circuit was used to analyse undiluted blood serum samples by flow injection analysis with the aid of an on-line coupled dialysis membrane. For this purpose, a volume of 200 pL of sample was injected into a de-ionized water carrier (donor) stream and a 7 mM tetraborate buffer of pH 9.2 was... 

M 20] [P 19] The pTAS module is made for performing colorimetric analyses as typically applied in cuvette tests, e.g. for on-site water analysis [30], A continuous test replaces copious manual pipetting of the sampling volumes. The module consists of a micro flow restrictor, a micro mixer and an optical microcuvette for colorimetric analysis. The sample is injected by a conventional FIA (flow injection analysis) system. By close connection, a dead volume of only 2.2 pi is given. 

Micro flow control devices open new possibilities for the miniaturization of conventional chemical and biochemical analysis systems. The micro total analysis system (pTAS) including microfabricated detectors (e.g. silicon based chemical sensors, optical sensors), micro flow control devices and control/detec-tion circuits is a practical micro electro mechanical system (MEMS). pTAS realize very small necessary sample volume, fast response and the reduction of reagents which is very useful in chemical and medical analysis. Two approaches of monolithic and hybrid integration of these devices have been studied. Monolithic and hybrid types of flow injection analysis (FIA) systems were already demonstrated [4, 5]. The combination of the partly integrated components and discrete components is useful in many cases [6]. To fabricate such systems, bonding and assembling methods play very important roles [7]. 

In flow injection analysis [32] with electrochemical detection a sample is injected into an electrolyte carrier stream dispersion of the sample plug into the carrier stream occurs so that electrolyte is effectively added to the sample—with consequent sample dilution—before reaching the electrode. Even so, by using a capillary flow injection system nanolitre sample volumes can be investigated [33]. In continuous flow systems, electrolyte often has to be added to the sample beforehand, also leading to sample dilution. 

A useful and rapid method of automated analysis is the technique of flow-injection analysis (FIA). The sample or a reagent is injected into the stream of a solution of constant composition. Calibration of FIA systems requires the injection of standard solutions, equal in volume to that of the sample, into the carrier stream. The backgrormd chemical composition of the standards should be equal, as nearly as possible, to that of the samples. Frequent standardization is not necessary because the measurement of peak height, albeit on a sloping base line, is relatively unaffected by cell voltage drift. Some difficulties can appear with peristaltic pumps, owing to extraneous potentials caused by pulsation of the stream. Cells with a small volume (<20 pi) or the cells of the wall-jet type are the most acceptable for continuous measurements. ... 

There have been several approaches to overcome the traditionally slow SEC separations, which are caused by the diffusion processes in SEC columns. Most of them are column-related (see High-Speed SEC Columns, Small Particle Technology, and Smaller SEC Column Dimensions ) one utilizes the column void volume (cf. Overlaid Injections ), while another replaces separation with simplified sample preparation (see Flow Injection Analysis ). Cloning existing methods and instrumentation is also reviewed with respect to the potential time gain (see Cloning of SEC Systems ). Benefits and limitations of each method are summarized in Table 1. 

Even if sufficient sample size, in volume, may not be available, enrichment techniques that concentrate trace metals in microliter samples are sometimes quite useful because modern instrumental detection systems such as AAS, ICP-AES, ICP-MS, etc. do not need a large sample size. Moreover, if trace metals that have been separated from their major substances can be concentrated in an extremely small area of the polytetrafluoroethylene (PTFE) tube in HSCCC, this would be an ideal flow-injection analysis system for determination of inorganics. From this point of view, the recently developed pH-zone refining technique has great potential for enrichment, especially for instrumental inorganic trace analysis. 

Flow Injection Analysis [10,11], Flow injection analysis involves injecting a known volume of sample solution into a continuous flowing liquid carrier stream usually of the same solvent that the sample is dissolved in (Figure 2.18). A loop of fixed volume is attached to a rotating valve which can be connected and disconnected manually or by computer to a flowing stream between sample analyses. As the loop is fixed the volume... 

Flow injection analysis (FIA) is a continuous flow method in which highly precise sample volumes are introduced into a stream that is segmented or non-segmented. The... 

Flow injection analysis is a continuous flow method in which highly precise sample volumes are introduced into a stream using segmented or unsegmented flow. The method must be accurate, precise and reproducible before it can be considered as a useful technique and the following test proves that this technique does meet all the requirements. Tyson [3], carried out several studies involving flow injection techniques and atomic spectroscopy with considerable success. 

To alleviate these drawbacks, alternative methodologies relying on the continuous provision of fresh extractant volumes to the solid sample under mvestigation have been developed, characterized, and contrasted with the classical end-over-end extraction procedures. The fundamental principles of these novel, dynamic (nonequilibrium) strategies, based primarily on the use of continuous-flow analysis (Ruzicka and Hansen, 1988), flow injection analysis (Ruzicka and Hansen, 1988 Trojanowicz, 2000 Miro and Frenzel, 2004b), or sequential injection analysis (Ruzicka and Marshall, 1990 Lenehan et al., 2002), are described in detail below, and their advantageous features and limitations for fractionation explorations are discussed critically. 

Flow injection analysis (FIA) is an automated method which consists in the injection of the sample solution to a continuous stream of an inactive carrier (e.g., a pH buffer or water) [49-51]. The diluted analyte is transported to a reaction spiral where a chromogenic reagent is added to the mixture. The dimensions of the spiral, the volume of the sample injected, and... 

The injected sample volume is by far the most important parameter affecting dispersion in flow injection analysis, as it has a pronounced influence on the height, width and area of the recorded peak (Fig. 5.11). 

FIGURE 5.11 Recorded peaks for different sample injected volumes. X — sample volumetric fraction S — injection instant. The recording tracings correspond to loop-based injections of 59,108,206,403 and 795 pL into a single line flow injection system. Adapted from Anal. Chim. Acta 99 (1978) 37, ]. Ruzicka, E.H. Hansen, Flow injection analysis. Part X. Theory, techniques and trends, with permission from Elsevier (Ref. [80]). 

FIGURE 5.17 Influence of the site of confluent stream addition, x = distance between injection port and confluence site A = peak height absorbance a, b = 25 and 1250 pL sample injected volumes. Other experimental conditions as in Ref. [84]. Adapted from Anal. Chim. Acta 198 (1987) 153, E.A.G. Zagatto, B.F. Reis, M. Martinelli, F.J. Krug, H. Bergamin-Filho, M.F. Gine, Confluent streams in flow injection analysis, with permission from Elsevier. 

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. 

Sample insertion relying on time-based introduction is inherent to segmented flow analysis and was the preferred approach before the advent of flow injection analysis. Manual injection using syringes with [50] or without [1] needles was used in the earliest flow injection systems (Fig. 6.7) but is now rarely used, except when very small sample volumes are available. 

In view of the excellent performance of a sampling loop as the volume-selecting element, loop-based introduction dominated during the fast development of flow injection analysis in the 1980s. Time-based introduction became popular again after the inception of sequential injection analysis and related techniques and the development of multicommutation. Nowadays, both time-based and loop-based introduction are exploited and use of an autosampler is generally advisable. 

Process control—continuous and discrete analyzers, p. 661 Automatic instruments, p. 664 Flow injection analysis, p. 665 Dispersion coefficient (key equation 23.1), p. 667 Sample volume, Sy2 (key equation 23.3), p. 670 Sequential injection analysis, p. 673 Microprocessors and computers in analytical chemistry, p. 674... 

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... 

Normal flow-injection analysis (FIA) involves using a peristaltic pump to aspirate the sample Into the loop of an Injection valve, which also quantizes the aspirated volume, and subsequently Inserting the loop contents into a carrier or reagent stream. 

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