Flow injection analysis characteristics

Haswell, S.J., Development and operating characteristics of micro flow injection analysis systems based on electroosmotic flow. Analyst 1997, 122, 1R-10R. 

One of the most basic characteristics of a compound is its molecular mass in this context, much of today s popularity of MS can be traced back to the simplicity of molecular mass readout from API spectra. A common experiment is flow injection analysis (FIA). Here, an autosampler is used to inject an aliquot of dissolved sample into a liquid stream, which is provided by an LC pump, to the MS-detector. FIA offers the advantages of easy automation and fast cycle times of about 30 s per sample. In order to increase throughput, multiprobe autosam-... 

In 1985, mono-segmented flow analysis was proposed [64] as a means of achieving extended sample incubation times without excessive sample dispersion. The sample was inserted between two air bubbles into an unsegmented carrier stream therefore the innovation combined the favourable characteristics of both segmented and unsegmented flow systems. Further development revealed other potential applications, especially with regard to relatively slow chemical reactions, flow titrations, sample introduction to atomic absorption spectrometers, liquid-liquid extraction and multi-site detection (Chapters 7 and 8). This innovation was also referred to as segmental flow injection analysis [65]. 

The system combines the advantageous characteristics of flow injection analysis, such as a high sample throughput and low detection limits, with those of sequential injection analysis such as robustness and versatility. It was initially exploited for industrial process control, with spectrophotometric detection, for the determination of highly acidic or alkaline protolytes using an ingenious titration procedure [109], free... 

In single-line (also called straight or single channel) flow systems, the required reactants are present in the sample carrier stream and are added to the sample zone as a consequence of dispersion. The configuration is associated with the inception of flow injection analysis and is characteristic of the sequential injection analyser. Flow injection systems comprising two or more streams that converge to form the main carrier stream into which the sample is inserted [134] are also considered as single-line flow systems. 

A. Alonso, M.J. Almendral, Y. Curto, J.J. Criado, E. Rodriguez, J.L. Manzano, Determination of the DNA-binding characteristics of ethidium bromide, proflavine and cisplatin by flow injection analysis. Usefulness in studies on antitumor drugs, Anal. Biochem. 355 (2006) 157. 

The classical manifold architecture is fully compatible with segmented flow analysis. It has also been exploited in flow injection analysis, but the inherent segmentation alters the characteristics of the analyser [163]. 

Alonso A, Almendral MJ, Curto Y, Criado JJ, Rodriguez E, Manzano JL. New fluorescent antitumour cisplatin analogue complexes, study of the characteristics of their binding to DNA by flow injection analysis. J Fluoresc 2007 17 390-400. 

Flow injection analysis offers many attractive features to biosensor analysis. The reproducibility and the speed are two dominant characteristics when combining FIA with proper sampling and sample handling. It can be used for both enzyme-based assays and immunochemical binding assays. 

The flow injection analysis (FIA) response curve is a result of two processes, both kinetic in nature the physical process of dispersion of the sample zone within the carrier stream and the chemical process of formation of a chemical species. These two processes occur simultaneously, and they yield, together with the dynamic characteristics of the detector, the FIA response curve. Simultaneous dispersion and chemical reaction have been studied in flow systems as used in chemical reaction engineering and in chromatography, and, therefore, the theories of these two areas are related to the theory of FIA. This is why most papers about FIA theory have adopted, as a starting point, the classical theory of flow in tubular conduits, with the intention of developing mathematical expressions for peak broadening, mean residence time, and fractional conversion of the analyte to a detectable product. 

In the field of chemical analysis, biosensors have undergone rapid development over the last few years. This is due to the combination of new bioreceptors with the ever-growing number of transducers [1]. The characteristics of these biosensors have been improved, and their increased reliability has yielded new applications. Recently, a new technique of enzyme immobilization has been developed to obtain biosensors for the determination of enzyme substrates [2]. It is based on the enzyme adsorption followed by a crosslinking procedure. Therefore, a penicillin biosensor can be obtained and associated with a flow injection analysis (FIA) system for the on-line monitoring of penicillin during its production by fermentation [3-4]. This real-time monitoring of bioprocess would lead to optimization of the procedure, the yield of which could then be increased and the material cost decreased. 

Because of a build-up of product in the enzyme membrane, enzyme electrodes require washing prior to contact with the next sample. The washing time varies from just 20 s for urease in conjvmction with an ammonia electrode to as long as 10 min for urease with a pH electrode. The washing time increases with enzyme membrane thickness, as also observed for additional membranes discussed above. It will also depend on the enzyme used and on the characteristic of the base sensor itself, and will be affected by diffusion and kinetic effects. The use of flow injection analysis simplifies the procedures, since the carrier stream serves to wash out between samples. 

Table 1.6 Characteristics of Multisyringe Flow Injection Analysis ...

Fang et al. [661] have described a flow injection system with online ion exchange preconcentration on dual columns for the determination of trace amounts of heavy metal at pg/1 and sub-pg/1 levels by flame atomic absorption spectrometry (Fig. 5.17). The degree of preconcentration ranges from a factor of 50 to 105 for different elements, at a sampling frequency of 60 samples per hour. The detection limits for copper, zinc, lead, and cadmium are 0.07, 0.03, 0.5, and 0.05 pg/1, respectively. Relative standard deviations are 1.2-3.2% at pg/1 levels. The behaviour of the various chelating exchangers used was studied with respect to their preconcentration characteristics, with special emphasis on interferences encountered in the analysis of seawater. 

Dean, J.R., Ebdon, L., Crews, H.M. and Massey, R.C., Characteristics of flow injection-ICP-MS for trace metal analysis. J. Anal. Atom. Spectrom., 3 (1988) 349-354. 

Direct-infusion MS is a very interesting approach, especially when sample characteristics allow MS analysis with minimum sample treatment. Thus, ESI can be used to directly ionize analytes in liquid samples in a high electric field. A small flow of the liquid sample is conducted through a capillary to the high electric field for ESI. Usually, sample solutions must be carefully cleaned and filtered to avoid potential capillary blocking. Following this idea, direct-infusion ESI-FTICR (Fourier transform ion cyclotron resonance) MS of a coffee drink combined with partial least-squares multivariate statistical analysis was successfully employed to predict the blend composition of commercial coffee varieties (28). In a different work, minimal sample manipulation was carried out to obtain detailed molecular composition of edible oils and fats analyzed by flow-injection ESI-Orbitrap MS for quality assessment and authenticity control purposes (29). Commonly, when using direct infusion approaches, sample needs to be treated to dissolve the compounds of interest in the appropriate solvent. 

Multi-commuted flow analysers are characterised by enhanced flexibility and easy operation and combine some of the attractive characteristics of both segmented and unsegmented flow analysis. In this way, segmented flow, flow injection and sequential injection analytical procedures are efficiently implemented in multi-commuted flow manifolds. 

Conversely, confluence flow injection systems rely on sample insertion into a chemically inert carrier stream and the required reagents are added by confluence. The configuration is characteristic of the segmented flow analyser. The carrier (or background) stream is a solution similar to the sample but without the chemical species under determination. Distilled water, soil extracting solution, ethanol and synthetic seawater are examples of chemically inert carrier streams for the analysis of natural waters, soil extracts, spirits and seawater, respectively. 

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