Air-segmented-flow-analysis

The development of air-segmented flow analysis was restricted to a single company (Technicon Corporation Inc.), owner of the main patents until the mid 1970 s. The first air-segmented system marked with the AutoAnalyzer trade name is shown in Fig. 2.3. 

After the intensive development of air-segmented flow analysis, some successful analytical procedures without stream segmentation were proposed, mainly in connection with enthalpimetric [29,30], chem-iluminometric [31] or spectrophotometric [32,33] detection. In these systems the time domain involved was generally short, thus air addition and removal was not performed. Either the sample or the wash solution was continuously aspirated towards the main channel and measurements were made under an almost steady state situation. Without air-segmentation, however, sample throughput was impaired and sample changing was cumbersome. 

The key to controlling sample dispersion in air-segmented flow analysis is the addition of confluent streams. After the confluence point, an increase in the length of each plug (Eq. 3.12) leads to an increase in the length of the entire sample zone. This does not result in a broader recorded peak, however, because the sample linear speed is... 

The standard setups for nutrient analysis are either manual or automated air-segmented-flow-analysis versions of a wet chemical treatment of water samples to convert the desired nutrient into a coloured compound with high molar absorptivity in a suitable range of the light spectrum. Flow-injection analysis is based on identical chemical procedures but requires different reagent recipes. A more detailed introduction into automated flow-analysis is presented in Section 10.3 at the end of this chapter. 

As the outlines of methods are nearly identical for manual analysis and automated air-segmented-flow-analysis (with regard to chemistry, sample pretreatment, preparation of standards and reagents), we have combined the analytical procedures for each nutrient. 

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]. 

Pulsating flows are beneficial with regard to segmented flow analysis, as the bubble additions are synchronised with the flow pulsation. In order to enhance the pulsating nature of the confluent stream of air to be added, some peristaltic pumps (including the widely used Technicon AAII) incorporate a lifting bar to successively pinch the air delivery tubing. 

FIGURE 5.2 Flow pattern inherent to segmented flow analysis. 1 = tube wall of part of a coiled reactor 2 = thin liquid layer adhering to it 3 = vortices inside the liquid phase 4 = air bubble outer large arrow = overall displacement of the segmented flow. Adapted from P.J. Worsfold, A. Townshend, C.F. Poole (Eds), Encyclopedia of Analytical Science, 2nd Edn, Oxford, 2005, v.3, p.24, E.A.G. Zagatto, PJ. Worsfold, Flow Analysis Overview, with permission from Elsevier (Ref. [4]). 

Exploitation of dialysis in flow analysis dates back to the 1950 s when the original air-segmented flow analyser was conceived (see 2.2). In 1963, a dialysis unit with a planar membrane was commercially available [279]. The first application of dialysis in unsegmented flow analysis dealt with... 

In segmented flow analysis, either the sample or a wash solution is aspirated to merge with an air (or immiscible solvent) stream (see Figure 2A), resulting in a segmented stream comprising a number of... 

Although segmentation of a flowing stream as a means of limiting analyte dispersion is occasionally employed in typical flow injection systems (e.g., Pasquini and de Oliveira, 1985 Tian et al., 1990 Sanchez et al., 2010), in a hybrid of a segmented flow analysis system with FIA, termed mono-segmented continuous flow analysis (MCFA) (Pasquini and de Oliveira, 1985), the sample is introduced sandwiched between two air bubbles. 

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). 

Sulphate In Waters, Effluents and Solids (2nd Edition) [including Sulphate in Waters, Effluents and Some Solids by Barium Sulphate Gravimetry, Sulphate In waters and effluents by direct Barium Titrimetry, Sulphate in waters by Inductively Coupled Plasma Emission Spectrometry, Sulphate in waters and effluents by a Continuous Flow Indirect Spectrophotometric Method Using 2-Aminoperimidine, Sulphate in waters by Flow Injection Analysis Using a Turbidimetric Method, Sulphate In waters by Ion Chromatography, Sulphate in waters by Air-Segmented Continuous Flow Colorimetry using Methylthymol Blue], 1988... 

Fig. 5.19 Continuous flow analysis with air segmentation (Skeggs). 

Flow injection analysis has been adapted to automatic air-segmented continuous flow systems, e.g., the Technicon AutoAnalyzer system. Several reducing... 

Segmentation of the liquid streams by air bubbles is a feature of continuous flow analysis. 

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. 

In air segmented continuous flow analysis, air bubbles help to reduce the interaction between adjacent samples (carry-over)... 

The samples for on-line analysis were taken through a polysulfone membrane [37]. The seven channel automatic analyzer system consisted of six air-segmented continuous flow-wet chemical analyzers (Skalar analytics) to measure the concentration of ammonia with ion selective electrode (Philips IS-570), phosphate with ammonium molybdate at 880 nm, reducing sugar with pHBAH at 410 nm, methionine with Na-nitroprusside at 505 nm, cephalosporin C with... 

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