Single-Line FIA Manifolds

An important feature in order to obtain optimum performance in terms of sensitivity and precision is that the rate of flow of the carrier stream pumped into the nebulizer is always greater than the natural aspiration rate of the nebulizer, that is, it is necessary to maintain a forced flow into 

Limited dispersion has also been used for the potentiometric determination of the calcium activity in serum or the so-called ionized fraction of calcium [21]. The calcium electrode was placed in a specially designed flowthrough cell (Fig. 4.4), which also accommodated the reference electrode, and by incorporating a pH glass capillary flowthrough electrode into the system, it was possible to measure simultaneously the pH and pCa of the injected sample at a rate of approximately 100 samples/h with high reproducibility. Inherent for the latter is that the design of the FIA 

Systems with medium dispersion are the most interesting from an ana- 

As illustrations of potentiometric determinations based on medium dispersion may serve the assay of nitrate [12, 13, 68], potassium [8, 13] and sodium [8], in which applications the mixing of sample and carrier stream is not aimed at promoting a chemical reaction, but to conditioning of the individual sample solutions before they are exposed to the electrode in order to measure them under optimal operational conditions. Thus, de- 

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Figure 4.1. Single-line FIA manifold for the determination of metal ions by flame atomic absorption spectrometry (AA). The sample (5) is injected into a carrier stream of diluted acid (5 X 0 M sulfuric acid), propelled forward by pump P, and transported to the nebulizer of the AA system, the distance between the injection valve and the AA instrument being reduced as much as possible (length 20 cm) in order to secure limited dispersion of the injected sample.

FiGURE 30.2 Single line FIA manifold (a) double line (b) and merging zone (c). The analytical path are composed by sample and reagent looping (Lj and L2), reagent flow (R), confluence (Y), coil (B), carrier flow (Ci and C2), waste (W) and detection cell. 

The greatest asset of the single-line manifold is its simplicity, which permits the use of simple means of propelling the carrier stream. Therefore, even a constant head or a gas pressurized reservoir [102, 253], which both yield a pulse-free stream allowing excellent reproducibility of measurement, may be employed. However, for all other FIA systems, two or more well-controlled channels are required and therefore a peristaltic pump is the best choice when designing a flexible FIA system. 

Manifolds of the most typical measuring systems used in FIA are shown schematically in Figure 1.3. Both in the simplest system with a single line to transport the carrier... 

FIGURE 1.3 Schematic manifolds of typical flow injection analysis (FIA) systems (a) single line manifold, (b) multiline configuration RCl, RC2—reaction coils. (Adapted from Ruzicka, J., 2009, Tutorial on Flow Injection Analysis (4th ed.). From Beaker to Micro fluidics, www.flowinjection.com.)... 

FIA methods based on ferric reducing power similar to the FRAP principle reaction have been used for the determination of ascorbic acid, vitamin E, and total iron. Table 30.1 summarizes most of these studies. Spectrophotometric detection is also used in many of these studies because of the chromogenic effect from Fe oxidation, which changes with complex ligands, such as TPTZ, o-phenanthroline, cyanide, and DPPH. Different FIA manifolds have also been investigated and proposed, from single to multiple lines. Therefore, like other chromogenic antioxidant tests, the FRAP assay has the potential for several flow injection adaptations. 

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