High-Sensitivity FIA

If a FIA procedure is required to reach the same level of sensitivity as a batch procedure, two obstacles have to be overcome the short reaction time, which is due to the short residence time and may result in a relatively low yield of reaction product, and an excessive dispersion of the sample zone, which results in an unwanted dilution of the species to be measured. Leaving aside at this stage the problem of too short a residence time, it might be helpful to consider an approach by means of which the dispersion can be minimized, yet still remain sufficient for supplying the middle of the sample zone with an adequate amount of reagent. Obviously, lack of reagent in the center of the sample zone will result in the absence of product to be sensed (cf. Chapters 2 and 3). Thus, instead of a sharp smooth peak, one will obtain either a double peak —which may be well pronounced or may merely appear as a noisy peak signal—or a nonlinear 

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Detectors to be used in FIA should idealiy be endowed with a number of attributes such as low flow-cell volume and noise, flow-rate-independent signal, fast and linear response over a wide concentration range and high sensitivity. FIA methodology utilizes a variety of analytical detection techniques such as optical (spectroscopic and non-spectroscopic), electric (amperometric, po-tentiometrlc, conductimetric, coulometric) and thermochemical. 

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