FIA Systems with Pretreatment of Sample in Packed Reactors

One of the great advantages of the FIA technology is the ease with which additional components can be added to the system to achieve a particular analytical objective. This is most notably exemplified by the incorporation of small packed reactors, which subject an injected sample to appropriate on-line pretreatment in order to facilitate the detection of analyte. Whatever the function, a packed reactor in a FIA system is therefore designed always to perform the same chemistry on each individual sample. This is in contrast to chromatography, where the purpose of the column is to separate each individual sample into several components. Besides, since the FIA apparatus is a low-pressure system, most often operated by sim- 

The principle of the FIA preconcentration technique is illustrated in Fig. 4.38, which demonstrates how reduced dispersion of the injected sample (i.e., D 1) might be achieved by introducing a relatively large volume of sample solution, the analyte content of which is retained on an incorporated miniaturized packed reactor within the FIA channel, from which column the analyte subsequently is released and passed to a detector. The method was originally proposed to enhance the sensitivity of measurement of cationic trace elements in very diluted aqueous samples using 

More advanced designs of the on-line preconcentration technique use sophisticated ion-exchange materials [576, 683, 684, 1217], time-based injection rather than valve injection [576, 712, 1228], and, most importantly, a countercurrent operation of the microcolumn [684, 712], an operation mode that prevents any matrix material from entering the flowthrough detector even during the preconcentration period. Thus, in Fig. 

Besides preconcentration, the ion-exchanger columns have found applications for speciation studies (Section 4.8) or for removal of interfer- 

A disadvantage of the conversion techniques discussed above is the lack of selectivity, and therefore it is not surprising that considerable effort has been invested in designing systems that could remedy this. Selective conversion methods have recently been published for the determination of cyanide and sulfide [1010, 1247]. The principle of these approaches are illustrated in Fig. 4.45. In the determination of cyanide (Fig. 4.45a) advantage is taken of the fact that this anion with Clu(II) forms a complex ion of defined stoichiometric composition. Thus, injecting the cyanide-containing sample into a manifold comprising a column of CuS, the cyanide will form soluble tetracyanocuprate, the copper released from the 

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