Dispersion in Eluate Transport and Post Column Reactions

3 Dispersion in Eluate Transport and Post Column Reactions 

After elution from the column, the eluate carrying the concentrate zone may either be transported directly to the detector or be further processed to produce a detectable species before being transponed to the detector. The former case refer to systems where the analyte can be determined without transformation, e.g. in AAS. ICPES or selective electrode potentiometric measurements. The latter category include most applications in spectrophotometry, fluorimetiy and chemilumine.scence, which usually require a post column reaction. In both cases, minimization of dispersion in the conduits between the column and detector is essential for obtaining better enrichment factors. 

For a direct transponation. the shonest and thinnest conduits that are practical should be used in order to avoid unnecessary dispersion. The dispersion contribution of various transport conduits in FI-AAS systems have been studied in detail, and the importance of tube diameter, length and configuration have been stressed [5]. The dispersion contribution of this seemingly unimportant system component may often be overlooked. However, to obtain optimum performance, careful minimization of dispersion is required, especially when the columns are small, and the concentrate zones in the eluate well-focused. A shortest possible length, not exceeding 20 cm of 0.35 mm i.d tubing has been recommended for the transport conduits in AAS applications, and should be also applicable to other detection systems which do not require post column reactions. 

In systems where post column reactions are required, reagent streams are usually merged with the eluate stream via a T-piece. Often the pH condition of the eluate may not be suitable for the reaction, in which case an appropriate buffer has to be introduced either with the reagent or before hand as a separate merging stream. Then, a certain length of reaction coil is necessaiy to allow sufficient development of the reaction. All these 

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