Column Separation and Preconcentration Systems for Spectrophotometry

1 for overcoming such matrix effects, i.e., matrix matching, and enhancement of mixing by using various reactors may be used to decrease the interfering effects, but complete elimination is difficult. 

In a detailed study on the compensation of Schlieren effects using a diode-array spectrometer, Zagatto et al.[49 recommended the use of a dual-wavelength spectrophotometer as a best solution. Almost complete compensation of Schlieren signals as high as 1 absorbance has been achieved using this approach. The method has been used successfully by Ferreira et al.[28] in the spectrophotometric determination of zinc in plants, following an on-line column separation. This, however, calls for special instrumentation which is not always available in the laboratory. 

Lacy et al. 60 proposed the use of peak area instead of peak height to alleviate Schlieren effect interferences. This may be effective when interference signals are not very serious compared to the analytical signals, but the approach also requires special functions from the spectrophotometer which are usually not available. 

In most cases a reasonable degree of compensation of Schlieren effects may be achieved by taking the following measures  

FI manifolds for column separation and preconcentration in spectrophotometry are diverse, and there is hardly one which may be considered typical. However, the reader may refer to the manifold used in the determination of boron just mentioned (63]. Another interesting contribution by Novikov et al.[ll] combined ion-exchange column preconcentration with on-line solvent extraction followed by spectrophotometric detection. The eluate from the column preconcentration was released into an on-line liquid-liquid extraction system. An advantage of this approach is that interferences from Schlieren effects are avoided, since the eluate does not flow directly to the detector. Selectivity and sensitivity are also enhanced due to the combination of two separation procedures. The system has been used successfully for the determination of lead in alloys, soil leachates and sea water. 

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