Experimental study of kinematic focusing. Comparison of electroinjection and sequential injection determination of copper

The recently predicted phenomenon of kinematic focusing was studied experimentally using copper ions and EDTA as reactants. Kinematic focusing occurs, in electroinjection analysis, when the detected reaction product moves at the same rate as the reagent present in excess. Thus, reaction product accumulates without dispersion at the front of the excess reagent. Cu-EDTA(2-) complex was observed at 254 nm to form an exceptionally sharp peak as the front of the EDTA zone passed by the detector. The concentrating effect of kinematic focusing was quantified by electroinjection of premixed Cu-EDTA(2-). Sensitivity was compared to that of sequential injection analysis using a 1 cm optical pathlength. Sensitivity was highest in the electroinjection mode, in spite of its 120 mu m capillary pathlength, due to kinematic focusing. (C) 1999 Elsevier Science B.V. All rights reserved.