AN AUTOMATIC BACK TITRATION METHOD FOR MICROCHEMICAL ANALYSIS

An automatic back titration method for microchemical analysis is intro duced, which is based on conventional volumetric analysis's principle and the use of flow injection analysis apparatus for the automation an d microminiaturization of the process. The sample and a known, but exc ess amount of a calibrated reagent solution are injected and propelled into a titration cell, where their reaction takes place. The excess o f the reagent is then titrated with a titrant containing an indicator and the end point is monitored photometrically. Since homogeneous mixi ng in the titration cell is obtained magnetically in the whole process , there is a linear relationship between the analyte's concentration a nd the volume of the titrant consumed. Nickel in the range of 10-70 g l(-1) is determined by the above method, in which 30 mu l of sample an d 500 mu l of EDTA are injected and the excess of EDTA is titrated wit h a standard zinc salt solution containing xylenol orange which could be blocked by nickel ion in a direct titration. This method is charact eristic of low sample and reagent consumption, high sampling rate as h igh as 45 samples h(-1), negligible effect of sample's viscosity, smal l carry-over effect (lower than 0.14%), and very good precision, whose relative standard deviations are as small as 0.24%. (C) 1997 Elsevier Science B.V.