FLOW-INJECTION ANALYSIS WIT POTENTIOMETRIC DETECTION FOR THE SPECIATION OF FLUORIDE AND CALCIUM

Three flow injection systems with potentiometric detection have been d eveloped for speciation of fluoride using a fluoride ion-selective ele ctrode with a single flow-through detector. Among systems with (i) spl itting of the sample zone and confluence point, (ii) flow reversal and (iii) resampling, the latter was most suitable. Its application was d emonstrated for a study of the effectiveness of releasing fluoride fro m complexes with AI(III). Several ligands were examined as decomplexin g agents such as EDTA, cyclohexane-l,2-diamine-N,N,N',N'-tetraacetic a cid (DCTA), citrate and 4,5-dihydroxy-1,3-benzenedisulfonic acid disod ium salt (Tiron). In Bow injection measurements, only Tiron was found suitable for decomposition of Al(III)-fluoride complexes. In stopped-f low measurements, it was observed that with use of citrate or DCTA abo ut a 10 min delay was required to release fluoride from AI(III) comple xes. A flow-injection system with resampling was also utilised for spe ciation of calcium with ion-selective electrode in ligand solutions an d in natural waters. (C) 1998 Elsevier Science B.V.