A Few Systems for Flow Injection Analysis Monitoring Submicro Amounts of Fluoride Ions

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A few flow systems for the selective pre-concentration and determination of submicro levels of fluorides have been developed. The systems consisted of two microcolumns, which were packed with new functional resins for selective sorption of fluoride, and a fluoride ion-selective electrode in a wall-jet type cell. Fluorides were adsorbed on each of the columns using a column switching device and eluted with a dilute sodium hydroxide. The flow systems are able to be applied to the determination of submicro amounts of fluorides in environmental and biological samples.For this study, several kinds of new functional resin for selective sorption of fluorides were prepared from anion-exchange resin and La(III), Ce(III) and Pr(III) chelates of alizarin fluorine blue (AFB) and its sulfonate (AFBS). These metal chelates were immobilized not only by ion-exchange but also by nonelectrostatic interaction between AFB and AFBS molecules and the matrix of the resin. These sorbents have specific and nonspesific binding sites for sorption of fluorides. The former were ternary complex formation sites and the latter were residual ion-exchange sites. Fluorides were sorbed strongly and specifically in the presence of electrolytes by the former sites. Fluoride uptake decreased with increasing pH due to competition between fluoride and hydroxide ions. In the sorbents modified with La(III) complexes of AFB and AFBS, the sorption and desorption of fluorides were found to be almost complete. In addition, the capabilities of the two sorbents for fluoride uptake were maintained even after being used ten times.