Determination of fluoride in M(SbF 6) x compounds

Abstract

The purpose of this study was to develop an analytical procedure to establish both the yield and purity of co-ordination compounds of the type M(SbF 6) x , where M=Mn, Pr, La or Ce, synthesised in our laboratory. Such an analysis requires an accurate determination of the metal concentration, the amount of SbF 6 − species and free and total fluoride. In this study, free and total fluoride were determined using a fluoride ion selective electrode (ISE) with the analytical technique adapted to the sample decomposition/pre-treatment procedure. Initial attempts, using alkaline carbonate fusion with NaKCO 3 and alkaline microwave decomposition/fusion failed to ensure the complete release of fluoride, leaving 25–35% of F − still bound. Good quantitative recovery of fluoride (>99%) and the complete decomposition of the samples were achieved by the reduction of Sb(V) to Sb(III) using Devarda’s alloy in strongly alkaline media. To avoid any error arising in the determination of fluoride by ISE, interference due to Sb 3+ and Al 3+ — originating from the Devarda’s alloy, was masked by the addition of diaminocyclohexanetetraacetic acid (CDTA)/citrate buffer and the calibration of the fluoride electrode was made using standards containing all the reagents used during sample decomposition/preparation. Antimony and fluoride did not interfere with the complexometric determination of manganese with ethylenediaminetetraacetic acid (EDTA).