Micropprocessor-controlled determination of fluoride in the presence of magnesium and calcium in sea water and blood plasma by a fluoride-selective electrode with standard additions

An automated standard additions method with an ion-selective electrode is used to determine free fluoride in plasma, urine and sea water; the amounts of pH buffer and sequestering agent are minimal. The presence of uncomplexed metal ions was allowed for in the data treatment using modified Nernst and Gran functions. After fusion with sodium hydroxide, non-volatile fluoride was determined in the plasma and urine of pediatric patients who had undergone methoxyflurane anaesthesia. Fluoride concentrations of 0.002–210 mg l^?1 were measured, generally to a precision of ±5%. The procedures reported are unusual in that complexing metal ions in the samples were not completely removed by sequestration, and that there are relatively large volume changes during the analyses of small samples. The calculation method described allows for both these features.