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Accurate determination of trace fluoride down to 6.6 mug/g in zinc concentrate samples is found to be most expediently performed potentiometrically with a fluoride ion-selective electrode and a single-point standard addition after decomposition of the sample by potassium hydroxide fusion. The lower limit of measurement may be reduced to 1.8 mug/g if distillation from tungsten oxide flux is used in place of the fusion, but the analysis takes longer. The need for reliable fluoride data for zinc concentrate standard reference materials is exemplified and results for CANMET zinc concentrate MP-1 are given. The failure of some of the methods used to analyse standard siliceous materials is discussed.