Fluoride Analysis in Sea Water and in Other Complex Natural Waters Using an Ion-Selective Electrode—Techniques, Potentialities, Limitations
Fluoride activities and concentrations can be measured simply and rapidly in a wide range of natural waters using an ion-selective electrode. Direct potentiometry is convenient in sea water and appears well-suited for in situ instruments. Known-addition techniques yield total concentration directly in sea water and in other fluids whose ionic composition is not well-defined, such as water from estuaries, rivers, or saline lakes, and no additional information about ionic strength or complexing ions is required. A combination of these methods provides information on the distribution of ions between free and complexed species. The general case is examined to define the range of. solutions in which such methods may be used with confidence. The principles apply equally well to electrodes for other ions. Accuracy and precision is given for measurements down to 0.02 mg F/Kg in a variety of solutions containing different interfering substances, and a simple approximate technique (good to a factor of 2) is discussed for measurements in rain water down to 0.0003 mg/Kg (0.3 ppb).
KeywordsFluoride Concentration Saline Lake Fluoride Level Estuary Water Total Ionic Strength
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