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SUMMARY —A method employing the fluoride ion‐selective solid‐state membrane electrode has been developed to determine the presence and amount of free fluoride ion in carbonated and noncarbonated beverages. Representative carbonated and non‐carbonated beverages containing known amounts of added fluoride were used to relate electrode activity measurements to fluoride concentration in parts per million. Calibration curves were constructed for each system wherein fluoride concentration (ppm), was plotted as a function of potentiometric measurements (millivolts); using the fluorideion‐activity‐electrode as the indicator electrode and a saturated calomel electrode (SCE), as the reference electrode. Beverages studied were selected to represent a range of pH values and complexity of organic and inorganic constituents present in order to demonstrate the ability of the fluoride‐ion‐electrode to selectively determine free‐fluoride ion.

An ultrasonic solubilization technique has been developed which is useful as a first step in the coulometric determination of the chloride content of crystalline organic compounds such as p-chlorobenzoic acid.

A coulometric method is described for measuring alien halide content (usually bromide and chloride) of iodine crystals at levels less than 50 ppm. Our method replaces the vintage visual turbidimetric (Nessler tubes) measurement of the USP and ACS methods with an accurate, precise electronic end point of a chloridometer. The limit of detection is about 1 ng chloride, with an uncertainty of about 3%. Our procedure avoids the inherent errors associated with visual comparison between sample, blank, and control systems with widely differing indifferent ion populations.