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A flow analyser with enhanced sampling frequency combining the features of flow-injection and continuous-flow analysis is described. Parameters of the analyser were optimized to ensure the highest rate of analysis allowed by the bubble-through flow cell with fluoride-selective electrodes. Fluoride was determined in 0.1-ml water samples with a sampling rate as high as 720 h−1 and a relative standard deviation better than 1%.

A fast-response flow cell with ion-selective electrodes was constructed for continuous-flow measurements in air-segmented streams without debubbling. The flow system was optimized for fluoride and chloride determinations. With a flow-rate of 4 ml min−1 a sampling rate of 480 h−1 was achieved for chloride determinations; the average relative standard deviation in all instances was better than 2%.