The concentration of fluoroborate is measured spectrophotometrically as the blue complex formed with methylene blue which is extracted into 1, 2 dichloroethane. Nitrates and nitrites interfere but these can be removed by reduction with zinc powder and orthophosphoric acid. The basic design of the coated tubular flow-through solid-state bromide-selective membrane electrode used by Van Staden was the same as that he used for the construction of a chloride-selective electrode. Henrickson and Selmer-Olson applied an autoanalyser to the determination of nitrate and nitrite in soil extracts. In an autoanalyser the water sample, buffered to pH 8.6 with aqueous ammonia–ammonium chloride, is passed through a copperised cadmium reductor column. Separation of the anions was conducted on a low capacity anion exchange column and anions were quantified by a conductiometric detection. Interfering chloride anions were removed by reaction with a silver saturated cation exchange resin.