W. J. van Oort, G. Veenendaal, E. Buijsman, and B. Griepink* Laboratory for Analytical Chemistry, the University, Croesestr. 77A, Utrecht, The Netherlands Received June 9, 1976 Verbesserung der Bestimmung kleiner Chloridmengen durch coulometrische Titration Best. von Chlorid; Coulometrische Titration; TFA statt Essigsfiure Especially in the coulometric titration of small amounts of chloride, 70 % acetic acid is widely used as a titra- tion solvent [2,4]. In speeding up ti~e analysis [1,3, 5] we found that acetic acid has two important draw- backs: i) its conductivity is rather low, resulting in higher working voltages and thus in an increased change of a lower current efficiency, and causing an enlarged signal to noise level at lower chloride quan- tities, and ii) the silver electrode response upon chloride addition controls the titration time to a very large extent. We tried to find a solvent with a better conductivity and enabling a faster electrode response, and having most of the favourable aspects of the 70 % acetic acid solution. At higher temperatures no sufficient improvement was obtained. So we tried among others t.-butanol (20-70 %), formic acid (40-70 %), mono- chloroacetic acid (70 %), tri-chloroacetic acid (70 %), tri-fluoroacetic acid, and other alcohols, DMSO and several ketones. We added 1% w/w NaCIO4 as well to decrease ohmic resistance. Fast electrode responses were obtained in the solutions of DMSO, alcohols and ketones. However, the adsorption of chloride on the AgCl-precipitate was high. Addition of gelatin, sodium fluoride or sodium nitrate did not sufficiently decrease the ad- sorption. At higher temperatures the adsorption still caused difficulties. Formic acid enabled a faster electrode response and had a lower conductivity, but it can not be recommend- * Corresponding author. Table 1 Chloride, Chloride Stand. dev. neq. given neq. (mean) in % rel. found Number of detns. 0.50 0.50 2.6 6