In many real objects along with potassium the ammonium ions are found. If for the determination of NH4 + several relatively simple methods are known, then for K+ these possibilities are less, and those are required more sophisticated equipment and expensive reagents. Using an sensitive electrode in the presence of tetraphenylborate ions, we developed previously a method for determination of the potassium content by the rest titration in samples that did not contained ammonium [1,2]. Taking into account the fact that the tetraphenylborate anion can precipitate the potassium ions as well as the ammonium ones, forming white substances, which are slightly soluble and have the solubility product (PS(K[B(C6H5)4] near the value of 3.24.10-8 and PS(NH4[B(C6H5)4] of 8.41.10-8 [3]), a new method for the determination of the content of potassium in the presence of the ammonium ion has been developed. So, initially both cations were precipitated with a known excess of tetraphenylborate by creating the conditions when the values of the ion product exceed the product of solubility. Later, the excess of tetraphenylborate has been potentiometrically titrated with a standard solution of potassium chloride using as indicator the tetraphenylborate-selective electrode [1,2]. Through this operation the equivalent and summary amount of both cations can be established. The content of ammonium is determined by acid-base titration and, from the difference, the content of potassium, present in the sample, can be calculated. A series of model samples with known concentrations of the potassium and ammonium ions were analyzed. Table. The results of determination of potassium and ammonium content in model samples Analyzing the results presented in the table, one may conclude that the values of the experimentally determined quantities are close to the real ones. This means, that during the implementation of the experiment we do not commit systematic error. In the samples with an ammonium content ≤ 10-6 mol, potassium can be only potenţiometrically determined. For these conditions, the value of the ionic product for ammonium and tetraphenylborate is less than their solubility product. The presented method is relatively simple, does not require sophisticated equipment, used reagents being available. References: [1] Revenco, M.; Dîru, M.; Stîmcovschi, A. Conf. Ştiin. cu Part. Int.:Interferenţe Universitare– Integrare prin Cercetare şi Inovare, Rezumatele comunicărilor, 2012, p. 71. [2] Dîru, M. Autoref. tezei de dr. în ştiinţe chimice, Chişinău, 2012, 28 p. [3] Kozitskii, V. In: Russian Chemical Bulletin, 1971, vol. 21 (1), 6-9.
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