TENSAMMETRIC DETERMINATION OF POTASSIUM ION IN MINERAL WATER

摘要

Alternating-current polarography of tetraphenylborate ion (TFB) produces a characteristic tensammetric (pseudocapacitive) peak at -0.95 V vs SCE in slightly acidic media (pH 4-5, acetate buffer) of 0.1 to 0.5 M NaCl Adsorption of TFB on the dropping mercury electrode in the potential region of 0-1 V was evidenced by electrocapillary measurements. The influence of different experimental parameters, such as pH, ionic strength, temperature and TFB conceniration, on the tensammetric signal was investigated. The tensammetric signal height depends linearly on the TFB concentration in a limited range (till about 0.3mM), while at higher concentration the peak height levels off a constant value. From the analytical point of view, TFB concentration should be measured on the basis of the tensammetric signal, but also by measuring the capacitive current at-0.4 V. The tensammetric peak current was used as an analytical signal in the amperometric back-titration of the potassium ion in different samples of bottled mineral waters. The method was validated by comparison with the grayimetric method. The method is fast, accurate and requires only moderate amounts on TFB.