The ammonium acetate saturation (AMAS) method was used to study the cation-exchange capacity (CEC) of zeolitic volcaniclastic materials from Santorini and Polyegos Islands, Greece. The AMAS method was tested with respect to the time required to saturate the samples of zeolites with ammonium (NH4+) ions, the efficient liberation of NH4+ ions, and the suitability of two widely used techniques to measure ammonia (NH3) (Kjeldahl ammonia distillation technique and the ammonia electrode technique). By using the inductively coupled plasma-mass spectrometry (ICP-MS) technique and measuring the number of cations exchanged during ammonium acetate (NH4OAc) saturation, it was found that the saturation period for zeolitic materials must be increased to 12-day cycles to ensure effective saturation. Following NH4OAc saturation, the AMAS method produces NH4+ solutions, after the NH4+-saturated samples of zeolites are washed with 10% NaCl. The amount of the NH4+ ions in solution (i.e., exchangeable cations) is a measure of the CEC. The NH4+ ions can not be directly measured and must be converted to NH3. The Kjeldahl ammonia distillation technique and the ammonia electrode technique for measuring NH3 give identical CEC results. However, the ammonia electrode technique, when used directly with the NH4+ samples of zeolite without 10% NaCl treatment, generally gives higher CEC values. The amount of NH4+ treated (converted to NH3), when the NH4+-saturated zeolitized samples were used directly, was higher than the amount of the NH4+ treated when the NH4+ solutions were obtained after washing the NH4+-saturated zeolitized samples with 10% NaCl. Therefore, washing with 10% NaCl does not facilitate the release of all NH4+ initially within the zeolite structure. A modified AMAS technique is proposed for measuring the CEC of zeolitic material.

A method for the estimation of urea in milk using ammonia electrode is described. Urea is first degraded by urease enzyme into ammonium ion and carbon dioxide at neutral pH. The ammonium ion is then converted into ammonia at alkaline pH. A linear inverse relationship was observed between logarithmic concentration of ammonia or urea and electrode response. Repeatability, expressed as a coefficient of variation, was 1·77% at a level of 8·92 mm-urea in milk. The method was validated in milk samples spiked with between 2×10−3 and 10×10−3 m-urea and recovery of added urea was quantitative. Whereas, preservative sodium azide at 0·5 g/l or 2 g/l level did not affect results, lower values of urea concentration in presence of Bronopol at 0·5 g/l were observed. Urea levels in milk samples estimated by this method were comparable to standard enzymatic method. The method is simple, fast and is not prone to interference from other milk constituents.