ITP Determination of Potassium and Ammonium in Fertilizers and Silage
A method for isotachophoretic determination of potassium and ammonium cations in fertilizers and silage was developed. A capillary of 0.4 mm i.d. and 100 mm effective length made of fluorinated ethylene–propylene copolymer was filled with an electrolyte system consisting of 10 mmol L−1 RbOH + 0.1% (w/v) hydroxyethylcellulose, adjusted to pH 9.0 with l-histidine (leading electrolyte) and 10 mmol L−1 lithium citrate (terminating electrolyte). Using contactless conductivity detection, the calibration curves in the tested concentration range up to 0.5 mmol L−1 were linear for both cations. The concentration detection limits for potassium and ammonium were 2.9 and 2.7 μmol L−1, respectively. RSD values of step lengths (n = 6) were 1.3% for potassium and 1.5% for ammonium. The separation time was about 20 min. Similar results were obtained with cesium cation used as the leading ion, however, in the system with rubidium better resolution of other cations present in tested matrices was reached. The elaborated method is simple to perform, sufficiently sensitive and accurate and can be recommended as an alternative procedure to the methods used so far for the determination of potassium and ammonium.
KeywordsCapillary electrophoresis Isotachophoresis Ammonium Potassium
This work was supported by grant No. 203/05/2106 of the Czech Science Foundation, grant IAA 400310703 of the Academy of Science of the Czech Republic, the Institutional Research Plan Z40310501, and the grant of the Czech Ministry of Education, Youths and Sports (project. No. MSM0021627502).
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