Determination of ammonium, calcium, magnesium, and potassium in silage by capillary isotachophoresis

A method for the simultaneous determination of ammonium, calcium, magnesium, and potassium in silage samples by capillary isotachophoresis was developed. The electrophoretic migration properties of ammonium, calcium, magnesium, potassium, and sodium were investigated in electrolyte systems with leading electrolytes containing the complexing agent crown ether (18-crown-6). It was determined that the electrolyte system consisting of 0.0075 mol/L sulfuric acid, 0.007 mol/L 18-crown-6, 0.1% hydroxypropymethyl cellulose as leading electrolyte, and 0.01 mol/L Bis-tris-propane as the terminating electrolyte is most appropriate for the determination of cations cited above. The results of this capillary isotachophoresis method were compared with atomic absorption spectroscopy, and both methods were found to be in agreement. The precision of the determination including sample pretreatment, expressed by the relative standard deviations was between 4 and 7% and 10% for calcium, magnesium, potassium, and ammonium, respectively. Detection limits were less than 200 ppm in the solid sample.