In order to imprve the speed at low of cost, a method of analysis of animal feed for sodium, potassium and magnesium by ultrasound-assisted leaching with a mixture of strong acids prior to analysis by flame atomic absorption spectrometry(FAAS) has been proposed. The influence of acid mixture composition, time, temperature and sample mass on the leaching recovery was examined in order to find the most suitable working conditions. The ultrasound- assisted leaching carried out at opzimized conditions (mixture of HNO3, HCl, H2O2, ultrasound bath, 60 °C, 30 min) was established to be a fast and quantitative method for the feed mixture sample preparation before determination of Na and K. Mg was found to be only partially extractable. The microwave ashing procedure was utilized as the standard for comparison of alternative methods of sample preparation. The leaching method followed by FAAS was applied to analyzed feed mixtures and the results indicate that it is appropriate for determination of Na, K content in feed mixtures (recovery for Na 97-101 %, K 97-102%).
