A method for fixed-NH4+ determination using a system immersed into an ultrasonic bath for NH3 extraction and ion chromatography for NH4+ determination is proposed. The method is faster, simpler and more sensible (LOD = 4.4 mg g-1 NH4+) than the classical Kjeldahl method.
fixed-ammonium; sandstone; ion chromatography; ultrasound-assisted purge-and-trap system