Nitrogen speciation analysis in solid samples by integrated pervaporation and detection

A simple method which shows the potential of pervaporation integrated with detection for speciation analysis has been used for the sequential speciation analysis of nitrogen (as ammonium and urea in solid samples). Ammonium is first converted into volatile ammonia, which is removed by pervaporation and detected by an ammonium ion-selective electrode located on the top of the separation unit. Urea is converted to ammonia by reaction with dissolved urease and detected in the same way. The determination ranges were established between 5 and 100 mg kg−1 and 25 and 400 mg kg−1, respectively, with good precision (ca. 3% r.s.d.). The 3σ detection limits were 1.3 and 21.9 mg kg−1, respectively. The determination of endogenous ammonium in, or urea added to soil samples verifies the usefulness of the method.