Method for monitoring urea and ammonia in wine and must by flow injection-pervaporation

An easy to automate flow-injection-pervaporation method for monitoring urea and ammonia in must and wine was developed. The method is based on separation of the ammonia from the sample matrix by pervaporation followed by its reaction with salicylate, hypochlorite and nitroprusside to form a diazonium salt with maximum absorption at 647 nm. Conversion of urea into ammonia catalysed by urease was mandatory before pervaporation. After optimisation by either the univariate or multivariate approaches as required, the linear range was established (between 0 and 25 mg l-1) for both analytes. Then, the assessment of the proposed method versus a reference one for urea and ammonia was studied in terms of repeatability (0.52 mg l-1 and 0.43 mg l-1, respectively), reproducibility (1.34 mg l-1 and 1.21 mg l-1, respectively), detection and quantification limits (LOD=0.9 and 0.6 mg l-1, LQ=1.02 and 0.67 mg l-1, respectively) and traceability. The sample throughput was 16 samples h-1. The method can be applied to the monitoring of the target analytes in must and young wine in order to control their contents, preventing formation of ethyl carbamate