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

Abstract

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.

Liquid-phase microextraction and fibre-optics-based cuvetteless CCD-array micro-spectrophotometry for trace analysis

“…A rectilinear calibration graph was obtained for the range 0.2-4 mg L −1 of ammonia; correlation coefficient and LOD were found to be 0.9985 and 46 g L −1 of ammonia, respectively. This sensitivity compared better than the literature values, 100 g L −1 by indicators colour change in FIA [80], 600 g L −1 by indophenol formation in FIA [81], 300 g L −1 by gas-diffusion and indophenol formation [82], 770 g L −1 by gasdiffusion and indicator colour change [83], 500 g L −1 by indicator colour change in SIA [84], and 70 g L −1 by multi-syringe FIA [85].…”

Pervaporation flow injection analysis for the determination of sulphite in food samples utilising potassium permanganate–rhodamine B chemiluminescence detection

“…Various examples of pervaporation flow injection (PFI) in food quality control have been reported including the determination of sulphide in Kraft liquors (Papaefstathiou, Luque de Castro, & Valcarcel, 1996), sulphur dioxide in wines (Mataix & Luque de Castro, 1998), diacetyl (Izquierdo-Ferrero, Romero, & Luque de Castro, 1997), urea (Gonzalez-Rodroguez, Perez-Juan, & Luque de Castro, 2002a, 2002b, ammonia in beers (Wang, Cardwell, Cattrall, Luque de Castro, & Kolev, 2003), and methanol and iron combined in vinegar (Gonzalez-Rodroguez et al, 2002a, 2002b. These are testaments to its versatility and robustness.…”

On-line pervaporation-capillary electrophoresis for the determination of volatile acidity and free sulfur dioxide in wines

“…Single or several parameters have been determined in wines after pervaporation, namely: volatile and total acidity [3], ethanol and glycerol [15], free and total sulfur dioxide [16], carbon dioxide and free sulfur dioxide [17], methanol, ethanol, ethyl acetate and acetaldehyde [18], urea and ammonia [19]. The appropriate flow-injection (FI) manifold and detector, together with the pervaporator, made the experimental setup in each case.…”