Ultrasound-assisted purge-and-trap extraction for simultaneous determination of low-molecular weight amines and ammonium in high salinity waters by ion chromatography

Abstract

Direct determination of ammonium and amines in high salinity water samples by ion chromatography using conductivity detection is impossible due to the presence of high potassium and sodium concentrations. This work describes a simple and fast method for the determination of ammonium, monomethylamine and monoethylamine in high salinity waters by ion chromatography. An ultrasound-assisted purge-and-trap extraction system was used to eliminate matrix interferences. This system was optimized using a full two-level factorial (23) design followed by a two-level factorial (22) design. In the first factorial design, the variables: extraction time, concentration of sodium hydroxide solution and analyte mass were tested. In the second factorial design, the mass of each analyte was maintained constant. Parameters of the analytical curves, prepared in different matrices: sulfuric solution and extracts from working standard solutions prepared in water and saline solution were compared. Limits of detection of 0.02, 0.03 and 0.03mgL−1 were found for ammonium, monomethylamine and monoethylamine, respectively. Saline waters from Brazilian oil industry, pre-treated to remove nitrogen compounds, were analyzed. Satisfactory recoveries (93–111%) of the analytes were obtained for all spiked samples. Precision was ≤10% (n=3). The proposed method is adequate for analyzing saline waters containing sodium to ammonium, monomethylamine and monoethylamine concentration ratios up to 56,000:1 and potassium to ammonium, monomethylamine and monoethylamine concentration ratios up to 24,000:1.