New and feasible method for total phosphorus and sulfur determination in dietary supplements by ion chromatography

Abstract

The microwave-assisted digestion of dietary supplements using diluted nitric acid under oxygen pressure for subsequent indirect determination of phosphorus and sulfur by ion chromatography (IC) was proposed. Different concentrations of nitric acid (from 1 to 14.4 mol L−1) and oxygen pressures (from 5 to 20 bar) were evaluated. Dissolved organic carbon and residual acidity were used to choose the most suitable digestion condition. Using the proposed method, it was possible to digest up to 1350 mg of dietary supplements using only 5 mol L−1 HNO3 under 5 bar of oxygen pressure. Comparing to conventional digestion procedure it was possible to digest up to 60% higher sample mass using HNO3 around 30% more diluted. Recoveries ranging from 96 to 102% were obtained when recovery tests using a standard solution or a mixture with certificate reference material were carried out. The concentration of P and S indirectly determined by IC agreed with the results obtained by conventional microwave-assisted digestion using concentrated HNO3 and subsequent determination by inductively coupled plasma optical emission spectrometry. Keywords: Sample preparation, Digestion under oxygen pressure, Diluted acid, Ion chromatography, Food safety, Routine analysis