Solid-phase reactor with copper(II) phosphate for flow-injection spectrophotometric determination of aspartame in tabletop sweeteners

Abstract

A flow-injection spectrophotometric method was developed for determining aspartame in tabletop sweeteners. Samples were dissolved in water and 250 μl of the solution were injected into a carrier stream of 5.0×10 −3 mol l −1 sodium borate solution (pH 9.0). The sample flowed through a column (13 cm×2.0 mm) packed with Cu 3(PO 4) 2 immobilized in a matrix of polyester resin and Cu(II) ions were released from the solid-phase reactor by the formation of Cu(II)(aspartame) 2 complex. The mixture merged with a stream of borate buffer solution (pH 9.0) containing 0.02% (w/w) alizarin red S and the Cu(II)–alizarin red complex formed was measured spectrophotometrically at 550 nm. The calibration graph for aspartame was linear in the 20–80 μg ml −1 concentration range, with a detection limit of 2 μg ml −1 of aspartame. The RSD was 0.2% for a solution containing 40 μg ml −1 aspartame ( n = 10) and 70 measurements were obtained per hour. The column was stable for at least 8 h of continuous use (500 injections) at 25°C. The proposed method was applied for determining aspartame in seven commercial tabletop sweeteners without interference of saccharin, acesulfame-k and cyclamate.