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

A flow-injection spectrophotometric method was developed for determining aspartame in tabletop sweeteners. Samples were dissolved in water and 250 mu l of the solution were injected into a carrier stream of 5.0 x 10(-3) mol l(-1) sodium berate solution (pH 9.0). The sample flowed through a column (13 cm x 2.0 mm) packed with Cu-3(PO4)(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 berate 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 mu g ml(-1) concentration range, with a detection limit of 2 mu g ml(-1) of aspartame. The RSD was 0.2% for a solution containing 40 mu g ml(-1) aspartame (n = 10) and 70 measurements were obtained per hour. The column was stable for at least 8h of continuous use (500 injections) at 25 degrees C. The proposed method was applied for determining aspartame in seven commercial tabletop sweeteners without interference of saccharin, acesulfame-k and cyclamate. (C) 1999 Elsevier Science B.V. All rights reserved.