A New Colorimetric Assay of Tabletop Sweeteners Using a Modified Biuret Reagent

A new, fast and effective colorimetric analysis of the artificial sweetener aspartame is presented for application in undergraduate laboratory courses. This new method incorporates the use of a modified biuret reagent for selective detection and analysis of aspartame in aqueous solutions. The modified reagent is less caustic than the traditional biuret reagent, which allows it to be used in an effective and simple assay of artificial tabletop sweeteners. Sample preparation is readily accomplished in three steps: (i) addition of the analyte to a 10.00 mL volumetric flask, (ii) addition of modified biuret reagent, and (iii) dilution with water. The modified biuret reagent consists of 60 mmol copper(II) sulfate pentahydrate dissolved into a solution containing 210 mmol potassium sodium tartrate and 500 mmol sodium carbonate. Spectroscopic analysis in the visible region of the electromagnetic spectrum (629 nm) allows for use of inexpensive and readily available laboratory instrumentation. The entire experiment may be completed in about two hours, giving the instructor ample time for discussion of artificial sweeteners, the Beer–Lambert Law, and coordination chemistry, when applied during a typical three hour laboratory period.