Resolution of an intense sweetener mixture by use of a flow injection sensor with on-line solid-phase extraction

An integrated solid-phase spectrophotometry–FIA method is proposed for simultaneous determination of the mixture of saccharin (1,2-benzisothiazol-3(2H)-one-1,1-dioxide; E-954) (SA) and aspartame (N-l-α-aspartyl-l-phenylalanine-1-methyl ester; E-951) (AS). The procedure is based on on-line preconcentration of AS on a C₁₈ silica gel minicolumn and separation from SA, followed by measurement, at λ=210 nm, of the absorbance of SA which is transiently retained on the adsorbent Sephadex G-25 placed in the flow-through cell of a monochannel FIA setup using pH 3.0 orthophosphoric acid–dihydrogen phosphate buffer, 3.75×10^–3 mol L⁻¹, as carrier. Subsequent desorption of AS with methanol enables its determination at λ=205 nm. With a sampling frequency of 10 h⁻¹, the applicable concentration range, the detection limit, and the relative standard deviation were from 1.0 to 200.0 μg mL⁻¹, 0.30 μg mL⁻¹, and 1.0% (80 μg mL⁻¹, n=10), respectively, for SA and from 10.0 to 200.0 μg mL⁻¹, 1.4 μg mL⁻¹, and 1.6% (100 μg mL⁻¹, n=10) for AS. The method was used to determine the amounts of aspartame and saccharin in sweets and drinks. Recovery was always between 99 and 101%. The method enabled satisfactory determination of blends of SA and AS in low-calorie and dietary products and the results were compared with those from an HPLC reference method.