Resolution of an intense sweetener mixture by use of a flow injection sensor with on-line solid-phase extraction. Application to saccharin and aspartame in sweets and drinks.

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-alpha-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 lambda = 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, 3.75x10(-3) mol L(-1), as carrier. Subsequent desorption of AS with methanol enables its determination at lambda = 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 microg mL(-1), 0.30 microg mL(-1), and 1.0% (80 microg mL(-1), n = 10), respectively, for SA and from 10.0 to 200.0 microg mL(-1), 1.4 microg mL(-1), and 1.6% (100 microg 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.