Spectrophotometric determination of aspartame in soft drinks with ninhydrin as reagent

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Abstract
A simple spectrophotometric method has been developed for the determination of aspartame in table-top sweeteners and soft drinks based on the reaction of aspartame with ninhydrin. The selectivity of the method was improved through extraction with propylene carbonate. The optimum conditions for the extraction of aspartame and for the reaction of aspartame with ninhydrin in propylene carbonate were assessed. The absorbance measurements were made at 585 nm. The calibration graph was linear in the range 7.5–35.0 µg ml–1 of aspartame with a slope of 0.0358 (p.p.m.)–1. The precision of the procedure was checked by calculating the relative standard deviation of ten replicate determinations on a cola sample containing 680 µg ml–1 of aspartame, and was found to be 2.4%. Many common ingredients of soft drinks do not interfere, and the tolerable levels of several common free amino acids are increased through extraction with propylene carbonate. The method was applied to the determination of the aspartame content of various synthetic and real samples, and the results obtained for the real samples were compared with those obtained using high-performance liquid chromatography.

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