Determination of erythrosine in glace cherries by solid-phase spectrophotometry

A new method for the determination of the colorant erythrosine in glace cherries by solid-phase spectrophotometry is proposed. The colorant was extracted with a mixture 1:1 (v/v) ethanol-water and fixed in C-18 silica gel at pH 2.6. Next, the erythrosine-gel system was dried and packed in a 1-mm silica cell and its absorbance was measured at 542 nm against a blank. Influence of: amount of gel, percentage of ethanol, shaking time, ionic strength and sample volume, was studied. Linear dynamic range was between 25.0 and 500.0 ng mL(-1) and th detection and quantification limits were 6.5 and 21.5 ng mL(-1) respectively. The relative standard deviation was 5.4% for samples containing 400.0 ng mL(-1) of colorant. The main advantages of this method are simplicity and cheapness of the extraction process and selectivity and sensitivity in the measurement process that can be adapted in each case to th needs of the analytical problem by the use of the appropriate volume of sample equilibrated with the gel. The method was applied to the determination of erythrosine in commercial products of glace cherries obtaining good results. HPLC was used as reference method.