Standard Dilution Analysis

Standard Dilution Analysis enables accurate and precise analysis of commercial samples without the need for volumetric glassware or precise aliquot transferal. The FD&C dye Blue No. 1 is determined in samples readily available in the grocery store: a light blue mouthwash, a dark blue mouthwash, a grape soda, a low-calorie sports drink, and a night-time cold medicine. Two solutions are mixed in the sample cuvette of a simple spectrophotometer. The first solution contains 50% sample and 50% water. The second solution contains 50% sample and 50% of a stock mixture containing known amounts of both FD&C Blue No. 1 and an internal standard, FD&C Yellow No. 6. The solutions are mixed in different proportions using the same cuvette, and the absorbance of each dye is measured at each dilution. The absorbance of Blue No. 1 at 630 nm is plotted against the absorbance of Yellow No. 6 at 480 nm. The concentration of Blue No. 1 in the sample is determined from the ratio of the slope and the intercept of this line. The accuracy of the method is excellent, with percent error no higher than 4%. In addition, the method offers an impressive run to run precision, with relative standard deviations lower than 3%. The method accurately corrects for any matrix effects in the sample. As an introductory level experiment, students would be able to perform high quality analysis of real samples without complex solution preparation.