Determination of Benzoic acid in soft drink

UV Spectroscopic Analysis of Caffeine & Benzoic Acid in Soft Drinks
An informal lab report is due on this experiment one week after completing the lab
In this experiment, we use ultraviolet absorbance to measure two major species in soft drinks. Caffeine is
added as a stimulant and sodium benzoate is a preservative. Benzoic acid is a food preservative and it is
widely used in acidic foods (pH 2.5 - 4). It is normally added as the salt, sodium benzoate. Although
benzoic acid is a man-made food additive, benzoic acid naturally occurs in several fruits, often in amounts
that exceed the recommended allowance set by the FDA.
2/25/2009 SEG
1
Chem 414
UV Spectroscopic Analysis of Caffeine & Benzoic Acid in Soft Drinks
An informal lab report is due on this experiment one week after completing the lab
In this experiment, we use ultraviolet absorbance to measure two major species in soft drinks. Caffeine is
added as a stimulant and sodium benzoate is a preservative. Benzoic acid is a food preservative and it is
widely used in acidic foods (pH 2.5 - 4). It is normally added as the salt, sodium benzoate. Although
benzoic acid is a man-made food additive, benzoic acid naturally occurs in several fruits, often in amounts
that exceed the recommended allowance set by the FDA.
In this analysis we will use non-diet soft drinks because the sugar substitute, aspartame, found in diet
drinks, also absorbs ultraviolet radiation. This slightly interferes in the analysis. We also avoid drinks
containing carmelized sugar, as this colorant absorbs in the UV region of interest. Therefore, in this
experiment we shall analyze Mountain Dew, a highly caffeinated soft drink, and Sprite, which does not
contain caffeine. There will be some UV absorbance from the matrix of these drinks. This does cause a
small systematic error, but this error is very small compared to the levels of caffeine and benzoic acid
being measured.However, as seen in the previous experiment, Beer’s law can be applied to solutions containing more
than one kind of absorbing substance. Provided there is no interaction among the various species (side
reactions), the total absorbance for a multicomponent system is given by: