Caffeine is a stimulant that most people are familiar with. Most typically we connect it with coffee and sodas, but it is also found in certain foods, such as chocolate. The amount of caffeine will vary within coffee brands and in different chocolate bars, but through analytical methods we can determine an amount in each. We can then compare the results to find whether there is more caffeine in chocolate or in coffee. For this experiment I will give a brief overview of caffeine, theobromine, coffee and chocolate. Through analytical methods, I will show that there is more caffeine present in a single serving of coffee than in a chocolate bar.
Caffeine is the common name for the chemical compound trimethylxanthine and is produced by many different plants, including coffee beans and cacao beans. Caffeine stimulates the central nervous system, heart rate, respiration, has mood altering properties, and acts as a mild diuretic (About.com). Theobromine is a chemical compound belonging to a class of alkaloid molecules known as methylxanthines. Methylxanthines naturally occur in caffeine. Theobromine affects people similarly to caffeine, but on a much smaller scale. Theobromine is a mild stimulant and a mild diuretic. (About.com).
In order to analyze coffee and chocolate, we'll need to separate the components to be studied, known as the the analytes. Both coffee and chocolate are complex mixtures with the analytes being caffeine and theobromine. The first step in the analytical process is sample preparation. Sampling is the process of selecting a representative amount from the initial product. Sample preparation converts that sample into a homogenous laboratory sample. A homogeneous sample has the same composition throughout. A heterogeneous sample has different composition from region to region. (Swain).
For this experiment I have chosen two popular chocolate bars and a store brand home-brew version of coffee. There are several methods to separate mixtures. Liquid extraction was used to remove the fat from our solid chocolates. The chocolates were frozen to make them stiff (and more brittle), and then ground up in a mortars and pestle into small pieces. In tubes, the solvent petroleum ether was placed with the finely ground chocolates. The tubes were then shaken. Caffeine and theobromine are insoluble in the ether. There was a suspension of the chocolate solid in the solvent. Each tube was then centrifuged leaving the solid residue at the bottom of the tube and the liquid containing the dissolved fat at the top. The liquid was poured out and what was remaining in the tube was the residue. The residue for each was transferred to a beaker with boiling water. Then some of the suspension was transferred to another tube to centrifuge. The insoluble chocolate residue remained at the bottom. The top liquid, known as the supernatant, contained dissolved analytes and tiny particles. Some of supernatant liquid was taken into a syringe and filtered into a...