ISC Course Analytical Chemistry

Various methods gave insight into the structure of citric acid.

How can you prepare lemonade without having any lemons? The aim of the ISC course "Analytical Chemistry" was to develop a recipe for an instant lemonade. To do this, it was first important to find out the ingredients of lemon juice. With help of titrations and specific detection, the students saw that lemon juice contains mainly fruit acids in addition to small amounts of sugar and vitamin C. However, the participants did not know which fruit acids were involved. In a next step, the they isolated citric acid from lemon juice. Among others, students determined its structure by mass spectrometry, nuclear magnetic resonance spectroscopy and X-ray crystallography. With this information, a specific detection for citric acid was found, so that the exact concentration of citric acid in lemon juice could be determined by photometry. It turned out that lemon juice contains practically no other fruit acids apart from citric acid. Thus, at the end of the course, a mixture of citric acid and sugar could be prepared, which, dissolved in water, resulted in a refreshing "lemonade".