Determination of Phosphorus Content in Cola Drinks by 31P NMR Spectroscopy Using External Calibration and Standard Addition Approaches

Both undergraduate and graduate students in chemistry are generally introduced to nuclear magnetic resonance (NMR) spectroscopy as a structure determination tool focusing on( 1)H and( 13)C measurements. However, NMR has also become an efficient analytical instrument with various applications including routine food analysis and quantitative impurity determination. These quantitation possibilities are rarely encountered in university laboratory practicals, especially in combination with the measurement of other nuclei. In the present paper, we introduce a laboratory practical regarding the determination of the phosphorus content of a cola drink sample using quantitative P-31 NMR (P-31 qNMR) spectroscopy. Two different calibration approaches are utilized: the external calibration based on dilution series and sequential standard addition. The described experiments have been done by bachelor students in chemistry for more than 10 years and have been part of a bioanalytical chemistry course for biotechnological engineering students for 2 semesters now. Experience has shown that this laboratory practical helps students understand various basic principles of calibration in quantitative instrumental analysis and provides a better understanding of how to run NMR measurements, while data evaluation conveys numerous important concepts. As tested, the practical can also be successfully used in online and distance education.