Regulatory control of energy drinks

Proton NMR spectroscopy has been used to measure several components of alcohol-free energy drinks, including caffeine and taurine, to check compliance with regulatory controls. In the EU, beverages with more than 150 mg/L caffeine must have special warning labels. In Germany, the requirements are stricter, defining maximum permissible levels of caffeine (320 mg/L), taurine (4000 mg/L), inositol (200 mg/L) and glucuronolactone (2400 mg/L).

There are several known HPLC methods designed to measure caffeine using diode array detection. but they cannot be extended to taurine because it has no chromophore. So, scientists in Germany and Russia have used ¹H NMR spectroscopy in the first reported application to measure regulated constituents in energy drinks, as described in Lebensmittelchemie.

The drinks were degassed and mixed with deuterated sodium 3-(trimethylsilyl)propionate in D₂O for locking and this compound was also used as the external standard. Then 1D NMR was sufficient to resolve a singlet for caffeine and 2D measurements were required for the other components. The limits of quantification were 3.8 mg/L for caffeine, 9 mg/L for taurine, 15 mg/L for glucuronolactone and 12 mg/L for inositol.

The method was suitable for about 90% of 73 drinks tested. The remainder were cloudy drinks containing fruit material and the spectra were blighted by matrix interferences. Improved sample preparation is needed for samples of this type. The average caffeine content was 0.30 g/L, just below the German maximum limit of 0.32 g/L.