Absolute determination of soluble potassium in tea infusion by gamma-ray spectroscopy

Potassium content in tea brew was determined by gamma-ray spectroscopy, using the 1461 keV gamma-ray from 40K, the naturally occurring radioactive isotope of potassium. We measured radiation with a shielded HPGe detector from individual test samples of tea leaves, before and after infusion preparation, and from commercial instant tea powder. The correction factor for the gamma-ray self-absorption in the extended source was determined with the help of Monte-Carlo simulations. This gamma-ray spectroscopy technique enabled the absolute determination of potassium content with a relative uncertainty smaller than 4%, at the one standard deviation confidence level, showing the feasibility of this method. An experiment to evaluate a possible systematic uncertainty due to K distribution heterogeneity in the sample was performed, with the result that the corresponding relative standard deviation is smaller than 2% at 95% confidence level.