Methylphosphonic acid as a 31P-NMR standard for the quantitative determination of phosphorus in carbonated beverages

Abstract

Methylphosphonic acid (MPA) is introduced as an internal standard for the determination of the phosphorus content of carbonated beverages (cola drinks) by quantitative ³¹P-NMR analysis. Phosphorus in cola beverages was analyzed as phosphate in ten commercially available drinks. Phosphate concentration in the studied samples was in the range of 3.5 to 6.1 mM. The preparation of the samples included: degassing of commercially available beverages, addition of MPA as an internal standard, D₂O for signal locking and a solution of NaOH to ensure a basic environment in the sample. The calibration graphs of the MPA standard and analyte showed a linear response in the concentration range of interest. The measured values of the phosphoric acid standard solutions lay within the confidence limits of the MPA, showing that these compounds give a similar response in NMR analysis. The measured concentrations of phosphorus were in good agreement with the values detected by the traditional spectrophotometric method. The presented ³¹P-NMR method using MPA as an internal standard is reliable and simple for the determination of the phosphorus content of cola type beverages.