Validation of a quantitative NMR method for suspected counterfeit products exemplified on determination of benzethonium chloride in grapefruit seed extracts

J Pharm Biomed Anal. 2008 Aug 5;47(4-5):958-61. doi: 10.1016/j.jpba.2008.03.021. Epub 2008 Mar 28.


A 1H-nuclear magnetic resonance (NMR) spectroscopy method for quantitative determination of benzethonium chloride (BTC) as a constituent of grapefruit seed extract was developed. The method was validated, assessing its specificity, linearity, range, and precision, as well as accuracy, limit of quantification and robustness. The method includes quantification using an internal reference standard, 1,3,5-trimethoxybenzene, and regarded as simple, rapid, and easy to implement. A commercial grapefruit seed extract was studied and the experiments were performed on spectrometers operating at two different fields, 300 and 600 MHz for proton frequencies, the former with a broad band (BB) probe and the latter equipped with both a BB probe and a CryoProbe. The concentration average for the product sample was 78.0, 77.8 and 78.4 mg/ml using the 300 BB probe, the 600MHz BB probe and CryoProbe, respectively. The standard deviation and relative standard deviation (R.S.D., in parenthesis) for the average concentrations was 0.2 (0.3%), 0.3 (0.4%) and 0.3mg/ml (0.4%), respectively.

MeSH terms

  • Anti-Infective Agents / analysis*
  • Benzethonium / analysis*
  • Citrus paradisi / chemistry*
  • Drug Contamination / prevention & control
  • Nuclear Magnetic Resonance, Biomolecular / methods*
  • Plant Extracts / analysis
  • Reference Standards
  • Reproducibility of Results
  • Seeds / chemistry*
  • Time Factors


  • Anti-Infective Agents
  • Plant Extracts
  • Benzethonium