An international quality assurance scheme for the quantitation of daidzein and genistein in food, urine and plasma

This quality assurance (proficiency testing) scheme was commissioned to enable the Food Standards Agency (FSA) to determine the quality of analytical results submitted by researchers measuring the concentrations of phytoestrogens in foods and biological fluids in FSA-funded research projects, and also, to demonstrate that FSA-funded laboratories are producing consistent and precise results. Non-FSA-funded laboratories from around the world were also invited to join in the scheme to increase the number participants. A secondary objective was to highlight the most successful methodologies used to analyse phytoestrogens. Test materials of infant formula, plasma and urine were prepared and tested by LC-MS/MS for homogeneity to establish the concentrations of two phytoestrogens, daidzein and genistein in these test materials. Twenty one laboratories were recruited to participate in the scheme. Test materials for analysis of daidzein and genistein were issued to participants on a four-monthly basis. The results and methods of analysis were correlated and a report for each round of testing, was produced to assess the competency of laboratories. After four rounds of testing the performances of laboratories were correlated and the validity of the methods of analysis used were assessed. The performances of most laboratories for analysis of both daidzein and genistein in infant formula and biological test materials varied widely. Suitable methods that performed well for the analysis of daidzein and genistein in infant formula test materials involved a solvent extraction step, followed by reverse phase HPLC with UV detection. For biological matrices, namely plasma and urine, acceptable performance for the analysis of daidzein and genistein was achieved by methods that have an enzyme hydrolysis step before either solid phase extraction or solvent extraction and separation by either GC or HPLC and detection by MS.