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A microbore high performance liquid chromatographic/electrospray/mass spectrometric (HPLC/ESI-MS) method has been developed for the determination of the phytoestrogens daidzein and genistein in soya flours and baby foods. The samples were hydrolysed and extracted with acetonitrile-water prior to analysis. LC was performed on a microbore Primesphere 5C8 column using a water/acetonitrile/acetic acid mobile phase at a flow rate of 60 microliters/min. Atmospheric pressure ionization in the form of pneumatically assisted electrospray mass spectrometry (ESI-MS) was used as the method of detection. The limit of detection was 0.2 mg/ kg for daidzein and 0.7 mg/kg for genistein in the flour and food samples. The method proved both robust and reliable when operated over a long time period (10 days, 463 injections) generating precision data with a coefficient of variation of 4-15%.

A previously reported proficiency test for the analysis of vitamin B(2) in liquid dietary supplement demonstrated bimodality. The same trend has now been observed in four subsequent tests of this type. The trend would not so easily have been observed without applying a fit-for-purpose standard deviation that is more generous than that predicted by the Horwitz equation. Since originally reporting the bimodal problem and hypothesising its cause by incomplete enzymic digestion of riboflavin-5-phosphate, there has been a general improvement in the reporting of the higher mode. This is thought to correspond to free riboflavin following complete digestion of the sample. Several individual participants appear to have learned from the experience and have changed their reporting of the lower mode to the higher mode.

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