Detection of impurities in dietary supplements containing L-tryptophan.

Impurities in nine dietary supplements containing L-tryptophan were evaluated using an HPLC methodology. In five tested products, the total impurities were higher than the thresholds described in the Food Chemical Codex or implemented in the EU for pharmaceutical grade L-tryptophan. In addition, liquid chromatography-mass spectrometry was used to specifically test for the presence of 1,1'-ethylidenebis-L-tryptophan (EBT). None of the tested products contained detectable amounts of EBT. High amounts of unidentified impurities in some dietary supplements point to potential health risks.