Impurities from polypropylene microcentrifuge tubes as a potential source of interference in simultaneous analysis of multiple lipid-soluble antioxidants by HPLC with electrochemical detection.

High-performance liquid chromatography (HPLC) with electrochemical detection was used to analyze lipid-soluble antioxidants and micronutrients in plasma. Small amounts of plasma samples are often extracted in polypropylene (PP) microcentrifuge tubes before HPLC analysis due to its convenience. We therefore investigated the effect of impurities released from different PP tubes during extraction on the electrochemical detection of retinol, lutein, alpha-tocopherol, gamma-tocopherol, retinyl palmitate, beta-carotene and total coenzyme Q10 by an HPLC system with a coulometric array detector (CoulArray HPLC). An array of eight electrical potentials and gradient elution were applied. Human plasma or ultrapure water were extracted in four different PP tubes. Peaks at different retention times with varied amounts of unknown compounds were detected from different PP tubes. Although all those unknown peaks could be differentiated from peaks of interest by the CoulArray HPLC, they caused busy chromatographs, and one peak had an overlap with the dominant peak of lutein. Moreover, that peak completely masked the lutein peak when only one oxidizing potential was applied. Our results suggest potential interference from PP tubes on electrochemical detection especially when using only one electrical potential or having poor separation for these antioxidants if PP tubes are not carefully tested.