Selenium enriched dietary supplement rapid screening method using XRF and DART-HRAM-MS for label verification

Abstract

Selenium is a biologically relevant trace element that is a common ingredient of commercially available dietary supplements. Label verification of dietary supplements enriched with selenium has been performed using liquid chromatography with inductively coupled plasma mass spectrometry (LC/ICP-MS) in research applications. While this method represents the gold standard, performing LC/ICP-MS analysis on dietary supplements can be cumbersome and comes with the cost of time, ultimately limiting the throughput of this technique. A rapid screening method would improve throughput and reduce the number of samples requiring the complete LC/ICP-MS characterization of selenium for dietary supplement label verification. A rapid screening method for the determination of total selenium using energy dispersive X-ray fluorescence (XRF) (limit of detection 4 μg g⁻¹, limit of quantitation 30 μg g⁻¹) and unbound “selenoamino acids” using direct analysis in real time high resolution accurate mass–mass spectrometry (DART-HRAM-MS) was successfully applied to 13 dietary supplements previously characterized by LC/ICP-MS. Overall, determining total and speciated selenium in enriched dietary supplements using the combined XRF/DART-HRAM-MS approach reduces the analysis time from several hours to less than 40 minutes per sample.