Determination of selenium in dietary supplements by optical emission spectrometry after alkaline dissolution and subsequent headspace solid phase microextraction

Headspace solid phase microextraction (HSSPME) of chemically generated selenium hydride from alkaline solution followed by thermal desorption (TD) coupled directly to a microwave plasma (MWP) source has been examined for the optical emission spectrometric (OES) determination of Se. Various chemical and operating parameters including the NaBH4 and HCl concentrations as well as the fiber exposure time and desorption temperature have been optimized. Alternatively, continuous hydride generation (HG) from alkaline medium and inductively coupled plasma (ICP) may be used for Se determination by OES. With the procedure developed, the determination of Se in dietary supplements at the tens of μg g−1 level and an accuracy of 3–6% could be performed even in the presence of the 1000-fold excess of Fe and Cu. Additionally, Se was determined in the NIST 8418 material (Wheat gluten) with a certified concentration of Se of 2.58 ± 0.19 μg g−1, and a value of 2.45 ± 0.25 μg g−1 was found using HG-HSSPME-MWP-OES. The detection limit for Se (3.2 ng ml−1) with the proposed procedure was comparable to those obtained with HG-ICP-OES and the calibration curve was linear of about 2 orders of magnitude.

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► Se is easily determined in dietary supplements by OES.
► Alkaline solubilization with TMAH may be used for sample preparation.
► The excess iron and copper do not interfere.
► HSSPME is useful for separation of Se in the form of SeH2 from alkaline medium.