Total selenium and selenomethionine in pharmaceutical yeast tablets: assessment of the state of the art of measurement capabilities through international intercomparison CCQM-P86

Abstract

Results of an international intercomparison study (CCQM-P86) to assess the analytical capabilities of national metrology institutes (NMIs) and selected expert laboratories worldwide to accurately quantitate the mass fraction of selenomethionine (SeMet) and total Se in pharmaceutical tablets of selenised-yeast supplements (produced by Pharma Nord, Denmark) are presented. The study, jointly coordinated by LGC Ltd., UK, and the Institute for National Measurement Standards, National Research Council of Canada (NRCC), was conducted under the auspices of the Comité Consultatif pour la Quantité de Matière (CCQM) Inorganic Analysis Working Group and involved 15 laboratories (from 12 countries), of which ten were NMIs. Apart from a protocol for determination of moisture content and the provision of the certified reference material (CRM) SELM-1 to be used as the quality control sample, no sample preparation/extraction method was prescribed. A variety of approaches was thus used, including single-step and multiple-step enzymatic hydrolysis, enzymatic probe sonication and hydrolysis with methanesulfonic acid for SeMet, as well as microwave-assisted acid digestion and enzymatic probe sonication for total Se. For total Se, detection techniques included inductively coupled plasma (ICP) mass spectrometry (MS) with external calibration, standard additions or isotope dilution MS (IDMS), inductively coupled plasma optical emission spectrometry , flame atomic absorption spectrometry and instrumental neutron activation analysis. For determination of SeMet in the tablets, five NMIs and three academic/institute laboratories (of a total of five) relied upon measurements using IDMS. For species-specific IDMS measurements, an isotopically enriched standard of SeMet (76Se-enriched SeMet) was made available. A novel aspect of this study relies on the approach used to distinguish any errors which arise during analysis of a SeMet calibration solution from those which occur during analysis of the matrix. To help those participants undertaking SeMet analysis to do this, a blind sample in the form of a standard solution of natural abundance SeMet in 0.1 M HCl (with an expected value of 956 mg kg(-1) SeMet) was provided. Both high-performance liquid chromatography (HPLC)-ICP-MS or gas chromatography (GC)-ICP-MS and GC-MS techniques were used for quantitation of SeMet. Several advances in analytical methods for determination of SeMet were identified, including the combined use of double IDMS with HPLC-ICP-MS following extraction with methanesulfonic acid and simplified two-step enzymatic hydrolysis with protease/lipase/driselase followed by HPLC-ICP-IDMS, both using a species-specific IDMS approach. Overall, satisfactory agreement amongst participants was achieved; results averaged 337.6 mg kg(-1) (n = 13, with a standard deviation of 9.7 mg kg(-1)) and 561.5 mg kg(-1) (n = 11, with a standard deviation of 44.3 mg kg(-1)) with median values of 337.6 and 575.0 mg kg(-1) for total Se and SeMet, respectively. Recovery of SeMet from SELM-1 averaged 95...

Determination of SeMet and Se(iv) in biofortified yeast by ion-pair reversed phase liquid chromatography-hydride generation-microwave induced nitrogen plasma atomic emission spectrometry (HPLC-HG-MP-AES)

“…6,8 Depending on the strain type, fermentation conditions (medium, pH, temperature, and aeration) and Se(IV) concentration, selenized yeast may contain up to 3 mg selenium per gram of the dry mass. 2,13 The primary organic, bioavailable and benecial selenium compound in yeast is selenomethionine (SeMet) incorporated into proteins hence its reliable quantication has become the essential part of quality control; it should also be ensured that the residual inorganic selenium has been efficiently eliminated. [10][11][12] The reported species identity and their abundance have varied for different protocols applied in the fabrication and analysis of Se-yeast, indicating a need for the implementation of quality control schemes.…”

A miniaturized microtiter plate protocol for the determination of selenomethionine in selenized yeast via enzymatic hydrolysis of protein-bound selenium

“…Most often, enzymatic sample extraction for subsequent Se speciation analysis is performed extracting 50-300 mg of sample using 20-60 mg of protease, and applying total filling volumes ranging from 2.5-10 mL. [3][4][5][6]10,11 The main goal of the present study was to reduce both the overall sample volume and the amount of enzyme as this would lead to a considerable savings in cost and to a reduced footprint for the extraction setup. However, the amount of enzyme should be kept to a level still convenient and accurate to weigh on a conventional analytical balance.…”

Atomic Spectrometry Update. Elemental speciation

“…A major interlaboratory comparison (CCQM -P86) for the determination tSe and SeMet in pharmaceutical yeast tablets, was reported by Goenaga-Infante et al 179 Fifteen laboratories, of which ten were National Measurement Institutes, from 12 countries took part in the comparison. As no methodology was prescribed, apart from moisture content determinations, a wide variety of analytical methods were used including single-step and multiple-step enzymatic hydrolysis, enzymatic probe sonication and hydrolysis with methanesulfonic acid for the determination of SeMet.…”