Development of two different liquid mobile phase separation systems (af4-icp/ms and uplc-esi/qda) for selenomethionine analyses in yeast and cashew nut (anacardium occidentale) samples

Abstract

Selenium (Se) is an essential micronutrient for mammals and it plays important biochemical functions in the organism. Its principal source in foods comes from the Selenomethionine (SeMet) compound, which is a non-volatile Se species soluble in aqueous solutions. This way, this work described the method development of two different liquid mobile phase separation systems (asymmetrical flow field flow fractionation – AF4 and ultra-performance liquid chromatography – UPLC) to analyze SeMet in yeast and cashew nut samples, respectively. Thus, several popular sample preparation techniques were evaluated for their suitability to determine SeMet in selenized yeast by AF4 coupled to inductively plasma mass spectrometry (ICP-MS), where alkaline extraction provided the best recovery/determination conditions since it minimized hydrolysis of the protein peptide bonds optimally required for AF4 separation. From the different AF4 membranes evaluated, the 5 and 10 kDa regenerated cellulose (RC) provided similar results, while the 500 kDa RC resulted in a significant analyte loss. The developed alkaline-AF4-ICP/MS method was validated and applied in real commercial Se yeast supplements providing results in accordance with already recognized methods. For the UPLC system (detection using a single quadrupole mass analyzer with photo diode array detector – QDa and electrospray ionization - ESI) an ultrasound assisted liquid-liquid microextraction (UALLME) was optimized through an experimental design to analyze SeMet in cashew nut sample. Results showed best recoveries when working with extracting solvent in extreme values of pH. Also it was detected strong interaction between the variables ‘sample mass’ and ‘extracting solvent pH’ in the analyte response (SeMet concentraition). Genistein presented as a suitable SeMet internal standard when was compared its efficiency with the SeMet similar compound (Selenium Methyl Selenocystin – SeMeSeC). The matrix matched calibration strategy was used to minimize the influence of coextractives in the analyte analyses by the UPLC-ESI/QDa. The UALLME-UPLC-ESI/QDa method was validated and applied in real cashew nut samples. Outcomes suggest the efficient use of the AF4 as an alternative method to traditional separation techniques for many applications; besides to highlight the importance to expand the researches about SeMet in cashew nuts from Ceará state (Brazil) due to the importance of this oilseed to the local economy.