Critical review on the selenium speciation data reported for the Se-accumulator plant Cardamine violifolia/hupingshanensis/enshiensis: time to move beyond the myth of abundant selenocysteine/selenocystine content

Selenium hyperaccumulator plants possess the potential to be raw materials for feed/food supplements. However, this valorization calls for selenium speciation, as different selenium species have strikingly different characteristics in toxicity, bioavailability, and stability. Under the erroneously used name Cardamine violifolia from the Brassicaceae family there have been recently discovered selenium hyperaccumulator plants from China that are able to accumulate almost 4 g Se kg -1 dry weight in their tissues. The relevant taxonomic name of this species is Cardamine hupingshanensis , a species not related to C. violifolia . Scientific reports dating back to 2013 on its selenium speciation have been providing completely contradictory results, claiming either selenocysteine/selenocystine or selenolanthionine to be its most concentrated water-soluble selenometabolite. This contradiction cannot be separated from a widespread and incorrect analytical approach that is based on the identification of selenometabolites solely on their chromatographic retention time and on their selenium content, with this latter feature detected either by liquid chromatography – inductively coupled plasma mass spectrometry (LC-ICP MS) or LC- atomic fluorescence spectrometry (LC-AFS) instrumental setups. The goal of this critical review is to evaluate all the selenium speciation approaches published on the selenium speciation of “ C. violifolia ” and to call attention to the propagation of incorrect analytical approaches in the determination of selenocysteine/selenocystine, not only in this plant but in all biological matrices. Besides presenting the pitfall of selenometabolite identification on the basis of elemental (inorganic) spectrometry, this review highlights the actually inevitable use of electrospray ionization – high resolution accurate mass MS in this analytical field.