Abstract: The production of selenium and selenomethionine certified reference material in yeast (Saccharomyces cerevisiae) and certification studies for its homogeneity, stability and characterization, have been accomplished before in our laboratory. Based on such results and experience of our laboratory in Metrology and according to literature, we discuss here the advantages and limitations of the calibration by “single point” as an alternative method to the classical calibration curve. The method traceability to the SI is checked in order to secure a robust determination. As the model analyte the mass fraction of the Se species selenomethionine is measured and compared in yeast samples. Results showed that a good agreement was obtained by both methods (the reference one of the calibration curve and “single point calibration”). This simple approach can be used for routine control of selenomethionine in commercial supplements of yeast samples, but the work carried out demonstrated its potential for the general routine quantitative analysis of the possible and important selenium species in other Se-enriched supplements commercialised in Latin America (i.e. mushrooms, garlic etc).

Resumen: La producción de material de referencia certificado de selenio y selenometionina en levadura (Saccharomyces cerevisiae) y los correspondientes estudios de certificación de homogeneidad, estabilidad y caracterización, se han llevado a cabo con anterioridad en nuestro laboratorio. Basándonos en los resultados y la experiencia de nuestro laboratorio en Metrología y según la bibliografía, discutimos aquí las ventajas y limitaciones de la calibración de “un punto” como un método alternativo a la curva de calibración clásica. Se verificó la trazabilidad del método al SI para asegurar una determinación robusta. Como analito modelo, se determina la especie de selenio, seleniometionina, presente en muestras de levadura. Los resultados obtenidos por ambos métodos (curva de calibración y la calibración de “un punto”) muestran una buena concordancia. Esta aproximación simple demostró su utilidad para el control rutinario de selenometionina en suplementos comerciales de levadura y su potencial para el análisis cuantitativo rutinario general de las otras importantes especies de selenio de interés en otros suplementos enriquecidos en Se comercializados en Latinoamérica (es decir, champiñones, ajo, etc.)

Abstract In this paper we discuss recent significant developments in the field of venom research, specifically the emergence of top-down proteomic applications that allow achieving compositional resolution at the level of the protein species present in the venom, and the absolute quantification of the venom proteins (the term “protein species” is used here to refer to all the different molecular forms in which a protein can be found. Please consult the special issue of Jornal of Proteomics “Towards deciphering proteomes via the proteoform, protein speciation, moonlighting and protein code concepts” published in 2016, vol. 134, pages 1-202). Challenges remain to be solved in order to achieve a compact and automated platform with which to routinely carry out comprehensive quantitative analysis of all toxins present in a venom. This short essay reflects the authors’ view of the immediate future in this direction for the proteomic analysis of venoms, particularly of snakes.

Nós investigamos o papel do plâncton no ciclo do vanádio (V) em Cabo Frio, Rio de Janeiro, Brasil, uma região com alta concentração de V nas partículas atmosféricas, devido ao aerossol marinho. As concentrações de V no plâncton variaram de 0,08-20,9 µg g-1 (zooplâncton), 0,1-28,4 µg g-1 (fitoplâncton > 64 µm) e < 0,0005-49,0 µg g¹ (pequeno fitoplâncton > 20 µm). A especiação de V associado a biomoléculas foi realizada por duas estratégias: (i) o acoplamento de cromatografia de exclusão de tamanho (SEC) para o fracionamento de espécies com espectrometria de massas com plasma indutivamente acoplado (ICP-MS) e (ii) cromatografia de exclusão de tamanho por troca aniônica com detector UV-Vis acoplado a espectrometria de massas com plasma indutivamente acoplado (SEC-AE-UV-Vis-ICP-MS). Os resultados mostraram uma única fração contendo V associada a uma biomolécula na faixa de 8 a 16 kDa, com ponto isoelétrico acima de 8. Resultados preliminares usando MALDI-TOF não permitem identificar a biomolécula, considerando a larga faixa de massa molecular obtida.

We investigated the role of plankton in the vanadium (V) cycle at Cabo Frio, Rio de Janeiro state, Brazil, a region with high V concentration in the atmospheric particles due to marine aerosol. The concentrations of V in plankton vary from 0.08 to 20.9 µg g-1 (zooplankton), 0.1 to 28.4 µg g-1 (phytoplankton > 64 µm) and < 0.0005 to 49.0 µg g-1 (small phytoplankton > 20 µm). The V speciation in biomolecules was performed by the use of two strategies: (i) coupling of size exclusion chromatography (SEC) for the fractionation of species with inductively coupled plasma mass spectrometry (ICP-MS) and (ii) with size exclusion anionic exchange chromatography with UV-Vis detector coupled to inductively coupled plasma mass spectrometry (SEC-AE-UV-Vis-ICP-MS). The results showed a single fraction containing V associated with a biomolecule in the range of 8 to 16 kDa, with isoeletric points above 8. The preliminary analyses using matrix-assisted laser desorption-ionization-time of flight (MALDI-TOF) do not permit to identify such biomolecule, considering the broader size range of the proteins obtained.

A metodologia analítica de diluição isotópica (IDA) pós-coluna foi empregada para realizar ensaios de especiação quantitativa de selênio (Se) em amostras de efluentes industriais através do acoplamento da cromatografia de íons ao ICP-MS, contendo um sistema composto por uma célula de reação (ORS). As interferências ocasionadas pelos dímeros de argônio nos isótopos 78Se e 80Se foram suprimidas pressurizando-se a câmara do octapolo com 4 mL min-1 de hidrogênio. Selenito [Se (IV)], selenato [Se (VI)] e selenocianato [SeCN-] foram separados por cromatografia de íons (IC) utilizando eluição isocrática com 20 mmol L-1 Na2CO3/2 mmol L-1 NaHCO3. Após a separação, os íons carbonato presentes no eluente foram convertidos a CO2 em linha por uma membrana supressora auto-regenerante, a fim de evitar a obstrução do nebulizador ou dos cones de interface do ICP-MS. Limites de detecção (3σ da flutuação da linha de base) de 0,18, 0,13 e 1,0 ng g-1 foram atingidos para Se (IV), Se (VI) e SeCN-, respectivamente. A quantificação do selênio, separadamente em cada espécie, foi executada empregando a análise de diluição isotópica (IDA) pós-coluna, adicionando de modo contínuo uma solução enriquecida com 77Se ao efluente da coluna supressora. Finalmente, as razões entre os isótopos 78Se/77Se ou 80Se/77Se foram monitoradas e a concentração da espécie correspondente de selênio avaliada. A metodologia proposta foi aplicada com sucesso para o estudo de especiação quantitativa do selênio em efluentes de refinarias de petróleo.

A post-column Isotope Dilution Analysis (IDA) methodology has been used to carry out the quantitative speciation of selenium (Se) in industrial wastewaters by ion chromatography coupled to ICP-MS with an octapole reaction system (ORS). The interfering argon dimers on the 78Se and 80Se isotopes were suppressed by pressurizing the octapole chamber with 4 mL min-1 of hydrogen. The inorganic Se species selenite [Se (IV)], selenate [Se (VI)] and selenocyanate [SeCN-] were separated by ion chromatography (IC) using isocratic elution with 20 mmol L-1 Na2CO3 / 2 mmol L-1 NaHCO3 as eluent. After the separation, the eluent carbonates were converted to CO2 on-line by a membrane self-regenerating suppressor, in order to avoid clogging problems in the nebulizer or in the cones of the ICP-MS interface. Detection limits (as 3σ of the baseline noise) of 0.18, 0.13 and 1.0 ng g-1 were achieved for Se (IV), Se (VI) and SeCN- respectively. Quantification of selenium in each separated species was performed using post-column isotope dilution analysis by continuous mixing of an enriched 77Se spike solution with the effluent from the suppressor column. Finally, the 78Se/77Se or 80Se/77Se isotope ratios were monitored and the concentration of the corresponding selenium species was evaluated. The proposed methodology has been successfully applied to study the quantitative speciation of selenium in petroleum refinery wastewaters.