Development of Mercury Analysis by NanoSIMS for the Localization of Mercury-Selenium Particles in Whale Liver.

Nanoscale secondary ion mass spectrometry (NanoSIMS) is a dynamic SIMS technique, which offers high spatial resolution allowing the mapping of chemical elements at the nanometer scale combined with high sensitivity. However, SIMS for mercury analysis is a challenging issue due to the low secondary ion yield and has never been done on NanoSIMS. The introduction of an rf plasma oxygen primary ion source on NanoSIMS enabled higher lateral resolution and higher sensitivity for electropositive elements such as most metals. In this paper, for the first time, mercury analysis by NanoSIMS was developed applying the new rf plasma O- ion source. All mercury isotopes could be detected as Hg+ secondary ions and the isotopic pattern corresponded to their natural isotopic abundances. Furthermore, Hg+ detection in HgSe nanocrystals has been investigated where polyatomic interferences from selenium clusters were identified and separated by high mass resolution (ΔM/M ≥ 3200). However, in the presence of selenium a strong matrix effect was observed, decreasing the Hg+ secondary ion yield. In addition, a detection of Se+ ions was possible, too. The newly developed method was successfully applied to nanoscale localization by chemical imaging of HgSe particles accumulated in the liver tissue of sperm whale (Physeter macrocephalus). This demonstrated the applicability of NanoSIMS not only for mercury detection in surface analysis but also for mercury mapping in biological samples.

Selenopeptides and elemental selenium in Thunbergia alata after exposure to selenite: quantification method for elemental selenium.

Three month old Thunbergia alata were exposed for 13 days to 10 µM selenite to determine the biotransformation of selenite in their roots. Selenium in formic acid extracts (80 ± 3%) was present as selenopeptides with Se-S bonds and selenium-PC complexes (selenocysteinyl-2-3-dihydroxypropionyl-glutathione, seleno-phytochelatin2, seleno-di-glutathione). An analytical method using HPLC-ICPMS to detect and quantify elemental selenium in roots of T. alata plants using sodium sulfite to quantitatively transform elemental selenium to selenosulfate was also developed. Elemental selenium was determined as 18 ± 4% of the total selenium in the roots which was equivalent to the selenium not extracted using formic acid extraction. The results are in an agreement with the XAS measurements of the exposed roots which showed no occurrence of selenite or selenate but a mixture of selenocysteine and elemental selenium.

Identification of arsenolipids and their degradation products in cod-liver oil.

Oils from marine samples are known to contain high concentrations of arsenolipids. However, their identification in lipid matrix poses a significant challenge especially when present in low concentrations. Here, we report the identification of sixteen arsenolipids in cod-liver oil. The fish oil was fractionated on a silica gel column and the fraction enriched with arsenic analysed using RP-HPLC online with ICP-MS and ES-Orbitrap-MS. Among the arsenolipids identified nine compounds have not been reported before. Structural assignment was achieved by arsenic signal from ICP-MS, retention time behaviour and accurate mass determination of fragment and molecular peaks. In addition, the unknown degradation products of arsenolipids eluting in the void volume were investigated using fraction collection, cation exchange chromatography and accurate mass determination, and were found to contain predominantly dimethylarsinic acid (DMA) with trace amounts of methylarsonic acid (MA), dimethylarsenopropanoic acid (DMAP) and dimethylarsenobutanoic acid (DMAB). This finding is essential in epidemiologic studies where urinary DMA and other arsenic metabolites have been used as biomarker in accessing human exposure to arsenic.

Investigation into mercury bound to biothiols: structural identification using ESI-ion-trap MS and introduction of a method for their HPLC separation with simultaneous detection by ICP-MS and ESI-MS.

Mercury in plants or animal tissue is supposed to occur in the form of complexes formed with biologically relevant thiols (biothiols), rather than as free cation. We describe a technique for the separation and molecular identification of mercury and methylmercury complexes derived from their reactions with cysteine (Cys) and glutathione (GS): Hg(Cys)(2), Hg(GS)(2), MeHgCys, MeHgGS. Complexes were characterised by electrospray mass spectrometry (MS) equipped with an ion trap and the fragmentation pattern of MeHgCys was explained by using MP2 and B3LYP calculations, showing the importance of mercury-amine interactions in the gas phase. Chromatographic baseline separation was performed within 10 min with formic acid as the mobile phase on a reversed-phase column. Detection was done by online simultaneous coupling of ES-MS and inductively coupled plasma MS. When the mercury complexes were spiked in real samples (plant extracts), no perturbation of the separation and detection conditions was observed, suggesting that this method is capable of detecting mercury biothiol complexes in plants.