Direct measurement of multi-elements in high matrix samples with a flow injection ICP-MS: application to the extended Emiliania huxleyi Redfield ratio.

The quotas of a limited number of trace elements in the extended Redfield ratios have been determined before and thought to reflect the requirements of phytoplankton. However, these quotas are found to be quite variable under different environmental conditions, suggesting that the cellular trace metal quota is not an accurate measure of cellular trace metal requirement. Here we present a method that has been developed and optimised for direct analysis of 32 elements simultaneously in small volume of cell lysate in buffers with a high salt matrix (800 µL, up to 30% TDS). We then demonstrate the application of the method to resolve the extended Redfield ratio of cell requirement by measuring the intracellular trace element composition of six Emiliania huxleyi strains isolated from different locations. The method uses a quadrupole-ICP-MS with a collision/reaction cell to resolve polyatomic interferences. The ICP-MS is interfaced with an Elemental Scientific Flow Injection Automation System (FIAS). The accuracy of the analysis according to this new method is verified by measuring 2 certified reference materials, BCR 273 and BCR 414. This work presents a number of running parameters, optimised for multi-element analysis of samples with a high TDS sample matrix. This method allows direct measurement of protein samples in their native state: no alteration or digestion is needed, which simplifies the steps for sample preparation. In this study with 6 E. huxleyi strains isolated from the environment, our method reveals significant differences between whole cell and intracellular metal quotas for all strains. The intracellular metal composition, interpreted as a truer representation of organisms' metal requirements, shows an environmentally dependent signal. This suggests that, compared with whole cell metal quotas, the metalloproteins are a better indicator of metal requirements of phytoplankton under various environmental conditions.

Dissolved trace element concentrations and fluxes in the Irrawaddy, Salween, Sittaung and Kaladan Rivers.

The Irrawaddy (Ayeyarwaddy) and Salween (Thanlwin) globally rank among the largest rivers for supplying dissolved and particulate material to the ocean. Along with the Sittaung and Kaladan rivers they have societal importance to Myanmar in terms water sources and food production. Despite their importance for global biogeochemical cycles and the ~50 million people who live in their catchments, the chemistry of these rivers is poorly known. This study presents a comprehensive survey of dissolved (<0.22 µm) trace element concentrations (Sr, Fe, Al, Ba, Mn, V, Rb, Cu, Zn, As, Li, Ni, Mo, Cr, U, Pb, Sb, Co, Cs, Tl and Cd) at 38 locations within these river catchments, spanning a period of 2 years. The results highlight the global importance of the Irrawaddy and Salween rivers for trace element global biogeochemical cycles; contributing between 1 and 17 % of global dissolved riverine fluxes to the land-ocean interface for the studied elements. Area normalized dissolved fluxes in these catchments are ~2 to 10 times higher than global average values for most elements, consistent with high rates of chemical weathering. In general, anthropogenic activities have yet to significantly perturb dissolved trace element fluxes in these river systems. The presented dataset should therefore serve as a useful 'natural' baseline, against which future perturbations driven by climate change and/or the development of Myanmar's mining industry could be assessed. Exceptions to this include As in the Sittaung River and Sb, Zn, Pb and As in the Salween River, which may already be significantly impacted by anthropogenic inputs. The former represents a water quality issue of concern for public health, and so constraining the exact sources of As in the Sittaung River should be considered a priority for future research.

Manganese-free chow, a refined non-invasive solution to reduce gastrointestinal signal for T1-weighted magnetic resonance imaging of the mouse abdomen.

Commercial mouse chow is designed to provide a complete, nutrient-rich diet, and it can contain upwards of 100 mg/kg manganese, an essential mineral. Manganese acts as a relaxation time-shortening contrast agent for both T1 and T2, and where standard chow is hydrated in the gastrointestinal tract, bright signals are produced when using T1-weighted imaging (T1WI). As a result of peristalsis, gastrointestinal hyperintensities result in temporally unstable signals, leading to image ghosting and decreased resolution from that prescribed. To avoid the problem, various methods of gastrointestinal tract modulation, including the use of intestinal cleansing with laxatives and dietary modulation, have been reported. Here, dietary modulation has been extended to the use of a biologically innocuous, long-term change of diet. In this study, we report on the use of a commercially available manganese-free chow to improve the image quality of the gastrointestinal tract. This manganese-free chow, apart from the omitted manganese which is available in tap water, is a complete diet and readily available. We investigated the time-dependent, diet-related gastrointestinal intensities on short-TR T1WI magnetic resonance imaging; monitored body mass, food and water consumption and standard blood biochemistry analysis following diet change; and determined manganese concentration in blood plasma following a five-day change to manganese-free chow. We show that the manganese-free chow presents a refinement to other gastrointestinal tract modulation, as it avoids the need for invasive procedures for gut voiding and can be provided ad libitum so that animals can be maintained with no need for prescribed diet change before imaging.