Search

In this study, we demonstrate the applicability of nitrogen microwave inductively coupled atmospheric pressure mass spectrometry (MICAP-MS) for Ca, Fe, and Se quantification in human serum using isotope dilution (ID) analysis. The matrix tolerance of MICAP-MS in Na matrix was investigated, revealing that high Na levels can suppress the signal intensity. This suppression is likely due to the plasma loading and the space charge effect. Moreover, 40Ca and 44Ca isotopic fractionation was noted at elevated Na concentration. Nine certified serum samples were analyzed using both external calibration and ID analysis. Overestimation of Cr, Zn, As, and Se was found in the results of external calibration, which might result from C-induced polyatomic interference and signal enhancement, respectively. Further investigations performed with methanol showed a similar enhancement effect for Zn, As, and Se, potentially supporting this assumption. The mass concentrations determined with ID analysis show metrological compatibility with the reference values, indicating that MICAP-MS combined with ID analysis can be a promising method for precise Ca, Fe, and Se determination. Moreover, this combination reduces the influence of matrix effects, broadening the applicability of MICAP-MS for samples with complex matrixes. [ABSTRACT FROM AUTHOR]

Marine flatfishes have a low metabolic rate and routinely encounter large fluctuations in salinity, and are therefore of interest in the study of diffusive water flux (a proxy for transcellular water permeability), oxygen consumption (ṀO2), ammonia excretion and urea-N excretion as a function of salinity and seawater [Ca2+]. These parameters were measured in two coastal marine flatfishes, Pacific sanddab and Rock sole acclimated to 31 ppt and exposed acutely (for up to 3 h), to environmentally relevant salinities of 45, 15.5, or 7.5 ppt. In both species, diffusive water flux and ammonia excretion rates increased as salinity decreased. ṀO2 and urea-N excretion rates remained relatively unchanged. Nitrogen quotient analysis indicated increased oxidation of protein at lower salinity. A second experimental series was performed on Rock sole to separate the effects of salinity from those of ambient [Ca2+]. In direct contrast to the significant increase seen at 7.5 ppt, reducing salinity from 31 ppt to 7.5 ppt while maintaining [Ca2+] at 10 mM or increasing it to 20 mM resulted in no change in diffusive water flux rate, demonstrating that reduced [Ca2+], rather than reduced salinity itself, is the primary cause for the increases in diffusive water flux. However, ammonia excretion rate increased when salinity was decreased and [Ca2+] was increased compared to 31 ppt with added [Ca2+]. Our results demonstrate that both diffusive water flux and ammonia excretion rates are a function of salinity, that neither are coupled to ṀO2, and that ambient [Ca2+] also plays a role in these rates. [ABSTRACT FROM AUTHOR]

[Display omitted] • Paracoccus denitrificans AC-3 possessed efficient NH 4 +-N and Ca2+ removal ability. • Strain AC-3 can tolerate a broad pH range and high levels of NH 4 +-N and Ca2+. • The NH 4 +-N removal pathways were primarily assimilation and secondarily HNAD. • Ca2+ was removed by forming calcite with CO 3 2− and HCO 3 −. • The calcite induced by strain AC-3 has unique morphology and elemental composition. The novel Paracoccus denitrificans AC-3 strain was isolated and displayed outstanding purification capability for high concentrations of ammonia nitrogen (NH 4 +-N) and calcium (Ca2+). Meanwhile, the strain exhibited excellent environmental adaptability within a wide pH range and high levels of NH 4 +-N and Ca2+. Nitrogen balance analysis demonstrated that the pathways of NH 4 +-N removal consisted of 80.12% assimilation and 16.60% heterotrophic nitrification aerobic denitrification (HNAD). In addition, Ca2+ was removed by forming calcium carbonate (CaCO 3) with carbonate (CO 3 2−) and bicarbonate (HCO 3 −). CO 3 2−and HCO 3 − were obtained from carbon dioxide (CO 2) hydration, which was catalyzed by carbonic anhydrase (CA) secreted by strain AC-3. The alkaline environment for carbonate precipitation was provided by CA and HNAD. The resulting CaCO 3 existed in the form of calcite and exhibited a unique morphology and elemental composition. [ABSTRACT FROM AUTHOR]