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Analysis of physiologic specimens such as blood, urine, and cerebrospinal fluid for electrolytes, especially sodium and potassium, began more than a century ago as physician-biochemists tried objective ways of assessing the most basic aspects of physiology-water-electrolyte and acid/base balance. Of the types of specimens, whole blood and the liquid serum or plasmaI separated from the formed elementsII became the medium in which these ions were measured, first with gravimetry, later by emission/absorption spectroscopy. Each reported results as a concentration per volume of plasma (mg/dL or mEq/L). Expected or normal ranges were established, which in the case of sodium were quite narrow relative to the average (140 +/- 5mmpl/L). The advent of ion selective electrode (ISE) technology made it possible to measure them directly in whole blood with minimal specimen preparation, but ISE's gave results consistently higher than the established norms by an amount equal to the 'normal' range. Since most initial evaluative blood work on a patient admitted to a hospital or clinic includes the electrolytes, physicians had become accustomed to the values and looked at the 'high' ISE values as 'errors'. In fact, it was the ISE that was measuring what the body's sensors detected and they specifically allowed differentiation in certain serious but less common disorders, a fact that was obscured by the inherent difference in values on normal subjects. Technically the matter is simple (though there are some complex nuances) - the electrolytes are dissolved in the water fraction of the plasma, not the plasma as a whole. Changing well established physician perspectives, however, was (and is) a different story. And now the rest of the story.... [ABSTRACT FROM AUTHOR]

Characterising the local structures (e.g., the cation distribution) of mixed‐metal ceramics by NMR spectroscopy is often challenging owing to the unfavourable properties (low γ, large quadrupole moment and/or low abundance) of many metal nuclei. 17O is an attractive option owing to the prevalence of oxygen within ceramics. The moderate γ and small quadrupole moment of 17O mean that the greatest barrier to accessing the information available from this nucleus is isotopic enrichment. We explore the challenges of ensuring uniform isotopic enrichment with 17O2(g) for the pyrochlore solid solutions, Y2SnxTi2–xO7, La2SnxZr2–xO7 and La2SnxHf2–xO7, demonstrating that high enrichment temperatures (900 °C for 12 hr) are required. In addition, for sites with very high symmetry (such as the tetrahedral OY4 and OLa4 sites with CQ ≈ 0 present here), we demonstrate that quantitative 17O NMR spectra require correction for the differing contributions from the centreband of the satellite transitions, which can be as high as a factor of ~3.89. It is common to use first‐principles calculations to aid in interpreting NMR spectra of disordered solids. Here, we use an ensemble modelling approach to ensure that all possible cation arrangements are modelled in the minimum possible number of calculations. By combining uniform isotopic enrichment, quantitative NMR spectroscopy and a comprehensive computational approach, we are able to show that the cation distribution in Y2SnxTi2–xO7 is essentially random, whereas in La2SnxZr2–xO7 and La2SnxHf2–xO7, OLa2SnZr and OLa2SnHf sites are slightly energetically disfavoured, leading to a weak preference for clustering of like cations. [ABSTRACT FROM AUTHOR]

The 31P chemical shift anisotropy (CSA) offers a potential source of new information to help determine the structures of aluminophosphate (AlPO) framework materials. We investigate how to measure the CSAs, which are small (span of ~20–30 ppm) for AlPOs, demonstrating the need for CSA‐amplification experiments (often in conjunction with 27Al and/or 1H decoupling) at high magnetic field (20.0 T) to obtain accurate values. We show that the most shielded component of the chemical shift tensor, δ33, is related to the length of the shortest P─O bond, whereas the more deshielded components, δ11 and δ22 can be related more readily to the mean P─O bond lengths and P─O─Al angles. Using the case of Mg‐doped STA‐2 as an example, the CSA is shown to be much larger for P(OAl)4–n(OMg)n environments, primarily owing to a much shorter P─O(Mg) bond affecting δ33, however, because the mean P─O bond lengths and P─O─T (T = Al, Mg) bond angles do not change significantly between P(OAl)4 and P(OAl)4–n(OMg)n sites, the isotropic chemical shifts for these species are similar, leading to overlapped spectral lines. When the CSA information is included, spectral assignment becomes unambiguous, therefore, although the specialist conditions required might preclude the routine measurement of 31P CSAs in AlPOs, in some cases (particularly doped materials), the experiments can still provide valuable additional information for spectral assignment. [ABSTRACT FROM AUTHOR]

Although the solid state is typically characterised by inherent periodicity, many interesting physical and chemical properties of solids arise from a variation in this, i.e. changes in the nature of the atom occupying a particular site in a crystal structure or variation in the position of an atom (or group of atoms) in different parts of a structure, or variation as a function of time. This lack of long-range order poses significant challenges, not just for the characterisation of the structure of disordered materials, but also simply for its description. The sensitivity of nuclear magnetic resonance (NMR) spectroscopy to the local, atomic-scale environment, without the requirement for long-range order, makes it a powerful tool for the study of disorder in the solid state. Information on the number and type(s) of coordinating atoms or through-space and through-bond connectivity between atomic species enables the construction of a detailed picture of the structure. After a brief description of the background theory of NMR spectroscopy, and the experimental methods employed, we will describe the effects of disorder on NMR spectra and the use of calculations to help interpret experimental measurements. We will then review a range of applications to different types of disordered materials, including oxides and ceramics, minerals, porous materials, biomaterials, energy materials, pharmaceuticals, polymers and glasses. We will discuss the most successful approaches for studying different materials, and illustrate the type of information available and the structural insight gained. [ABSTRACT FROM PUBLISHER]

The structural chemistry of materials containing low levels of nonstoichiometric hydrogen is difficult to determine, and producing structural models is challenging where hydrogen has no fixed crystallographic site. Here we demonstrate a computational approach employing ab initio random structure searching (AIRSS) to generate a series of candidate structures for hydrous wadsleyite (β-Mg2SiO4 with 1.6 wt% H2O), a high-pressure mineral proposed as a repository for water in the Earth's transition zone. Aligning with previous experimental work, we solely consider models with Mg3 (over Mg1, Mg2 or Si) vacancies. We adapt the AIRSS method by starting with anhydrous wadsleyite, removing a single Mg2+ and randomly placing two H+ in a unit cell model, generating 819 candidate structures. 103 geometries were then subjected to more accurate optimisation under periodic DFT. Using this approach, we find the most favourable hydration mechanism involves protonation of two O1 sites around the Mg3 vacancy. The formation of silanol groups on O3 or O4 sites (with loss of stable O1–H hydroxyls) coincides with an increase in total enthalpy. Importantly, the approach we employ allows observables such as NMR parameters to be computed for each structure. We consider hydrous wadsleyite (∼1.6 wt%) to be dominated by protonated O1 sites, with O3/O4–H silanol groups present as defects, a model that maps well onto experimental studies at higher levels of hydration (J. M. Griffin et al., Chem. Sci., 2013, 4, 1523). The AIRSS approach adopted herein provides the crucial link between atomic-scale structure and experimental studies. [ABSTRACT FROM AUTHOR]

A combination of 89Y and 119Sn NMR spectroscopy and DFT calculations are used to investigate phase evolution, local structure and disorder in Y2Zr2−xSnxO7 ceramics, where a phase change is predicted, from pyrochlore to defect fluorite, with increasing Zr content. The ability of NMR to effectively probe materials that exhibit positional and compositional disorder provides insight into the atomic-scale structure in both ordered and disordered phases and, by exploiting the quantitative nature of the technique, we are able to determine detailed information on the composition of the phase(s) present and the average coordination number (and next-nearest neighbour environment) of the cations. In contrast to previous studies, a more complex picture of the phase variation with composition emerges, with single-phase pyrochlore found only for the Sn end member, and a single defect fluorite phase only for x = 0 to 0.6. A broad two-phase region is observed, from x = 1.8 to 0.8, but the two phases present have very different composition, with a maximum of 13% Zr incorporated into the pyrochlore phase, whereas the composition of the defect fluorite phase varies throughout. Preferential ordering of the anion vacancies in the defect fluorite phase is observed, with Sn only ever found in a six-coordinate environment, while remaining vacancies are shown to be more likely to be associated with Zr than Y. Our findings are then discussed in the light of those from previous studies, many of which utilize diffraction-based approaches, where, in most cases, a single phase of fixed composition has been assumed for the refinement procedure. The significant and surprising differences encountered demonstrate the need for complementary approaches to be considered for a detailed and accurate picture of both the long- and short-range structure of a solid to be achieved. [ABSTRACT FROM AUTHOR]

The article offers advice on how to deal with apparent differences in patient values between properly vetted and functioning laboratory systems. Topics discussed include communication and collaboration with healthcare teams outside the laboratory, comparison of point-of-care systems such as the enhanced blood gas analyzers, and sharing the methods and data with other stakeholders.