Quantification of manganous ions in wine by NMR relaxometry

Quantifying Dissolved Transition Metals in Battery Electrolyte Solutions with NMR Paramagnetic Relaxation Enhancement

Transition metal dissolution is an important contributor to capacity fade in lithium-ion cells. NMR relaxation rates are proportional to the concentration of paramagnetic species, making them suitable to quantify dissolved transition metals in battery electrolytes. In this work, ⁷Li, ³¹P, ¹⁹F, and ¹H longitudinal and transverse relaxation rates were measured to study LiPF₆ electrolyte solutions containing Ni²⁺, Mn²⁺, Co²⁺, or Cu²⁺ salts and Mn dissolved from LiMn₂O₄. Sensitivities were found to vary by nuclide and by transition metal. ¹⁹F (PF₆^-) and ¹H (solvent) measurements were more sensitive than ⁷Li and ³¹P measurements due to the higher likelihood that the observed species are in closer proximity to the metal center. Mn²⁺ induced the greatest relaxation enhancement, yielding a limit of detection of ∼0.005 mM for ¹⁹F and ¹H measurements. Relaxometric analysis of a sample containing Mn dissolved from LiMn₂O₄ at ∼20 °C showed good sensitivity and accuracy (suggesting dissolution of Mn²⁺), but analysis of a sample stored at 60 °C showed that the relaxometric quantification is less accurate for heat-degraded LiPF₆ electrolytes. This is attributed to degradation processes causing changes to the metal solvation shell (changing the fractions of PF₆^-, EC, and EMC coordinated to Mn²⁺), such that calibration measurements performed with pristine electrolyte solutions are not applicable to degraded solutions-a potential complication for efforts to quantify metal dissolution during operando NMR studies of batteries employing widely-used LiPF₆ electrolytes. Ex situ nondestructive quantification of transition metals in lithium-ion battery electrolytes is shown to be possible by NMR relaxometry; further, the method's sensitivity to the metal solvation shell also suggests potential use in assessing the coordination spheres of dissolved transition metals.

Nuclear spin relaxation in aqueous paramagnetic ion solutions

A Brownian shell model describing the random rotational motion of a spherical shell of uniform particle density is presented and validated by molecular dynamics simulations. The model is applied to proton spin rotation in aqueous paramagnetic ion complexes to yield an expression for the Larmor-frequency-dependent nuclear magnetic resonance spin-lattice relaxation rate T_{1}^{-1}(ω) describing the dipolar coupling of the nuclear spin of the proton with the electronic spin of the ion. The Brownian shell model provides a significant enhancement to existing particle-particle dipolar models without added complexity, allowing fits to experimental T_{1}^{-1}(ω) dispersion curves without arbitrary scaling parameters. The model is successfully applied to measurements of T_{1}^{-1}(ω) from aqueous manganese(II), iron(III), and copper(II) systems where the scalar coupling contribution is known to be small. Appropriate combinations of Brownian shell and translational diffusion models, representing the inner and outer sphere relaxation contributions, respectively, are shown to provide excellent fits. Quantitative fits are obtained to the full dispersion curve of each aquoion with just five fit parameters, with the distance and time parameters each taking a physically justifiable numerical value.

Detection of Authenticity and Quality of the Turkish Delights (Lokum) by Means of Conventional and Fast Field Cycling Nuclear Magnetic Resonance Relaxometry

Turkish delights (lokum) are traditional confectionery products that contain mainly sucrose as the sugar source and starch as the gelling agent. However, manufacturers sometimes might prefer to use corn syrup instead of sucrose to decrease the cost. This jeopardizes the originality of Turkish delights and leads to production of adulterated samples. In this study, Turkish delights were formulated using sucrose (original sample) and different types of corn syrups (SBF10, SCG40, and SCG60). Results clearly indicated that corn-syrup-containing samples had improved textural properties and were less prone to crystallization. However, this case affected authenticity of the products negatively. Both time domain nuclear magnetic resonance (TD NMR) and fast field cycling nuclear magnetic resonance (FFC NMR) techniques were found to be effective to discriminate the original samples from the corn-syrup-containing samples. In addition, quantitative analysis of FFC NMR showed that, apart from the rotational motions, molecules in Turkish delights (mainly water and also sugar molecules) undergo two types of translational dynamics.

Water dynamics in eggs by means of Nuclear Magnetic Resonance relaxometry

¹H Nuclear Magnetic Resonance relaxometry has been applied to reveal dynamical properties of water molecules embedded into egg yolk and white of three species: turkey, chicken and quail. Two fractions of water molecules, referred to as confined-water and free-water fractions, have been revealed. It has been demonstrated that translation diffusion of the confined-water fraction is three-dimensional. The dynamics of the confined-water has been quantitatively described in terms of diffusion coefficients and rotational correlation times. The parameters have been compared for egg yolk and white for all the species. In addition to these quantities, the number of the confined-water molecules per unit volume has been provided for all cases. The obtained parameters provide insight into the dynamics of water in eggs of different origin and allow to identify similarities and differences between them in connection to the structure of the network formed by the macromolecular fraction of egg yolk and white.

Nuclear Magnetic Resonance with Fast Field-Cycling Setup: A Valid Tool for Soil Quality Investigation

Nuclear magnetic resonance (NMR) techniques are largely employed in several fields. As an example, NMR spectroscopy is used to provide structural and conformational information on pure systems, while affording quantitative evaluation on the number of nuclei in a given chemical environment. When dealing with relaxation, NMR allows understanding of molecular dynamics, i.e., the time evolution of molecular motions. The analysis of relaxation times conducted on complex liquid–liquid and solid–liquid mixtures is directly related to the nature of the interactions among the components of the mixture. In the present review paper, the peculiarities of low resolution fast field-cycling (FFC) NMR relaxometry in soil science are reported. In particular, the general aspects of the typical FFC NMR relaxometry experiment are firstly provided. Afterwards, a discussion on the main mathematical models to be used to “read” and interpret experimental data on soils is given. Following this, an overview on the main results in soil science is supplied. Finally, new FFC NMR-based hypotheses on nutrient dynamics in soils are described