Absolute quantification of Na+ bound fraction by double-quantum filtered 23Na NMR spectroscopy

The effect of salt content on the structure of iota‐carrageenan systems: 23Na DQF NMR and rheological studies

“…[11 -13] Recently, 23 Na single-quantum (SQ) and double-quantum-filtered (DQF) NMR experiments have been shown to be very effective tools for quantifying levels of total and 'bound' Na + ions in heterogeneous systems. [14] To further our understanding of the effects of Na + ions on iotacarrageenan gel structure and properties, we have investigated the rheological macrostructure of these gels and their microstructure using NMR spectroscopy. In this study, we used T 1 -relaxation SQ and DQF 23 Na NMR experiments to observe Na + ions in 1% (w/w) iota-carrageenan systems containing Na + concentrations of 0-3% (w/w).…”

Distribution and mobility of phosphates and sodium ions in cheese by solid‐state 31P and double‐quantum filtered 23Na NMR spectroscopy

“…In order to achieve that, the optimal creation time, τ opt , that maximizes the DQF signal intensity must be determined through the transverse relaxation time measurement. [22,23] The two components observed on the DQF spectra are characterized by two different relaxation times: the 'fast' (T For each cheese, the corresponding relaxation times were then extracted from the evolution of the total DQF signal intensity, I DQ , as a function of the creation time, τ (Fig. 7) In comparison to the cheese C1, the SQ and DQF signals of C2 exhibit larger line widths and shorter relaxation times.…”

“…The basic four-step phase cycle of the sequence to eliminate SQ coherences is: ϕ = 0, 90, 180, 270; ϕ = 2 (0, 180). [18,22] All 23 Na NMR experiments were performed with a delay between scans (repetition time) of 200 ms. In order to determine the optimum duration of the creation time τ (τ opt ) that maximizes the amplitude of the DQF signal, 23 Na DQF NMR spectra were acquired with δ = 10 µs for 32 τ values, ranging from 100 µs to 30 ms. SQ (π /2 pulse) and on-resonance DQF (using τ opt ) acquisitions were recorded with identical numbers of scans (2048), recycle delays (200 ms) and receiver gains.…”

“…The DQ filtration places the two relaxing magnetizations in antiphase and the resulting spectrum is the sum of two lines of equal areas but different widths. [22] Thus, the respective dynamics of total and 'bound' sodium ions can be characterized by measuring SQ and DQ transverse relaxation times. Moreover, the relative quantification of the 'bound' sodium fraction can be achieved by comparing the areas of SQ and DQF signals.…”

“…with different mobility states) of sodium ions on two model systems: cationic exchange resin [22] and iota-carrageenan gel. [23] In carrageenan gel with increasing sodium content, the relative quantification of the 'bound' sodium fraction, based on DQF signal analysis, was directly correlated to the gel hardness.…”