Artefacts and pitfalls in diffusion measurements by NMR

Low-field NMR instrumentation offers a user-friendly and cost-effective means for assessment of water and oil droplet size measurements in food emulsions. Examples are given of major food application areas, and these are supported with validation data in terms of precision and equivalence to other methods. The NMR method gives the same results as other techniques, such as microscopy, laser diffraction and electric sensing, but with similar or better precision. NMR distinguishes itself by a simple and non-perturbing sample preparation procedure (in addition to the aforementioned advantages). For reliable results, the NMR parameters should be properly chosen and adjusted. A survey is given of experimental NMR parameters than can have an impact on the performance of water and oil droplet size determination. Copyright  2002 John Wiley & Sons, Ltd. KEYWORDS: NMR;1 H NMR; droplets; emulsion; foods; laser diffraction; microscopy INTRODUCTIONIn food research, the pressure to bring products faster to the market has become stronger, and the systems under investigation are becoming ever more complex both in structure and in chemical composition. 1 NMR spectroscopy has become an indispensable technique that can relate meso-and microstructural parameters to consumer-related features, such as shelf-life and mouthfeel.2 However, NMR is still considered an expert technique, whereas the rapid pace of product development requires understanding and/or control of food structures at the laboratory bench/kitchen table or manufacturing plant. In recent decades, low-cost and easy-to-handle benchtop NMR systems 3 have been developed which can determine phase-compositional 4 and microstructural 5 parameters of food materials. These systems operate at low field, typically 0.47 T (20 MHz for 1 H), and this poses intrinsic limitations on sensitivity and resolution. Nevertheless, these systems have gained a considerable position in food industry laboratories, with applications ranging from research and development to process and product control.The classical NMR application in the microstructural domain is the assessment of water droplet size distributions in food emulsions.6 -8 These methods are being used to explain and predict physical and microbiological stability of water-in-oil food emulsions, 9 such as margarines and low-calorie spreads. A more recent development is the assessment of oil droplet size distributions in oil-in-water systems.10 These systems also are fairly abundant as Ł Correspondence to: J. P. M. van Duynhoven, Unilever R&D Vlaardingen, Olivier van Noortlaan 120, 3133 AT Vlaardingen, The Netherlands. E-mail: john-van.duynhoven@unilever.com mayonnaises, cheese, dressings, spreads, etc. 11 Both the water and oil droplet size distribution measurements are based on the restricted diffusion of the liquid inside a droplet, a phenomenon that can be described analytically. The droplet size determination by low-field NMR has several significant advantages over other, and perhaps more obvious, methods. A summary of the typical ch...

Section: B 0 Field Homogeneitymentioning

confidence: 99%

Scope of droplet size measurements in food emulsions by pulsed field gradient NMR at low field

Duynhoven

Goudappel

Dalen

et al. 2002

“…Also, the preparation of oriented samples is tedious, control of water content is difficult and internal magnetic field gradients of the sample may perturb the measurements. 31 There are inherent advantages in combining diffusion measurements with MAS: the resonances of lipids and of small membrane-embedded molecules such as drugs are well resolved, and the high spinning frequencies average the perturbing internal field gradients. 32 Diffusion in multilamellar liposomes occurs in the plane of the bilayers, as diffusion perpendicular to the plane is negligibly small.…”

Section: Diffusionmentioning

confidence: 99%

Multi‐dimensional pulsed field gradient magic angle spinning NMR experiments on membranes

Gaede

Gawrisch

2004

The benefits of gradient techniques in the study of lipid membranes are demonstrated on a sample of 1-palmitoyl-2-oleoyl-sn-glycero-3 phosphocholine (POPC) liposomes embedded with ibuprofen. Most techniques from gradient NMR spectroscopy on solution samples are directly applicable to membrane samples subjected to magic angle spinning (MAS). Gradient-enhanced homo- and heteronuclear chemical shift correlation techniques were used to make resonance assignments. Gradient NOESY experiments provide insight into the location and dynamics of lipids, ibuprofen and water. Application of gradients not only reduces experiment time but also the t(1) noise in the multi-dimensional spectra. Diffusion measurements with pulsed field gradients characterize lateral movements of lipid and drug molecules in membranes. The theoretical framework for data analysis of MAS diffusion experiments on randomly oriented multilamellar liposomes is presented.

“…This has led to the need of assuring the reproducibility of diffusion data [3,6,12] for the sake of the comparison of data obtained with different systems or different techniques and to the development of elaborate pulse sequences and instrumentation. [13 -15] A very elegant approach to ensure diffusion data accuracy and reproducibility is the use of relative diffusivity, [16 -18] also applied when metal oxide nanoparticles are involved.…”

Section: Introductionmentioning

confidence: 99%

DOSY technique applied to palladium nanoparticles in ionic liquids

Durand

Fernández

Barrière

et al. 2008

Multinuclear ((1)H, (31)P, (19)F and (11)B) diffusion ordered spectroscopy (DOSY) technique has been applied to palladium nanoparticles systems dispersed in ionic liquids (ILs). Even if the nanoparticles themselves cannot be detected through NMR, observation of the solvent (methanol) and the IL ([BMI][PF(6)] or [BMI][NTf(2)]), their diffusion coefficients and their changes in the presence of nanoparticles allow us to draw significant assumptions about the organisation of palladium nanoparticles in the IL. For comparison, the corresponding molecular precursors ([PdCl(2)(cod)] or [Pd(2)(dba)(3)]) have been also studied.