Diffusion Manual Outline

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2 Table of Contents Chapter 1 Section 1.1 Section 1.2 Section 1.3 Chapter 2 Chapter 3 Section 3.1 Section 3.2 Section 3.3 Section 3.4 Introduction to Diffusion Introduction Some Theory Measuring Diffusion Hardware and Probe Configuration Measuring Diffusion Preparation Acquisition DOSY Data Analysis using ILT DOSY Data Analysis using XWINNMR: Fitting Diffusion Coefficients Appendix
3 Chapter 1 Section 1.1 Introduction to Diffusion Introduction Self-diffusion is a measure of the translational motion of a molecule. Diffusion is closely related to molecular size as illustrated by the Stokes-Einstein equation seen below: D = k T f where k is the Boltzman constant, T is the temperature and f is the friction coefficient. For the simple case of a spherical particle of a hydrodynamic radius r s in a solvent of viscosity η, the friction factor is given by f = 6 π η r s Translational diffusion can be used to determine the size and shape of individual molecules as well as molecular aggregates. This provides an excellent way of analyzing complex mixtures without having to physically separate out each individual component. Pulsed-field gradient (PFG) NMR can be used to measure translational diffusion by applying externally controlled magnetic field gradients. These gradients spatially encode the position of each nuclear spin. This spatial distribution can be decoded after waiting a short time by applying a second gradient. If the waiting time is very short between the encoding and decoding gradients the spins will not have had a chance to change position and in turn the magnetization will refocus without a net phase change. However the spins that have moved during the waiting time between the encoding and decoding steps will acquire a net phase change. The summation of the accumulated phases over the entire sample will lead to partial cancellation of the observable magnetization and hence an attenuation of the NMR signal. This signal attenuation is dependent on the strength of the applied gradients, the time between the gradients (diffusion time) and the diffusion coefficient of the molecules under study. Section 1.2 Some Theory Nuclear spins within a homogeneous magnetic field precess at the Larmor frequency according to the equation ω o = γB o where ω o is the Larmor frequency γ is the gyromagnetic ratio and B o is the strength of the magnetic field
Page 1: 1 MEASURING DIFFUSION BY NMR Bruker
Page 5 and 6: 5 Figure 1.1 Simple gradient echo e
Page 7 and 8: 7 Figure 1.4 Shows the attenuation
Page 10 and 11: 10 Chapter 2 Hardware and Probe Con
Page 12 and 13: 12 Enter the first gradient amplitu
Page 14 and 15: 14 2. Fill out the table accordingl
Page 16 and 17: 16 Section 3.4: DOSY Data Analysis
Page 18 and 19: 18 The equation is in the form I (q
Page 20 and 21: 20 Appendix Pulse Sequences and Cor
Page 22 and 23: 22 } } { (0) | (0) | (0) } p19 { (0
Page 24 and 25: 24 GRADIENT2(cnst23) d16 d30 4u BLK
Page 26 and 27: 26 ledbp2s Another good way to decr
Page 28 and 29: 28 loop l20 { p16 { (0) | (0) | (0)
Page 30 and 31: 30 } p19 { (0) | (0) | (0),sin(cnst
Page 32 and 33: 32 GRADIENT(cnst21) d16 p1 ph6 GRAD

Diffusion Manual Outline

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