Diffusion PFG Gradients

모든 스핀솔브 모델에 그라데이션 코일을 장착하여 강력한 펄스 필드 그라데이션을 생성할 수 있습니다. 

(주)비케이인스트루먼트는 Magritek사의 독점대리점으로 Benchtop NMR Spectrometer 장비를 보다 합리적인 가격으로 제공합니다! 

저희 (주)비케이인스트루먼트에서 보유하고 있는 Spinsolve 데모 장비를 통해 NMR Sample 측정도 가능합니다. 

샘플 측정과 관련하여 온라인 문의 게시판으로 문의 주시면 자세하게 안내 도와 드리겠습니다!  

The benefits of pulse field gradients: 

· Separate the spectra of different components in a mixture by molecular size (DOSY-type experiments)

· Measure self-diffusion coefficients to understand molecular mobility (PFG diffusion measurements)

· Accelerate the acquisition of modern 2D NMR experiments (Ultra-fast 2D NMR)

DOSY (Diffusion-ordered spectroscopy)

Complex NMR spectra of mixtures can be easily separated based on the molecular self-diffusion coefficient. Consider for example the spectrum of a mixture of procaine and 

paracetamol in D2O. This is shown in the middle scan of Figure 1, along with the spectra of the pure compounds above and below. If we had only the mixture available, but not the 

pure compounds, it would be hard to figure out how many and which compounds are present in the mixture. These spectra, along with all the others shown in this post, were 

acquired on a Spinsolve benchtop NMR spectrometer with additional hardware to enable PFGs for measuring diffusion. 

An experiment called Diffusion Ordered Spectroscopy (DOSY) creates a two-dimensional plot by acquiring a set of spectra as a function of the amplitude of the gradient. The 

chemical shift is measured along the horizontal axis, and along the vertical axis the self-diffusion coefficient is shown.  There are tools around which perform this analysis, and one 

of them is the DOSY Toolbox. Using this toolbox, we have inverted the data set to create the DOSY spectrum shown in Figure 2.

What is obvious from this 2D spectrum is that the peaks are aligned along horizontal lines. Each of these lines corresponds to a different self-diffusion coefficient, and therefore a 

different component of the mixture. We can immediately separate the solvent peak, as well as the other two components, although their diffusion coefficients differ by a little more 

than 10%. This makes DOSY a very powerful tool for mixture analysis in NMR spectroscopy when the components have different diffusion coefficients.

Measurement of self-diffusion coefficients

To demonstrate the possibility to determine diffusion constants, we took an example where we have three different species with three different nuclei. In this way, making use of 

the full power of the Spinsolve, we measure the diffusion coefficient of each nuclei to access the molecular mobility of each species in the sample. For the experiments we used 

mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4) and lithium tetrafluoroborate (LiBF4) at different lithium concentrations. The diffusion coefficients were 

measured with a stimulated – echo sequence run for each particular nuclei.

The excellent quality of the data is demonstrated by the highly linear behaviour of the individual diffusion curves.  The values or the maximum gradient strength, δ and ∆ were 

optimized for the different samples in order to achieve a signal attenuation that covers a good dynamic range. Linear fitting of these data points gives the self-diffusion coefficients 

for the three different nuclei and thus the three different ions in the different samples. As expected, the diffusion coefficients decrease with increasing lithium salt concentrations 

due to an increase in the viscosity of the samples. Plotting the different self-diffusion coefficients as a function of the concentration of the lithium salt, a linear dependence of the 

diffusion coefficient is revealed, within the investigated concentration range. 

Convenient software interface

· Easy user interface implemented in the standard Spinsolve® software

· Direct access to parameters related to the diffusion experiment (e.g. max. gradient strength, number of steps, δ and ∆)

· Plotted integrals and fully automated analysis done by the Spinsolve® software.

Multi-nuclear PFG spectroscopy on a benchtop NMR spectrometer

Molecular diffusion is the mechanism that defines molecular mobility in solutions. The study of diffusion processes is of interest in widespread fields in science where transport of 

mass needs to be determined. NMR is the method of choice to quickly determine self-diffusion coefficients of chemical species in solution. A commonly used NMR technique requires 

the combination of pulsed field gradients with a stimulated echo sequence (PGSTE). The spectroscopically resolved version of this sequence makes it possible to measure the 

diffusion coefficient of different molecules in a mixture by measuring the diffusion attenuation of the signal of each particular chemical group of each molecular structure. The 

diffusion version of the Spinsolve is a benchtop spectrometer that comes with gradient coils to make this type of experiments possible. The power of the combination of pulsed field 

gradients with spectroscopy has been demonstrated in the past to acquire DOSY (Diffusion Ordered SpectroscopY) type experiments. In this application note we take advantage of 

the multinuclear feature of the Spinsolve spectrometers to get access to a bigger variety of molecules that could be present in a mixture. The possibility to measure the signal of 

different nuclei is also advantageous in cases where signal overlapping in the 1 H spectrum does not allow for accurate separation of each component. To demonstrate the power of 

multi-nuclear diffusion measurements we have chosen an example where 1 H, 19F, and 7 Li provide access to three different molecular species. Read more …

 

• PGSTE-measurements-of-three-different-nuclei.pdf