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Monday, September 17, 2007

Resolution Enhancement

If you have a partially resolved multiplet or partially resolved chemical shifts, you can enhance the resolution in the spectrum by treating your free induction decay with exponential and Gaussian functions before Fourier transformation. The upper trace of the figure below is the proton spectrum of benzene-d5 (i.e. C6D5H). The lower trace is the same data after treatment of the FID with a mixture of Gaussian and exponential functions. The signal in the resolution enhanced spectum shows the expected 1:2:3:2:1 multiplet due to H-D coupling. The enhancement of resolution is at the expense of the signal-to-noise ratio and quantitation.You can easily use this for your own data using TOPSPIN or XWINNMR as follows:

"lb -1" (The more negative lb - the more resolution enhancement)
"gb 0.4" (gb is a value between 0 and 1. The larger the number, the more resolution enhancement)
"gm" (This command calculates the Gaussian weighted FID)
"ft" (This command carries out the Fourier transform)
"apk" (This command calculates the proper phase correction. You may have to phase the spectrum manually)

Try it on your own data with different values of "lb" and "gb" to get a feel for what it can do for you.

To learn more about what you are doing, read the online TOPSPIN manual or take CHM 4380/8309B.

3 comments:

Anonymous said...

this post proved quite valuable to me (as someone who should probably take up manual reading)
anyways great blog, i expect to visit regularly
keep up the good work

Cameron Foster said...

Hi,

Thanks for the post. I have always benefited a great deal from the topics that you post. I am always looking to find ways to improve data quality other than just increasing signal/noise.

I just had a question that is somewhat related to this topic. Not necessary processing, but data acquisition.
Here is a link:
http://jcp.aip.org/resource/1/jcpsa6/v136/i21/p211104_s1?bypassSSO=1

It is called "Phase incremented echo train acquisition in NMR
spectroscopy"

Have you used this technique? If so, can you elaborate on how the phase is modulated? It looks like the pulse lengths for the initial and refocusing pulses are just shortened or lengthened (Ex: 180 degree pulse +/- some integer fraction pi). Is this somewhat correct?

I am not sure how useful it, but wanted to see if you had some experience with it.

Thanks again,
Cameron

Glenn Facey said...

Cameron,

Thank you for the comment. I have not tried this technique so cannot comment on it.

Glenn