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Removing the Effects of an Inhomogeneous Field

An inhomogeneous magnetic field is the cause of peak asymmetry and/or line splitting. If you can't solve this problem by shimming the magnet, you can remove the asymmetry computationally, with Reference Deconvolution. The iNMR implementation is limited to 1-D spectroscopy. You need a reference singlet. iNMR looks at the shape of this peak, subtracts the shape from all the peaks in the spectrum and adds a symmetric Gaussian or Lorentzian shape instead.

To Apply Reference Deconvolution:

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Start from a frequency domain spectrum. It is convenient to prepare the display, with the zoom and cut tools, in such a way that both the reference singlet and other peaks of interest are clearly visible.

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Select your reference singlet with the mouse. The TMS peak or the chloroform peak are classic choices. The selection should be as narrow as possible (select the peak, not the baseline).

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Choose Process > Reference Deconvolution. iNMR calculates it and shows the result. To compare the corrected and uncorrected spectra, click Toggle.

You can use the usual navigation keys to inspect the shapes. The keys are always enabled on the Mac. To enable them on Windows, click on the word “interact”.

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Move the slider called reference if you want to enlarge or narrow the selection around the reference peak.

Move the slider called target to vary the final line-widths.

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Check the Lorentzian shape option if you don't like the Gaussian shape.

Check the option Si satellites selected if your reference peak belongs to a sililated compound and you have selected the Si satellites too.

Reference Deconvolution works better with a higher digital resolution. Remember to zero-fill your spectra, if they are to undergo this treatment.

As long as iNMR remains open, it remembers the selected peak (your reference). You can therefore reuse it. Do NOT select anything and re-issue the command Process > Reference Deconvolution with the same or with another spectrum (if the number of points remains the same). For example, you can deconvolute a row of a 2D spectrum, using as reference a peak contained into a different row.

Literature: KR Metz, MM Lam, and AG Webb. 2000. "Reference Deconvolution: A Simple and Effective Method for Resolution Enhancement in Nuclear Magnetic Resonance Spectroscopy". Concepts in Magnetic Resonance. 12:21-42.

Related Topics

Visual Weighting

Measuring the Area by Fitting to a Model

 

Web Tutorial

Reference Deconvolution in Practice