Correcting Field Inhomogeneity by Reference Deconvolution
An inhomogeneous magnetic field is the cause of peak asymmetry and/or line splitting. If you cannot 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 analyzes the shape of this peak, removes the corresponding distortion from the whole spectrum, and replaces it with a symmetric Gaussian or Lorentzian line shape.
To Apply Reference Deconvolution:
- Start from a frequency-domain spectrum. It is helpful 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.
- Select your reference singlet with the mouse. The TMS peak and 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 performs the calculation and displays 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 the word “interact”. -
Move the slider called reference to enlarge or reduce the portion of the reference peak used in the calculation.
Move the slider called target to vary the final line-widths. -
Check the Lorentzian shape option if you do not like the Gaussian shape.
Check the option Si satellites selected if your reference peak belongs to a silylated compound and you have selected the Si satellites too.
Reference Deconvolution works better with 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. Simply make no new selection and run Process > Reference Deconvolution again, either on the same spectrum or on another spectrum with the same number of points. For example, you can deconvolute a row extracted from a 2-D spectrum using a reference peak selected in 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.
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