General Procedures For All Spectra
1. Preliminary Notes
2. Loading the Sample
A. The probe should contain a sample at all times. When you arrive at the instrument with your research sample, you should remove the standard sample from the magnet and replace it with your sample as follows:
3. Locking the Instrument
A. To display a swept lock signal, choose Windows/lock from the XWIN-NMR menu. You should now see a continuous wave deuterium NMR spectrum of your solvent. This should be a trace across the screen with the signal in the middle of it.
4. Shimming the Magnet
A. To obtain a high resolution spectrum it is essential that all parts of the sample are exposed to the same magnetic field. The homogeneity of the field is generally assessed by noting the intensity of the lock signal, the more intense the signal the better the field. In practice, the shims most likely to require adjustment are the spinning ones, namely Z Z2 and Z3 shims, and the non-spinning shims X and Y. To adjust the homogeneity by hand (often adequate for routine spectra and almost always faster than by automated computer shimming) you must first make sure that the lock trace is visible. If it has gone off the screen during the locking procedure it can be brought back by lowering the LOCK GAIN level. A sample procedure follows:
Running a 1H Spectrum
5. Setting the Parameters
A. From the XWIN-NMR menu choose File/New. A edc window will appear containing the file name parameters. Enter a new NAME. Generally only the Name parameter needs to be changed. NOTE: The first time you use XWIN-NMR you will need to change other parameters to EXPNO=1, PROCNO=1, DU=datanmr, User=<username>. Click on SAVE
6. Acquiring the Spectrum
A. To start the acquisition type zg to zero the memory and go (start the acquisition). You can watch the progress of the acquisition by choosing Acquire/observe fid window from the menu, or by typing acqu.
7. Transforming the Data
A. A complete description of processing parameters and their meaning can be found in the XWIN-NMR Software
8. Manipulating the spectrum
A. The spectrum can be expanded vertically and horizontally using the mouse, clicking on the buttons to the left of the spectrum. *2, /2, *8, /8 multiply or divide the vertical scale by 2 or 8. To expand the horizontal scale, left click anywhere in the spectral window. Then middle click on the desired expansion limits. Left click again to unlock the mouse from the expansion. To expand the vertical scale by an arbitrary amount, left click and hold the double arrow button to the right of /8. Move the mouse vertically until the peaks are desired height. Release the mouse button.
9. Phasing the Spectrum
A. The spectrum will usually not have all the signals upright in an absorption phase. To correct this type apk (automatic phase correction). For spectra with well separated narrow lines, apk will usually work well.
10. Setting the Reference
A. The spectrometer cannot provide an exact chemical shift without being calibrated to a standard (usually TMS). Click on the calibrate button to the left of the spectrum. A small arrow will appear on the spectrum. move the arrow to the reference peak with the mouse, and click the middle mouse button. A window will appear with the current frequency value. Enter the reference frequency. A chart of chemical shift values for solvents is on the console.
11. Changing SW and O1 for Increased Resolution
12. Integrating the Spectrum
A. It is often useful to integrate 1H spectra. The simplest way to define the integral range is by entering abs. The command abs performs an automatic baseline correction and also automatically defines the integral ranges. The integrals will not appear on the screen, but will appear on the plot.