Peak Pick

(adapted from Alan Shusterman, Reed College)

Peak pick is a procedure for obtaining the resonance frequencies (or chemical shifts) of selected peaks.

The procedure involves:

1. selecting the desired unit for peak position (Hz or ppm)
2. expanding the spectrum region containing your interesting peaks so that the smallest peaks of interest are clearly visible
3. setting the threshold intensity bar below the tops of these smallest peaks
4. performing the "peak pick" operation
5. (optional) removing peaks from the peak pick list

Peak picking tip #1: expand before picking. It is not necessary to expand regions before peak picking, but it is usually a good idea. If you peak pick on a full spectrum, you are likely to get peak positions for many uninteresting peaks and this can needlessly complicate your interpretation of the peak pick data.

Peak picking tip #2: build a list of peaks. SpinWorks picks peaks only in the region displayed in the program window. Peaks that are not displayed are not picked. Therefore, you can zoom from region to region and pick just the peaks you want in each region. All of the picked peaks are added to a list that SpinWorks maintains. If you make a mistake, you can remove peaks from the list (or clear the entire list).

1. Select desired unit for peak position

• Click PeakPick: Peak Pick (on plot) Units: Hz (note: PPM can be useful if you are trying to establish the chemical shift of a pattern precisely)

2-4. Expand, set threshold, pick peaks

• Adjust the horizontal scale so that the peaks you want are visible
• Adjust the vertical scale so that the top of the smallest important peak is visible
• Adjust the threshold line (dashed gold line) by click-dragging the box at the left end of this line so that the threshold is below the smallest peak of interest
• Click PeakPick: Pick Peaks and Append to List
• Click OK in the message box

Steps 2-4 can be repeated again and again by bringing new regions into the display window. If you want to see all of the peaks that have been picked so far, click .

5. (Optional) Removing peaks from the peak pick list

• Adjust the horizontal scale so that only the peaks you want to remove are visible
• Adjust the vertical scale so that the top of the smallest peak to be removed is visible
• Adjust the threshold line (dashed gold line) so that it lies below the smallest peak to be removed
• Click PeakPick: Clear Peaks in Region

Step 5 can be repeated again and again by bringing new regions into the display window. If you want to see the peaks that are still picked, click . If you would like to remove all of the picked peaks from the list, click PeakPick: Clear Peak List

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