Arrays of 2-D Experiments
Relaxation studies and other arrayed experiments are conceptually identical whether acquired as 1-D or multidimensional experiments. The differences are mainly practical. In the 1-D case, all the data are contained in a single file, while in the 2-D case you usually have many data sets that need to be processed one by one. In the 1-D case, it is relatively easy to identify a peak by its frequency, while in 2-D you will likely prefer to identify atoms by their names. For these reasons, the treatment of 2-D arrayed experiments is very different. It is performed under the CPM (Cross Peaks Manager), and you should already be familiar with this module.
With iNMR, you can easily generate a table of values (integrals or peak heights). Further analysis of these values requires an external application such as Excel or ProFit.
How to Tabulate an Array of 2-D Experiments
- Process all experiments and perform baseline correction. It is not necessary to measure the integrals at this stage.
- Create a new CPM using the command: Tools > Cross Peaks M. Add all the experiments and identify each with a tag. For relaxation experiments, it is advantageous to use numerical tags. If you have many experiments, it is better to use the command “Add Whole Folder” (located just under the command “Edit this Menu”). With “Edit this Menu”, you can only add documents that are currently open. With “Add Whole Folder”, you can add all your documents with a single command if they reside in the same folder, whether they are open or not.
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Choose the spectrum with the best signal quality.
Assign all peaks of interest in this reference spectrum using the peak-picker tool.
Define the integration limits for each peak; these limits will be applied to all experiments.
Integration limits defined in other experiments will be ignored.
Alternatively, you can estimate volumes via Gaussian fitting.
In this case, you must
perform the fitting across all experiments. If a peak is not fitted in a particular experiment,
the corresponding value will be calculated via standard integration.
If you wish to monitor the height of the cross-peak instead of the volume, do not define integration limits and do not perform fitting in the reference spectrum. You can mix integrals and heights within the same table (though not within the same column). -
While keeping the reference spectrum as the foremost window,
choose "Copy Table" from the “Actions” menu of the CPM.
Open a spreadsheet in your preferred external application and select: Edit > Paste.
Moving Peaks
If you are monitoring the height of a cross-peak, slight frequency variations between experiments can be problematic. You can resolve this by assigning the cross-peaks in every experiment. Copy them from the reference spectrum using the “Copy Peaks” command. Paste them into the other spectra using “Paste Peaks”. Both commands are located under the Actions menu of the CPM. To relocate the assignments, select them with the Peak-Picker tool and choose: “Move to the Nearest Max”.
Moving Integrals
Suppose you want to monitor signal growth or decay using standard integration, but the chemical shifts vary from one spectrum to another. In this case, your approach will differ: assign all peaks in all spectra. Define the integration limits in a single spectrum. Keeping this spectrum in the foreground, select the command “Move Integrals”. This will copy the integration limits to all spectra, adjusting them exactly to where the peaks have moved. Now, for each spectrum, use the “Copy Integrals” command. Paste and combine the results into an external spreadsheet.
From Fitting to Plain Integration
If you have fitted the volume of a cross-peak, iNMR will prioritize the fitted volume over standard integration. If you are not satisfied with the fitting, select the cross-peak with the peak-picker tool and choose the option: “Set the Value of this Integral”. Then, set the value to zero. If the fitted area is zero, iNMR will default to plain integration.
Related Topics
Studying Growths and Decays, Relaxation, Kinetics and Diffusion