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Arrays of Bidimensional Experiments

Relaxation studies and other arrayed experiments are conceptually the same if acquired in the traditional 1-D mode or if the dimensionality is higher. There are merely practical differences. In the 1-D case, all the data is contained into a single set (experiment), 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 read the names of the atoms. For these reasons, the treatment of 2-D arrayed experiments is very different. It is performed under the CPM (Cross Peaks Manager), and it will be an advantage if you are already familiar with this module.

With iNMR you can easily generate a table of values (integrals or peak heights). The numerical analysis of these values requires an external application of your choice (for example: Excel or ProFit).

How to Tabulate an Array of 2-D Experiments

Step 1

Process all the experiments and correct the baselines. It is not necessary to measure the integrals.

Step 2

Create a new CPM with the command: Tools > Cross Peaks M. Add all the experiments and identify them 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” (just under the command “Edit this Menu”). With “Edit this Menu” you can only add open documents. With “Add Whole Folder” you can add all your documents with a single command, if they reside into the same folder, whether they are open or not.

Step 3

Choose the best-looking spectrum. Assign all the peaks of interest with the peak-picker tool into this reference spectrum. Define the integration limits for each peak. Those limits will be used for all the experiments. Integration limits defined in other experiments will be ignored. You can alternatively estimate the volume by Gaussian fitting. In this case, you have to perform the fitting in all the experiments. If a peak is not fitted in a particular experiment, the corresponding value will be calculated by standard integration.
If you want to monitor the height of the cross-peak, instead of the volume, do not define the integration limits and do not perform the fitting in the reference spectrum. You can mix integrals and heights into the same table (but not into the same column, of course).

Step 4

Still keeping the reference spectrum as the foremost window, from the “Actions” menu of the CPM choose: Copy Table.
Open a spreadsheet with your preferred external application an choose: Edit > Paste.

Moving Peaks

If you are monitoring the height of a cross-peak, a slight frequency variation from experiment to experiment will be problematic. You can solve the problem by assigning the cross-peaks in all the experiments. Copy them from the reference spectrum with the command “Copy Peaks”. Paste them into the other spectra with “Paste Peaks”. Both commands are under the Actions menu of the CPM. To relocate the assignments, select them with the Peak-Picker tool and choose the option: “Move to the Nearest Max.”.

Moving Integrals

Let's say you want to monitor the growth or decay of signals using plain integration. Let's also say that the chemical shifts of your peaks change between different spectra. Your approach will be different. Assign all the peaks in all the spectra. Define the integration limits into a single spectrum. Keeping this spectrum on the fore, select the command “Move Integrals”. It will copy the integration limits into all the spectra and they will be moved exactly where the peaks have moved. Now, for each spectrum, use the command “Copy Integrals”. 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 prefer the fitted volume to the integration. If you are not satisfied by 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

DOSY processing