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Studying Growths and Decays, Relaxation, Kinetics and Diffusion

FT-NMR allows easy acquisition of arrayed experiments. While the techniques implemented and the purposes can be quite different, many experiments share at least two aspects:

  1. They are built as a series of similar 1-D spectra of the same sample.
  2. They monitor the change of intensity of one or more signals.

The analysis of such experiments requires first the measure of the intensity of those signals over time, then the modelling of the numerical values (e.g.: fitting them with an exponential curve). The last step is a common operation in many scientific fields and can be performed with a wide variety of software, from spreadsheets to statistical packages, including specific applications for fitting models to experimental curves. The reader almost certainly has such a program and she will prefer using it instead of iNMR. iNMR itself is also a fine alternative.

Here we describe how to proceed in the case of pseudo-2D data sets (when the series of spectra come as a single matrix). iNMR also has the facilities to integrate a series of independent files.

How to Tabulate an Arrayed Experiment:

Step 1

Process the whole series of spectra as a single matrix ( In case each row requires a different phase correction you can resort to the command phrow()). Carefully correct the baseline. Create a text file called “zeta.txt” (or simply “zeta”) containing the numerical values for the abscissa in the final table. You can use a script to extract these values from the original files. iNMR will look for this file into the same folder containing the data points (e.g. the FID). If the zeta file is not found, iNMR will simply number the rows as 1, 2...

Step 2

Extract the reference spectrum (the first row in many experiments; the last row in inversion recovery experiments).

Step 3

For each signal to monitor, choose a way to measure the intensity: By integration? (Over which interval?) By peak height? In the former case, define the integration limits as usual, in the latter case, you can mark the selected peak(s) with ⌘-click (on the Mac) or Alt Gr-click (on Windows) or perform a peak-picking.

Step 4

Now open the tabulator with the command Edit > Tabulator. From the top menu of the tabulator, choose what you want to import (integrals or peak or marks, etc...), then click the button “Create New Columns”. You can import new peaks how many times you like. When a new frequency is added, any old entry with a near value is deleted. You can set the range to clear in the upper part of the module. Set to zero if you don't want to delete any existing frequency.

Step 5

Return to the whole experiment with the command File > Close Extract. Click the button “Update” to populate the table with the intensity values.

Step 6

You can keep adding frequency values (columns) to the table; you can also change, sort or remove them. You can enlarge the integration interval or set it to zero. In this case iNMR will search for the nearest maximum into each row and estimate its height by parabolic interpolation. If you don't like this automatic search, set the integration interval to any non-zero value, like 0.000001.

Step 7

You can optionally have both integration and automatic search if you check the box near the frequency value, under the column named “<>”. Use this option if the frequency of the peak changes during the experiment.

Step 8

If you click the tab named “Plot” and select a frequency inside the leftmost column (named “ppm”), you can verify if the sampled intensities lineup along a regular curve (or not). Verify in real time the effect of all the options.

Step 9

Check “T1” to let iNMR calculate the rate of growth or decay. You can either stop here or repeat the last calculation with an external application.

Step 10

Before saving the table, if you prefer comma-separated-values, turn on the corresponding option among the general preferences.

You can copy the table to the clipboard, drag it directly to a destination or save it to a file. For the latter operation, click the “Export” button. From this moment on you will be working with the external application.

All the frequencies and intervals will be saved automatically for future use. If you select one or more frequency values, the button “Show” will create corresponding vertical marks in the main window to reveal the corresponding peaks.

If you are monitoring a reaction, it is not a good idea to measure its rate directly by the intensities. If you can calculate the mixture percentages at each stage, you can estimate the rate of the reaction with more accuracy from them. Any spreadsheet application allows it.


When you add a new frequency, iNMR can delete the old frequencies near to it. The apparent effect is that no new frequency has been added. To disable this mechanism, set the clearing range to zero. iNMR does not remember how you created a new column: you are free to edit the frequency values and the integration ranges, even to add and remove these ranges.

Related Topics

Tabulating the Integrals of a Series of Spectra

DOSY processing


Web Tutorial

Tutorial: Relaxation Studies and Arrayed Experiments