Measuring the Integrals
To evaluate the relative quantities of the different nuclei in your sample, you rely on the integrals. It is important to separate two main tasks:
- Preventing the baseline from contributing to the integrals.
- Defining the limits of each integral.
The third task, calculating the integral, is trivial in comparison. iNMR calculates the integrals on the fly, just before displaying them. In this way they are always updated and reflect the latest corrections.
The dialog to manage the integrals cannot be found under any menu. It appears when you double-click an existing integral with the Integrator tool.
Working with the Integrals:
- Defining the Integration Limits:
- Select each region to integrate and choose Tools > Integrator (or first choose the tool, then select the region).
- Removing an Integral Region:
- Click the region with the integrator tool.
- To remove all the regions, choose View > Delete All Integrals.
- Normalizing the Values:
- Double-click an integral. The dialog appears, reporting the current value of the selected integral. Choose a new value. If you choose 1, the selected integral will become the unit of measure of all the integrals. You can type any other value. The remaining integrals will be normalized accordingly.
- Another option (percentages) calculates the normalization factor in such a way that the sum of all the integrals is 100. Beware that if you create or remove an integral, the values will no longer correspond to percentages. You have to return to this dialog.
- You also have the option of showing the absolute values.
- Changing the Number of Decimal Digits:
- Double-click an integral and choose the number of digits from the menu. If you choose 3, the trailing decimal zeroes are not shown. Use this trick to prevent the integral labels from overlapping with each other.
- Visualizing the Integral Curves (1-D):
- You can move and amplify the curves with the keyboard.
- Removing the Baseline at a Local Level (1-D):
- Ideally, you should choose integral regions wide enough that the intensity of the signal is negligible at the boundaries (it is all inside the region). Adjusting an integral means subtracting the straight line that connects the first and last points of the region.
- To activate this option, double-click an integral and click Adjust. iNMR extrapolates the correction line from 2 or more points (at your discretion). The first 2 points are at the boundaries and belong to the integrated range. The other points are contiguous, but outside the range.
- This practice is discouraged by theory, which says that a Lorentzian curve never actually goes to zero, even at the greatest distance from the center. A global baseline correction is preferred.
- Generating Lists and Tables of Integrals:
- You can copy both the integration ranges and the list of integrals with Edit > Copy > Integrals. Read more.
- Outstanding Results (1-D):
- If you shrink or enlarge the regions a little, it is easy to get the theoretical integral ratios. It is a sign of accuracy and the spectrum becomes more readable. There is a console command that performs this job. Read more..
- Semi-Automatic Integration:
- A single click on a peak creates a small integral. This semi-automatic method underestimates the intensities and cannot recognize the multiplets. In 1-D it is better to use the command View > Auto-Integrate.
- Vertical Labels ?
- You can hide brackets and values with the ampersand key ( & ); please note that label rotation is not supported. Learn to use the Cutter tool, if possible. You can change the font size with Format > Show Fonts.
When two signals are too close to each other, it becomes impossible
to measure their intensity with the integrals (you can only get the sum of the intensities).
In such a case, you can fit the peaks with a series of theoretical curves.
Fitting is also implemented for isolated signals. In this case
the purpose is to minimize the effect of noise on the measured integrals.