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Integration

The issues to understand from this page are:

Study Tip : Don't under estimate what the integration can tell you. It might seem simple, but it can be a powerful tool when used wisely.

What do we mean by integration ?

Integration is a mathematical term that means the area under a curve. In NMR, the curve is the spectra, and the integration is a measure of the area of the peaks in the spectra. The key thing, is that the area of the peak is proportional to the number of atoms that it represents. So in an H NMR, the integration of a peak gives the area of the peak and this area gives us a measure of the number of H atoms it represents, i.e. the number of H of that type. In many modern NMR spectra, the peaks on the spectra often look to be "lines" rather than peaks, and this tends to lead to students thinking about peak height rather than area... but it is the area that is important.

How do we measure the integration ?

There are two methods that may be encountered. First though, we should point out that the area is measured by the spectrometer itself and plotted on the spectra, we are talking about what we need to do to interpret that information:

1. Numbers on spectra method (modern)

The numbers are typically printed under the peak, often with a bar or two marks that represent the limits of the integration (i.e. the x axis start and end points for the area measurement). FYI : the limits are set by the person processing the spectrum. In the example to the right, the green bar shows the limits and the area = 3.00

integration


2. Steps on integration curve (traditional)

Older instrumentation used to plot a second curve (in the example to the right in blue) above the actual spectra where the integration was recorded as a series of steps. The height (represented by the arrow in the furthest right image) of this step needs to be measured with a ruler and recorded (e.g. in mm) and then compared to other steps in the same spectrum to get the relative ratio.

integration measuring step height

Using integration information

Limitations


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organic chemistry © Dr. Ian Hunt, Department of Chemistry University of Calgary