Quantitative measurements and integration

The extensive use of integration in proton NMR arises from the well-used doctrine that the area of an NMR resonance is proportional to the relative 

The second fundamental requirement is for the data be sufficiently well digitised for the lineshape to be defined properly. To minimise intensity errors it is necessary to have at least four acquired data points covering the resonance linewidth, although many more than this are preferable, so it is beneficial to use the minimum spectral width compatible with the sample and to adjust the acquisition times accordingly. The spectral width should not be too narrow to ensure the receiver filters do not interfere with resonance intensities at the edges of the spectrum. 

The extensive use of integration in proton NMR arises from the well-used doctrine that the area of an NMR resonance is proportional to the relative number of nuclei giving rise to it. In fact this is strictly true only under well-defined experimental conditions, and in routine proton spectra integrals may only be accurate to within 10-20% or so. Whilst this level of accuracy is usually sufficient for the estimation of the relative proton count within a molecule, it is clearly inadequate for quantitative measurements where accuracy to within 

When seeking to determine the concentration of a solute by NMR spectroscopy, it is always necessary to measure it against that of a known caUbrant. T)rpically, this would demand the addition of a suitable reference compound to the anal)rte solution against which the integrated intensity of a solute resonance may be compared following the protocols described above for quantitative measurements. However, the use of an internal chemical reference may impose constraints that may not be readily met, making this approach undesirable. The reference material needs to be soluble in the anal)tie solution, it must be inert to the solute, its resonance(s) must not overlap that of the solute and its relaxation properties should be similar to that of the solute. In addition to these practical considerations, one simply may not wish to add a reference contaminant to a precious sample. An alternative approach to this use of an internal chemical reference is to introduce a synthetic tf reference signal as in the ERETIC method (Electronic REference To access In Vivo Concentrations) [7, 8]. 

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