Dear Aarthy,

Yes. These values are for the area under the peak. In the past scientists used low resolution NMR and the calculated the number of hydrogens according to the area under each peak.

I think in the case of the study described in the attached paper the NMR was done at 4 C which results in broad peaks for the protons of the compound. This obliged the authors to calculate the area under each peak to estimate the number of protons.

Using Mestrenova you can get the integration for each peak of the compound's proton. However, the NMR will be a high resolution NMR. You are not going to see broad peaks as the ones obtained in the paper's study.

Hoping this will be helpful,

Rafik

Dear Michael,

Thanks for the correction regarding the 4 C. However, I have a quite good experience with NMR. 

Rafik

Dear Michael,

I know that the NMR used is with high resolution. I mistakenly thought that NMR was conducted at 4 C which restricts the rotation of some functional groups in the tested compounds and thus making the peaks broad.

Rafik

Dear Aarthy,

the numbers given for the integrals are in arbitrary units. The only meaningful content is their relative magnitude. So an integral of 500 units just means that it corresponds to twice the number of protons as an integral of 250 units. In order to calculate the number of protons corresponding to the integrals you must know the number of protons for (at least) one of the integrals. Then you can apply the Rule of Three to calculate the number of protons for the other integrals.

Ludger

Dear Aarthy,

I agree with Ludger. The values shown are in arbitrary units. With the sum of all integral values expected for the compound, you could find the relative number of protons for the specific region of interest using the Rule of Three.

However, you should take care of relaxation rates in NMR (T1, T2, exchange rates, ...) which could lead to bad estimations of the number of protons. The authors should use large values of relaxation delay (RD) to ensure a complete relaxation of all the atoms of the compound before to restart another measurement.

Ideally, a titration curve should be done to confirm that you have a good relationship between integrals and amounts of compound. This is not a so easy point to manage. Anyway, you can have a overall look and make the hypothesis that what you see is true, but it could not!!!

Hope it helps,

Gildas

I agree with Ludger and Glidas. The values shown are arbitrary units. Integral value for a known number of protons is required to estimate number of protons under each integral. However, T2s (spin-spin relaxation rate) will alter these ratios as the lipid samples are viscous. In a study involving mixture of fatty acid esters of glycerol, if composition of individual fatty acids are required, it is better to resort to chemical methods of methanolysis and measurement by GC. Low temperature crystallization and urea complexation can only separate selectively few components like saturated fatty acids from the mixture as shown in the paper.

Hello,

In this paper they seem to compare intensities of specific structural-marker peaks for different structures of fatty acids between different conditions of isolation. So in the Fig 2A they have a marker-peak with intensity of 500-something, and in the next condition in 2B it is 935, so they have concentrated this type of fatty acid with their crystallization, as I read this bit of the paper.

The page you posted does not give all the details, but I can only assume they use an internal standard at the same concentration for each sample, so they can accurately make these comparisons. And then the 500 and 935 are values in relation to this internal standard.

In MestReNova you can also use an internal standard and integrate that, and then all your other structural-reporter peaks will be given numbers in relation to that peak. If you set the IS to 1, or 100 (whatever you want) you can get similar comparisons between samples. Just make sure you use a suitable internal standard that does not evaporate too easily.

Thank you ALL for your views and suggestions.