Thank you very much for your detailed answer. Unfortunately the spectra was recorded a few years ago and I don't have the same sample to record a new spectra with your suggestions. The sample was an asphaltene. So it doesn't including any olefinic hydrogens, with this assumption what if I use three points (start, 5ppm and end) to correct the baseline?

I am going to sent you a private message including a picture.

Deniz

For asphaltene it should be ok since there are only aromatic and alkyl regions. You won't be removing any signals by baseline correction.

Thank you for your precious answer dear Majumdar. As you mentioned there are only aromatic and saturated hydrogens in asphaltenes so I don't expect to see any signal belong to olefinic hydrogens which are ussually appears between 4.5 - 6.5 ppm. In this case maybe 5 points baseline correction (start, 4.5, 5.0, 6.5, end) is also a valid approach. Still I'm not sure which is a better approximation (3 points or 5 points).

Deniz