If we analyze the extract of two plants from the same species (for example) and there are very similarities between the two IR spectra except for the intensity of one peak at the same wavenumber. Could I presume that the different intensity of the peak is due to (co-respond to) the different concentration of the same compound in those extracts?
You have also to consider the impact of measurements, incl measuring configuration, number of samplings, use of inernal standard and noise, etc.. You can build up linear relationship between concentration to the intensity of one specific peak, only if the peak intensity variation due to measuring itself can be minimised or eliminated.
Thank you, Dr. Jp Wu, With respect to your answer, for other cases could you explain more about how to choose/determine a certain peak that most likely has a linear relationship between peak and concentration of the corresponding compound base on experience and expertise.
It is case dependent. The general principle is 1, to find the characteristic peak without cross contamination, so that it can be used to discriminate the compound interested from the rest of materials. 2, try to find the strongest or stronger peak among those met 1. 3, select one from 2with intensity least variable to the measurements, i.e. number of samplings. 4, subject to the matetials and measurement methods, internal standard is either not necessary or definitely needed. 5 apply appropriate data processing or algorithm to acheive linear relationship, either by univariate or multivariate approaches.
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