I have been given 1HNMR, MALDI-ToF-MS and GPC spectra for a laboratory synthesized sample of polycaprolactone.

The number average molecular weight (Mn) obtained from their analysis differed significantly though:

Mn(1HNMR) = 3186,41 g/mol
Mn(MALDI) = 4751,64 g/mol
Mn(GPC) = 6750,81 g/mol

I tried to find in the literature an explanation for that pattern but found only that 1HNMR is the more reliable one for being quantitative source, while MALDI can present inconsistencies due to chain breakage during ionization and that GPC might present wrong molecular masses if the calibration is not done correctly (in this case, calibration was done with PS). I am also considering that the analysts made no mistakes in the generation of these spectra, as it was performed by a professor in laboratory course on the subject.

So, I wanted to ask, does anyone have an insight as to why those three techniques are presenting such inconsistent results for this sample?

(Also, this is my first question here, so any remarks on question posing are also welcome)

Thanks for the help!

  • 1
    $\begingroup$ Do not assume that a calibration exists. This said, if you go technique by technique you will find pros and cons, as you succinctly listed abive5. For details let's wait for a true polynerist. $\endgroup$
    – Alchimista
    Commented Mar 22, 2021 at 10:18
  • $\begingroup$ Above read "perfect calibration". $\endgroup$
    – Alchimista
    Commented Mar 23, 2021 at 9:37


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