1) If I want to choose an internal standard for NMR, which characterization must it have?
2) If I want to choose an internal standard for GC FID, which characterization must it have?
3) When I want to know about the quantity of a material, I must use GC FID or NMR?
1) In a nutshell: Just check that the peaks of the internal standard do not overlap with the spectrum(a) of your target compound(s). For further advice you can refer to:
https://www.sigmaaldrich.com/analytical-chromatography/analytical-standards/application-area-technique/organiccrm.html
2) Similar boiling point and similar polarity
3) For quantitative purposes, GC is the recommended technique. I just want to point out that you can use GC only if your target compound(s) has(have) a boiling point below 300-350 °C, or if you can quantitatively derivatise it. Otherwise you have to use other techniques like liquid chromatography and spectroscopies (including NMR).
selection of IS depends of type of analyte - can you define it as well as source of samples/matrix components?
regards,
GB
Hallo
1: Like written before, generally, every standard substance is fine which does not show too much overlap and from which you know the detailed concentration. For ideal quantification by NMR you should use direct excitation, meaning standard 1H 1D NMR. The standard way how to record 13C NMR, which uses the NOESY effect to enhance the 13C signal, is not quantitative. What is also beneficial, is a long (up to 20s) interscandelay (d1), such that different relaxation times do not affect the quantification.
- Badges
- Science topic