Spectrus: Choosing acquisition parameters for quantitative NMR (qNMR)

Description
Quantitative NMR requires specific acquisition settings so that signal integrals are directly proportional to the number of nuclei. If relaxation delays are too short or pulse angles are inappropriate, integrals may be biased and not suitable for quantitation.

Solution

1. Set the pulse angle:
   • Use a 90° pulse (or a carefully calibrated angle recommended for qNMR on your instrument).
2. Set the relaxation delay (D1):
   • Choose a delay at least 5× the longest T1 of nuclei being observed; 20–30 s is common for 1H qNMR if T1 values are not known.
3. Use sufficient scans:
   • Acquire enough transients (scans) to obtain good signal-to-noise without compromising the long relaxation delay.
4. In Spectrus, after acquisition:
   • Perform accurate phase and baseline correction.
   • Integrate both analyte and internal standard peaks.
5. Verify linearity:
   • If possible, run test samples with known concentrations to confirm that integrals scale linearly.
6. Use the integrals, along with internal standard information, to calculate analyte concentration or purity.