qNMR Experiments

Key Parameters for Quantitation

by Joseph Ray, Naperville (IL)

• Good signal to noise
• 90° pulse sufficiently short to excite the entire region uniformly
• Delay between pulses of at least 5 T1’s
• Flat base line to start with and baseline correction
• Filter bandwidth set to at least twice the sw
• Enough data points to give 15 to 20 points per peak - remember that you lose half the points to the imaginaries in Fourier transformation
• Acquire at least 32k and zero fill several times – memory is cheap
• Exception to 32k for other nuclei requiring 1H decoupling - it is important to limit the acquisition time to as short as possible to avoid NOE build up during the acquisition so < 32k may be necessary with zero filling to make up the difference
• Zero filling should only be done after dc correction and line broadening otherwise it introduces baseline artifacts
• Gated decoupling for non-hydrogen analysis
• Careful phasing on a spectrum that has been greatly expanded in the vertical direction
• Careful integration
  • Place a single integral over the spectral limits of interest
  • Adjust bias and slope on the full integral
  • Cut integral into smaller regions as close as possible to the peak
  • Consistently include or exclude satellites or account for them when they overlap

See also Joseph Ray's Anecdotes On Quantitative NMR From The Early 1970ies.

...more under construction...please bear with us!