{H1}P31 Experiment

P31 is a senstive nucleus to detect. At natural abundance (~100%), P31 has a relative sensitivity of 6.7% of that of H1 compared to 0.017% for C13. For P31-containing compounds, 1D P31 spectra can be collected with or without H1 decoupling. By comparing the two spectra, H1 coupled P31 peaks can be identified. H1 decoupling can be done either with a broadband decoupling scheme (to cover multiple H1 peaks) or with a weak power to decouple one or a group of H1 peaks at a time. For high-resolution P31 spectrum when the acquisition (and decoupling) time is long (>1 sec), selective H1 decoupling with weak power is preferred in order to minimize probe and sample heating.

P31's has a wide chemical shift range (roughly +/-200 ppm). For P31 chemical shift tables, refer to the following online pages:

P31 Referencing

  1. For accurate P31 referencing, add TMS or DSS (in aqueous solution) to your deuterated solvent. Use 1H signal from TMS or DSS for 0.0ppm reference and P31 is indirectly referenced (relative to 85% H3PO4)) according to IUPAC standard .
  2. For rough referencing with the lock signal, simply type setref.
  3. For traditional referencing with a separate 85% H3PO4 sample: Make another sample with the same solvent (deuterated) and volume as your your actual sample with the compound. Lock and shim with this sample first. Then, turn the lock off (lock status shown as OFF) and load the H3PO4 sample. Collect a quick P31 spectrum and reference the signal to 0ppm. Next, load your compound sample, keep lock off and collect data.

Pulse sequence

P31 seq

Procedure (on NMR500 with SWP)

Step 1: Lock and shim

Step 2: Optional: collect H1 spectrum without P31 decoupling

Step 3: Load parameters and tune X-channel for P31

Step 4: Set and submit experiment

Step 5: Processing

Step 6: Finishing up: tune probe X-channel to C13 and recable


Sample #1:
  • 1% CH3I (99% C13-labeled) + 1% trimethyl phosphite in cdcl3
  • Data collected in Dec 2010
P31 H1 dec

Bottom: H1-coupled P31 spectrum

  • CH3I reacts with trimethyl phosphite to form (CH3)P(=O)(OCH3)2 with the P31 direct bonded CH3 partially 13C labeled. A P31 multiplet peak around 33ppm is broadened by J-coupling to C13 and H1.

Top: H1-decoupled P31 spectrum

  • H1 decoupling collapses the broad P31 multiplet into three sharp peaks: two outer peaks from P31 bonded to 13CH3 and the center one from P31 bonded to 12CH3.
Sample #2:
  • 0.0485M Triphenyl phosphate in cdcl3
  • Data collected in Dec 2010
  • P31 couples to H1's in phenyl ring.


P31 H1dec TPP

Bottom: H1-coupled P31 spectrum

Top: H1-decouped P31 spectrum

H. Zhou updated Dec 2010