When acquiring X nuclei spectra such as 11B, 31P or 29Si, the spectrum must be referenced to something other than the solvent, since the solvent likely does not contain these nuclei. Either an internal standard or indirect referencing can be used. Sometimes internal standards will react with your compound, or the correct internal standard from literature can be difficult to obtain. Indirect referencing can provide accurate referencing without having to add an internal standard.
First, acquire both a 1H and X nucleus 1D spectrum, as normal.
- For calibrating 1H data, calibrate to the TMS/DSS peak (if using an internal standard), or the residual solvent peak.
- To calibrate, zoom in to the general area of the peak you want to calibrate.
- Click the Calib. Axis button or type .cal
- The cursor will turn red, and then click on the center of the solvent peak.
- Enter the corrected chemical shift in the pop-up box.
Indirect Referencing for X Nuclei:
- Acquire and calibrate a proton spectrum as directed above
- In the proton spectrum, type s sf to get the spectrometer frequency for 1H (should be 600.39000XX on the AVIII600)
- Find the constant for the Frequency Ratio Ξ in the table below.
- Equation to calculate the indirect referencing constant:
600.39000XX (from step b)/100*Freq Ratio from table below
- Go to the X nucleus spectrum (11B, 29Si, etc.) and type s sf
- Enter the value calculated in step (d)
- Now your X nucleus spectrum is calibrated without having to use an external or internal standard.