PROTON AXIS
Definitions:
* Proton resonance at the extreme downfield position of
DSS compound is used as the mark for zero position in the proton chemical
shift scale.
* ppm1H(x) = {[tof(x)tof(0)]/Freq1H(0)} x 1e6 ...(1)
tof(x)  transmitter offset frequency for a given resonance
'x'
tof(0)  transmitter offset frequency that corresponds
to the 'zero' position of the chemical shift axis
Freq1H(0)  Absolute frequency
in MHz, if the transmitter were to be positioned on the 'zero' position of
the chemical shift axis.
Standard Values:
At a given lock frequency setting, values of Freq1H(0)
and tof(0) are absolute and remain constant. They change a little over time
when the magnetic field strength changes.
At 25 deg. C, using a DSS sample, the following
values were computed for the two spectrometers at CABM.



Freq1H(0) 


tof(0) 


Referencing:
For any given data set, on the proton axis, if the transmitter
offset, called tof(x) is known, the corresponding ppm value of that position
can be simply computed using equation (1).
NITORGEN AXIS
Definitions:
* ppm15N(x)
= {[dof(x)dof(0)]/Freq15N(0)} x 1e6
...(2)
dof(x) decoupler offset frequency in Hz for a given position
'x' on the 15N axis.
dof(0)  decoupler offset frequency
in Hz that corresponds to the 'zero' position of the 15N chemical shift axis.
Freq15N(0)  Absolute frequency in MHz, if the decoupler
were to be positioned on the 'zero' position of the chemical shift axis.
Standard values:
Freq15N(0) is related to Freq1H(0) by the following relation.
Freq15N(0) = 0.101329118 x Freq1H(0)
The standard values computed for the two CABM machines
at 25 deg. C are the following.



Freq15N(0) 


dof(0) 


Referencing:
For a given data set, with the value of dof(x) for the
15N axis use equation (2) to calculate the corresponding ppm value.
CARBON AXIS
Definitions:
* ppm13C(x)
= {[dof2(x)dof2(0)]/Freq13C(0)} x 1e6
...(3)
dof2(x) Second decoupler offset frequency in Hz for a
given position 'x' on the 13C chemical shift axis.
dof2(0)  Second decoupler
offset frequency in Hz that corresponds to the 'zero' position of the 13C
chemical shift axis.
Freq13C(0)  Absolute frequency in MHz, if the second decoupler
were to be positioned on the 'zero' position of the 13C chemical shift axis.
Standard values:
Freq13C(0) is related to Freq1H(0) by the following relation.
Freq13C(0) = 0.251449530 x Freq1H(0)
The standard values computed for the two CABM machines
at 25 deg. C are the following.



Freq13C(0) 


dof2(0) 


Referencing:
For a given data set, with the value of dof2(x) for the
13C axis use equation (3) to calculate the corresponding ppm value.
APPENDIX
The values of tof(0), dof(0)
and dof2(0) are estimated in the following manner:
dof(x)dof(0) = Freq15N(x)Freq15N(0) (A1)
dof2(x)dof2(0) = Freq13C(x)Freq13C(0) (A2)
In equations A1 and A2, definitions
of Freq15N(0) and
Freq13C(0) are the same as we have seen before. These values are given
under the 'standard values' shown before.
Freq15N(x) is the exact frequency
value at which the first deocupler irradiates the sample, when the decoupler
is placed on a position corresponding to some arbitrary resonance 'x' on the
Nitrogen axis. 'dof(x)' is the associated offset value.
Freq13C(x) is the exact frequency value at which the second deocupler irradiates the sample, when the decoupler is placed on a position corresponding to some arbitrary resonance 'x' on the Carbon axis. 'dof2(x)' is the associated offset value.