Setting the chemical shift reference in 2D spectra

see also setting the reference using the cursor, using the Math subroutine

Due to poor digital resolution and/or inaccurate referencing by the spectrometer software, crosspeaks in a contour plot do not always align perfectly with the high resolution 1D spectra displayed as "borders" along the edges of the contour plot.  This example is an HMBC spectrum acquired on our JEOL Eclipse+ 400.  The 1D spectra were referenced during processing, and the 2D peak doesn't quite match.  

It is possible to use the cursor to set the reference for the contour plot, but poor digital resolution often precludes setting it exactly.  Using the cursor, the difference between 1D and 2D peaks can be measured in Hz, and the offset values manually adjusted.  For details on setting offset values, see offsets.

We have empirically determined that the correction required for data from our spectrometer is 10 Hz in the ¹H dimension and 70 Hz in the ¹³C dimension.  To make this correction quick and convenient, the following macro was written to adjust the offset values.

NutsMacro 2D referencing
; for 1H, correction is +10 Hz
; put 10 into register 1
set math register 1 10

; put O1 (offset for 1H dimension) into register 0
do math register 0 OF1

; add 10 to O1
do math +

; put result into offset value
do math of1

; for 13C, correction is -70 Hz
; put 70 into register 0
set math register 0 70

; put O2 (13C offset parameter) into register 1
do math register 1 OF2

; compute of2 - 70
do math -

; put result into offset value
do math of2

end

The result for the spectrum shown above shows the contour plot well aligned with the 1D spectra.

Last updated: 12/12/03