Baseline correction within the Integration subroutine (ID subcommand B)
When the integration line is not flat, it means the spectrum’s baseline is not flat. This can be corrected using one of the NUTS baseline correction tools, but it can also be corrected from within the integration subroutine. The integral is very sensitive to slight tilt in the baseline, so viewing the integral while making the correction is often very helpful. It is important to understand that this operation does not just adjust the displayed integral trace to be flat. It actually changes the data, permanently.
This spectrum clearly needs baseline correction.
On entering the Integration routine, the integral trace is far from flat.
Enter the Integration baseline correction routine by typing B.
The left mouse button controls zero-order correction (DC offset of the baseline, which appears as a tilt of the integral trace).
The right mouse button controls the linear correction (linear tilt of the baseline, which appears as a curved integral trace).
Start by holding down the left mouse button and move the mouse left and right to try to make the integral trace flat in regions of the spectrum that have no peaks.
Clearly, this baseline requires more than just zero order correction.
Hold down the right mouse button and move the mouse left and right to try to make the tilt the same over the entire spectrum.
The curvature that was evident above is now gone.
Users with a single-button mouse should hold down the shift key and use the mouse button when the instructions call for use of the right mouse button.
(Caution should be exercised when applying a linear correction, as large curvature can inadvertently be entered.)
The final correction is made with the left mouse button to remove the tilt seen in the previous screen.
When a satisfactory integral trace is obtained, type <Enter> to exit the baseline correction routine and apply the correction to the spectrum.
Notice how much flatter the baseline is than in the first screen.
It is important to understand that what this accomplishes is an interactive adjustment of the DC offset and linear tilt of the baseline of the spectrum. If it is applied on a zoom region, rather than the entire spectrum, it will result in changes to the baseline of the entire spectrum, not just the displayed zoom region. The DC and tilt correction will be applied to the currently displayed zoom region. However, to avoid discontinuities in the baseline, the rest of the spectrum, on both sides of the current zoom region, will have its DC offset changed so that the baseline of the spectrum remains continuous. As a result, integration values in the other parts of the spectrum will be changed. This is similar to using the BF command.
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Last updated: 6/13/07.