Integration
Chromatogram Comparison

The most exact method to compare two or more samples or chromatograms is to compare their numerical results. However, in many cases, it may be sufficient to overlay the chromatograms. This is referred to as a chromatogram comparison.

What can be compared?

Chromatogram comparison always compares single channels. It is irrelevant whether these channels are from the same sample or from different samples. Theoretically, Chromeleon can display an unlimited number of chromatograms simultaneously.

However, the presentation may be confusing when many chromatograms are displayed. That is why Chromeleon prompts you to confirm that you want to view more than 20 chromatograms. This is to avoid that too many chromatograms are displayed due to an operator error. Displaying many chromatograms at a time may decrease the system performance.

How are chromatograms compared and displayed?

To compare chromatograms, display them in the Integration window. One chromatogram is the active chromatogram. To make a chromatogram the active chromatogram, select it with the mouse. Only for the active chromatogram, additional information, such as the decoration, etc. is displayed. The names of all chromatograms displayed are indicated above the Integration window. The name of the active chromatogram is written in a different color. Click the name of any chromatogram to select it as the active chromatogram.

Select Decoration on the context menu to edit the appearance of the window and the active chromatogram.

How do I select the chromatograms or channels to be compared?

• Select one or several samples in the Browser and drag them into the open Integration window. Chromeleon automatically attempts to load the Channel of the current sample. If this is not possible, for example, because the channel does not exist, the system loads the default channel. The default channel is the first channel that appears in the list when you open a sample. (Select Open on the context menu in the Browser.)

• Select Add Overlay on the File menu to display a specific channel of any sample in an opened integration window.

• Select Open > All Channels to compare all channels of a single sample.

• Select Compare to compare a specific channel in several selected samples.

• Perform a query to compare samples with certain properties.

• Hold down the CTRL key and click the Next Chromatogram icon () to display the chromatogram of the next sample in addition.

• Hold down the CTRL key and click the Previous Chromatogram icon () to display the chromatogram of the previous sample in addition.

• Hold down the CTRL key and click the Next Channel icon () to display the next channel of the same sample in addition.

• Hold down the CTRL key and click the Previous Channel icon () to display the previous channel of the same sample in addition.

Placing chromatograms and channels in relation to each other

External factors such as the flow rate, solvent, column quality, detector amplification, etc. considerably influence the appearance of the chromatogram.

As you cannot modify these conditions later, you must use other ways to perform the comparison as exactly as possible. Adapt the position and the size of a chromatogram to match another. Chromeleon provides several options. You can:

• Assign chromatograms an offset in x- and y-direction.

• Normalize the chromatogram time, i.e. you can overlay the chromatograms at a specific retention time.

• Normalize the peak height, i.e., you can adjust the height of a specific peak.

• Stretch and compress chromatograms.

• Subtract chromatograms from each other.

Select Decoration on the context menu of the active chromatogram and enter the settings in the Comparison tab page.

For more information, refer to  Comparing Chromatograms.