Creating and Using Report Tables
Calculating the Retention Time Difference of Two Channels

If data acquisition is performed with two different detectors (for example, in an APS), the retention times may be different. In this case, the retention time deviation should be documented in a separate column.

A special formula allows you to determine for a peak how the retention time of one channel deviates from the retention time of the current channel.

 Note: 

You can create the related column in both the Printer Layout and screen report. In this case, the Report Publisher add-on module is not required.

Follow the steps below to subtract the retention time of a channel from the retention time of the current channel:

• Double-click in the header of an unused or newly inserted column to open the Properties Report Column dialog box.

• In the Formula field, enter the following formula (also, refer to the explanation below):
  (retention_time - smp.chm("TIC").peak("By Retention Time", peak.retention_time, 0.100, "AN").retention_time)*60.

• In the Header field, enter the column header, e.g., "Ret.Diff. (UV-MS)".

• In the Dimension field, enter "s" (for seconds).

• Usually, two positions after the decimal point (i.e., "0.00") will be sufficient.

Explanation and possibly required modifications

To use the formula efficiently, you do not need to understand the formula in detail. It will be sufficient to know the parts you may wish to modify:

• Channel: The formula calculates the retention time difference between the TIC channel and the current channel for a peak. In the formula, replace TIC with a different channel if you want to subtract the retention time of this channel from the retention time of the current channel.

• Dimension: Usually, the retention times are in minutes. However, the retention time difference is relatively small for one peak. That is why the value is multiplied by a factor of 60 to convert it into seconds. You may delete this factor. In this case, set the entry in the Dimension field to "min".

• Peak detection: The main part of the formula refers to peak detection in another channel: peak("By Retention Time", peak.retention_time, 0.100, "AN"). The expression in brackets finds the peak that is nearest to the expected retention time ( = N) in a windows of ± 0.100 min (absolute = A) around the expected retention time (determined in the peak table of the QNT Editor). This is required to find the peak in a different channel.