Offset between the 2D-LC valve and the first ²D detector

For 2D-LC data analysis, the transfer time to the first ²D detector is required for an additional correction: In 2D-LC, multiple cuts stored in different sample loops may be injected sequentially. Therefore, the ²D detector sees a series of ²D chromatograms.

Figure Continuous ²D detector signal ("diagnostic signal")

The series of ²D cut chromatograms are then split into individual chromatograms.

Figure Using the first ²D detector transfer time for cutting ²D chromatograms

The vertical lines correspond to 2D-LC valve switches and mark begin and end of ²D chromatograms. The transfer time of the first ²D detector (see 2D-LC flow path) is needed to compensate this offset. Note that the offset is included to the retention times of ²D chromatograms. Retention times in the second dimension are therefore defined same as in the first dimension as the time between the injection (by the 2D-LC valve) and the first detector in the (second dimension) flow path. However, no data is available between retention time zero and the first ²D detector transfer time.

Using the correct transfer time is crucial for cutting chromatograms correctly. With a wrong transfer time to the first ²D detector, chromatograms are cut incorrectly and may contain eluent from different sample loops.

Figure Wrong signal cutting in case of a wrong transfer time

A wrong transfer time to the first ²D detector also affects the contour plot:

Figure Left image: aligned signal using the correct transfer time; right image: not aligned.