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Why do I see steps in my baseline?

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Applies to

ECD

Summary

A typical stepwise pattern in the baseline is seen.

Cause

  1. In pulse mode measurements using an AD convertor, small steps may be observed. This is due to a mismatch in the pulse duration vs data rate. For example, in case of a 1s pulse duration and a data rate of 10 Hz, 10 identical data points are acquired each second. In such case it is best to match the data rate with the pulse duration (1 or 2 Hz).
  2. When a chromatogram is recorded and data acquisition software is used, this stepwise pattern is seen when zooming in extremely far. At a certain point the bit resolution is reached and small steps are seen. It is comparable to zooming in on a picture file. At a certain point the pixels are seen as small squares.

 

Fig. 1. Bit resolution steps in data are seen when zooming in with CDS software. It is caused by insensitive detector range setting in combination with extreme zoom factor in CDS.

 

Remedy

If more detail is needed, use the detector electronics to “zoom in”, not the CDS software. In other words: use a more sensitive range setting. At some point however, there will always be a bit resolution limit.

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