By Anonymous on Tuesday, July 6, 2004 - 10:18 pm:

Hi,

We are using an Agilent HPLC 1100 and a DAD detector. Recently we encounter some problems: negative peaks in the chromatograms. It is the same chromatograms that we are getting normally except that everything is "inverted".

The method is as follows:
MP A: 0.05%TFA in H2O
MP B: 0.05%TFA in ACN

Time A(%) B(%)
0 100 0
8 95 5
9 100 0
11 100 0

We have encounter this problem thrice. We tried to use H2O to wash the system and the detector (as advised by the vendor), it works but the problem returns after a while. The method is validated and we did not make any changes to the settings. Can anyone enlighten us on this? Thanks in advance!

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By rob burgess on Wednesday, July 7, 2004 - 07:30 am:

Have you got the polarity settings right on your detector? If not its simple to change.

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By Anonymous on Wednesday, July 7, 2004 - 05:50 pm:

Hi Rob,

Thanks for your reply. How do we check the polarity settings?

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By rob burgess on Thursday, July 8, 2004 - 04:34 am:

We use hand held control modules to control our Agilent systems. Its just then a matter of going to the detector settings and changing there. Consult your user manual if in doubt.