Subtraction of Blank peak areas from ares in a test sample

Hi,In our Blank chromatogram (sample name Blank 1, located on the beginning of a sample set) two small peaks appear (Peak 1+2). During our method development it wasn't possible to remove these peaks.In the chromatograms of the following standard and test samples both peaksalso appear and coelute with two other peaks at the same retention time. Both peaks (Peak 1+2) are listed with the same name in the component table. Is it possible to subtract the blank peak areas of this two peaks from the areas of the two peaks in standards and test samples before calibration?I tried to solve this problem with the aid of custom fields and a inter sample calculation, but found no working solution. Neither in the empower help nor in the documents from a custom fields seminar appropriate information to my problem was found.  Any ideas to entries in component table columns and formulas in custom fields?


  • Hi Gerhard

    This can be done with an intersample calculation like the one described in the attachment.

    let me know if you need further advise.

    best regards


  • Hi Rune,

    we carried out the steps shown in your attached pdf-file, but in our column Area_Subtr no subtraction occured. I think it's the best that I first list our basic ideas for this analytics.

    - both peaks that should be subtracted are not located under the standard and internal standard

    - we  need an internal Standard (C17:0, line 6 in the component table)

    - therefore later calculation is running via response

    - our goal is the calculation of the fatty acid profile via standard calibration and obtained amounts (without peaks like Blank, internal standard  or BHT)

    - we are not shure, if our constructed component table is correct (for example column CCompRef1, Curve Reference)

    best regards


  • Hi again

    I think the problem is that you have entered "Don´t process and report" for you blank in the sample set and your calibration and quantitate only works for the labels s and u so the blank injection is never processed. Try and change the processing to normal for the blank and se if this helps.

    Otherwise I think you should contact you local Waters office and get some help from them.

    best regards


  • Hi rune,

    the problem was the entry "Don´t process and report" for our blank in the sample set. We changed the entry to "normal" and all works.

    Thanks for your ideas


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