Configure processing method for blank subtraction

Preparations

• To be able to carry out the procedure as described, you need the privilege Processing Method > Edit signal parameters . Privileges are configured in the Control Panel.

• If the project enforces method approval, the method status must be Generic. For details, see Method approval.

• You have acquired the signal for a blank run, that is, a solution with the same solvent, additives, etc. as the samples, but without the compounds of interest.

• You have acquired the blank run with the same detector (same signal name or same signal description) as the samples.

  For non-MS signals, the signal is typically the short name of a detector, for example, DAD1A. The signal description then includes more details, for example, DAD1A, Sig=235,10 Ref=550,60. By matching the one or the other, you define how flexible the processing method can be used with different acquisition methods.

1. In the Processing Method window, select the General > Signals node and the Blank Subtraction tab.

2. Under Injetions with blank subtraction applied, choose for which injections you want to subtract a blank.

   If you prepare your calibration standards differently they may not show the same matrix effects as the samples. In this case, choose Calibration standards only or Samples only (exclude cal. standards).

3. Choose how you want to use blanks:

   • To use blanks as defined in the sequence:

     Select Use blanks defined in the sequence.

     The signals of blank runs in the sequence will be subtracted.

     The subtracted blank is either:

     • the blank (sample type Blank or Double blank) last acquired prior to the current injection,

       or

     • the blank defined in the Blank column of the Injection List.

   • To use a specific blank outside of the sequence:

     Select Use specific blank, and click Browse to open a list of all currently loaded injections. Select the injection that you want to use as a blank.

     NOTE: The injection must be loaded so that you can select it in the method. It does not need to be loaded during reprocessing.

4. Under Signals with blank subtraction applied, choose for which signals you want to subtract the blank. Choose All signals to subtract blanks for both MS and non MS signals.

5. If required, select that blanks will also be subtracted if data rates are different.

   If a blank and a sample have different data rates, the data rate of the blank is adjusted. Data points are removed or created by interpolation (MS signals: linear interpolation; non-MS signals: spline interpolation). A corresponding warning is shown in the injection tree.

   Independent of the status of this check box, if a blank and a sample have different run times, blank subtraction is only performed on the common time range. A corresponding warning is shown in the injection tree. The new signal will contain corrected and not corrected data points.

6. Only relevant for non-MS signals (With MS signals, signal name and signal description are the same) : Select a suitable signal matching option. By default, the signal of a blank run will be subtracted if its name matches the signal name of the sample.

7. Check the blanks in the Blank column of the Injection List window.

   By default, the blank last acquired prior to the current injection (Last blank) is selected. If required, select a different blank from the current sequence.

8. Reprocess the data with the changed processing method.