Impurities% calculation from two different injection volumes/concentrations


Being very novice in Empower usage, a step-by step response will be please very helpful and very much appreciated.

We have an Empower 3 interface,

Our case is the following:
-We need to calculate impurities% from a sample analyzed at two injection volumes (20µL and 60µL).
-20µL serves for main component assay and two specified impurities (not separated at 60µL).
-60µL serves for other non specified impurities. Main componenet and specified impurities not integrated.

We do the following calculation in Excel sheet: 
Impurity% = 100 x impurity ratio / inter-sample sum of impurity ratios
Impurity ratio = corrected peak area / API response coefficient
corrected peak area = peak area / relative response factor
API response coefficient = API area in assay sample / (sample concentration x injection volume)

We would like to shift this excel calculation to Empower custom fields calculations.

Thanks in advace for any help,

Kind regards,
Analytical Dvpt Manager
PolyPeptide Group


  • The different injection volumes makes this a bit tricky.  Other assumptions: All are processed on the same channel/wavelength.  Feel free to tweak names as I just made those up.  None of this is tested and is solely off the top of my head as a best guess as to where to start.  There may certainly be a few spots to gain efficiency or additional levels of control.  I would question whether or not you may need an LOQ test somewhere…if your method says something like sum values >LOQ or something.  And finally, be sure to put a “summarize custom fields” at the end of the sample set prior to processing.  Good luck!

    Labels: U0# based on sample with a 20 vs 60 added for injection volume.  For example, U0120 vs U0160 and U0220 vs U0260

    API Area Coefficient: Configure as Peak/Real

    Name: APIAC

    Formula: Area/Amount*Injection Volume

    Note: for the amount, I’m assuming that you are using your standard calibration and sample dilution field such that this would be the concentration in the correct units per your method.


    Corrected Peak Area: Configure as Peak/Real

    Name: CPA

    Formula: Area/Relative Response

    Impurity Ratio for 20 µL injection: Configure as Peak/Real

                    Name: IR20

                    Formula: CPA/API[APIAC]

                    Where, API= your actual main component name, note that since the main component is in this same injection, you don’t need the more complicated formula like for the 60 µL injection below.


    Impurity Ratio for 60 µL injection: Configure as Peak/Enum/Use as Field

                    Name: IR60

                    Formula: Enum(EQ(Label, “U0160”), EQ(Label, “U0260”), EQ(Label, “U0360”)…etc…extend to how many samples you have.

                    Translation table:

    0=CPA/U0120..(API[APIAC]) (fc)

    1=CPA/U0220..(API[APIAC]) (fc)

    And so on for how many samples you have…

    Where, API= your actual main component name


    IR sum for the two peaks in the 20 µL injection: Configure as Result/Real and you must put “API” as the Peak Label in your processing method’s component list for your main component as this will then not add the API peak into the sum which I’m assuming is what you’d want as I know I would not want my API added to a sum of impurities.

                    Name: IRSUM20

                    Formula: SUM(IR20*(NEQI(Peak Label, “API”))

    IR sum for the peaks in the 60 µL injection: Configure as Result/Real

                    Name: IRSUM60

                    Formula: SUM(IR60)

    Impurity %: Configure as Peak/Real

                    Name: PI

                    Formula: 100*IR/(IRSUM20+IRSUM60)

  • Thank you very much MJS for your time.

    We will try the calculation and share the output.

    Many thanks !

    Kind regards,
  • Hi MJS,

    I work with Nazim who send you the message. I tried to apply your calculus but in the formula for Impurities %, I don't understand what is IR.

    Do I create a formula for samples at 20 µL and samples at 60 µL or it is calculate with the same formula?

    Thank you,
  • IR = impurity ratio

    above example uses CF using both 20 ul and 60 ul injections then final CF for API response coeff using 20UL OR 60UL CF

    Not straight forward but should work but will require some testing of CF's