Standard Addition calculations using custom fields in Empower

Dear communityWhile there is no simple option for doing Standard Addition calibration in Empower, I am quite sure that a number of users have worked out ways to get Empower to do this automatically for them. It is a big requirement in the analysis of therapeutic peptides in plasma where there are already low concentrations present. Any ideas?.Heather

Comments

  • Hi Heather,

    I have used Empower to do parts of the standard addition calculation, but without access to custom fields, I couldn't finish the deal.  The linearity is performed as usual, with the only caveat being the concentration of the "unspiked" sample could not be entered as zero.  We were using some custom fields, so this may have to do with the attributes of those fields.  We worked around it by entering as small of a non-zero number as we could (e.g. 0.00000001).

    From there it should be a fairly simple operation if you have access to create custom fields (I do not, so I can't help directly with this).   Something like below

              Unknown Concentration = (neg)Intercept/Slope

              Sample Amount = Unknown Concentration * Dilution / Sample Weight * 100% (or 1e6 ppm)?

    If you have an unspiked sample and three spike levels, you would want to pull the last sample thatw was calibrated to get your results (the earlier ones would have only partial calibrations associated with them)

    For each set of samples, you would need to be sure to clear calibration before starting again.

    Hope this is helpful,

    Kevin

  • Thank Kevin

    I presume you are designating your spiked samples as Stanadards. to get it to draw the cal curve. Or maybe I am wrong.

    Your final formula is so close to regular Calibration / Quanitication, I wonder that we cant use a "trick" to force the normal calibration to pick up the right values. I am sure there are some experts out there who have solved this.

    Heather

  • Hi Heather,

    Yes the group of spiked samples (unspiked plus each spike level) were all designated standards to get it to calculate a curve.

    The trick isn't the second equation - that is pretty standard.  But getting the concentration from the slope and intercept is the trick.  I'm afraid you can't do that without a custom field.

    Good Luck,

    Kevin

  • Arh Yes, now a custom field with b and c from the cal curve should do that trick. .....  Slope ( b) is used in the Std calculation by default, so what we are really needing to add is the "c" factor: A prize at Inform in Philadelphia for the person that can remind me how I did it ( many) years ago!!

  • Empower uses the equation y = Bx + A to calibrate/quantitate, your "c" factor should correspond to the field "A" in Empower

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