What is a Control sample used for?

I cant understand why you would run a control sample and what its used for. According to Empower help: "Inject Controls – Makes an injection from the specified vials containing
controls. During processing, a control sample is integrated and
quantitated. When processed, calculated amounts or concentrations of
the control samples are compared to specified values, and % Deviation
is computed."

What exactly are these specified values and how does this link to % Deviation? Can anyone shed some light please?

Answers

  • Hi

    use inject control as part of std concordance

    ie std 1 (sample type - standard) injected 6 times and std 2(sample type -control) and then used to calculate % recovery

    add a custom field (peak, real , calculated) = 100-%deviation 

  • In most of my methods, I use the bracket-overlap quantitative method for samples.  However, my system suitability includes a standard verification so my 5/6 injections of Std A for suitability and 1 injection of Std B for a verification are injected as controls.  This allows me to enter standard amount values and calculate the agreement as a ratio.  The other path would be to inject Std As as standards and generate a one-time calibration for quantifying the recovery of Std B.

    We went down this path long ago and I don't recall exactly why any more.  Maybe we felt it was simpler (especially if you ever had to manually integrate one of the Std A injections for some reason), possibly so people wouldn't be confused if with a different calibration using 5/6 injections associated with the sample set instead of only 2, or maybe just to satisfy some method approver that asked for it that way as that is what they always had done.

    As a result of the ratio calculation approach, I generally have not relied upon the %deviation value within my methods.  As ydan1977 alludes to, it is effectively a slightly different calculation for agreement and it is built-in which, if you write the method appropriately, gives you one more potentially validated field that you don't have to worry about.
  • Thanks for the reply MJS. To clarify, when you say calculate agreement as a ratio do you mean the area in Std B divided by the average areas of the 6 injections of Std A? I thought the % deviation meant how far the point is from the line in the calibration curve. 
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