Calibration Best Practice

[daniel rodger]

Hi,

I started at a new company and their QC dept. operates calibrations in a different way than I'm used to.

They run STD1, STD1, STD2. They check if the two STD1's are in agreement and if so proceed. If STD2 is in agreement with the second STD1 then proceed. The avearge of the response factor for the second STD1 and STD2 is calculated and this is used in the calibration table.

How do people feel about this??

I would normally have SST standards, Calibration standards, and then check standards. I would only ever calibrate from the calibration standards (there many be multiple of them though) and I feel like, above, STD2 is a check std.

Cheers
Dan

[HPLCaddict]

If STD1 and STD2 are in agreement, there should not be any significant influence on the result no matter if you use STD1, STD2, or STD1+STD2 for calibration.
So it's just a matter of company policy how to proceed with calibration...and of course of GMP. If your STD2 is defined as "check standard" in the SOP, then QA or auditors might insist that these should not be used for calibration but only the "calibration standards". But this is something that has nothing to do with analytical science .

[James_Ball]

Are STD1 and STD2 different concentrations?

If they are different concentrations and you calibrate from average RF from STD1 and STD2 then the only really valid results can be those between STD1 and STD2 concentration with maybe 20% above and below.

If it is used for results of any concentration then it reminds me of a method given to us once by a lab we were doing contract work for. They calibrated using standards of 0.1, 0.5 and 1.0ppm and their check standard was 5ppm. According to their records the check standard always passes, but when I checked the method, the concentration of the check standard was actually 10ppm from their preparation info. They were running a 10ppm and it was always calculating out to be 5ppm simply because it was so far above the curve

From what I always heard best practice using average response factor calibration is to use 5 calibration concentrations. Some use 3 but 5 is more widely accepted. One and two point calibrations are only good if the result is always very near the calibration concentrations.

[DR]

If it's what's in your new company SOPs, then that's what you need to do.

That said, it your's appears to be a needlessly complicated way to do it.

We use lots of single point standard methods because we're in Pharma. Assays typically produce results near that single point and/or higher and lower results are acceptable because we have validation reports demonstrating an adequate linear range, LOD, LOQ etc.

We typically establish system suitability with 5 or 6 std injections, inject brackets of samples and standards, then base calculations on the average of all of the standards (provided, of course that there are no significant deviations from the std response of the initial std injections).

Simple, effective.