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- Posts: 26
- Joined: Wed Jun 05, 2019 3:57 pm
I have an HPLC method that is using the calibration points of 0.5, 1, 2, 4, 6 and 10ppm.
My R2 is 0.999 and accuracy and precision at 10 and 4ppm are 99.9% and <1%RSD.
My problem is with my 0.5ppm value. My %RSD is still very good but the accuracy jumps to 110% with independent 0.5ppm standards; even ones made from the same stock solution as my calibration 0.5ppm.
I don't want to lose accuracy down at the 0.5ppm as this is where a lot of test samples will be but unfortunately my calibration range must be up to 10ppm as this is the upper limit for the test samples.
Is it a valid approach to make a calibration range of say 0.5-2 ppm and analyse my samples. If any sample is above my highest calibration point of 2ppm, I will re-analyse the sample with a new calibration range of 2-10ppm? If every sample is below the 2ppm calibration limit...I can just state that they pass as they're obviously below 10ppm?
99.99% of samples for this method will sit around 0.5 - 1ppm so it seems silly to lose accuracy at this level as the upper calibration points seem to be causing this inaccuracy?
Thank you for any help.