Chromatography Forum

Trouble with calibration restults. Sometimes when I hand calculate the average of the calibration concentrations, they do not match the concentration I have entered in the calibration table (other times they do match exactly). This is after updating the calibration, so it's not a mismatch there, and sometimes the difference is quite small, in the 4th figure, other times it is a larger difference.

This is running on GC/FID with an internal standard and calculating by ISTD%.

Any ideas on why the concentrations do not match?

If I understand you correctly, you are recalibrating and averaging the results. In Chemstation, it does not take your last value and the new value and average the two results. If you have done several recalibrations and averaged, say 9, and you then make a 10th recalibration, it will take 9/10 of the old value and 1/10 of the new value.

Gasman

Set up a Sequence Table and have the first line be Calibration, Replace then have second line be Calibration, Average.

When you do a Sequence Summary Report, the software will replace the existing calibration amount with the last injection results from that "Replace" line, and then average that with all the injections on the "Average" line, then use that calibration for sample injections starting on the 3rd line.

Thank you Gasman! I didn't know which it did, and always wondered. It's been a hypothetical question up to now but it's good to know.