by

**Yijun** » Mon Sep 21, 2020 3:33 am

tom jupille wrote:

It's almost impossible to tell based on the very limited information you have given. Some thoughts:

- how negative is the intercept? If you are doing a multi-point calibration, statistical software (even Excel) will calculate the standard error of the intercept. If your intercept is within that standard error, then it's not a problem except insofar as it affects the LOD and LLOQ

- if you are covering a wide range (2 orders of magnitude or more), your data points at the low end should be more closely spaced than those at the high end (a given percentage error at the high end has more effect than one at the low end.

- are there visible problems with peak shape that might affect quantitation (for example, severe tailing(?

- is your analyte stable under your chromatography conditions? Is there a chance that some might be adsorbed by active sites on the column packing?

Hi Tom

Thanks for replying

--The standard error is about 0.028, the intercept is -0.087. So it is not just error of the intercept.

--The range i am covering is from 0.05%~1.5% (0.05%, 0.20%, 0.50%, 1.0% and 1.5%), very normal range for impurity.

-- The peak sharp looks good.

-- The analyte is stable.

-- I am also suspecting there might be some absorption on the column or in the LC system including the tube and injection system. If that, how can i do to remove the absorption?

Thanks

Yijun

The LINEST results are :

308.3437111 -0.086832727

5.706067321 0.028049147

0.998973689 0.03984903

2920.091147 3

4.636944756 0.004763836