Negative y intercept LCMS

Discussions about GC-MS, LC-MS, LC-FTIR, and other "coupled" analytical techniques.

3 posts Page 1 of 1
Hi all,
What are some possible causes of a negative y intercept (i.e. a positive x intercept) in a calibration curve (ESI LCMS method)?
The standards seem to have been prepared correctly (they're MeOH based standards spiked into a blank urine matrix).

Thanks for your help :)
Welcome to the forum.

This is a hardy perennial. Possible causes include non-linearity, adsorbtive (or other) losses of analyte, a signal threshold set too high, not taking the purity of the standard into account, poor repeatability, .....

What your particular problem is will depend on the details of your analysis - tell us those and we will be able to help.

A search of the archives will throw up plenty to keep you busy also.

Peter
Peter Apps
Hi Peter, thanks for your reply.
So the issue is with Pholcodine. I use a mass-labelled codeine as internal standard.
I'll double check the purity when I'm in the lab next week.
For adsorbtive and other losses- do you think degradation of analyte in the standard master is likely? While codeine is reasonably stable in MeOH, I'm not sure about Pholcodine.

Thanks for your help.
3 posts Page 1 of 1

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