Internal Standard recoveries dropping after calibration

[japapp]

Hello.
I'm running an HP 5890 GC with an HP 6890 MSD attached. I've just cleaned the source. I target tuned the MS after letting it set overnight.
Also, I've recently replaced the IS/SURR valve. My issue is this. I calibrated the instrument - the calibration looked fine maybe 5 compounds on linear curve fit but all other analytes are on average response. Looks lovely. Next morning I prep and run an ICV - secondary source calibration check - and my internal standards have all dropped to 60% so all compounds are failing high. I've run several rinses and the IS appears to be steady now. Should I simply recalibrate or is there an obvious underlying issue that I'm not aware of. Did the MS just need to stabilize a little longer? Thanks for your help.

[James_Ball]

Hello.
I'm running an HP 5890 GC with an HP 6890 MSD attached. I've just cleaned the source. I target tuned the MS after letting it set overnight.
Also, I've recently replaced the IS/SURR valve. My issue is this. I calibrated the instrument - the calibration looked fine maybe 5 compounds on linear curve fit but all other analytes are on average response. Looks lovely. Next morning I prep and run an ICV - secondary source calibration check - and my internal standards have all dropped to 60% so all compounds are failing high. I've run several rinses and the IS appears to be steady now. Should I simply recalibrate or is there an obvious underlying issue that I'm not aware of. Did the MS just need to stabilize a little longer? Thanks for your help.

Did the ICV pass recovery while the IS was low? If so then it would be that the entire system sensitivity dropped overnight. If the ICV failed high then you lost IS from the vial overnight.

What autosampler are you using? Purge and Trap I am guessing.

[LindseyPyron]

I assume you are running purge and trap. What you described is a typical moisture problem from the build up of water in the MS. A combination of chnages to your purge and trap and MS conditions might be able to help. If you want to send me some details on your parameters, we can see if we can help. ( lpyron@estanalytical.com )