Calibration curve slope

[zimanli]

I did 3 calibration curves on 3 different days, and I had some problems with them:
1. the slope is increasing.
2. the absolute response for the same solution increases.

Is this due to solvent evaporation from my standard solution or from the contamination of my system?

Thanks a lot!

[chromatographer1]

Could be either one or both,

OR

it could be another reason based on sample introduction or detector response.

Ain't analytical chemistry fun?

best wishes,

Rod

[zimanli]

Thanks for your reply!

I found that I used split injection on one day and splitless injection on the other 2 days.

[KC]

shoot some acetone blanks and if you get a peak at the retention of your analyte you may well have coated your inlet with your test substance and it bleeds off with each injection. Is an acetone blank clean? What do 3 or 4 injections of acetone in succession look like. If it is tapering off raise injector temp 30 C and shoot another. If it gets bigger then I would definately guess that is the problem

[zimanli]

I would try what KC suggested. It is a good way to rule out contamination. Thanks

[Peter Apps]

KC has been recommending acetone blanks. Before you follow that advice have a look at the thread on "Peak tailing - chlorinated aromatics with phenol and aldehydes" started by khirth.

Peter