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- Posts: 13
- Joined: Wed Oct 25, 2006 4:53 pm
Dear Colleagues,
I do have a problem with one forensic method I am implementing. That's amphetamine family drugs. There are problems with peak tailing as comounds are bases, thats old an 100 times sloved problem ind different ways. Anyway the main prolem what ruines my life now is strange phenomena. I am not sure what generates it.
Phenomena: Even using isocratic run, Retention times of all the peaks with each following injection are shifting by getting shorter (equally for each compound). And every shift in time is equal to previous shift. Column has small internal volume, so it couldn't be just stupid lack of column equilibration with used mobile phase composition. It's fluched with tens of column volume before injections. The same problems occurs with the gradient. Just after half a day retention timne sof peaks are becoming more or less stable. I was playing around a lot.
Could it be something with formic acid interaction with stationary phase? Maybe there are some procceses going behind that are slow and needs time an a lot of flushing.
Maybe you have experienced something similar? Anything similar with retention times shifting? I would be very greatful for any hints.
The conditions:
2.2 µm particle column (suppose to be fast LC) 3 mmx75 mm;
Mobile phase: A: 0.5 % formic acid in water
B: ACN
All chromatogram is about 4.5-5 mins (4 compounds)
Starting ratio of eliuents is more or less 95% (A) / 5% (B)
Tried different gradient shapes (with short isocratic start or with sudden gradient form very start).
Thankyou in advance
Zydrunas
I do have a problem with one forensic method I am implementing. That's amphetamine family drugs. There are problems with peak tailing as comounds are bases, thats old an 100 times sloved problem ind different ways. Anyway the main prolem what ruines my life now is strange phenomena. I am not sure what generates it.
Phenomena: Even using isocratic run, Retention times of all the peaks with each following injection are shifting by getting shorter (equally for each compound). And every shift in time is equal to previous shift. Column has small internal volume, so it couldn't be just stupid lack of column equilibration with used mobile phase composition. It's fluched with tens of column volume before injections. The same problems occurs with the gradient. Just after half a day retention timne sof peaks are becoming more or less stable. I was playing around a lot.
Could it be something with formic acid interaction with stationary phase? Maybe there are some procceses going behind that are slow and needs time an a lot of flushing.
Maybe you have experienced something similar? Anything similar with retention times shifting? I would be very greatful for any hints.
The conditions:
2.2 µm particle column (suppose to be fast LC) 3 mmx75 mm;
Mobile phase: A: 0.5 % formic acid in water
B: ACN
All chromatogram is about 4.5-5 mins (4 compounds)
Starting ratio of eliuents is more or less 95% (A) / 5% (B)
Tried different gradient shapes (with short isocratic start or with sudden gradient form very start).
Thankyou in advance
Zydrunas
Zydrunas Stanius
Vilnius, Lithuania
Vilnius, Lithuania
