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- Posts: 2
- Joined: Tue Apr 04, 2017 1:11 pm
System: GP50 gradient pump (Dionex, Sunnyvale, USA) equipped with an autosampler FAMOS (LC packings); DC amperometry detector (Dionex, Sunnyvale, USA) with Glassy Carbon Working Electrode; C18 analytical Kinetex column.
Targeted hormones: dopamine, DOPAC, serotonin, 5HIAA (from Sigma); 1 µM
Mobile phase :75 mM NaH2PO4, 7 mM octane sulfonic acid (OSA) and 13 % MeOH, pH 2,79. Degassed with helium. Between injections, the column is reconditioned by washing with 90 % MeOH during 5 min and then re-equilibrated with buffer during 20 min.
Temperature and pressure are constant and flow rate is fine.
All my results are consistent. However, there is sometimes a shift of dopamine retention time (always a 2.5 min shift) without any impact on DOPAC, serotonin and 5HIAA RT. The peak is just moving while the mobile phase is the same (in a 2L glass), the sample is the same (same tube, maintained at 10°C) and the system is not turned off between injections.
I really appreciate if somebody could help me with suggestions…
Thank you !!