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- Posts: 8
- Joined: Mon Feb 29, 2016 5:21 pm
I have a problem regarding retention time instabilities in an multicomponent LC_MS/MS assay.
Column: Accucore RP-MS 15 cm, 3mm ID, 2.7 µm particles
Solvent A: Water/Methanol 95/5 v/v + 0.2 % FA + 10 µM LiOAc
Solvent B: Methanol + 10 µM LiOAc
Flow 0.4 mL/min
Column Temp: 35 °C
Dionex Ultimate 3000 quarternary low pressure gradient pump
Gradient:
0 min 100 % A
0.3 min 65 % A
4.5 min 5 % A
5 min 2 % A
10 min 2 % A
10.1 min 100 % A (flow to 0.8 ml/min)
15 min 100 %A
The fast initial gradient slope is due to a mismatch of injection solvent ( 95 % EtOH, not changeable), else the peakshape of the first eluter ( ~ 5 min ) is bad. Starting a linear ramp at higher % B does not work properly.
The phenomenon: LC runs of identical samples give a large variation in RT (more than a minute) on consecutive days.
An experiment for repeatability was set-up: 2 bottles of Solvent A were prepared by weighing in all components by the same person within one hour.
Analysis using either solvent A1 or A2 (on different channels on the HPLC) gave a retention time difference of 2 minutes!
I have no clue which screw to turn at the moment, does anybody have an idea?
Thanks
Georg