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- Posts: 3
- Joined: Wed Jun 19, 2024 7:35 pm
- Location: Canada
Essentially, the retention time of the levulinic acid only (not at all the sugars) is affected by the sample concentration. Not in the expected manner, where high concentrations saturate the column, reducing the r.t., but rather higher concentrations consistently increasing the r.t. (from sample concentrations of 0.1 mg/ml --> 10 mg/ml). Rather annoyingly, it sweeps right across the range of the sugar peaks. Any ideas on what might be causing this, and how to fix it?
We use a mobile phase of 5% methanol in water, but have observed the same effect with 10% methanol (not strictly advised with this column but we were trying things out...). Also saw the effect operating at both 0.5 ml/min and 0.35 ml/min. Our column oven is limited to 80C so we can't explore the recommended operating temperature range of 80-90C. For a sense of scale, doubling sample concentration might increase levulinic acid r.t. anywhere from 30 s to 60 s, at a flow rate of 0.35 ml/min.
We are considering adding dilute formic acid to the mobile phase (unrecommended -> manufacturer specs recommend pH 7), or neutralising the levulinic acid with a base like dilute NaOH prior to analysis. Does anyone have experience and advice for trying such techniques with ligand/ion exchange columns?