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- Posts: 5
- Joined: Mon May 22, 2017 4:04 pm
Hi,
I'm trying to analyse polar pesticides, e.g. fosetyl, phosphonic acid, perchlorate,...
I'm following QuPPE v 9.3 for sample preparation.
First experiments were conducted using a Hypercarb column. Although the column was primed was spinach extract as suggested, peaks were broad, retention times were unstable (+- 2 min) and recoveries were <10% against solvent standard and increased to 140% after correction of internal standard.
Therefore, results were not satisfying.
I switched to a zwitterionic HILIC column (Sequant ZIC HILIC, 250 x 4,6 mm, 5µm)
Recoveries increased to 60% against solvent standard and to 95% after correction of internal standard (using the same extracts as above, so this seems to be rather a high signal suppression and mathematical overcorrection issue less than an extraction efficiency issue)
Unfortunately, I do not get stable retention times on the HILIC column (+- 1 min)
I've tried:
- equilibration 20x column volumes after each injection (HILIC seems to need longer equilibration times than RPLC)
- using buffered eluents (5 mM ammoniumformiate + 0.3% formic acid, pH 3)
- prepare eluents freshly
- diluent matches starting condition
- different column temperatures
Do you have any suggestions how to overcome this retention time shifts?
Is Ion Exchange chromatography less prone to retention time shifts? I've found a paper that seems to be relevant (Anna Bauer et al, Determination of Fosetyl and Phosphonic Acid at 0.010 mg/kg Level by Ion Chromatography Tandem Mass Spectrometry)
I'm trying to analyse polar pesticides, e.g. fosetyl, phosphonic acid, perchlorate,...
I'm following QuPPE v 9.3 for sample preparation.
First experiments were conducted using a Hypercarb column. Although the column was primed was spinach extract as suggested, peaks were broad, retention times were unstable (+- 2 min) and recoveries were <10% against solvent standard and increased to 140% after correction of internal standard.
Therefore, results were not satisfying.
I switched to a zwitterionic HILIC column (Sequant ZIC HILIC, 250 x 4,6 mm, 5µm)
Recoveries increased to 60% against solvent standard and to 95% after correction of internal standard (using the same extracts as above, so this seems to be rather a high signal suppression and mathematical overcorrection issue less than an extraction efficiency issue)
Unfortunately, I do not get stable retention times on the HILIC column (+- 1 min)
I've tried:
- equilibration 20x column volumes after each injection (HILIC seems to need longer equilibration times than RPLC)
- using buffered eluents (5 mM ammoniumformiate + 0.3% formic acid, pH 3)
- prepare eluents freshly
- diluent matches starting condition
- different column temperatures
Do you have any suggestions how to overcome this retention time shifts?
Is Ion Exchange chromatography less prone to retention time shifts? I've found a paper that seems to be relevant (Anna Bauer et al, Determination of Fosetyl and Phosphonic Acid at 0.010 mg/kg Level by Ion Chromatography Tandem Mass Spectrometry)
