During the liquid phase chromatograph experiment, we always face some issues, like the retention time shift. It’s a headache problem, and there are so many factors causing the peak retention time shift, like if the mobile phase fully balanced; if the mobile phase and stationary phase are well selected; if solvent effect is existing. But what if we exclude those influences, there are still problems, what can we do?
Let’s see the case:
Citric acid compounds is soluble in water and its retention peaks and peak type are going well on the reverse phase C18 column as acid system mobile phase, and the peak retention time is moving ahead constantly with feeding times increasing.
We adjust the mobile phase and change the column, this status still exists.
The problem is still there, that means it’s not the mobile phase system or the column that causes this phenomenon, so we preliminary infer that it’s caused by the sample itself.
After analyzing the matter, we can see it’s acid compound. As the water is the solvent, the matter can’t keep the molecule state very well, because the water pH is partial neutrality even weakly alkaline. In this environment, the compound’s chromophore is influenced by other combined molecule’s other parts or the solvent, it makes the compound absorption peak position moves, and is causes the sample state isn’t stable after dissolution. That’s why we need to improve the solvent stability
The mobile phase is used as sample dissolving solvent, the peak retention time shift is improved, but not very well.
We change to Phosphoric acid water (pH 2.0) as the sample dissolving solvent, the peak retention time shift issue is solved.
- What influences the peak retention shift is not only the mobile phase or the stationary phase. After we exclude those factors, there is still RT shift there, so we can consider the problem from the sample own point of view.
- The sample state after dissolving relates the sample retention time, peak area stability, peak type and etc. When selecting the solvent, we need consider those factors.
If you have any problem or require further information, please contact info@welchmat