LCMS analysis of three derivatives of Laccaic acid (structures A, B, and C are g
ID: 977629 • Letter: L
Question
LCMS analysis of three derivatives of Laccaic acid (structures A, B, and C are given below the chromatogram) using Reverse Phase column and isocratic elution is shown below.
In the chromatogram, A and B came together, while C gave two peaks as shown below:
What modification you will make to the method to separate Laccaic acid A and B?
The two peaks for Laccaic acid C were due to acid form and ionic form of lactic acid.
Identify the peak for ionic and acid form (based on retention time)
HELP ME PLEASE!!!
Explanation / Answer
It is evident from the structures of the Laccaic Acid A and B that the Laccaic Acid B is more polar due to presence of the free hydroxyl group where as the polarity of the Laccaic Acid A is reduced to some extent due to acetylation of the amine group. So, if we change the stationary phase into a Hydrophilic one (Normal Phase Chromatography) the compounds will be well separated. The molecule A will be elluted first with a less polar solvent where as the molecule B will be elluted only when the solvent becomes polar.
Reversed-phase chromatography employs a polar (aqueous) mobile phase. As a result, hydrophobic molecules in the polar mobile phase tend to adsorb to the hydrophobic stationary phase, and hydrophilic molecules in the mobile phase will pass through the column and are eluted first. So, the peak with a lower retention time is due to the acid form of molecule C and the peak with a higher retention time is due to the ionic form.
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