Reversed Phase High Performance Liquid Chromatography Using Carboxylic Acids in the Mobile Phase |
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Abstract: | Abstract This report describes the use of different carboxylic acids as mobile phase modifiers. The effect on retention of acid chain length, pH, and eluent composition for a series of phenylalkanols, phenol, and the amines aniline, N-methylaniline, and benzylamine is discussed. The retention of both neutral and positively charged compounds is influenced by the dissociation equilibrium of the carboxylic acid in the mobile phase. By using l-pentanol to coat excess exposed silanol groups on the reversed phase column used, the inflection in the retention of both neutral and charged solutes as pH is changed occurs at the pKa of the acid in the mobile phase. In addition, by using an acid and amine with the same or similar pKa values, selective ion-pairing of this pair over others with dissimilar pKa values can be promoted. Application of this technique to the selective retention of amino acids and peptides was unsuccessful. |
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