Improving alkaloid selectivity and resolution by adjusting the pH of the mobile phase

Nowadays an extensive number of alkaloid drugs are available and administered for numerous ailments. Presently, scientists use both natural sources, such as plants and fungi, as well as apply synthetic chemistry to obtain new alkaloids drugs.  Reproducible alkaloid analysis is, therefore, critical for scientists from the initial screening stages in drug discovery to method development and quality control.

When dealing with UHPLC/ HPLC analysis of drug samples, selectivity and resolution are key parameters.  Reversed phase analysis based on silica stationary phases is the most common technique but it is limited to acidic and neutral pH conditions.  Kromasil EternityXT UHPLC/HPLC columns can operate within a wider pH window; therefore, we illustrate the benefit of using these new columns to exploit selectivity and resolution at high pH to analyse a mixture of alkaloids. 

Figure 1 shows two chromatographic results for an alkaloid mixture. As seen in the figure, at low pH, the compounds tend to elute earlier since they are in ionised form and resolution is limited.  On the other hand, at high pH there is complete separation.  The most significant changes in retention times between the two pH conditions are given by lidocaine, noscapine and diphenhydramine which, at pH 10.5, are in their neutral state.  Also, diphenhydramine’s peak shape improved under basic conditions.

Due to the outstanding mechanical and chemical stability under a wide pH range, the new Kromasil EternityXT UHPLC/HPLC columns exhibit consistent results over time.  Figure 2 illustrates lifetime studies carried out at low and high pH using Kromasil EternityXT C18.  As seen in the figure, the efficiency of the columns as well as retention times of the compounds remain unchanged after 1000 injections. This excellent performance of Kromasil EternityXT UHPLC/HPLC columns confirms their utility for discovery and development as well as for routine analysis in the laboratory.