Small Molecule Pharmaceuticals
In this application note, LC/MS of several compounds associated with drugs of abuse are compared at high and low pH using a generic gradient in positive ion mode electrospray (ESI+). Normally, it could be expected that the ionization state of analyte molecules would be dependent on the pH of the mobile phase, and the ionization efficiency in LC/MS with electrospray in positive ion mode will be dramatically lowered in high pH mobile phases since the compounds become neutral. However, many researchers investigating different types of samples (including proteins, peptides, and amino acids) have observed either insensitivity to an increase of mobile phase pH, or even increases in sensitivity. High pH mobile phases do not suppress the ionization of basic compounds in ESI+. Positive ions are formed abundantly, and analyte responses are often better in high pH compared to low pH acidic mobile phases. This finding is significant as it extends the applicability of generic elution methods to the analysis of polar basic compounds that were previously difficult to retain.
Publication number: 5991-6523EN
Publication Date: December 11, 2015