Analysis of basic compounds by reversed-phase liquid chromatography-electrospray mass spectrometry in high-pH mobile phases.
The separation of basic compounds in high-pH mobile phases results in extended retention, excellent peak shapes and good chromatographic efficiency. A severe decrease in sensitivity with electrospray mass spectrometric detection in positive ion mode (ESI+-MS) is expected under conditions that suppress analyte ionization in solution. We compared the responses of a large number of various basic drugs covering a wide range of hydrophobic (log P 0.09 to 7.6) and basic character (pKa 6.8-10) in LC-ESI+-MS/MS in 0.1% formic acid in water and acetonitrile, to responses in 10mM ammonium hydrogencarbonate buffers of different pH (7.8-11), and acetonitrile. Contrary to common expectations, high-pH mobile phases do not affect negatively the responses of basic compounds in ESI+. Analyte responses and limits of detection are comparable, or most often better in high pH compared to acidic mobile phases.
D000097:Acetonitriles; D001639:Bicarbonates; D002021:Buffers; D002853:Chromatography, Liquid / Q000379:methods*; D006863:Hydrogen-Ion Concentration; D004364:Pharmaceutical Preparations / Q000032:analysis* / Q000302:isolation & purification; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
D000097:Acetonitriles; D001639:Bicarbonates; D002021:Buffers; D004364:Pharmaceutical Preparations; C027043:ammonium bicarbonate; C032159:acetonitrile