Atmospheric pressure ionization and liquid chromatography/mass spectrometry—together at last

The evolution of atmospheric pressure ionization techniques which are now routinely applied as liquid chromatograph/mass spectrometer (LC/MS) interfaces is described. Electrospray and related methods, as well as atmospheric pressure chemical ionization combined with the heated nebulizer interface, both began as specialized ionization techniques which became much more widely accepted when combined with tandem mass spectrometry. Today, both are widely used for quantitative and qualitative LC/MS and LC/MS/MS analyses. Important events in the development of these methods are described, along with key elements in the evolution of the ion source-to-vacuum interface techniques that contributed to their success.