New ultraviolet signal actuated switching valve for the measurement of low level impurities by liquid chromatography/mass spectrometry

A new ultraviolet (UV) signal actuated switching valve for diverting the main matrix compound to waste, preventing it entering the ion source of the mass spectrometer is described. Sensitivity for trace impurities eluting after the drug substance cimetidine or related compounds could be enhanced by a factor of 4–5. The increase in sensitivity was dependent on the type of ion source which interfaced the mass spectrometer. The benefit of the switching valve was greater with a line of sight type source than with an orthogonal one. The detection limit for a trace compound in a matrix compound was improved by up to a factor of 10 with the line of sight type source but only by a factor of 5 with the orthogonal source. Copyright © 1999 John Wiley & Sons, Ltd.