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

A new ultraviolet (UV) signal actuated switching valve for diverting the ma in matrix compound to waste, preventing it entering the ion source of the m ass spectrometer is described. Sensitivity for trace impurities eluting aft er 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 i on source which interfaced the mass spectrometer, The benefit of the switch ing valve was greater with a line of sight type source than with an orthogo nal 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 onl y by a factor of 5 with the orthogonal source. Copyright (C) 1999 John Whey & Sons, Ltd.