A GC/MS arrangement and mass spectrometer

A Gas Chromatography/Mass Spectrometer (GC/MS) arrangement, comprising: a GC unit 2; an MS unit 4; a fluid transfer line 3 between the units; a carrier gas valve 10, for selectively supplying carrier gas to the transfer line; at least one monitoring unit 5, 6, for monitoring at least one operational condition of the MS unit; and, a controller 7 connected to the at least one monitoring unit, configured to close the carrier gas valve when a predetermined operational event is detected by the monitoring unit. The valve is preferably a normally-closed solenoid valve. A mass spectrometer is also disclosed, comprising: a vacuum pump; a source assembly; system and source control units, in communication; a pressure sensor; and, an isolator, in connection with the pressure sensor, which isolates voltage or power to part of the source assembly if the pressure detected is above a predetermined level.