Automated calibrant system for use in a liquid separation/mass spectrometry apparatus

An automated calibrant system is provided for use in a liquid separation/mass spectrometry (LS/MS) apparatus. The calibrant system is pneumatically pressurized to forcibly move a reference liquid from the calibrant system to an ion source. The ion source is in fluid communication with a switching valve and with a mass spectrometer. The switching valve communicates effluent from a liquid separation system to the source when the switching valve is in a first position, and communicates one or more reference liquids from the calibrant system to the source when the switching valve is in a second position. The switching valve, and liquid handling valves in the calibrant system, can be individually activated manually or by automated means to alternate between analytical and calibration modes of operation in the LS/MS apparatus. A method is also provided for calibrating a mass spectrometer in a LS/MS apparatus during processing of a liquid sample by the liquid separation system.