Calibration of a mass spectrometer

Abstract

Apparatus and method are provided for calibrating a mass spectrometer. The calibration hardware includes a relatively small, relatively low pressurized tank for containing calibration gas. The calibration gas tank is preferably located inside the same housing that contains the ion source assembly and the analyzing section of the mass spectrometer. Each of the calibration gas and sample gas, whose components are to be determined, communicates with its own associated valve. These two valves control the flow of a selected one of the sample gas and the calibration gas to the ion source assembly. The calibration gas valve has an extremely low leakage rate and can be controlled to permit the passage of very low flow rates of calibration gas, which can be of benefit in checking the linearity associated with the ion source assembly pressure. For each calibration procedure, very small amounts of calibration gas are utilized, in a range around 10.sup.-5 STD cc. A related method for conditioning an electron multiplier device is also disclosed in which the gain of one or more selected channels thereof is modified so that the output signal strengths of the device are comparable in magnitude. Calibration of the mass spectrometer occurs frequently and automatically. In one emobodiment, the mass spectrometer calibration is a direct function of each mass spectrometer measurement. Consequently, improved accuracy and heightened sensitivity are achieved in the mass spectrometer, while reducing the use or loss of valuable calibration gas.