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EI Source Calibration Valve

Exhibit no. 801

All mass spectrometers require calibration of their mass scale. It is needed to compensate for subtle changes in electronics, cleanliness of surfaces and ambient conditions that can affect measured m/z values. Mass scale calibration is accomplished by introducing a sample, which provides several peaks of well-known m/z values evenly distributed over the mass range. The m/z values in the recorded spectrum are then correlated to the mass reference list. Besides mass calibration, instrument tuning is required to optimize the mass resolution and signal intensity. Various compounds are used for calibrating and tuning mass spectrometers; their selection depends mainly on the ionization method used. In GC/MS, fluorinated compounds like perfluorotributylamine or perfluorokerosene are most popular. Many instruments use a vial with the reference compound and an electromechanical valve. During the calibration and tuning procedure, the valve opens so that the reference compound can diffuse into the ion source.

The exhibit is a calibration valve for EI source from the 5972 MSD single quadrupole mass detector manufactured by Hewlett-Packard in 1993. The solenoid valve was threaded into a hole in the bottom of the vacuum manifold and controlled by the data system. Perfluorotributylamine (PFTBA) was used as the calibration compound.

Wikipedia: Electron ionization

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