Open ion source

Fig. 4.8 Open ion source (ieft) and dosed ion source (right)...

Mass Spectrometers for Stress MS. The requirements of a mass spectrometer for stress MS are more stringent than those for conventional mass spectrometry. The events to be monitored are short-lived, typically < 1 sec, and the total amount of evolved compounds is small, between 10" and 10" g. In addition, a source vacuum housing versatile enough to accept readily the various devices for mechanically loading polymeric samples is required. The mass spectrometer must have a large, open ion source. 

The sensitivities and/or detection limits of the stress MS system are summarized in Table I. The large, open ion source of the TOFMS together with its vacuum housing is ideally suited for insertion of the mechanical degradation apparatus. 

Solvent-divert system. Used in conjunction with an interface, it permits temporary interruption of the flow from a chromatograph to a mass spectrometer by briefly opening a valve to a pumping line. Thus effluent present at a high concentration (usually solvent) does not enter the mass spectrometer ion source. 

Vacuum-lock inlet. An inlet through which a sample is first placed in a chamber the chamber is then pumped out, and a valve is opened so that the sample can be introduced to the mass spectrometer ion source. A vacuum-lock inlet commonly uses a direct-inlet probe, which passes through one or more sliding seals, although other kinds of vacuum-lock inlets are also used. 

Several Interface designs are available for GC/MS and selection depends on the circumstances of the experiment [3-6,8,25,26]. Column flow rates of 1-2 ml/min (adjusted to STP) into the ion source are compatible with modem mass spectrometer vacuxim systems. This is also the optimum floi te range for open tubular capillary columns of conventional lensions. Coupling such columns to a modern mass spectromet er, therefore, presents... 

Fig. 5.18. Reservior inlet of a JEOL JMS-700 sector instrument with the septum injection port opened. The operation valve switches between evacuation, isolation and admission of the sample a needle valve allows regulation of the sample flow. The GC transfer line crosses in the upper background from the GC (left) to the ion source housing (upper right).

H. D. Versatile new ion source for the analysis of materials in open air under ambient conditions. Anal. Chem. 2005, 77, 2297-2302. 

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