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The Design of a New Direct Probe Inlet for a Mass Spectrometer

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Christopher Baker, John Manura and John Manos

We have designed a new probe inlet for use on a mass spectrometer which incorporates design features to improve the performance of the direct probe technique. Direct probes have been used on mass spectrometers for many years. One of the potential problems with the technique is the design of many of the direct probe inlets. These inlets have seals which wear with use and also in many designs the probe can be removed too far from the inlet causing venting of the mass spectrometer if the user is not careful. The new design has a new type of seal which provides for longer seal life and also has a safety mechanism which minimizes the risk of venting the mass spectrometer when removing the probe from the inlet.

This new probe inlet is designed specifically for use on the Hewleff-Packard 5989 MS Engine, however the inlet could be modified for use on other mass spectrometers. The HP probe inlet uses a graphite seal which has demonstrated limited life due to decreased sealing capability and due to the release of small graphite particles, after repeated use, which could create possible contamination. The new seal design provides for much longer seal life while minimizing contamination due to seal wear. The design utilizes a custom PTFE and Viton® o-ring seal to provide longer seal life and clean operation. These new seals have been used for over two thousand probe analyses without any problems. The previous inlet required changing of the seals every one or two hundred analyses. The PTFE sealing surface does not release any particles with use therefore reducing the potential for contamination. The new probe inlet also prevents possible venting Gf the mass spectrometer during removal of the probe. A probe quide and stop mechanism will not allow the probe to be removed past the inlet seal until a release is pressed on the inlet. This feature also serves to eliminate damage to DCI probe tips during entrance of the probe into the mass spectrometer.

This paper will detail the new probe inlet design and demonstrate the improved performance on a Hewlett-Packard mass spectrometer.

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