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4 Operational and Maintenance Supplies

The supplies needed to operate and maintain the GC/MS system will depend largely on the type of analyses. However, some general remarks can be made.

The typical supplies used with GC will of course be needed. These include appropriate column nuts and ferrules for the column being used, septa, inlet liners appropriate to the type of analysis and other seals as required by the particular inlet manufacturer. As for column ferrules, graphite is suitable for the inlet end of the column, but most manufacturers recommend the use of graphitized vespel for the mass spectrometer end of the column. Also, in regard to septa, high performance septa are available that dramatically decrease the frequency of septa changes.

It is very important that columns and septa be of the low bleed type. This is since the column is installed in the high vacuum chamber of the mass spectrometer, and the column phase is stressed more than a typical (GC only) column. Further, whatever column phase does bleed will contaminate the mass spectrometer, so that the use of low bleed columns lowers the necessity of mass spectrometer source and quadrupole cleaning. Most of the major column manufacturers offer the common stationary phases in a low bleed configuration, typically designated with an ``MS'' suffix on the column designation.

All solvents used should be of the Mass Spectrometry Grade and stored only in glass. While many users attempt to use HPLC grade solvents, these often are filtered (so have low solid particulate concentrations) but contain detectable dissolved impurities. Typical solvents used for GC type analyses will still be suitable for GC/MS, and high purity water, methanol, acetone, methylene chloride and perhaps toluene will be needed for maintenance and cleaning tasks.

The mass spectrometer will require periodic replacement of the source filaments and detector. It is certainly reasonable to keep spare filaments in the lab, but electron multipliers should not be purchased in advance and kept stocked. Experienced users can often observe symptoms that the detector is failing, and so as long as storage time is less than a month or so, the detector can be ordered before it is actually needed.

Depending on degree and manner of use, the mass spectrometer ion source will require cleaning several times per year. Some users purchase an extra source so that a clean source can be kept ready to install, and the dirty one can be cleaned as time permits. Sources can be cleaned in-house, by service personnel according to a service contract or via mail-in service. If the sources are cleaned in-house, cleaning supplies such as 600 (or greater) grit aluminum oxide, 1200 (or greater) grit wet/dry abrasive paper, swabs, nylon lint-free gloves, ultra sonic cleaner, and a clean work station will be useful supplies.

A dessicator is recommended to store filaments, spare sources or other components that may be installed inside the high vacuum chamber.

The vacuum system will also require periodic maintenance. Particularly, the mechanical pump oil will need to be changed approximately twice per year, though actual maintenance periods will be specific to the application. Mechanical vacuum pumps use a relatively low vapor pressure oil such as Inland 19, which should be kept in stock. Further, the used oil will contain contaminates consistent with the type of samples injected on the instrument. Therefore, the used oil may be required to be treated as hazardous waste with proper disposal (though the contaminates are often at trace levels).

Finally, a reasonable set of tools will be required for routine maintenance. These include wrenches of appropriate size, screwdrivers (sizes from jewelers style to ordinary), forceps, etc. Column installation tools such as a flowmeter and magnifier will be usefull as well. In addition, many instruments use hex head or torx head fasteners. Some gas chromatographs require special tools for the removal of inlet nuts or the inlet liner itself. An ohm meter (or even better, a multi-meter) will be needed to verify that ion source components are electrically isolated before installation, and may be helpful for some troubleshooting tasks. Tuning the quadrupole will require a non-conducting screwdriver to reduce added capacitance while tuning.

next up previous
Up: GC/MS Buyer's Guide Previous: 3 Physical Plant Requirements
John S. Riley, DSB Scientific Consulting