GCMS FAQ

Q How can I improve the sensitivity for my analytes?

A If your MS is properly tuned and sensitivity to all analytes is still poor, then this is most commonly a GC or sample preparation problem. Common places to look are the injection, the position of the GC column in the injection port, transfer line between the GC and the MS or the method of sample extraction and concentration. Using a new standard solution is often a useful troubleshooting tool.

Q Why are my peaks of interest showing up in blanks?

A  This can be either a sample preparation or system cleanliness problem. Try changing the solvents used in the preparation of the sample and blank, as well as the solvents in the sample wash bottles. If this doesn’t solve the problem it could be the hardware is contaminated- Try a new syringe and septum. Remove and clean the split vent line. Lastly, do a run without any injection, to see if the peaks show up just by heating the column.

Q How do I maximize(maintain) the electron multiplier life?

A As recommended by the manufacturer: The lifetime of an EM is directly related to the current that flows through it and the extent of contamination or condensation that it experiences. To maximize electron multiplier life:

• Maintain the best possible vacuum, especially in the analyzer manifold
• Use extreme caution and be conservative with venting, pumpdown and all vacuum system procedures to keep pump fluid background to a minimum.
• After venting, allow four hours for pump-down and thermal equilibration before scanning.
• Actively look for background contamination and leaks and repair them immediately.
• Don't tune excessively. PFTBA can result in higher background over an extended period of time.

For trouble shooting tips on LCMS instruments see our LCMS page or

More FAQs in our ChromaForum