Q:  What does it mean if I see spurious peaks showing up in the GC at variable retention times?

A:  This may indicate you did not wait long enough, and stopped the run before all peaks had eluted.  The remaining peaks are coming out during your next run.

Q:  What does it mean if all my peaks are "doubled."

A:  This is due to an error of injection technique. When the syringe is inserted into the injector, the needle must contain air, not sample. If there is sample in the needle it will vaporize and move onto the column upon insertion into the hot injector. The rest is injected when you depress the plunger, so effectively you are making two injections several seconds apart. Wait until all peaks have eluted and redo.

Q:  Do I have to inject at the same time as the person using the other injector?

A:  No, not unless you are using a temperature ramp (programmed increase in temperature). This is common in the research lab, but in Chem 113A we will keep the oven at one temperature.

©2001,2002 Daniel A. Straus