Problem: We are consistently seeing peak(s) around 14-18 amu over
40 abundance in the autotune spectra on an Agilent 5973 MSD
connected to an Agilent 6890 GC. We had a technician come out and
the only solution to the problem is to do a startup.m method that
starts at 60C, Initial Time =0, Ramp of 30 to 250 for a final time
of 10 mins, run time is 16.33 mins. The Front Inlet parameters are
Split mode at 250C, pressure at 5.30 psi, split ratio – 23.5:1,
split flow – 35.7 ml/min, total flow 39.3 ml/min. The tech checked
for leaks through out the entire system

The general.m method that we use for the analysis is a bit different
being in a splitless mode, start temp of 60C, Initial time 2 mins,
rate 30C, 300C for 5 mins.. Front Inlet splitless 250C, 5.30
pressure, purge flow 35.7, total flow 39.3.

We created a new method called gensplit.m where the only thing we
changed in the method was the split mode and the peaks were greatly
reduced.

The questions, other than the problem stated above, are:
1. Why are we seeing these peaks? What could they be – water,
nitrogen, oxygen??
2. Is it really a problem to run an autotune using a different
method than what you are running the samples on? I don't think so
as the autotune is checking the MS of the instrument. When I
compared the startup.m to the general.m the only differences are in
the GC parameters and none in the MS parameters.
3. Any advantages or disadvantages to running split or
splitless?

Some people think that is moisture built up in the GC system and
when we do the startup.m, the moisture is burned off as the peaks
are lower if the autotune is done immediately after the startup.m
methods ends. But could it be another contaminant?

The analysis on this GC/MS is for controlled substances, qualitative
analysis only.

Thank you for your help.

Christy Keller
San Bernardino County Sheriff's Department
Scientific Investigation Division