Recently, an overhaul was conducted on our Shimadzu GC/MS. Both source and trap filaments were replaced inside the ion source box, the heart of the system. This is where your sample gets zapped by an electron beam turning it into fragments. The two filaments (doohickeys that produce the beam) were barely alive and have since been put out of their misery. Additionally, the ion source box was scrubbed from top to bottom, ridding it of extraneous ions produced from the blasts.
A helium purifier has also been replaced which scrubs our carrier gas. This provides a smoother baseline when injecting into the GC port.
Bottom line – the unit is fully optimized for its nanogram range detection limit. Here are some tips to keep it that way:
1) Begin with 1uL of sample for GC or a “spec” of solid for direct insertion. More than that may contaminate the system for the next person.
2) Remember to set the detector no greater than 1.10 kV. It’s an electron multiplier that won’t give you better data if you ramp it up. You’ll only be shortening its life.
3) Any questions contact Joe at the info provided on the instrument. He will be more than happy to assist.
St. John's University Chemistry 
That´s good, i have one, and is a very nice equipment, but you have to keep it in time with the maintenance…