Optimal Conditions for GC-MS

Electronic Pneumatic Control (EPC) modules control pressure against a restrictor. In the case of the inlets that restrictor is the column. There must be enough pressure and enough flow for good control. While it may look like it's working at very low flows or very low pressures, there are fluctuations that could affect the retention times or peak areas.   Imagine your thumb on the end of a water hose. With the flow very, very low, use your thumb pressure to change the flow from 1 cup per minute to 1.03 cups per minute.  Now think about how that would work with high flow and adjusting between 1 gallon per minute and 1.03 gallons per minute. 

20 ml/min is only 0.3334 microliters per millisecond. Dosing that out with liquid isn't super hard but great control with gas, especially hydrogen and helium, is difficult.   5psi - and control at, say, 0.1% accuracy per millisecond, would mean being able to read, adjust, and get feedback in 0.005 psi increments over the entire internal volume of the injection port subsystem 1000 times per second. 

Adjusting gas flows and pressures accurately is difficult and even more so the lower the pressures and flows. See:

How Does Carrier Gas Flow and Vacuum Work Together in GC/MS

VOC by Purge and Trap is a big subject. To comment on 40:1 split ratio needs more context and should be its own post/reply.  From the Mass Spectrometer's perspective the issue is water management.

Optimal GC/MS conditions?  Another complicated subject. Let me think about that and I may post again later.