Does anyone know why the first few standard points would be higher at the beginning of a run, then settle down over the course of the run? I am allowing at least three injections for column conditioning and instrument equilibrium. I have noticed though, if I don't use the first three level injections, I get R values of .99 or better. But, if I include them in my calibration curve, I get R values of .98. I have noticed a trend, that when the nitrogen doer gets lower my calibration curve gets lower. Any thoughts? I am operating an API 3000 Triple Quad on a nitrogen doer. Doers are about 150 feet away from instrument. The gas at the table is at a pressure of 80 psi.

Depending on the compound, it is possible to have nonlinearity at the bottom and top end. What are the levels of your calibration points? What is S/N at your bottom point?

It's important to make sure that your N2 pressure meets the manufacturer's requirements. Note the pressure on your regulator(s) as the level in the dewar gets lower.