Chromatography Forum

I have a 5890 with a 5972 MS. I run sem-volatiles on this instrument with a RESTEK RTX5-MS column. I have recently replace this column with a new one (same type) and cleaned my source (I have also had a service call recently). Now when I run calibration, all of my PAH's, phthalates, and some pesticides are going quadratic. Any suggestions?
Thanks,
Amy

It sounds like you are overloading either the column or the ion source. The 5972 has a somewhat limited linear range, and if you exceed this range the curve have lower response factors at high concentration, and may give a better fit with a quadratic curve. If you are doing splitless injections raise the column in the liner about 5 mm. This allows less material on column and may resolve the problem.

From my experience, quadratic curves are caused by not enough sensitivity at the lower conc's. An inverse quadratic curve (flatter at the higher conc's) is usually a sign of overload.

In addition, most instruments are fairly linear up to a 40-fold calibration range, anything larger may be exceeding the instruments limit.

Thanks for the help. I repositioned the column a little higher in my inlet, and that helped the PAHs and phthalates a bunch. I have some other problems now, but I will repost as a second question.
Amy