T-infusion of deuterium labeled standards shows how ion-suppression occurs during electrospray ionization of metanephrines. Using this type of experiment helps visualize the difference in sensitivity caused by complicated ion-suppression phenomena. Ion suppression is a fantastic and interesting phenomena, read more about it from Tom Annesley, who among other things, is a fantastic science writer: http://www.clinchem.org/content/49/7/1041.long
Marney LC, Laha TJ, Baird GS, Rainey PM, Hoofnagle AN.
Clin Chem. 2008 Oct;54(10):1729-32. doi: 10.1373/clinchem.2008.104083. Epub 2008 Aug 7.