Reproducing daughter‐ion spectra using the transmission oscillation properties of quadrupole collision cells

The transmission oscillation properties of parent ions through an RF‐only quadrupole are investigated as a function of collision energy, radicfrequency of the quadrupole, and type and pressure of target gas. It is shown that small variations of collision energy can result in substantial differences in daughter‐ion spectra obtained from the same parent ion. Since absolute values of collision energy are difficult to determine, reproducible daughter‐ion spectra are problematical to acquire. In this work we show that reproduction of daughter‐ion spectra, using the transmission properties of the collision cell, is possible. The characteristics of an RF‐only quadrupole (Q * ) are such that the parent ion intensity at the second detector varies as a function of collision energy and displays sinusoidal properties. By using the nodes and anti‐nodes of the parent‐ion transmission it is possible to achieve reproducible daughter‐ion spectra of a wide range of biopolymers. The tuning of Q * is mass‐dependent and not compound‐dependent. Hence it is possible to optimize and tune Q * using an isobaric (or almost) standard such as one of the ions of perfluorotri‐n‐butylamine (electron ionization) or a glycerol cluster ion (fast‐atom bombardment mass spectrometry) before subjecting valuable sample to tandem mass spectrometry.