Application of matrix calculations. II. Mass scaling of cad fragment spectra

Abstract

Two calibration methods for fragment mass spectra, derived by means of collisionally-activated dissociation (CAD) in a tandem mass spectrometer, are discussed here. The instrument has variable dispersion and is equipped with an electro-optical, simultaneous-detection system. Without dispersion variation the masses of the fragment ions can be calculated by applying merely one calibration function. This function relates, at any value of the magnetic field of the mass analyzer, the momentum of a fragment to its position on the detector. The dispersion can be changed by means of an electrostatic quadrupole lens, behind the sector magnet, which acts upon the energy of the fragmentations. A calculation method is introduced here which opens the possibility of nominal mass scaling without a calibrant, even when the instrument is operated with varied dispersion. The method is based upon the representation of the ion-optical devices of the instrument by transfer matrices. Both of the mass-scaling procedures discussed here can be used for nominal mass assignment up to about m/z 1000. Attention has been given to the influence of the kinetic energy lost upon collision on the shifts of peaks in the CAD mass spectrum.