CALIBRATION POINT FOR ELECTRON IONIZATION MS MS SPECTRA MEASURED WITHMULTIQUADRUPOLE MASS SPECTROMETERS

A protocol for establishing standard instrument conditions for measure ment of product ion MS/MS spectra from parent ions produced by electro n ionization is presented. Within this protocol, the ion at m/z 231 (C 5F9+) from perfluorokerosene or perfluorotributylamine is selected as the parent ion and subjected to collision-induced dissociation. The re lative intensities of product ions at m/z 69, 131, and 181 are monitor ed as a function of collision energy while keeping the target gas pres sure constant within the range of 10(-4)-10(-6) torr (measured), or a beam attenuation of approximately 30-70%. The collision energy at whic h the ion intensities for product ions at m/z 69 and 181 are equal is defined as the calibration point at that collision gas pressure; the i ntensity of the ion at m/z 131 is very close to this value as well. El ectron ionization MS/MS spectra taken at the calibration point using t wo different multiquadrupole instruments show good reproducibility for several test compounds. The high degree of similarity may aid in the establishment of a MS/MS spectral library.