Examination of the best pressure range for ion/molecule reactions of anthraquinones in an external source ion trap mass spectrometer

This study outlines some observations of the pressure effect for gas phase ion-molecule reactions of anthraquinone derivatives with dimethyl ether in an external source ion trap mass spectrometer. At the reagent pressure of 7 .998 x 10(-2) Pa, formation of the protonated ions, [M + 13](+), [M + 15](), and [M + 45](+) ions, of anthraquinones can be observed. However, at the pressure of 1.066 x 10(-2) Pa, formation of molecular ions and many fragme nt ions of the M+. or [M + H](+) ions have been observed. Since the pressur e effect is notable within a small range of pressures for many compounds, i t is important to draw attention to the use of the ion trap with an externa l source where other factors such as ion source residence time may play a r ole. This can also provide some information for better and more careful con trols of the reagent pressure in order to obtain fair CI spectra in an exte rnal source ion trap mass spectrometer.