CONTINUOUS-FLOW FAST-ATOM-BOMBARDMENT MASS-SPECTROMETRY - A CONCEPT TO IMPROVE THE SENSITIVITY

For application of continuous-flow fast atom bombardment (CFFAB), an ion source for a sector field mass spectrometer was designed which gives improved sensitivity and much better long-term stability than a source with standard ion optics. The optics are based on two sets of static quadrupoles and a conical ion extraction device. It was shown that the gain in sensitivity has to be assigned mainly to the reduction of the chemical background in the CFFAB mass spectra. The reason for this reduction appears to be the exclusion of matrix fragment ions sputtered from the outer parts of the FAB target, whereas the center is continuously refreshed by the liquid emerging the capillary. The benefits of using this source were demonstrated in the course of the determination of the drug ifosfamide to a level of 1.5 ng cm-3 using selected ion recording and in the analysis of a Gramicidin S sample, where a minor component at a level of approximately 1 pmol was detected.