Accurate Mass Measurements in FAB

Example The positive-ion high-resolution (HR) FAB spectrum of a cationic fluorescent marker dye shows the signal of the analyte ion enclosed by a set of mass reference peaks due to the admixture of PEG 600 (Fig. 9.13). The elemental composition of the analyte can be assigned with good accuracy exp. m/z 663.3182, calc, w/z 663.3158 for [C37H42O4N4F3] exp. m/z 664.3189, calc. m/z 664.3186 for [ C C36H4204N4F3].  

Note Scanning of a magnet is affected by hysteresis. This causes the reproducibility of mass calibration to improve after several scan cycles have passed. For best results with dual-target probes, it is therefore recommended to skip the first few scans. 

---