Cesium iodide, calibrant

Example Cesium iodide is frequently used for mass calibration in fast atom bombardment (FAB) mass spectrometry (Chap. 9) because it yields cluster ions of the general formula [Cs(CsI)n] in positive-ion and [I(CsI)J in negative-ion mode. For the [Cs(CsI)io] cluster ion, m/z 2730.9 is calculated instead of the correct value m/z 2731.00405 by using only one decimal place instead of the exact values Mi33Cs = 132.905447 and M1271 = 126.904468. T e error of 0.104 u is acceptable for LR work, but definitely not acceptable if accurate mass measurements have to be performed. 

Mass spectrometry. (+)Fast atom bombardment (FAB) mass spectrometry was carried out with a JEOL JMS-SX/SX102A mass spectrometer. Dried samples were dissolved in methanol-water, mixed with (thio-) glycerol, and applied to a direct insertion probe. During the high resolution FAB-MS measurements, a resolving power of 10,000 (10% valley definition) was used. Cesium iodide, glycerol, or polyethylene oxide (MWav = 600) was used to calibrate the mass spectrometer. 

Cesium iodide or cesium carbonate cluster ions were proposed [25-26]. A mixture of 2.5% cesium iodide in sodium iodide is recommended by Waters. The use of cluster ions of a variety of cesium salts for calibration up to m/z 10,000... 

S. Pleasance, P. Thibault, P.G. Sim, R.K. Boyd, Cesium iodide clusters as mass calibrants in ESI-MS, Rapid Commun. Mass Spectrom., 5 (1991) 307. 

Example Bombardment of cesium iodide or gold delivers cluster ion series which are useftil for mass calibration of the instrument over a wide range. Csl works equally well in positive- and negative-ion mode to yield [(CsI) Cs] and [(CsI) I] cluster ions, respectively (Fig. 10.5). Starting from n = 0, [(CsI) Cs] cluster ions have been observed up to m/z 90,000 [39]. Larger [(CsI) Cs] cluster ions dissociate to yield smaller ones [(CsI) Cs] [(CsI) Cs] + (Csl) [40]. 

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