Ion Dissociation in Tandem Mass Spectrometry

Although the MS-MS instrumentation is extensive, there is only one basic principle: the measurement of the mass-to-charge ratios of ions before and after dissociation in the reaction region. The change in mass of an ion carrying a single charge is the most commonly measured process and can be represented by the following equation:

Figure 5 (A) FAB-MS-MS collision induced dissociation product ion spectrum of the (M # H) # ion from a standard sample of paracetamol following ascending chromatography on diol bonded phase. Collision energy, 60-40 eV; collision gas, argon at an indicated pressure of 3.0x10~6 mbar. (B) FAB-MS-MS collision induced dissociation spectrum of the (M#H)# ion from paracetamol extracted from urine and following ascending chromatog-raphy on diol bonded phase. Collision energy, 60-40 eV; collision gas, argon at an indicated pressure of 3.0 x 10~6 mbar.

where Mp+ represents the precursor ion, Md+ represents the product ion and Mn represents the neutral fragment. The precursor ion may be the ion representing the relative mass of the species but need not necessarily be so; the precursor ion could be any ion formed within the mass spectrometer. However, molecular ions, and ions generated within the ion source, are the major subjects of MS-MS experiments. The product ion, Md+, represented in the above equation may be one of many fragment ions formed by simultaneous dissociation within the reaction region, and as such indicates a direct relationship between it and the precursor ion. The neutral fragment Mn, being uncharged, is not normally detected. However, since Mp+ and Md+ are measured the mass of the neutral fragment may be calculated by difference. These three variables form the basis of most MS-MS experiments and it is this basis that makes tandem mass spectrometry such a powerful analytical tool.

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Solar Panel Basics

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