Fast atom bombardment mass pressure problems

To achieve sufficient vapor pressure for El and Cl, a nonvolatile liquid will have to be heated strongly, but this heating may lead to its thermal degradation. If thermal instability is a problem, then inlet/ionization systems need to be considered, since these do not require prevolatilization of the sample before mass spectrometric analysis. This problem has led to the development of inlet/ionization systems that can operate at atmospheric pressure and ambient temperatures. Successive developments have led to the introduction of techniques such as fast-atom bombardment (FAB), fast-ion bombardment (FIB), dynamic FAB, thermospray, plasmaspray, electrospray, and APCI. Only the last two techniques are in common use. Further aspects of liquids in their role as solvents for samples are considered below. 

Mass Spectral Analysis of KAS Precursor. Fast atom bombardment (FAB) is the only technique that can be used for salts like the KAS precursor. FiAB requires that the sample be dispersed in a non-interactive matrix for analysis. Unfortunately, all three typical matrix materials, viz. TEA, p-nitrobenzylalcohol (NBA) and glycerol, interact/react with the sample. This problem was encountered during analysis of the spinel precursor (72). NBA was found to interact least with the spinel precursor and was used as the matrix in those studies (72). On this basis, an NBA matrix was used with the KAS precursor. EG can also be used as matrix but its high vapor pressure compared to other matrix materials, leads to much lower intensities for ion fragments. Results of FAB analyses done in both EG and NBA are shown in Table II. At the outset, nominal mass analysis by positive ion FAB were in accord with expectations. The molecular ion peak expected from the proposed precursor structure was seen, along with peaks resulting from interaction with the NBA matrix (Table II). 

---