Field ionization and field desorption spectra of a variety of organic tln compounds are reported. In contrast to the electron Impact spectra, In which only very low molecular Ion abundances are observed, the field ionization spectra are dominated by the molecular ion and show llttle If any fragmentatlon. The colllsional activation spectra of these fleld ionized molecules allow a rapid and unambiguous structure elucidatlon. Several examples are reported which demonstrate that the components of a mlxture of unknown composition can be ldentlfled unequivocally by using the comblnation of field ionization and collisional actlvatlon.Collisional activation (CA) spectra have been used extensively during the past 8 years in fundamental studies such as ion structure work ( I , 2). There is, however, a growing interest to explore the analytical potential of this method. Thus, it has been demonstrated that CA spectra of field ionized (3) or field desorbed (4-9) molecules give important structural information which is often not available from the field ionization (FI) and field desorption (FD) spectra alone. In addition we have demonstrated in 1974 that the CA technique can be used for a direct mixture analysis (3). For this purpose two-stage mass spectrometers such as double focusing instruments of reversed geometry (the magnetic sector precedes the electric sector) are of particular advantage. Here the ionized components of the mixture are mass selected and thus separated by the magnetic field before they undergo a highenergy collision with a neutral target gas. The resulting collision-induced fragments of each component are mass analyzed by using the electric sector. These collision-induced fragments reflect the structure of the unknown component of the mixture in much the same way as the electron impact spectrum of the pure sample does. A variety of applications of this technique using electron impact (EI) (10, 11), field ionization (3,12), or chemical ionization (CI) (13)(14)(15)(16)(17)(18)(19)(20) have been reported and reviewed (21,22).The most significant contributions to this field have been made by Cooks and co-workers (13-20) who used chemical ionization as primary ion source and were able to demonstrate that the analysis of unknown mixtures is possible with high sensitivity and little or no pretreatment of the sample.This and several subsequent papers will explore the analytical potential of a combination of field ionization or field desorption and collisional activation in more detail. Organic tin compounds have been chosen in this study as these compounds are produced industrially in large quantities, e.g., as fungicides, bactericides, and wood preservatives. As organic tin compounds are of medium toxicity, it is of interest to explore their ecological impact (23). Thus the availability of analytic techniques for their identification is of interest. EXPERIMENTAL SECTIONThe E1 spectra of the tin organic compounds were measured on a Varian MAT 44 S instrument (electron energy 70 eV, source temperature 250 "C). Th...
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