Reduction in Liquid Secondary Ion Mass Spectrometry. Comparison of the Fission Fragment and Liquid Secondary Ion Mass Spectra of Organic Dyestuffs

Mass spectral characterization of the intact chromophore of organic dyestuffs, frequently prepared as salts, is relatively facile with desorption ionization. The mass spectra obtained, however, may show the presence of chemically altered forms of the chromophore. Comparison of the fission fragment (FF) and liquid secondary ion mass spectra (liquid SIMS) of a series of dyes reveals enhanced (C + 1)⁺ and (C + 2)⁺ Intensities in the liquid SIMS spectra of some of the materials examined. This enhancement appears to be related to reduction reactions occurring in the liquid matrix of the SIMS experiments which result in dye species weighing 1 and 2 amu more than the original chromophore. The absence of the liquid matrix in the FF experiments precludes such reactions, and hence the (C + 1)⁺ and (C + 2)⁺ intensities observed in the FF spectra are those calculated from the natural abundances of the ¹³C and ¹⁵N isotopes incorporated in the dye molecules. While the mechanism(s) by which reduction takes place have not been established, the role of the matrix may be in providing radical species that facilitate reduction.