Similarly, when the synthetic process is contaminated even momentarily with chlorine, the iodine monochloride being a stronger oxidant than iodine, oxidation products can be formed with molecular weights about 16 mass units higher than those for the authentic compound before oxidation. Sensitivity, in a mass spectra illustrating these higher oxidation products, is further enhanced by substances that tend to trap the targeted material and provide a protective buffer between the target and the stainless steel support:
When this material is further modified ostensibly by reduction, the higher mass ions (1068), associated with the authentic sulfenate-linked benzyl carbamate dimer when desorbed from a stainless steel target, completely disappear. Such gentle reduction with iodide in the mass spectrometer probably does not reduce the higher oxidation states such as sulfinates [R-S(=O)-O-R2] or sulfonates [R-S(=O)2-O-R2] or their respective sufinic and sulfonic acids:
However, it is quite likely that iodide can reduce any sulfenic acid groups in the matrix. Unfortunately, when iodide ions are made "acidic" as in these MALDI mass spectrometer analyses, iodide can readily oxidize to iodine. Under certain circumstances, such as extremes of pH, iodine then can easily oxidize sulfenic acid groups to higher oxidation states, a process conceivably catalyzed by metal ions that bind sulfur tightly. Thus, the very high molecular weight species desorbed from the stainless steel support with an "acidic" matrix readily disappear upon reduction (of the metal?) with iodide ions, but interpretation of these results is complicated by the oxidation of iodine under acidic conditions. Production of higher oxidation states for sulfur (than those observed for the authentic compound desorbing from the inert target support) are still possible under these mildly reductive conditions through an oxidation by iodine catalyzed by residual surface metal ions.
||WWW Links||Outline||e-mail us|