Summary and Conclusions

Presented in this chapter are results demonstrating the utility of metal cationization in EESI for the on-line sampling and ionization of compounds in an aerosol. EESI is

described in detail and practical aspects of EESI operation are discussed. Protonation of sugars, which is currently not efficient enough to detect using ESI, were demonstrated using EESI with an acid additive. One of the primary benefits to an electrospray-based ionization method is the ability to choose the electrospray solvent for the best extraction of an analyte of interest or to improve ionization using an additive such as a metal cation. The efficacy of using metal cationization to improve analyses of levoglucosan and glucose was evaluated and resulted in improved signal intensity and improved MS/MS dissociation for glucose. The results from dissociation of levoglucosan are obscured by a contaminant present when using acetic acid as a solvent additive for EESI.

Figure 3.11. High resolution mass spectra of the solvent blanks containing both formic acid and acetic acid as an additive.

Metal cationization in EESI was also demonstrated for the analysis of the pyrolysis products of ethyl cellulose. Results suggest that extra care must be taken to prepare

solutions in non-glass containers to avoid sodium contamination. Previous results for EESI of the pyrolysis products of ethyl cellulose were likely contaminated with sodium and the peaks observed were sodiated rather than protonated as assumed.

In the search for the identity of the contaminant at m/z 163 that obscured the dissociation data presented in Section 3.2, it was shown that the contaminant was present in solvents with acetic acid as an additive and not present in solvents with formic acid as an additive based upon MS/MS studies. The water reactivity of the structures present at m/z 163 were assessed using an ion-molecule reaction in a quadrupole ion trap. Ions of interest were isolated in the trap and allowed to adduct to water for 10 seconds before mass

analysis. These results showed that the contaminant present in acetic acid was very reactive with water while protonated levoglucosan is barely reactive with water.

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