Qualitative and quantitative characterization of a microencapsulated protein with pyrolysis-atmospheric pressure ionization mass spectrometry

Solid, microencapsulated protein as well as the microencapsulating species were investigated for their qualitative and semi-quantitative characterization. Quartz tube pyrolysis (Py) was used to process the solid sample and the selective and sensitive technique of atmospheric pressure ionization quadrupole mass spectrometry (API-MS) was chosen for the analysis. Selected protein and technical polymer standards provided a reference identification data set for the microencapsulated samples, and the standards data set was subjected to multivariate and graphical analysis procedures for semi-quantitative assessment of the microencapsulate components. API, however, is an ionization technique that produces nonlinear analyte responses when a mixture of compounds is present in the ion source as opposed to the technique of electron ionization. Concentration and proton affinity determine the relative distribution of compound mass spectral responses in API. The sample microencapsulate compounds were found to contain derivatives of polyhexose polymers as the encapsulating species, and poor semi-quantitative information was obtained for these microcapsule shell polymers. The Py-API technique, however, produced satisfactory semi-quantitative information for the core protein analyte of interest. Protein pyrolyzate products have relatively high proton affinities because of the saturated and unsaturated nitrogen functional groups as compared to the shell material which contains oxygen functional groups. Approximately 15% of the Py-API mass spectral response was attributed to complex proteinaceous substances, and was confirmed by independent experiments.