Characterization and applications of paper spray ionization mass spectrometry

Abstract

A survey of literature indicates an increased interest in developing direct analysis of samples with minimum preparation. Paper spray ionization mass spectrometry (PSI/MS) was developed for this purpose over the last four years. More than 50 manuscripts have been published describing this technique but several aspects remain to be characterized and optimized. The overall objectives of this work are as follows: (i) to construct a lab-made PSI/MS set up and optimize parameters for the orientation of the paper substrate, (ii) to develop new achievement to understand the ionization mechanism, (iii) to understand the chemistry on the paper using different papers, (iv) to distinguish between solubility and micro-flow of the sample across PSI and liquid extraction surface analysis (LESA), (v) to demonstrate the potential of PSI as a metabolites fingerprinting technique (vi) to develop new approach for direct analysis of solid tissues without sample preparation, and (vii) to develop new achievement to understand the interaction between analyte and surface of the paper. Silica nanoparticles were used in this study. The orientation of the paper substrate and the optimal type of paper was determined. Interestingly, when the paper was dried in an oven to reduce a water content and non-polar solvents were used, the ionization was inhibited. When non-polar solvents were used on paper acclimatized to normal lab humidity, ionization was observed. These results indicate that residual water on the paper surface plays a role in the ionization mechanism. The results showed the hydrophilic properties of the paper leads PSI to be utilized as a separation/ionization technique at one-step. The sensitivity was compared over two instruments and two surface ionization techniques. The results showed better peak response in the MS/MS system. It was demonstrated that PSI has low accuracy to obtain a profile for complex samples such as saffron. Mechanical press extraction and paper substrate coated with silica nanoparticles were developed as potential improvements for the PSI method. Together, the data in this study demonstrate the potential of PSI as an alternative technique for direct analysis.