Abstract
Paper Spray Ionization (PSI) is commonly applied for the analysis of small molecules, including drugs, metabolites, and pesticides in biological fluids, due to its high versatility, simplicity, and low costs. In this study, a new setup called Solvent Assisted Paper Spray Ionization (SAPSI), able to increase data acquisition time, signal stability, and repeatability, is proposed to overcome common PSI drawbacks. The setup relies on an integrated solution to provide ionization potential and constant solvent flow to the paper tip. Specifically, the ion source was connected to the instrument fluidics along with the voltage supply systems, ensuring a close control over the ionization conditions. SAPSI was successfully applied for the analysis of different classes of biomolecules: amyloidogenic peptides, proteins, and N-glycans. The prolonged analysis time allowed real-time monitoring of processes taking places on the paper tip, such as amyloid peptides aggregation and disaggregation phenomena. The enhanced signal stability allowed to discriminate protein species characterized by different post translational modifications and adducts with electrophilic compounds, both in aqueous solutions and in biofluids, such as serum and cerebrospinal fluid, without any sample pretreatment. In the next future, application to clinical relevant modifications, could lead to the development of quick and cost-effective diagnostic tools.
Highlights
Since its development in 20107, Paper Spray Ionization (PSI) has been successfully applied for the analysis of drugs and metabolites in biofluids[9,11], forensics[12], and food safety[13]
We focused on the identification of post-translational modifications (PTMs) and covalent adducts with small molecules
Four types of commercially available paper were tested with regard to the ability of facilitating the ionization of the analytes: filter paper (Sigma-Aldrich, St.Louis, MO, USA), chromatographic paper grade 1, chromatographic paper 3MM CHR, and polydivinylidene fluoride (PVDF) membrane (GE Healtcare, Chicago, IL, USA)
Summary
Since its development in 20107, PSI has been successfully applied for the analysis of drugs and metabolites in biofluids[9,11], forensics[12], and food safety[13]. The proposed solution allows for the simultaneous and direct control of the applied voltage, solvent flow rate, and composition, extending the analysis time up to one hour. Under these conditions, real time monitoring of processes and reactions occurring on the paper can be performed. The detection of changes in the glycosylation pattern of proteins and in the relative abundance of specific protein species could be an intriguing field of application of PSI since these modifications are related to a large number of disorder[26,27,28] Analysis of biofluids such as serum and cerebrospinal fluid (CSF) was performed without including any pretreatment. The possibility of analyzing stable protein adducts can be a valuable tool to assess exposure to potentially mutagenic molecules[29] and could be used to build reliable and fast screening methods which would require only few microliters of blood
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