Direct drug screening and lipid profiling using ambient mass spectrometry
Mass spectrometry (MS) stands in an outstanding position in analysis of biological specimens owing to its abundant structural information, high accuracy, incomparable sensitivity, high speed, and the large variety of its applications. The ion source, an instrumental part for converting the analyte into ions, has played an important role in analyzing biological specimens by MS. However, the performance of conventional spray-based ionization methods always suffers from chemical interferences derived from complex biological matrices. A series of sample extraction, purification, and separation steps is required before the ionization, so as to ensure excellent performance of MS analysis. In order to simplify the MS procedure, ambient mass spectrometry (AMS) was developed, where the analyte can be directly sampled and ionized from complex biological matrices without or with minimal sample preparation. It is beneficial if the developed methods can be appropriately used in wide applications. At the same time, the simple procedure is complicated by declining qualitative and quantitative performance. The goal of the present research is to develop and improve spray-based AMS methods to meet real applications. Three problems need to be solved to meet with the aim: (1) How to collect and process the sample according to its physical and chemical characterizations. (2) How to effectively extract and ionize the target analyte with reduction of matrix effect. (3) How to produce sufficient and accurate structural and quantitative information on the mass spectrum. In this study, paper spray as a new spray-base AMS method has been used for two applications: (1) Direct drug abuse monitoring for forensic and therapeutic use and (2) Quick screening of antibiotics in food for the food safety. In addition to selecting proper paper substrates and solvents, the quantitative performance of paper spray has also been enhanced by treating the paper substrate with oxidation reagent. Moreover, pipette spray was developed as a very sensitive ionization cartridge by integrating the paper-based extraction function with the nano-ESI ion source for direct identification and quantitation of drugs in complex biofluids. Internal standards can be preloaded in accurately confined area on the paper substrate, so that excellent LOQ was achieved for analyzing antimicrobials in milk and abused drug in whole blood. Finally, to the best of the author’s knowledge, the isomeric structures of unsaturated lipids from tissue samples, were first directly determined with systematic structure profiles by the AMS, which was implemented by extraction spray and on-line Paternò-Büchi (PB) reaction. C=C double positions of target unsaturated lipids can be determined according to their unique fingerprint fragments derived from the PB reaction. The small sample consumption of the extraction spray also enables the profiling of spatial distributions of their isomeric ratios in tissues.
Ouyang, Purdue University.
Analytical chemistry|Biomedical engineering
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