| Summary: | 碩士 === 國立交通大學 === 應用化學系所 === 92 === Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is widely used in the analysis of various types of analytes. In conventional MALDI-MS analysis, good co-crystallization of analyte/matrix is required, which mainly relied on the good solubility between the analytes and the MALDI matrix. MALDI matrices play the roles as the light absorber and the proton donor to assist the desorption/ionization of analytes during MADLI-MS analysis. However, the requirement of good co-crystallization of matrix/analyte always causes some difficulties during analysis. In this thesis, inorganic materials were alternatively used as the MALDI matrices for the analysis of peptide, proteins, and DNA to avoid the problems arising in the conventional MALDI-MS analysis.
Carbon nanotubes (CNTs) generated from using anodic aluminum oxide (AAO) as a reactive template were examined as the MALDI matrix because CNTs have good absorption capacity in the laser wavelength that used for the MALDI-MS analysis. Owing to high amounts of sodium and potassium ions presenting in the CNTs, sodium and potassium adducts of analytes dominated the CNT MALDI mass spectra, which resulted in high detection limits and poor mass resolution. The addition of a high concentration of citrate buffer to the MALDI sample preparation can effectively render the protonation of analytes and also effectively suppress the sodium and potassium adducts of analytes. The largest detectable mass is therefore extended to ca. 12,000 Da.
Additionally, citric acid treated CNTs were employed as affinity probes to selectively concentrate traces of positively charged analytes from sample solutions through electrostatic interactions. Because amphiprotic species, such as peptides and proteins, have unique isoelectric points (pI), by varying the values of pH of the sample solution, specific target proteins or peptides can be concentrated selectively on the surface of the citric acid-treated CNTs. Using this approach, low concentrations of protein enzymatic digest products can be concentrated and characterized by using CNT MALDI-MS analysis.
Sol–gel/diaminobenzoic acid (DABA) hybrid materials were also generated to be used as the MALDI matrices for the analysis of oligonucleotides. It is because that DABAs have good molar absorptivity at wavelength of 337 nm. Furthermore, two amino functional groups attached to the aromatic ring in DABAs can also suppress the cation adductions of oligonucleotides and leave the protons to the oligonucleotides during MALDI-MS analysis. This matrix system can be used as an alternative for the analysis of oligonucleotides.
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