| Summary: | 碩士 === 臺灣大學 === 化學研究所 === 98 === Analyzing low-molecular organic acid by capillary electrophoresis usually adds cationic surfactant such as cetyltrimethylammonium bromide（CTAB）in the running buffer. Dynamic coating CTAB on capillary can reverse the EOF, thus reducing the analysis time and ensuring all analytes could be detected. However, CTAB will reduce the sensitivity of organic acid and pollute the ion source of the mass spectrometer seriously. This research uses liquid-junction/low-flow interface in combination with the PTFE connecting column to prevent the CTA(cetyltrimethylammonium) cation enter the ESI source as well as the signal suppression of the analyte. Under reversed polarity and CTAB dynamic coating, the EOF and the analyte with negative charge all moved toward the detection side. However, without the adding CTAB, the EOF and the analyte were moved in the opposite directions in the connecting column. Thus, we use PTFE tube to reduce the EOF to let the mobility of the analyte can be larger than that of the EOF. And the analyte can reach the detection side at the same time the CTA cation will be staied in the liquid junction because of its positive charge. The experimental results shown that while the concentration of the analyte is 50 ppm, the system with low-flow interface cannot detect the analyte, but the system with liquid-junction/low-flow interface in combination with the PTFE connecting column successfully detected all the analytes.
Moreover, CTAB can also be used in the peptide separation in capillary electrophoresis. Better separation efficiency of similar peptides was achieved under the conditions of micellar electrokinetic chromatography（MEKC）. So we added high concentration CTAB into the buffer to separate the tryptic-digested peptides of myoglobin by MEKC. The experimental results showed that even though the separation of peptides with similar m/z was improved by MEKC. However, there was still no significant benefit obtained in the separation of overall digested peptides of myoglobin.
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