| Popis: |
When nitrous oxide is added to nitrogen carrier gas, certain compounds can be detected with much greater sensitivity than is normally possible. This selective sensitization can be attributed to ion-molecule reactions between analytes being eluted and O− and NO− generated in situ in electron-capture detectors when the carrier gas contains nitrous oxide. The enhancement of response for various compounds by selective electron-capture sensitization (SECS) using nitrous oxide-doped nitrogen carrier gas has been observed for methane, ethane, n-propane, n-butane, n-pentane, n-hexane, benzene, ethanol, methylisobutylketone, hydrogen and carbon dioxide. With SECS, it becomes possible to detect picogram levels of several hydrocarbons with electron-capture detectors. For carbon dioxide the response is sensitized by a factor of 5000 in the presence of nitrous oxide; for methane the peaks are about 10 times larger; and for hydrogen the enhancement is about 40-fold greater than in the absence of nitrous oxide. Examination of the degree of sensitization (or desensitization, in the case of chlorofluorocarbons) may be useful as an indication of the identity of unknown peaks in a chromatogram if identical samples are detected in the presence and absence of a sensitizing gas such as nitrous oxide. Detector stability is not adversely affected by injection of microliter volumes of solvents. SECS has been used to detect hydrogen and methane at the 1-ppm level in samples of ambient air and human breath. |
