微小化氬氣電漿放射光譜應用於氣相層析偵測器之開發

Abstract

本研究使用石英管及市售不鏽鋼管柱製作簡易電漿裝置，透過高壓交流電激發背景氣體氬氣產生電漿，配合光譜儀分析氬氣電漿的放射光譜，透過波長選擇、電壓條件最佳化、電極間距最佳化及載流氣體流速最佳化後，偵測CN分子碎片放光波長385-387 nm，調整電壓10.3 kV，電極間距0.57 mm，載流氣體流速3 mL/min。分析9個不同官能基之化合物，可以從結果推斷本研究所開發之偵測器適合偵測低沸點低極性的有機分子，各化合物的偵測下限約為30 pg，本研究亦透過改變載流氣體純度及改變載流氣體的組成探討電漿內的氮原子來源，當氬氣純度從99.99%提升至99.9995%，層析圖訊號面積下降約8%、訊號高度下降約14%，表示載流氣體可能為氮原子的來源之一，但並非主要來源。透過在電漿裝置內混入氧氣及氫氣的實驗結果中，混入氧氣後氮原子會和氧氣反應，致使有機分子主要以氫原子放光為主，大幅降低了偵測器感度，而從混入不同百分比的氫氣後，可以看出氫氣會和氮原子反應而消耗氮原子，致使CN放光減弱，間接證明了本研究所偵測的波長為CN放光。 本研究成功研發出新型電漿氣體偵測器，兼具裝置微小、成本低廉、可重複使用、壽命長及高靈敏度等優點，期許未來能應用於微小化氣相層析系統。In this study, we develop a micro plasma sensor using quartz tube and commercial alloy column. Alloy column served as electrodes and gas inlet / outlet. Take advantage of spectroscope, we can analysis argon micro plasma emission spectroscopy for the detection of the volatile organic compounds. We selected wavelength in 385-387 nm which is CN emission, applied voltage was set to 10.3 kV, electrode gap was 0.57 mm, the carrier gas flow rate was 3 mL/min after optimization. We analyzed 9 different kinds of functional group compounds, the sensor exhibited higher sensitivity in low boiling point and polarity compounds. The lower limit of detection of those 9 different compounds was about 30 pg and the linear dynamic range of calibration curve was 2 orders (1-100 ng). We also switch the argon gas from 99.99% to 99.9995% in order to find out the source of the nitrogen atom. The peak area and height were only reduced 8% and 14%, respectively. The result demonstrated that the impurity of argon gas may be the one of possible nitrogen sources, but not the major one. The experiment with modifying the composition of background gas, we added up 10% of oxygen gas and 0.5-10% of hydrogen gas. The result indicated that the carbon containing species transform into CN in plasma system indirectly. We construct a micro argon plasma detector which is low cost and long lifetime. With appropriate improvement it can be applied for micro gas chromatograph system.