利用微電漿光譜技術檢測水溶液中重金屬離子之高壓電路模組開發

Abstract

本研究利用針尖至水溶液的常壓微電漿系統針對水溶液中的各種重金屬進行定性與定量的檢測。常壓微電漿系統擁有裝置體積小、微電漿能量密度高、需要的水溶液體積小以及無需昂貴的真空設備等優勢，提供了裝置可攜式的可能性。 本研究使用的電極為金屬針與銅膠帶，並定義金屬針為高壓端，銅膠帶上的小濾紙為低壓端。於小濾紙上滴上微量的待測水溶液後以電漿激發汽化放光，接著利用光纖與光譜儀收取光譜，最後利用光譜分析待測溶液中的重金屬成份。 本研究先以放大器輸出大功率高壓直流電作為驅動電漿之電源，研究其電漿電壓電流與鎮流電阻對於光譜上金屬特徵光強度的影響，並以實驗結果作為改良自製升壓模組系統檢測重金屬的能力的基礎。 自製升壓模組系統為直流至高壓直流的升壓模組，其中包含低頻與高頻震盪電路、電晶體、變壓器以及倍壓整流電路。透過震盪電路與電晶體可以將輸入之直流電轉為交流電，接著經由固定匝數比的變壓器轉為高壓交流電，最後再經由整流倍壓電路輸出高壓直流電。了解自製升壓模組運作原理，並結合放大器的實驗結果，本研究提出在倍壓電路下游並聯一大電容，使其在不改變輸入電源功率的條件下大大提升重金屬的偵測能力。最後加入IGBT控制電漿產生的時間以獲取更多具有代表性的實驗數據並且透過統計學的理論作為基礎，提出取樣數不同在定量分析上有很大的不同之處。 本研究利用上述研究成果提出未來的發展方向，將9 V直流供應器以9 V行動電源取代；市售光譜儀以手機式光譜儀或是樹梅派的CCD晶片取代；用於控制IGBT的任意波型產生器改用手機或是Arduino控制，最終達成實質上的可攜式重金屬檢測裝置。

This work presents a pin-to-solution type microplasma device which is used for analyzing the heavy metals in solution under atmospheric pressure. The atmospheric pressure microplasma devices have several advantages such as small in size, high energy density, requirement of small amount of sample, and doesn’t need any expensive vacuum equipment, which provides the possibilities for the microplasma devices become portable. The pin-to-solution type microplasma device used steel pin and copper sheet as its electrodes. A tiny piece of filter paper was laid onto the copper sheet and the solution sample was pipetted to the filter paper. The steel pin was defined as anode and the solution in the filter paper was defined as cathode. The microplasma was generated between the steel pin and the filter paper. The sample was vaporized by the microplasma and was analyzed by collecting the optical emission spectra with optical fiber and lens. In this work, the amplifier was first used to output a DC high voltage and was used as a power source for driving the microplasma. The relationship between plasma’s IV characteristic and the intensities of heavy metals on the spectra was investigated, and the results gave the ideas which were then used for improving the home-made high voltage circuit module. The home-made high voltage circuit module in this work was designed to convert DC voltage to DC high voltage, 9 V DC to 3 kV DC for example. The circuit module was composed of oscillating circuits, transistor, transformer and voltage multiplier circuit. First, the oscillating circuits and transistor converted the input DC voltage to AC voltage, and then AC voltage was boosted through the transformer. Second, the AC voltage was doubled and rectified with the voltage multiplier circuit, and finally, the high DC voltage was obtained. With the better understanding of how HV circuit module works and the relationship between plasma’s IV characteristic and the intensities of heavy metals, we found that adding a capacitor in parallel with the HV circuit module greatly increase the intensities of heavy metals on the spectra without changing the power capability. In addition, we added an IGBT to the circuit, which allows us to use a function generator to control the ignition timing of microplasma and acquire more experimental data. Finally, we used statistical theory as the basis to support that there was a big difference between N=1 and N=3 while doing the quantitative analysis. Furthermore, the experimental results were used to provide the future development direction. The 9 V DC can be provided by a 9 V portable power bank; the commercialized spectrometer can be replaced by smart-phone based spectrometer or the CCD module on Raspberry Pi, and the function generator which was used to control IGBT can be replaced by cellphone or Arduino. Finally, a portable device for detecting heavy metals in solution can be virtually achieved.