以微電漿光譜法檢測水中重金屬之系統硬體優化與操作參數之研究

Abstract

電漿被稱為物質的第四態，其高能量與高反應性的特性被廣泛應用於各種領域，而當電漿與水溶液接觸或產生在水中時，則被稱為水溶液電漿，藉由電漿與水溶液間的化學反應產生許多高反應性物質，並利用這些高反應物質來達到材料合成、分析檢測等應用。本研究以白金電極為電路之正極，水溶液作為負極，並利用微型電腦與微型控制器結合作為控制系統，配合高壓電源製造脈衝式直流高壓以產生電漿，目標為開發一線上重金屬檢測平台，實現即時檢測多種重金屬。研究內容分為三個部分，分別為水對電漿光譜強度之影響、電極狀態之影響、操作參數之研究。 第一部分為水對電漿光譜強度之影響，由於水會吸收某範圍內之光強度，本研究藉由調控電極與光纖間距進行強度上的分析，以找出較合適之間距，並比較了不同間距下對於重金屬檢測的影響，發現縮短間距有助於鋅及鎳的檢測。此外，由於電漿於電極上方加熱後產生之氣泡內生成，故可藉由被吸收之光強度分析各條件下產生之氣泡大小，結果顯示當單一脈衝長度較短時，所生成之氣泡較小，而加大電壓則使氣泡較大。 第二部分為電極狀態之影響，為實現遠端檢測，我們必須確保長時間下能夠維持一定的檢測水準，故電極狀態之衰退成為了其中一個課題。我們研究了在不同脈衝條件下產生之電漿對於電極表面的損傷以及對於所得到之光譜的影響，發現較短脈衝長度會使電極表面周圍受損較為嚴重，且隨著電極狀態衰退，鉛之放光強度也隨之變弱。 第三部分為操作參數之研究，將此系統之電極尺寸、單一脈衝長度以及電壓進行調控，觀察其產生電漿時所伴隨之電訊號，並分析調控這些參數所產生之電漿對於銅、鎳、鉛與鋅四種重金屬所得到之光譜影響，期望能達到最佳之檢測效果，將檢測能力以偵測極限與線性程度作為指標進行比較。結果顯示鉛及鋅適合較大之電極尺寸與較低電壓，而銅及鎳適合較小之電極尺寸與較長單一脈衝長度。

Plasma is known as the fourth state of matter and is characterized by its high energy and reactivity, making it widely applicable in various fields. When plasma interacts with solutions, it is called plasma in solution. Through chemical reactions between plasma and the solution, numerous highly reactive species are produced, which are used for material synthesis and analytical detection applications. This study uses a platinum wire as the positive electrode and solution as the negative electrode, utilizing a microcomputer and microcontroller as a control system. Combined with a high voltage power supply, this system generates pulsed DC high voltage to ignite plasma. We aim to develop an online heavy metal detection platform for real-time detection of multiple heavy metals. This study consists of three parts: the effect of water on plasma spectral intensity, the impact of electrode conditions, and parametric studies. The first part is the effect of water on plasma spectral intensity. Since water absorbs light intensity within a certain range, this study analyzes the intensity by adjusting the distance between the electrodes and the optical fiber to find an optimal distance. It compares the effects of different distances on the detection of heavy metals and finds that shortening the distance helps in the detection of zinc and nickel. Additionally, because the plasma is generated within bubbles formed above the electrode after heating, the size of the bubbles can be analyzed by the absorbed light intensity under various conditions. The results show that shorter single pulse lengths produce smaller bubbles, while increasing the voltage results in larger bubbles. The second part is the impact of electrode conditions. For remote detection, it is important to maintain detection capability over a long time. Therefore, electrode decay is a significant issue. This study investigates the damage to the electrode surface caused by plasma under different pulsed conditions and its effect on the resulting spectra. The results show that shorter pulse lengths cause more severe damage to the area around the electrode surface, and as the electrode condition decays, the emission intensity of lead becomes weaker. The third part is the parametric studies. This system's electrode size, single pulse duration, and voltage are adjusted to observe the electrical signals during plasma generation. The influence of these parameters on the spectra of these four heavy metals: copper, nickel, lead and zinc is analyzed to achieve optimal detection results. Detection capability is compared based on detection limits and linearity. The results show that larger electrode sizes and lower voltages are suitable for lead and zinc, while smaller electrode sizes and longer single pulse lengths are suitable for copper and nickel.