微電漿光譜法應用於水溶液中重金屬之高速檢測平台之建立

Abstract

水溶液電漿與水的接觸產生許多的化學反應，使其廣泛應用於多個領域，近年來受到許多人的關注。本研究透過白金電極於水中產生電漿，並且利用微型電腦及微形控制器，操控脈衝模組產生高壓直流脈衝並同步光譜儀收光，建立線上重金屬檢測平台。本研究包含三個部分，分別為系統的建立、光譜與電性診斷、重金屬的定量分析。 第一部分為系統的建立，本研究測試兩種不同的開發板能產生之最短脈衝時間，並且結合兩種開發板之優勢，建立水溶液電漿的控制系統。水溶液電漿檢測系統中最重要的是電漿產生單元，本研究針對三種不同的光路設計，對電漿放光之收光系統進行優化，最後選用裸光纖徑向收光進行測試。 第二部分為光譜與電性診斷，利用系統光譜儀與高壓脈衝訊號同步的特性，針對電流波型與光譜之間的關係進行探討，水溶液電漿特徵電流波型分為兩部分，前半部分為氣泡產生時間，後半部分為電漿產生時間，其中在單一光譜多個高壓脈衝的條件下，越短的脈衝間隔時間，所受到前一個脈衝的熱歷史會越嚴重，從而使氣泡產生時間縮短，使電漿生成時間拉長，最終致使光譜訊號強度隨著脈衝間隔時間越短，而有越強的訊號。在低導電度下，電流波型於電漿產生時間中，會有如產生氣泡時的電流峰值，我們認為與氣泡脫離有關，致使在相同電壓下，導電度越低氣泡脫離的頻率則會越來越高，而光譜訊號強度則會越低，增加電壓可以使低導電於電漿產生時間的氣泡脫離頻率下降，因此於低導電度下，若要於電漿產生階段有穩定電漿產生，需要拉高電壓使氣膜或氣泡附著，從而使電漿光譜穩定且訊號增強。 第三部分則是利用不同導電度與不同濃度進行金屬鉛之線性回歸，透過兩種不同的定量方式進行線性度與偵測極限的比較，最後利用兩種未知導電度與金屬鉛濃度的水溶液，進行導電度與濃度的預測，並探討其差異原因。

The contact between aqueous solution and plasma generates numerous chemical reactions, leading to its extensive application in multiple fields. In recent years, it has attracted significant attention from many people. And this study aims to generate plasma under solution by using the high-voltage direct current pulse module which is synchronized with a spectrometer through a microcomputer and microcontroller. Finally, we establishing an online, continuous platform for heavy metal detection. This study consists of three parts: system establishment, spectroscopic and electrical diagnostics, and quantitative analysis of heavy metals. The first part involves system establishment. Two different single-chip microcomputer capable of generating the shortest pulse duration were tested in this study. The advantages of both boards were combined to establish a control system for plasma in liquid. The most critical component of heavy detection system is the plasma generation unit. This study optimized the light collection system for plasma emission by designing three different optical paths and finally selected bare optical fibers for radial light collection for testing. The second part focuses on spectroscopic and electrical diagnostics. By utilizing the synchronization feature between the spectrometer and high-voltage pulse module, the relationship between current waveforms and spectra was investigated. The characteristic current waveform of plasma in solution can be divided into two parts: bubble generation time in the first half and plasma generation time in the second half. Under the condition of multiple high-voltage pulses in a single spectrum, a shorter pulse interval leads to a more severe thermal history from the previous pulse, resulting in a shorter bubble generation time and a longer plasma generation time. Consequently, the spectral signal intensity becomes stronger as the pulse interval becomes shorter. Under low conductivity, the current waveform during plasma generation time exhibits a peak similar to when bubbles are generated. We believe this is related to bubble detachment. As the conductivity decreases under the same voltage, the frequency of bubble detachment increases, resulting in lower spectral signal intensity. Increasing the voltage can decrease the frequency of bubble detachment during the plasma generation time for low conductivity, thereby achieving stable plasma generation and enhancing the stability and signal intensity of plasma spectra. The third part involves linear regression of metallic element lead using different conductivities and concentrations. The linearity and detection limits were compared using two different quantitative methods. Finally, we predict two unknown aqueous solutions for conductivities and lead concentrations and results show that the prediction of conductivities and concentration is closed to the reality.