- 學位論文
以離子層析／化學放光偵測法 對砷物種之檢測
A Study of Determination of Arsenic Species by Ion Chromatography with Chemiluminescence Detection
摘要
砷是大自然中常見的一種元素，普遍被視為一種類金屬，常以砷 酸鹽類的型態存在於自然界中，常見的氧化態為+3、+5、-3。隨著人 類生活水準的提高，砷酸鹽類的使用量日益增加，而砷對環境的汙染 也隨著用途的增加，而不容再忽視。 本研究主要以魯米諾-過氧化氫為反應基礎，並利用離子層析法 結合化學放光法以及流動注射法，進行水中的三價砷以及五價砷檢 測。放光試劑會藉由三價砷的催化反應而放光，但五價砷在此反應中 並不具有催化的能力，所以必須先將其還原成三價砷才能進行分析偵 測。 由於五價砷難以在系統內快速地進行還原反應，故五價砷採取在 系統外進行離線還原反應，結果顯示在室溫下進行五分鐘的反應便可 得到95％以上的還原率。 在飲用水、井水、池水的實際樣品的檢測分析上，可以發現As(III) 之良好的添加回收率，介於80~100%之間，且在總砷的檢測上，經過 還原步驟處理之後，皆有不錯的添加回收率，且證明還原方式之可行 性。 三價砷的檢量線結果均在250～5000μg/L 的範圍內線性效果良 好，三價砷的方法偵測極限則為46 μg/L。 本研究所研發之離子層析/化學放光系統可以偵測到三價砷並分 離可能影響分析物之干擾物，而且有相當好的靈敏度，分析時間較 短，且相對的便宜，以及無須太繁瑣的前處理過程，可大大降低樣品 污染的機率。此方法適合應用在低濃度的砷物種分析檢測。
並列摘要
Arsenic is an element found in the nature and commonly known as a metalloid element. Its common form in the nature is salts with oxidation states of +3, +5, and -3. Despite its toxicity, arsenic is an essential element in our body, whereas in the environment, arsenic is considered a toxic metal and its presence, especially in drinking water, is closely monitored via methods such as inductively-coupled plasma—mass spectrometry detection (ICP-MSD) or atomic absorption spectroscopy (AAS) with hydride generation detection. The goal of this research is to develop a fast and economic method for arsenic speciation in aqueous samples by analysis of As(III) ion with ion chromatography-chemiluminescence detection (IC-CLD). The IC-CLD method in this research uses an IC column for separation of As(Ⅲ) ion with some interferences. The CLD system used in this research is luminol/hydrogen peroxide. At the absence of a catalyst, the luminol/hydrogen peroxide system undergoes a slow luminol oxidation reaction; the presence of a catalyst accelerates the oxidation reaction, thus more light is given off. The light given off is measured as a linear function of catalyst (As(Ⅲ)) concentration and this forms the basis of the CLD detection method. Because As(V) ions cannot be detected by the CLD system, arsenate ion has to be pre-reduced to As(III) for the determination of total arsenic concentration, and the As(V) concentration is calculated by taking the difference between the total arsenic and the As(III) concentrations. On-line post-column reduction is impractical due to the slow reduction reaction, hence off-line reduction method was adopted instead. The reduction efficiency under room temperature for as little as five minutes is at least 95%. From the method of calibration, the linear range of this method is found to be 250 to 5000 μg/L, which spans across two orders of magnitude. The method detection limit (MDL) for As(III) is found to be 46 μg/L. Based on the results of these experiments, it can be concluded that IC-CLD with luminol/hydrogen peroxide system and an off-line reduction of As(V) to As(III) is an viable technique for the speciation of arsenic. This method has high selectivity and requires little sample preparation, short analysis time, and inexpensive instrumentation to achieve low-level arsenic speciation.