離子層析／化學放光偵測法對鉻物種與鐵物種之分析研究

Study of Determination of Chromium and Iron Species by Ion Chromatography with Chemiluminescence Detection

徐家駿(Chia-Chun Hsu)

指導教授 ： 葉華光

中原大學/理學院/化學系/碩士(2007年)

https://doi.org/10.6840/cycu200700279

摘要

在自然界鉻主要以鉻鐵礦[Fe(CrO2)2]的型式存在。工業上則以元素鉻、三氧化二鉻(Cr2O3)、三氧化鉻(CrO3)、鉻酸(H2CrO4)以及鉻酸鹽或重鉻酸鹽之用途最廣。鉻的用途隨著工業的發達及人類生活水準的提高而日益增加，相對地，鉻對環境污染的可能性也隨其用途的增加而加劇。
本研究主要是利用離子層析法結合化學放光法，進行三價鉻、六價鉻以及二價鐵在水中檢測分析。使用CS5A離子層析管柱先將三價以及六價鉻分離，放光試劑會藉由三價鉻的催化反應而放光，但六價鉻在此反應中不具有催化的能力，所以須將其還原成三價鉻才能偵測得到。
三價鉻以及六價鉻檢量線製備結果均在0.20到20 μg/L線性效果良好，方法偵測極限均為0.040 μg/L，準確度分別為98%及99%，精密度分別為0.70%及2.6%，均符合品保品管目標。
進行干擾測試時，添加Cr(Ⅲ)和Cr(Ⅵ)於Ni(Ⅱ)、Cu(Ⅱ)、Zn(Ⅱ)、Co(Ⅱ)、Mg(Ⅱ)、Ca(Ⅱ)、Fe(Ⅱ)及Fe(Ⅲ)金屬溶液中，當樣品中Fe(Ⅲ)濃度大於1 mg/L時，會降低檢測六價鉻訊號大小；而Fe(Ⅱ)的存在會把Cr(Ⅵ)還原成Cr(Ⅲ)。
檢測的真實樣品為近海沿岸海水、河川水以及地下水。三價鉻及六價鉻在近海沿岸海水中的平均回收率為100%及84%；在河川水中的平均回收率為96%及36%；在地下水中的平均回收率為102%及52%。不論在近海沿岸海水、河川水以及地下水實際樣品，三價鉻均有好的添加回收率；而六價鉻的添加回收則需視樣品中是否含有鐵離子的存在。
二價鐵檢量線製備結果在0.10到5.0 μg/L有良好線性關係，其方法偵測極限為0.0088 μg/L。
本實驗研究主要利用離子層析／化學放光系統偵測三價鉻、六價鉻以及二價鐵，與其他檢測方法相比較，有較高的靈敏度，分析時間較短，並且無須太繁瑣的前處理過程，可降低樣品污染的機率。此方法適合應用在低濃度的鉻物種分析檢測。

關鍵字

離子層析 ； 化學放光 ； 鐵 ； 鉻

並列摘要

Chromium exists in the nature principally as chromite (Fe(CrO2)2). Industries consume chromium in various forms including chromium metal, chromium (Ⅲ) oxide (Cr2O3), chromium (Ⅵ) oxide (CrO3), chromic acid (H2CrO4), and various chromates (CrO42-). Most of the chromium usage is by the steel industry for steel production and, accompanying the increasing need for steel, chromium pollution has dramatically over the years. Chromium exists in aqueous samples either as the trivalent (Cr3+) or hexavalent (CrO42- or Cr2O72-) form. Trivalent chromium is a natural essential element in our body, while the hexavalent form is considered toxic to humans.
The goals of this research is to develop a fast and economic method for chromium speciation in aqueous samples by simultaneous analysis of trivalent and hexavalent chromium ions with Ion Chromatography- Chemiluminescence Detection (IC-CLD).
The IC-CLD in this research involves the use of an IC mixbed column for separation of Cr(Ⅲ) and Cr(Ⅵ) ions before reducing the Cr(Ⅵ) ions to Cr(Ⅲ) after the column separation. The reason for reducing the hexavalent form to trivalent form is because hexavalent chromium does not possess catalytic activity for luminescing agent used in this study. 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, and thus more light is given off. The light given off is measured as a linear function of catalyst (Cr(Ⅲ)) concentration and this forms the basis of the CLD detection method.
From the method of calibration, the linear range of this method was found to be 0.20 to 20 μg/L, spanning across two orders of magnitude. The method detection limit (MDL) for both chromium species was found to be 0.040 μg/L. Accuracy measurements with another stock standard for Cr(Ⅲ) and Cr(Ⅵ) showed 98 and 99% accuracy, respectively, with RSD at 0.70 and 2.6%, respectively.
Interference study was done by placing the chromium species in solutions containing Ni(Ⅱ), Cu(Ⅱ), Zn(Ⅱ), Co(Ⅱ), Mg(Ⅱ), Ca(Ⅱ), Fe(Ⅱ)and Fe(Ⅲ). The results showed that iron is the only species that interferes with the chromium analysis. The Cr(Ⅵ) ion signal was found to decrease with concentration of Fe(Ⅲ) exceeding 1 mg/L, while the Cr(Ⅵ) signal totally disappeared with the presence of low (ppb) level of Fe(Ⅱ). This is most likely because Fe(Ⅱ) is a strong enough reducing agent to reduce Cr(Ⅵ) ions to Cr (Ⅲ) upon contact.
Real samples from coastal sea water, river water, and underground water were collected, acidified, and analyzed. The average recoveries for coastal sea water were 100 and 84% for Cr(Ⅲ) and Cr(Ⅵ), respectively, 96 and 36% for Cr (Ⅲ) and Cr (Ⅵ), respectively, for river water; and 102 and 52% for Cr (Ⅲ) and Cr(Ⅵ), respectively, for underground water. Cr(Ⅲ) had excellent recoveries for all water samples, while Cr(Ⅵ) recoveries tend to be affected by the presence of Fe(Ⅱ) in these real samples.
From the method of calibration, the linear range of this method was found to be 0.10 to 5.0 μg/L, spanning across two orders of magnitude. The method detection limit (MDL) for Fe(Ⅱ) species was found to be 0.0088 μg/L.
Based on the results of these experiments, it can be concluded that IC-CLD with luminol/hydrogen peroxide system is an viable technique for the simultaneous detection of Cr(Ⅲ) , Cr(Ⅵ) and Fe(Ⅱ) species. This method has high selectivity and requires little sample preparation, short analysis time, and inexpensive instrumentation to achieve low-level speciation of chromium.

並列關鍵字

Iron ； Ion Chromatography ； Chromium ； Chemiluminescence

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