厌氧环境下邻菲罗啉分光光度法测定纤维水镁石中Fe(II)与Fe(III)

纤维水镁石中同时存在有不同价态的Fe即Fe(II)与Fe(III),这对开展水镁石相关研究具有重要意义。而不同价态Fe含量测定过程中存在Fe(II)在空气中易氧化成Fe(III)而导致测定不准确的问题。针对该问题,实验采用厌氧培养箱作为操作环境,对纤维水镁石的处理均在厌氧条件下进行。利用邻菲罗啉与经盐酸羟胺还原产生的总Fe(II)显色反应原理测定纤维水镁石中的总Fe,之后测定过程中不加盐酸羟胺与邻菲罗啉反应测定溶液中的Fe(II),利用总Fe与Fe(II)的差值测定Fe(III),从而实现了邻菲罗啉分光光度法对纤维水镁石中Fe(II)与Fe(III) 的准确测定。试验发现在波长为510nm,显色体系pH值为2~5,显色时间为10min条件下,Fe(II)质量浓度在0.02~5.0mg/L范围内与其吸光度符合比尔定律,校准曲线的相关系数为0.9999。采用实验方法对两个纤维水镁石样品分别进行6次平行测定,结果显示总Fe、Fe(II)及Fe(III)的相对标准偏差(RSD,n=6)均小于1%。采用电感耦合等离子体原子发射光谱法(ICP-AES)进行全Fe测定结果对照,结果表明两种方法的测定结果保持一致。

Determination of Fe(II) and Fe(III) in fiber brucite by phenanthroline spectrophotometry under anaerobic condition

Fe(II) and Fe(III) coexists in fiber brucite, which has important significance to the study of brucite. During the determination of iron content with various valence states, Fe(II) is easily oxidized to Fe(III) in air, leading to the poor accuracy. Aiming at this problem, the anaerobic incubator was employed for the treatment of fibrous brucite under anaerobic conditions. Fe(III) was firstly reduced to Fe(II) using hydroxylamine hydrochloride, and total Fe in fiber brucite was then determined based on the coloring reaction between phenanthroline and Fe(II). Meanwhile, the content of Fe(II) in solution without addition of hydroxylamine hydrochloride was also determined by phenanthroline spectrophotometry. The difference between total Fe and Fe(II) was the content of Fe(III). Thus the accurate determination of Fe(II) and Fe(III) in fiber brucite by phenanthroline spectrophotometry was realized. It was found that Beer′s law was obeyed for absorbance and mass concentration of Fe(II) in range of 0.02-5.0mg/L under the following experimental conditions: the wavelength was 510nm, the pH of coloring system was 2-5, and the coloring time was 10min. The correlation coefficient of calibration curve was 0.9999. Two fibrous brucite samples were determined according to the experimental method, and the standard deviations (RSD, n=6) of total Fe, Fe(II) and Fe(III) were all less than 1%. The content of total Fe was also determined by inductively coupled plasma atomic emission spectrometry (ICP-AES), and the found results were consistent with those obtained by experimental method