Alvarez M B, Malla M E, Batistoni D A
Departamento de Química e Ingeniería Química, Universidad Nacional del Sur, (8000) Bahía Blanca, Prov. de Buenos Aires, Argentina.
Fresenius J Anal Chem. 2001 Jan 1;369(1):81-90. doi: 10.1007/s002160000592.
Two existing sequential chemical extraction schemes, involving respectively five and six leaching steps with solutions of increasing dissolving power, were compared. The methods have been applied to surface sediment samples collected in a marine estuary zone potentially exposed to contamination arising from nearby industrial activities. A certified reference material (MURST-ISS-A1) consisting of an Antarctic bottom sediment for which no information regarding phase dependent concentration is available, was also analyzed. In order to evaluate the partition of metals among different geochemical forms, the concentrations of cadmium, chromium, lead and zinc were measured in the liquid extracts by Zeeman-corrected flame atomic absorption and by inductively coupled plasma-atomic emission spectrometry. The total metal concentrations were determined after strong acid attack, and the adequacy of this total digestion/dissolution technique was verified by its application to the reference material. Comparison of total metal concentrations with the sum of concentrations associated with the individual phases was employed to assess possible analyte losses or contaminations. Precisions for both sequential procedures were comparable, but some inconsistencies in mass balances were found in one of the samples for the distribution of Zn in the soluble/exchangeable fractions and for Cd in the bound to carbonates form. In addition, the six steps procedure produced lower concentration values in the case of elements associated to the residual fraction. For the five steps method mass balances showed acceptable agreement, with average recoveries in the 87 to 106% range. On the whole, differences in metal distributions were observed, being more marked for the bottom sediment. Significant proportions of the studied elements, with the exception of Cr, were found as easily extractable forms. X-ray diffraction and petrographic observation of the surface sediments allowed qualitative correlation between the leaching results obtained and the presence of defined geochemical phases.
比较了两种现有的连续化学萃取方案，分别涉及五个和六个浸出步骤，使用溶解能力逐渐增强的溶液。这些方法已应用于在一个可能受到附近工业活动污染的海洋河口区域采集的表层沉积物样本。还分析了一种由南极海底沉积物组成的有证标准物质（MURST - ISS - A1），对于该物质，没有关于相依赖浓度的信息。为了评估金属在不同地球化学形态之间的分配，通过塞曼校正火焰原子吸收光谱法和电感耦合等离子体原子发射光谱法测量了液体提取物中镉、铬、铅和锌的浓度。在强酸消解后测定了总金属浓度，并通过将该总消解/溶解技术应用于标准物质来验证其充分性。将总金属浓度与各相相关浓度之和进行比较，以评估可能的分析物损失或污染情况。两种连续程序的精密度相当，但在其中一个样品中，发现锌在可溶/可交换部分的分布以及镉在与碳酸盐结合形式中的分布存在一些质量平衡不一致的情况。此外，对于与残余部分相关的元素，六步程序产生的浓度值较低。对于五步方法，质量平衡显示出可接受的一致性，平均回收率在87%至106%范围内。总体而言，观察到了金属分布的差异，在底部沉积物中更为明显。除铬外，所研究元素的很大一部分以易于提取的形式存在。对表层沉积物进行的X射线衍射和岩相观察，使得获得的浸出结果与特定地球化学相的存在之间能够进行定性关联。
