Study On Determination Of Heavy Metals In Seawater Based On Flow Injection Micro Column Preconcentration And Separation-Atomic Absorption Spectrometry

The factors that low content, high background values and loss in sample treating have been the emerged problems in the heavy metal determination in seawater samples. Sample pretreatment, including separation and concentration, has enhanced the classical analytic method of atomic absorption spectrometry (AAS). Manual pretreatment is not only a long and hard work, but also a way to bring about a series of problems, Especially for the samples with complex matrix and low element contents. Flow injection analysis(FIA) has caused a revolutionary change in areas of automation, miniaturization and online from seawater sample pretreatment. It improves greatly the efficiency, reliability and rate of analysis, reduces sample contamination, and also decrease the amount of material consumption and wastewater discharge. Moreover, it makes some difficult or/even impossible manual operations very efficient and easily implemented. Therefore, with the project implementation, from a perspective of marine heavy metals pollution, State Standard Method of China and its existing problems, the applications of flow injection micro column preconcentration and separation coupling with AAS on-line concentration were discussed. At the same time, the new techniques of on-line preconcentration in recent years were discussed based on micro column system and filling materials, to provide a reference for further research. Amino Methylene Phosphonic Acid Resin (APAR) used in this study is a kind of chelating resins with unique advantages of easy preparation, long lasting life and excellent repeatability. The AAS, with the merits of low cost and fast analysis, high sensitivity, good precision and accuracy, and wide linear range, has been widely applied in trace analysis. The purpose of the present work is to establish a new marine industry standard to monitor copper, zinc, lead and cadmium in seawater. The main research contents are as follows:1. An analytical method for the determination of Pb(Ⅱ) in sea water based on micro-column pre-concentration coupled with flame atomic absorption spectrometry (FAAS) was established in this study. Pb(Ⅱ) was adsorbed on the micro-column packed with D412 chelating resin in medium of 0.2 mol·L^-1 ammonium acetate at pH value of 6 and could be eluted with 4mol·L^-1 nitric acid. The eluent was joined to the nebulizer of the atomic absorption spectrometer for on line determination of Pb. In case of 20mL sea water was injected in analysis, determination sensitivity for Pb(Ⅱ) is increased by about 35 times, with detection limit of 1.3μg·L^-1, relative standard deviation (RSD) of 1.2% (n = 11, C_Pb(Ⅱ) = 200μg·L^-1). Effect of concomitants on the Pb(Ⅱ) determination was discussed. The proposed method has been applied to the analysis of real samples taken from Hangzhou Bay.2. A flow injection separation and preconcentration system coupled to graphite furnace atomic absorption spectrometry (GFAAS) was used to determine the Cd (Ⅱ) in seawater samples. The micro column material was 412 chelating resin. The standard solution was prepared from 3.5% artificial simulated seawater. In experiments, a series of analysis conditions, including acidity, sample flow rate, eluant concentrations and coexisting ions were optimized respectively. Under the optimum conditions, in case of 3mL seawater was injected in the experimental system, the detection limit was 0.2×10^-3 ug·L^-1, the relative standard deviation was 2.86% (n=11, C_Cd(Ⅱ) = 4μg·L^-1). Effect of concomitants on the Cd(Ⅱ) determination was discussed. The proposed method has been applied to the analysis of real samples taken from Hangzhou Bay, the recovery is 94%.3. Surface seawater samples of Yangshan Port were collected in Jan, 2011. The contents of dissolved copper, zinc, lead and cadmium in seawater were determined by flow injection micro column preconcentration and separation coupled with FAAS and GFAAS respectively. The results were obtained as follows: (1) The mass concentrations of dissolved copper, zinc, lead and cadmium were 11.7μg·L^-1,18.81μg·L^-1,4.21μg·L^-1 and 0.91μg·L^-1, respectively. The contents of the above heavy metals have reached the national second-class water quality standards. (2)The relative standard deviation (RSD) of experimental results are less than 5%. The recoveries in between 91%⁹9%.