摘要
随着科学技术的发展,在进行复杂样品的分析时,常常需要测定痕量甚至超痕量元素,分析对象也日益复杂多样,要求分析方法快速、简单、重现性好。虽然现代仪器分析方法的检出限越来越低,但要直接分析这些组分的含量也往往遇到困难,这是因为,一方面存在基体干扰,或缺乏相应的校正标准和试剂,另一方面样品本身的物理化学状态有的不适合直接测定,或分析方法对含量极低的组分灵敏度不够。因此必须借助各种有效的分离富集技术,以提高分析方法的选择性和灵敏度。
分散液液微萃取(DLLME)是在液相微萃取的基础上发展起来的一种新型样品前处理技术,该方法使用微量萃取剂,并通过分散剂使萃取剂以微滴形式均匀分散在溶液中形成乳浊液,增大了萃取剂和样品溶液的接触面积,使目标分析物快速地萃取到萃取剂微滴中,然后通过离心使分散在溶液中的萃取剂沉积到试管底部,由于萃取剂用量很少而且与目标分析物接触面积大,所以可以达到很高的富集倍数和萃取效率。该方法集采样、萃取和浓缩于一体,具有操作简单、快速、环境友好、成本低、富集倍数大、回收率高等优点,在痕量分析领域具有广阔的应用前景。
由于石墨炉原子吸收光谱(GFAAS)进样量少、分析迅速,将DLLME与GFAAS联用可以大大降低方法的检出限。本论文的目的是,将DLLME与GFAAS联用建立痕量元素分析的新方法,并将其应用于实际样品中痕量元素的分析检测。主要内容概括如下:
(1)以CCl_4为萃取剂,DDTC(二乙基二硫代氨基甲酸钠)为络合剂,乙醇为分散剂,对影响钯的分散液液微萃取效率的各种因素进行了优化,确定最佳萃取条件,并将其与GFAAS联用进行了环境水样中痕量钯的分离测定。
(2)以GFAAS为检测手段,CCl_4为萃取剂,APDC(吡咯烷二硫代氨基甲酸铵)为络合剂,甲醇为分散剂,对影响砷的分散液液微萃取效率的各种因素进行了优化,选择最佳萃取条件,建立了一种环境水样中痕量砷的检测新方法。
(3)以DDTC为络合剂,CCl_4为萃取剂,甲醇为分散剂,根据DDTC与银的络合性能比其与铜的强,运用置换分散液液微萃取的方法实现对银的分离测定,并对影响银的萃取效率的各种因素进行优化,确定最佳萃取条件,与GFAAS联用建立了一种痕量银的分析新方法。
Rapid, sensitive, simple, accurate and reproducible analytical methods are required for the determination of trace elements in environmental, geological and biological samples. The direct determination of extremely low concentrations of trace elements by modern atomic spectroscopic methods, such as inductively coupled plasma atomic emission spectrometry ( ICP-AES ) and atomic absorption spectrometry ( AAS ) is often difficult. The limitations are associated not only with the insufficient sensitivity of these techniques but also with matrix interference. For this reason, the separation and preconcentration of trace elements is often required.
Dispersive liquid-liquid microextraction (DLLME) is a novel method of preconcentration, which is based on a ternary component solvent system like homogeneous liquid-liquid extraction ( HLLE ) and cloud point extraction ( CPE ). In this method, the appropriate mixture of extraction solvent and dispersive solvent is injected into an aqueous sample rapidly by syringe, and a cloudy solution is formed. The analyte in the sample is extracted into the fine droplets of extraction solvent quickly. After extraction, phase separation is performed by centrifugation, and the enriched analyte in the sediment phase is determined by chromatography or spectrometry methods. The advantages of the DLLME method are simplicity of operation, rapidity, low cost, high enrichment factor and low consumption of organic solvent .This method has been successfully applied in the analysis of environmental samples.
Graphite furnace atomic absorption spectrometry ( GFAAS ) is usually selected due to less injection and rapidity in the determination of trace elements. DLLME coupled with GFAAS can improve the limit of detection. The aim of this dissertation is to systematically study on the DLLME and its application to the preconcentration of trace elements. The major contents are described as follows:
1. A new method for the determination of trace palladium was developed by DLLME preconcentration and GFAAS detection. In the proposed approach, diethyldithiocarbamate ( DDTC ) was used as a chelating agent, and carbon tetrachloride and ethanol was selected as extraction and dispersive solvent, respectively. Some factors influencing the extraction efficiency of palladium and its subsequent determination, including extraction and dispersive solvent type and volume, pH of sample solution, concentration of the chelating agent and extraction time, were studied and optimized. The proposed method was applied to the determination of trace palladium in water samples with satisfactory results.
2. DLLME was successfully used as a sample preparation method for the determination of trace arsenic with GFAAS. In this extraction method, ammonium pyrrolidine dithiocarbamate ( APDC ) was used as chelating agent, and carbon tetrachloride and methanol was selected as extraction and dispersive solvent, respectively. Some factors influencing the microextraction efficiency of arsenic and its subsequent determination, such as pH of sample solution, the type of extraction and dispersive solvent and their volume, concentration of the chelating agent, the time of extraction were studied, and the optimized experimental conditions were established. The proposed method was applied to the determination of trace arsenic in water samples with satisfactory results.
3. A novel displacement dispersive liquid-liquid microextraction approach was developed for the selective determination of trace silver in water samples by GFAAS. In this extraction method, DDTC was used as a chelating agent, and carbon tetrachloride and methanol was used as extraction and dispersive solvent, respectively. Some factors influencing the microextraction efficiency of silver, such as solution acidity, concentration of the chelating agent and Cu~(2+), the volume of dispersive solvent were studied, and the optimized experimental conditions were established. The proposed method was successfully applied to the determination of trace silver in water samples with satisfactory results.
引文
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