Research On Ionic Liquid-based New Materials And Methods For The Trace Analysis Of Heavy Metal Lead

Lead is an accumulative toxicant heavy metal element. It is of great importance to determine lead in various environmental samples accurately and rapidly.Due to its low content in samples and the complex of matrix, it is usually necessary to carry out preconcentration and separation precedure for lead prior to its instrumental analysis.Liquid-liquid extraction (LLE) is an effective separation method. However, the extraction solvents used in LLE are usually of high volatility and toxicity. Consequently, it is necessary to develop alternatives to common organic extractants. Room temperature ionic liquids have negligible vapor pressure, high thermal stability and good dissolve capacity for organic and inorganic compounds, which are widely accepted as green solvents.Solid phase extraction (SPE) is a comparatively new sample preparation technique, which is a combination of liquid-solid extraction and liquid chromatography. It is estimated that about half of the environmental samples analyzed were pretreated with SPE. However, the materials for SPE in China are mainly imported.In this paper, a new type of ionic liquid----1,3-di(n-butyl)imidazolium hexafluorophosphate ([DnBIM][PF6]) was synthesized and characterized, then used as liquid-liquid extractant to enrich the trace lead in water. Furthermore silica gel was modified using [DnBIM][PF6], thus a novel material for solid phase extraction was preparated, which was used in the enrichment and separation of trace lead in aqueous samples, and followed by the determination of trace lead with cheap and rapid flame atomic absorption spectrometry (FAAS). The major contents are described as follows:Chapter 1:Summarized the main analysis methods of the lead, introduced the characteristics of ionic liquid,liquid-liquid extraction and solid-phase extraction theoretical foundation and the application in environmental analysis.Chapter 2:The intermediate ([DnBIM][Br]) was synthesized from trimethylsilyl imidazole and 1-Bro mo butane under microwave radiation, the yield can reach 92% or more at this step. Then 1,3-di(n-butyl)imidazolium hexafluorophosphate ([DnBIM][PF6]) was prepared using ([DnBIM][Br]) and KPF6 by anion exchange. At this step, the yield is 68%.Compared with traditional methods, the reaction time required was greatly reduced. The structure of the synthesized product was confirmed by FT-IR,1HNMR and 13CNMR, elemental analysis and the purity of the product was determined to be above 96.0% using high performance liquid chromatography.Chapter 3:The trace lead in water was enriched by the new symmetry 1,3-di(n-butyl)imidazolium hexafluorophosphate([DnBIM][PF6]) ionic liquid, then determined by FAAS. Dithizone as used as the chelant to make lead transfer to ionic liquid phase, then use the nitric acid to back extract lead. The result showed that the recovery of lead was 99%, the enrichment factor was 100, the limit of detection (LOD) was the 0.02μg/L, and the relative standard deviation (RSD) was 2.6%.Chapter 4:A new material for SPE was prepared, which was a chemically modified silica gel using ionic liquid [DnBIM][PF6]. The ionic liquid was fixed on the surface of silica gel, which can greatly reduce the loss of ionic liquid during extraction. Firstly, alkyl of epoxy silicone was synthesized with silica gel (as a carrier), and KH-550 (as silane coupling agent), and then ionic liquid silica gel was prepared with 1,3-di(n-butyl)imidazolium hexafluorophosphate. The synthetic product was identified by infrared spectroscopy and thermal analysis, and its adsorption characteristics for lead chelate wer evaluated.Chapter 5:A novel determination method for trace lead was proposed, using ionic liquid modified silica gel for solid phase extraction combined with flame atomic absorption spectrometry. The effects of sample pH, sample volume, flow rate, eluent type, concentration, volume, velocity and coexisting ions, were studied. The analytical performance of the method was evaluated. Under the optimized conditions and using 100mL sample solution, the limit of detection (LOD) was 0.036μg/L, the relative standard deviation (RSD) was 3.5%, and the enrichment factor was 50. The method was successfully applied to the determination of trace lead in tap water, beer, beverages and with satisfactory results.