| Room temperature ionic liquids(RTILs),presenting unique physical and chemistry properties,have aroused increasing interest for their promising role as alternative medium in synthesis,electrochemistry and analytical chemistry.Recently,the applications of ionic liquids in the extraction of metal ions have also started to draw attention.Because of its extremely low concentration or complicated matrices in environmental and biological samples,the separation and preconcentration methods are required and recommended before detection.For the modern sample preparation technology,the trend on the sample pre-treatment is to reduce the usage of solvents and miniaturization.Therefore,a newly developed pre-treatment technology must be fast,effective and simple.As a new and important part of RTILs,task-specific ionic liquids(TSILs) are designed by varying the structure of an IL(especially the side chain of its cation) to have specific properties.They have higher selectivity and practicality than the conventional ionic liquids.Task-specific ionic liquids can be used for the supports of organic synthesis, catalysis,ion conductive materials,separation of specific metal ions from aqueous solutions and so on.In the analytical field,they are mainly used for the separation of the organic compounds,metal ions and CO2 from gas streams.Recently,most of TSILs for extraction applications described in literature are based on imidazolium-,piperidinium-, pyrrolidinium- and pyridinium cations and fluorine containing anions,whereas diverse functional groups are generally appended to the cation.There are few reports about the anion-specific ionic liquids for the extraction of metal ions.In this article,a series of hydrophobic ionic liquids,such as 1-alkyl-3-methylimidazolium hexafluorophosphate([C,mim][PF6]),1-butyl-3-methylimidazolium diethyldithiocarbamate and 1-butyl-3-methylimidazolium ethyl xanthate,were synthesized based on the N-methylimidazole.Moreover,the separation and preconcentration of the trace metal ions were analyzed with these ionic liquids as the extraction solvents.The major contents are described as follows:1.Direct Determination of Cadmium and Lead in 1-butyl-3-methylimidazoliumHexafluorophosphate by Graphite Furnace Atomic Absorption Spectrometry The ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate(BMIMPF6), was synthesized based on the N-methylimidazole,and characterized by the FTIR spectra. The effect of BMIMPF6 on the determination of cadmium and lead by graphite furnace atomic absorption spectrometry(GFAAS) has been studied.Several acids such as phosphoric acid,hydrochloric acid,hydrogen peroxide and nitric acid were used as potential chemical modifiers.According to the results,HNO3 is feasible as a matrix modifier for the direct determination of cadmium and lead in 10%(v/v) BMIMPF6 by GFAAS.It suggested that both the aqueous standard and ionic liquid standard methods could be used for the calibration of Cd and Pb in ionic liquid samples.The direct determination of Cd and Pb in the water samples was well performed by the proposed method.Compared to the nondirective methods,the proposed method offers the advantages of rapidity,sensitivity and simplicity.2.Ionic liquid-based ultrasound-assisted dispersive liquid-liquid microextraction combined with graphite furnace atomic absorption spectrometry for sensitive determination of cadmium in water samplesA new method was developed for the determination of cadmium in water samples using ionic liquid-based ultrasound-assisted dispersive liquid-liquid microextraction (IL-based USA-DLLME) followed by graphite furnace atomic absorption spectrometry (GFAAS).The ionic liquid of 1-hexyl-3-methylimidazolium hexafluorophosphate (HMIMPF6) was used as the extraction solvent.Some effective parameters on complex formation and microextraction,such as the concentration of NaDDTC,pH,volume of extraction solvent,extraction time,salt effect and the coexisting ions have been optimized. Under optimal conditions,high extraction efficiency and selectivity were reached for the extraction of 1.0 ng of cadmium in 10.0 mL of water solution employing 73μL HMIMPF6 as extraction solvent.The optimal conditions were pH=5.0～6.0,NaDDTC (0.05%,m/v) and extraction time＞2 min.The linear range of the method was 20～150 ng L-1 Cd.The detection limit was 7.4 ng L-1 and the characteristic mass(Mc,0.0044 absorption) of the proposed method was 0.018 pg for Cd.The relative standard deviation (RSD) for eleven replicates of 50 ng L-1 Cd was 3.27%.The enrichment factor of the method is 67.The proposed method was successfully applied to the determination of trace cadmium in environmental water samples.In order to validate the method,the developed method was applied to the determination of cadmium in the Environmental Water Reference Material GSBZ 50009-88(200921) and tea standard reference material GBW-10016(GSB-7),and the results obtained were in good agreement with the certified value.This method was free of volatile organic solvent by using the ionic liquid as the green extraction solvent and offers the advantages of simplicity,rapidity and sensitivity.3.The synthesis and extraction application of two new anion-specific ionic liquidsTwo new hydrophobic anion-specific ionic liquids,1-butyl-3-methylimidazolium diethyldithiocarbamate(abbreviated as BMIMDDTC) and 1-butyl-3-methylimidazolium ethyl xanthate(abbreviated as BMIMC3H5OS2) were synthesized.The qualitative analysis was assisted by the FTIR spectra,1HNMR and TG,and the characteristics were studied. The performance of the prepared ionic liquids was test by preconcentration of trace metal ions(Pb,Cd,Cu,Ni,Zn,Mn,Fe and Cr) from aqueous solutions.The results showed that BMIMDDTC can be used for the quantitative extraction of copper and cadmium.The optimal value of pH is 1.0-10.0 for Cu and 3.0～7.0 for Cd,respectively.Meanwhile, the BMIMC3H5OS2 can be used for the quantitative extraction of copper,cadmium,nickel, lead and zinc.The optimal value of pH is 1.0～5.0 for Cu,1.0～11.0 for Cd,2.0～4.0 for Ni,1.0～7.0 for Pb and 2.0～8.0 for Zn,respectively.The application of ionic liquids was brodened by the synthesis of the anion-specific ionis liquids.This work indicates that more analytical methods for the extraction of metal ions can be developed.4.Determination of cadmium in water samples using liquid-liquid microextraction with 1-butyl-3-methylimidazolium diethyldithiocarbamate,followed by graphite furnace atomic absorption spectrometryA method of graphite furnace atomic absorption spectrometry(GFAAS),after liquid-liquid microextraction using BMIMDDTC,was developed for the determination of cadmium.Some effective parameters on complex formation and microextraction,such as pH,volume of extraction solvent,extraction time,salt effect and the coexisting ions have been optimized.Under optimal conditions,high extraction efficiency and selectivity was reached for the extraction of 0.3 ng of cadmium in 1.0 mL of water solution with 12μL BMIMDDTC.The optimal conditions were pH=3.0～7.0 and extraction time＞2 min. The calibration graph was linear in the range of 20～300 ng L-1 in the aqueous phase with detection limit of 7.7ng L-1.The characteristic mass(Mc,0.0044 absorption) of the proposal method was 0.024 pg.The relative standard deviation(RSD) for eleven replicate measurements of 100 ng L-1 Cd was 6.29%.The enrichment factor of the method is 100. The proposed method was successfully applied to the determination of trace cadmium in environmental water samples.In order to validate the method,the developed method was applied to the determination of cadmium in the Environmental Water Reference Material GSBZ 50009-88(200921) and tea standard reference material GBW-10016(GSB-7),and the results obtained were in good agreement with the certified value.The proposed method offers the advantages of rapidity,sensitivity,simplicity and good anti-interference capability.
|
PDF Full Text Request