Application Of Room Temperature Ionic Liquids In Chemical Vapor Generation Of Transition And Noble Metals

Room-temperature ionic liquids(RTILs) have tremendous applications in various fields of chemistry due to their unique properties,such as negligible vapor pressure,good thermal stability,tunable viscosity,miscibility with water and organic solvents,and good extractability for various organic compounds and metal ions. Analytical applications of RTILs are also intriguing regarding the fact that they can be easily handled and used in wide variety of environments.There is a great deal of research on RTIL application as separation media for chromatography and capillary electrophoresis,solvents for extractions,sensing materials for chemosensing, matrices for MALDI-MS,electrolytes for electrochemistry and also as solvents for analytical spectroscopy,such as near infrared spectroscopy,fluorescence spectrometry and Raman spectroscopy.In this dissertation the exploitation of RTILs for the chemical vapor generation(CVG) of transition and noble metals,the mechanism of the enhancement effect of RTILs,and its application to flow injection-CVG-atomic fluorescence spectrometry(FI-CVG-AFS) for the determination of trace Au,Cu,Ag,and Ni are described.We report the first application of an RTIL in the CVG of transition and noble metals following reduction of acidified analyte solution with KBH₄.Copper,silver and gold were selected as model analytes,and N-butylpyridinium tetrafluoroborate ([C₄Py][BF₄]) was used as a model RTIL.The RTIL-enhanced CVG of copper,silver and gold was evaluated by FI-CVG-AFS.The addition of[C₄Py][BF₄]leads to a 4.8-, 2.7- and 3.6-times improvement in the CVG efficiencies for copper,silver and gold, respectively.Interference from Zn²⁺,Fe³⁺,Co²⁺,Ni²⁺,Pb²⁺,Se^â…£and As^â…¢was also reduced in the presence of[C₄Py][BF₄].The role of the RTIL was supposed to be inhibition of further coalescence of the metal nanoparticles which may constitute the volatile metal species leaving the solution and/or reaching the atomizer,and hence prevention of the loss of volatile metal species.With the consumption of a 0.5 mL sample solution,the detection limits(3σ) for Cu,Ag and Au are 19,15 and 6.3μg L^-1, respectively.The precisions(RSD,n=11) for eleven replicate measurements of the standard solution containing 50μg L^-1 Cu,Ag and Au were 4.4%,5.2%and 4.7%, respectively.The developed RTIL-enhanced FI-CVG-AFS method was successfully applied to determination of trace Cu,Ag and Au in several certified biological and geological reference materials.To get insight into the mechanism of the effect of RTILs on the CVG of noble metals,gold was taken as a model element,and eight RTILs were examined. FI-CVG-AFS was selected for detecting Au,and UV-vis spectrophotometry was used to elucidate the interactions of RTILs and the analyte.The RTILs involved include [C₄Py][BF₄],[C₄Py]Br,[C₁₆mim]Cl,[N₄₄₄₄]Br,[C₄mim]Br,[C₂mim]Br,[C₄mim][BF₄] and[N₄₄₄₄][BF₄].All the RTILs resulted in 3-24 times improvement in sensitivity for Au,depending on their nature.For the RTILs with identical anion,the RTILs with the cations of short chain exhibited better enhancement effect than those with long alkyl chain length or complex branch chain.For the RTILs with identical cation,the RTILs with Br^- gave the best enhancement effect.The formation of ion pairs between the cation of RTILs and the anion species of gold via electrostatic interaction,and/or the substitution of the Cl^- in the anion species of gold by the anion of RTILs likely enabled amore effective CVG reaction to occur.The RTILs also facilitated the generation of small bubbles and provided an electrostatic stabilization to protect the unstable volatile gold species and to help fast isolation of volatile gold species from the reaction mixture.[C₄mim]Br gave the best improvement in the sensitivity(24 times) among the RTILs studied,and also reduced the interferences from common transition and other noble metals.Based on the enhancement effect of[C₄mim]Br,a novel FI-CVG-AFS a detection limit(3σ) of 1.9μg L^-1 and a precision of 3.1%(50μg L^-1,RSD,n=11) was developed for the determination of trace gold in geological samples.RTIL in combination with sodium diethyldithiocarbamate(DDTC) were used to synergetically improve the CVG of nickel.Volatile species of nickel were effectively generated through reduction of acidified analyte solution with KBH₄ in the presence of 0.02%DDTC and 25 mmol L^-1[C₄mim]Br at room temperature.Thus,a new FI-CVG-AFS method was developed for determination of nickel.The combination of [C₄mim]Br with DDTC gave an enhancement factor of 2400.With consumption of 0.5 mL sample solution,a detection limit of 0.65μg L^-1(3σ) and a sampling frequency of 180 h^-1 were obtained.The relative standard deviation for eleven replicate determinations of 20μg L^-1 Ni was 3.4%.The developed FI-CVG-AFS method was successfully applied to determination of trace Ni in several certified biological reference materials.