ABSTRACT
This study investigated the retention mechanism of a congeneric group of imidazolium ionic liquid cations with alkyl functional groups of different lengths, an aryl substituent, and one pyridinium cation on a pentafluorophenylpropyl silica-based stationary phase. The influence of organic modifier type and content in the mobile phase on the retention mode of alkylimidazolium ionic liquid cations shows a 'U-shaped' relationship. The use of this stationary phase gives excellent linearity and detection limits in the ppt range. The method is also readily applicable to the highly selective analysis of plant extracts previously spiked with ionic liquids.
ABSTRACT
Ionic liquids (ILs) are nowadays emerging as alternative green solvents for various technological applications. In this context, their environmental impacts need to be assessed, and relatively simple and reproducible analytical techniques are required in order to do this. These must be applicable not only to different natural matrices but also to the very low concentrations likely to be present in environmental systems. Moreover, in the case of solid environmental samples, liquid-solid extraction procedures are prerequisite for gaining further insight into IL distribution in these matrices. This paper reports on extraction methods for isolating IL residues from a number of plants, seeds and soils. The efficiency of five organic and inorganic acids in these extractions ranged from 70.2% to 83.5%, depending on the matrix and acid used. IL recovery rates were highest for phosphoric and trifluoroacetic acids. Recoveries of alkylimidazolium IL from all the plant matrices increased with alkyl chain length. The inference from this study is that IL polarity and steric hindrance both influence the mechanism of their sorption onto the plant matrix, which has a significant impact on the extraction efficiency. Saturated ammonium chloride mixed with a large quantity of methanol was the most effective solvent for extracting soil-bound ILs. The extraction efficiency is inversely proportional to the distribution coefficients of particular soils: the higher the value of K(d), the lower the recovery rate. Both methods of extraction were validated for their analytical performance parameters.
Subject(s)
Environmental Monitoring , Ionic Liquids/isolation & purification , Chromatography, High Pressure Liquid , Ionic Liquids/analysis , Ionic Liquids/chemistry , Plants/chemistry , Poaceae/chemistry , Reproducibility of Results , Secale/chemistry , Soil Pollutants/analysis , Solanum tuberosum/chemistry , Solvents/chemistry , Spectrometry, Mass, Electrospray IonizationABSTRACT
The usefulness of ion-pair reagents in selective solid reversed-phase extraction of one N-butyl-4-methylpyridinium and four short-chain alkylimidazolium ionic liquid cations from aqueous media was investigated using various concentrations of alkylsulfonates with different alkyl chain lengths. Final recoveries of the two cations with the shortest alkyl residues were poorer than those of the other, more hydrophobic compounds. Moreover, the recovery values were little affected by the different concentrations of the reagents. In nearly all cases, the best recoveries were obtained with the 1-heptanesulfonate reagent. The analytical performance parameters included excellent linearity over four orders of magnitude, with limits of detection ranging from 0.01 to 0.06 ppm, and very good precision and accuracy. The method was successfully used to extract ionic liquids from spiked seawater and freshwater samples. Recoveries and limits of detection were quite similar to those obtained with preconcentrated standard solutions.
ABSTRACT
This study reports on optimization of the RP-HPLC separation of imidazolium and pyridinium ionic liquid cations using a variable-size simplex algorithm. Under the optimized conditions, all critical pairs of ionic liquids were successfully separated in a single chromatographic run. The mobile phase at the point corresponding to the optimum consisted of 10% MeOH and 90% 15 mM KH(2)PO(4)/H(3)PO(4) with pH 3.43. The coefficients of asymmetry for all of the compounds analyzed at the simplex algorithm optimum ranged from 0.83 to 2.91.
Subject(s)
Chromatography, High Pressure Liquid/methods , Ionic Liquids/chemistry , Algorithms , Imidazoles/isolation & purification , Pyridinium Compounds/isolation & purificationABSTRACT
The mechanism of ionic liquid sorption onto selected natural soils differing in their organic content, cation exchange capacity, and particle size distribution was investigated in detail. Isotherms were employed to describe sorption. In most cases,the maximum achievable surface concentrations were well above CEC values. This observation may indicate that initially sorbed solutes modify the sorbent, a process favoring further sorption. The experimental data suggest that if a multilayer process occurs, such a mechanism will be applicable to all ionic liquids; but saturation of the second layer occurred only with the longest alkyl chain compound. The shorter alkyl chain cations did not reach saturation in the concentration range investigated here. The influence of the varying pH and ionic strength of an aquifer on sorption strength was also determined.
