Recent trends in the use of organized molecular systems combined with chromatographic techniques in environmental analysis

The establishment of new analytical methods which improve quality and sensitivity in the determination of environmental pollutants in liquid and solid samples is demanded. The use of micellar systems have become an advantageous tool for the extraction of pollutant compounds, due to their easy handling, biodegradability, and the one-step procedure, and they are compatible with the hydroalcoholic mobile phases used in HPLC. The focus of this review is to present recently developed methods and the main trends in the use of micellar media combined with solid-phase microextraction and solid-phase extraction in the chromatographic analysis of organic compounds in different types of environmental matrix, including water, sediments, and biological samples. Selected samples illustrate the benefits of these systems in the whole of analytical process. The advantages of micellar media over conventional extractants are reduction of solvent usage, low cost, easy handling, and non-toxic procedure.     

Effect of binary extractants and modifier–diluents systems on equilbria of propionic acid extraction

Propionic acid is an important carboxylic acid widely used in chemical industries. The recovery from aqueous waste streams and fermentation broth is of research interest. Extraction of carboxylic acids by reactive extraction using extractant-diluent, mixed extractants in diluents and extractants in mixed diluents etc. are emerging areas of study. With this aim reactive extraction of propionic acid was carried out to study: (i) effect of binary extractants (tri-n-octylamine(TOA):tri-n-butylphosphate (TBP), TOA:Aliquat 336 and TBP:Aliquat 336), (ii) effect of modifier (1-decanol) in different diluents (kerosene, n-octane, n-heptane, petroleum ether, butyl acetate, MIBK, 2-octanol, dodecanol, hexane) and (iii) effect of phase volume. Improved extractions using binary extractants and binary diluents were observed. Since liquid–liquid extraction is dependent on effect of modifier concentration, effect of phase volume, presence of single or binary extractants and binary diluents, the study will be useful in the design of reactive extraction process for propionic acid recovery.     

表面活性剂从碱性氰化液中萃取金

溶剂萃取法从碱性氰化液中提取金的工艺相对于传统锌置换法和活性炭吸附法具有潜在的优势,因而备受青睐。本文综述了近几年来从碱性氰化液中溶剂萃取金的研究进展。文中对表面活性剂/改性剂萃取Au(Ⅰ)的机理、萃取及反萃取行为进行了总结,报道了表面活性剂种类、改性剂种类、稀释剂以及盐析剂等各种因素对萃取过程的影响。同时,在萃取机理方面,提出一种基于氢键的超分子萃合物模型,在反萃取方面,介绍了阴离子交换法、转化还原法及直接电解有机相3种方法。     

A Short Review of the Separation of Iridium and Rhodium from Hydrochloric Acid Solutions by Solvent Extraction

Iridium and rhodium are among the platinum group metals. The properties, production processes, and aqueous chemistry of both metals are reviewed. The separation of Ir(IV) and Rh(III) from hydrochloric acid solution is dependent on the characteristics of the solvent extraction systems. In most of the extraction conditions, Ir(IV) is selectively extracted over Rh(III) by either amines or neutral extractants. Rh(I) can be selectively extracted over Ir(III) by neutral extractants after Rh(III) is reduced in the presence of a reducing agent. The separation of these two metals using cationic extractants has also been reported. Although selective extraction of one metal over the other is possible, more efficient solvent extraction systems need to be developed.     

The Chemistry of Separations Ligand Degradation by Organic Radical Cations

Solvent based extractions of used nuclear fuel use designer ligands in an organic phase extracting ligand complexed metal ions from an acidic aqueous phase. These extractions will be performed in highly radioactive environments, and the radiation chemistry of all these complexants and their diluents will play a major role in determining extraction efficiency, separation factors, and solvent-recycle longevity. Although there has been considerable effort in investigating ligand damage occurring in acidic water radiolysis conditions, only minimal fundamental kinetic and mechanistic data has been reported for the degradation of extraction ligands in the organic phase. Extraction solvent phases typically use normal alkanes such as dodecane, TPH, and kerosene as diluents. The radiolysis of such diluents produce a mixture of radical cations (R^•+), carbon-centered radicals (R^•), solvated electrons, and molecular products such as hydrogen. Typically, the radical species will preferentially react with the dissolved oxygen present to produce relatively inert peroxyl radicals. This isolates the alkane radical cation species, R^•+ as the major radiolytically-induced organic species that can react with, and degrade, extraction agents in this phase. Here we report on our recent studies of organic radical cation reactions with various ligands. Elucidating these parameters, and combining them with the known acidic aqueous phase chemistry, will allow a full, fundamental, understanding of the impact of radiation on solvent extraction based separation processes to be achieved.     

Determination of trace benzene derivatives in aqueous samples by ultrasonic enhanced hollow fiber liquid-phase microextraction prior to gas chromatography

A new method was developed for the determination of trace compounds in water samples using ultrasonic-enhanced hollow fiber liquid-phase microextraction (U-HF-LPME). The ultrasonic radiation, which produces mechanical vibration and ultrasonic cavitation, could be used for accelerating the diffusion mass transfer process. Thus, ultrasonic was introduced into the HF-LPME procedure to enhance the mass-transfer rate during the aqueous and extraction solvent phases. Experimental parameters such as the extraction solvent, the extraction time, the ultrasonic frequency and power, the extractant volume, and ionic strength of the sample were assessed and optimized. Under optimal conditions, HF-LPME was achieved within 10 min. The high enrichment factor in the range of 120-666 and a good relative recovery in the range of 97-103% were evaluated with the relative standard deviations (RSDs, n = 5) of 0.3-7.0%. The limit of detection was in the range of 0.8-3.0 μg/L. The method was applied to the analysis of groundwater, lake water, and seawater. The results showed that the method can determine trace benzene derivatives in real samples with RSD values of 1.1-4.2%. The results demonstrated that U-HF- LPME is a rapid, accurate, and effective sample preparation method, and could be successfully applied for the determination of trace compounds in analytical chemistry.     

Headspace Single Drop Microextraction for the Analysis of Fire Accelerants in Fire Debris Samples

Fire accelerants such as gasoline, kerosene, and diesel have commonly been used in arson cases. Improved analytical methods involving the extraction of fire accelerants are necessary to increase sample yield and to reduce the number of uncertain findings. In this study, an analytical method based on headspace single drop microextraction (HS-SDME) followed by gas chromatography–flame ionization detection (GC-FID) has been developed for the analysis of simulated fire debris samples. Curtain fabric was used as the sample matrix. The optimized conditions were 2.5 μL benzyl alcohol microdrop exposed for 20 min to the headspace of a 10 mL aqueous sample containing accelerants placed in 15-mL sample vial and stirred at 1500 rpm. The extraction method was compared with the solvent extraction method using n-hexane for the determination of fire accelerants. The HS-SDME process is driven by the concentration difference of analytes between the aqueous phases containing the analyte and the organic phase constituting the microdrop of a solvent. The limit of detection of HS-SDME for kerosene was 1.5 μL. Overall, the HS-SDME coupled with GC-FID proved to be rapid, simple and sensitive and a good alternative method for the analysis of accelerants in fire debris samples.     

Green analytical chemistry in sample preparation for determination of trace organic pollutants

The principles of green chemistry are applied to not only chemical engineering and synthesis, but also increasingly analytical chemistry. We describe environment-friendly analytical techniques applied to isolate and to enrich trace organic pollutants from solid and aqueous samples. Amounts of organic solvents used in analytical laboratories are reduced by applying solventless extraction, extraction using other types of solvent, assisted solvent extraction and miniaturized analytical systems.     

Die entwicklung edelmetallselektiver extraktionsmittel und ihre anwendbarkeit in der analytischen chemie

Summary The classical fire assay technique is still the most important procedure for the isolation and determination of precious metals. However, the lead collection system is basically suitable for extracting gold and silver, less for platinum, palladium and the rare precious metals. Extensive corrections are required to achieve accurate results. Many attempts are published to improve the situation by applying alternate collectors, additional chemical separations and instrumental determinative methods, such as atomic absorption and plasma emission spectrometry.Promising methods could be employed if certain separating media (solvent extractants, ion-exchange resins) are provided which extract precious metals selectively and reversibly. In such a case the final calibration step can be carried out with standard solutions of definite composition.The designing of ler made extractants has to consider the complex nature of the solution chemistry of precious metals. Hence, the relationship between metal properties and solvent extraction and ion exchange is briefly surveyed. The outlook with respect to the authors' research activities is focussed on the synthesis, characterization and application of new organic liquid and solid extractants (modified polystyrene and silica gel). These materials are based on chelating formazans and ion-exchanging tetrazolium salts. The selectivity, efficiency and mechanism of metal extraction and re-extraction are reviewed with respect to the effects of substituents attached to the metal binding groups, the influence of organic solvents and the nature of various supports (silica gel, polystyrene). Certain analytical applications are presented, e.g. the determination of silver, gold, platinum and palladium by means of formazan extraction, sorption on to tetrazolium-resins and DCP-emission spectrometry. The methods offer the advantages of selectivity and simplicity.

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Herrn Prof. Dr. G. Tölg zum 60. Geburtstag gewidmet     

Nitric Acid Extraction into TODGA

Advanced solvent extraction processes, namely DIAMEX, SANEX or GANEX, for the separation of the minor actinides (americium and curium) are under development within Europe. The tridentate diglycolamide ligand, TODGA, shows many interesting properties and is under investigation in conjunction with a variety of other extractants for the DIAMEX and SANEX processes as well as the GANEX process. In order to successfully demonstrate these processes, understanding the acid extraction into the organic phases is critical to process flowsheet design and modelling. Here nitric acid extractions into TODGA have been measured and models produced using an equilibrium based approach accounting for nitric acid activities in the aqueous phase.     

Solvent extraction of ionic solutes in aqueous solutions

Extraction of ionic solutes in aqueous solutions into various organic solvents is reviewed by showing several examples. The extraction of strong acids into polar organic solvents and nonpolar solvents containing hydrogen-bonding extractants is described as the first example and the extraction of simple metal salts into strongly dielectric or solvating polarsolvents and nonpolar solvents containing solvating extractants is then reported. Finally, the solvent extraction of anionic metal complexes with bulky cations into nonpolar solvents as ion-paris is described and the statistical method for such extraction equilibria is considered.     

Analysis of organic pollutants in sewage by supercritical fluid extraction

Summary Analytical methods have been developed for the determination of organic pollutants of intermediate polarity in sewage. Water samples are first passed through a solid phase adsorption cartridge. The analytes are then extracted from the absorbent with supercritical CO₂ into a small volume of trapping solvent. Finally, the extracts are analyzed directly by capillary gas chromatography and gas chromatography-mass spectrometer. The various parameters (pressure, temperature, type and concentration of modifiers, trapping solvent, flow rate and volume of supercritical fluid and equilibrium time) influencing the efficiency of extraction were studied. Extraction efficiencies for the test compounds are >70%, and relative standard deviations are <4.6% (n=3). The methods established were applied to the analysis of sewage at the Lanzhou Wastewater Treatment Plant, China. 66 organic pollutants were detected, of which 15 compounds appeared in the list of priority pollutants suggested by the US EPA.     

Analytical developments and applications of ionic liquids for environmental studies

Ionic liquids (ILs) are considered advanced solvents with interesting properties that have led to remarkable improvements in the performance of analytical methods and their practical application. Analytical chemistry has profited from the evolution of ILs in diverse contexts, ranging from their applications in microextractions to uses as matrices for mass spectrometric determinations. Their use in sample preparation has meant significant improvements in terms of miniaturization and analytical performance, and given place to new techniques based on liquid-liquid and solid-phase extractions; the latter greatly driven forward by the combination of ILs with nanomaterials. Furthermore, electrodes have been prepared by combining ILs with different modern materials, significantly improving the sensitivity and selectivity of electroanalytical methods. Moreover, the implementation of ILs as additives to mobile and stationary phases in separation techniques has been proved to improve liquid and gas chromatography, as well as capillary electrophoresis, in terms of the number of analytes that can be efficiently separated and of the useful life of columns, representing also a promising alternative to environmentally dangerous organic solvents. Additionally, their application as matrix modifiers and as ion-pairing additives has introduced their use in mass spectrometry. In this review, the design and implementation of innovative and highly efficient analytical methods based on ILs for the sensitive and selective determination of diverse analytes in environmental matrices is described. Critical issues that have arisen from their application and future challenges in electrochemical, separation and preconcentration techniques based on these solvents are also presented.     

肉类食品中杂环胺检测的样品前处理及分析方法的研究进展

杂环胺是畜禽、鱼肉等食品在高温烹饪过程中生成的一类致癌、致突变化合物,高效、高选择性的样品前处理方法和高灵敏的分析方法是食品中痕量杂环胺分析检测的关键。本文综述了近年来溶剂萃取、固相萃取和固相微萃取等样品前处理方法,以及液相色谱、液相色谱-质谱等分析方法在食品中痕量杂环胺检测中的应用,结合现有研究对其发展趋势进行了展望。共引用文献51篇。     

Vapor-phase extraction of organic substances from aqueous media

A method for the vapor-phase extraction of dissolved organic substances from an aqueous medium into an organic solvent was developed. This method allowed us to introduce hydrophilic extractants into extraction. The experimental results were discussed in terms of the kinetic model proposed for the mechanism of vapor-phase extraction. The analytical capabilities of this method were demonstrated using the study of sulfide mineral waters as an example.     

Membrane Methods of Substance Separation in Analytical Chemistry

A review of the membrane methods of substance separation used in analytical chemistry is presented. Membrane methods based on gas-diffusion separation and dialysis extraction, membrane filtration, membrane extraction, and chromatomembrane separation are considered. The possibility of combining membrane methods with modern methods of substance determination, such as flow-injection analysis, gas and liquid chromatography, capillary electrophoresis, mass spectrometry, and so on is discussed. The list of references consists of 200 items.     

Stoichiography and present-day analytical chemistry of solid inorganic substances and materials

The article covers factors that determine fundamental difficulties of chemical phase analysis of a mixture of solid phases of inorganic compounds. Stoichiographic principles and methods, novel for analytical chemistry and leading to the efficient solution of the problems of phase analysis, are discussed. Conditions of the selective separation of mixtures of multiphase multielement solid compounds and principles of the new method, fan-like separation, ensuring the extraction of individual phases from unseparated mixtures, are considered. An idea of a complex method of solving analytical problems by stoichiography methods in proposed. The problem of the multiplicity of objects of analysis is discussed and general principles of the efficient solution of problems of the detection and identification of components of complex mixtures of unknown chemical composition are considered.     

Importance of weak interactions in the formulation of organic phases for efficient liquid/liquid extraction of metals

Recent experimental studies demonstrate the need to take into account weak interactions in the understanding of solvent extraction processes. This well-established industrial technology now beneficiates of a supramolecular approach, complementary to the traditional analysis based on coordination chemistry. In this article, we focus on the integration of a colloidal approach in the analysis of solvent extraction systems: organic phases used are complex fluids, in which extracting molecules self-assemble into reverse aggregates. We detail the available analytical tools used towards characterization of these organic phases and emphasize the recent results in aggregation-driven extraction. All experimental data are discussed in light of theoretical approaches which propose adequate thermodynamic models and shed light on the importance of entropy on the phenomena. Diluent effects and synergism have been successfully rationalized, efficient new formulations based on a physicochemical analysis have been proposed and the door is now open for further development at industrial scale.     

Liquid–liquid extraction of thorium(IV) by fatty acids: a comparative study

In this paper, extractants that have the potential to be sustainably regenerated, are proposed for thorium(IV) removal from nitrate aqueous phases. These extractants are oleic (OA), palmitic (PA) and lauric (LA) acids. The advantages of using these acids are their sustainability, their biocompatibility and their non-toxicity, this makes these simpler and greener compared to other extractants (organophosphorus, azote derivatives, macrocyclic crown, etc…) used for metal extraction. These acids were applied as chelating agent for Th(IV) liquid–liquid extraction. The extractions were carried out in chloroform as an organic phase through the formation of thorium–OA, thorium–PA and thorium–LA complexes. The synergistic extraction of Th(IV) with these extractants in the presence of tributhylphosphine (TBP) has been investigated. The effect of different variables, such as time contact, pH of the aqueous phase, concentration of fatty acid, TBP addition on fatty acids, ionic strength and temperature, is reported. The results showed that the extraction kinetics using LA and OA were fast than with PA. The KNO₃ addition does not seem to highly influence the extraction yield, and no important synergy effect was noticed in the presence of TPB. Thermodynamic data for Th(IV) solvent extraction are also reported in this paper.     

State of the art of environmentally friendly sample preparation approaches for determination of PBDEs and metabolites in environmental and biological samples: A critical review

Green chemistry principles for developing methodologies have gained attention in analytical chemistry in recent decades. A growing number of analytical techniques have been proposed for determination of organic persistent pollutants in environmental and biological samples. In this light, the current review aims to present state-of-the-art sample preparation approaches based on green analytical principles proposed for the determination of polybrominated diphenyl ethers (PBDEs) and metabolites (OH-PBDEs and MeO-PBDEs) in environmental and biological samples. Approaches to lower the solvent consumption and accelerate the extraction, such as pressurized liquid extraction, microwave-assisted extraction, and ultrasound-assisted extraction, are discussed in this review. Special attention is paid to miniaturized sample preparation methodologies and strategies proposed to reduce organic solvent consumption. Additionally, extraction techniques based on alternative solvents (surfactants, supercritical fluids, or ionic liquids) are also commented in this work, even though these are scarcely used for determination of PBDEs. In addition to liquid-based extraction techniques, solid-based analytical techniques are also addressed. The development of greener, faster and simpler sample preparation approaches has increased in recent years (2003–2013). Among green extraction techniques, those based on the liquid phase predominate over those based on the solid phase (71% vs. 29%, respectively). For solid samples, solvent assisted extraction techniques are preferred for leaching of PBDEs, and liquid phase microextraction techniques are mostly used for liquid samples. Likewise, green characteristics of the instrumental analysis used after the extraction and clean-up steps are briefly discussed.