An inkjet-printed microfluidic device for liquid-liquid extraction

A microfluidic device for liquid-liquid extraction was quickly produced using an office inkjet printer. An advantage of this method is that normal end users, who are not familiar with microfabrication, can produce their original microfluidic devices by themselves. In this method, the printer draws a line on a hydrophobic and oil repellent surface using hydrophilic ink. This line directs a fluid, such as water or xylene, to form a microchannel along the printed line. Using such channels, liquid-liquid extraction was successfully performed under concurrent and countercurrent flow conditions.     

Enhanced flavour extraction in continuous liquid-liquid extractors

Continuous liquid-liquid extraction is a versatile, reliable and robust sample preparation technique, but there is a tendency for the solvent to make channels through the sample, causing uneven and incomplete extraction. A simple, cheap magnetic stirrer that prevents channelling improves extraction efficiency by between 2.8 and 17.6 times.     

A microfluidic chip based liquid-liquid extraction system with microporous membrane

A robust and simple approach for microfabricated chip based liquid-liquid extraction was developed for on-chip sample pretreatment. The chip based extraction system was composed of two microfabricated glass plates with a microporous membrane sandwiched in between. A simple bonding approach using epoxy was used to achieve bonding and sealing of the L-L extraction chip. Gravity was employed to drive the aqueous and organic flows through separate channels in the extraction system, separated by the membrane. During extraction, the analyte in an aqueous sample stream was transferred through the membrane into the organic stream. The fluorescence intensity of the analyte extracted into the organic stream was monitored in situ by a laser induced fluorescence detection system. The performance of the system was demonstrated using an aqueous solution of butyl rhodamine B (BRB) and isobutanol as sample and extractant, respectively. The system proved to be an efficient means for achieving chip based microporous membrane liquid-liquid extraction. The precision of fluorescence measurements was 1.5% R.S.D. (n = 4). A linear response range of 1 × 10⁻⁷ to 1 × 10⁻⁴ M BRB was obtained with a regression equation: I = 8.00 × 10⁶ C + 4.91. An enrichment factor of ca. 3 was obtained with an extraction efficiency of 69%.     

Surfactant-enhanced liquid-liquid extraction in microfluidic channels with inline electric-field enhanced coalescence

Continuous microfluidic liquid-liquid extraction is realized in a microfluidic device by generating emulsions with large interfacial areas for mass transfer, and subsequently breaking these emulsions using electric fields into easily separated segments of immiscible liquids (plugs). The microfluidic device employs insulated electrodes in a potassium hydroxide-etched channel to create large electric fields (100 kV m(-1)) that drive coalescence of the emulsion phase. The result is a transition from disperse to slug flow that can then readily be separated by gravity. Extractions of phenol and p-nitrophenol from an aqueous to hexane-surfactant solution serve as model systems. In addition to the increased surface area in the emulsion, extraction efficiency is enhanced by reverse micelles resulting from the presence of surfactants. The surfactant concentration is varied approximately 1-10 wt% and a general two-parameter model is developed to quantify the extraction behavior and demonstrate the effectiveness of reverse micelle enhanced extraction.     

Improved microfluidic chip-based sequential-injection trapped-droplet array liquid-liquid extraction system for determination of aluminium

An improved microfluidic chip-based sequential-injection trapped-droplet array liquid-liquid extraction system with chemiluminescence (CL) detection was developed in this work. Two recess arrays were fabricated on both sides of the extraction channel to produce droplet arrays of organic extractant. A chip integrated monolithic probe was fabricated at the inlet of the extraction channel on the glass chip instead of the capillary probe connected to the microchannel, in order to improve the system stability and reliability. A slotted-vial array system coupled with the monolithic probe was used to sequentially introduce sample and different solvents and reagents into the extraction channel for extraction and CL detection. The performance of the system was demonstrated in the determination of Al³⁺ using Al³⁺-dihydroxyazobenzene (DHAB) and tributyl phosphate (TBP) extraction system. The operation conditions, including extraction time, concentration and flow rate of the CL reagents, were optimized. Within one analysis cycle of 12 min, an enrichment factor of 85 was obtained in the extraction stage with a sample consumption of 1.8 μL. The consumption of CL reagent, bis(2-carbopentyloxy-3,5,6-trichlorophenyl)oxalate (CPPO), was 120 nL/cycle. The detection limit of the system for Al³⁺ was 1.6 × 10⁻⁶ mol/L with a precision of 4.5% (R.S.D., n = 6).     

The liquid-liquid diffusive extraction of hydrocarbons from a North Sea oil using a microfluidic format

Extraction of a GC-amenable hydrocarbon fraction from oil by liquid-liquid diffusion across a laminar interface can be performed in a microfluidic format. Analysis of figures of merit, determined using standard analytical techniques, show this method to be an effective new tool for rapidly processing small quantities of oil and petroleum for GC analysis. Methods based upon similar microsystems devices could find widespread use in a variety of fields, including those associated with organic geochemistry and oil exploration and production, where the manipulation of petroleum constituents (greater than C14) is necessary for analytical purposes.     

A microfluidic chip based sequential injection system with trapped droplet liquid-liquid extraction and chemiluminescence detection

A microfluidic chip-based sequential injection system with trapped droplet liquid-liquid extraction preconcentration and chemiluminescence detection was developed for achieving high sensitivity with low reagent and sample consumption. The microfabricated glass lab-chip had a 35 mm long extraction channel, with 134 shrunken opening rectangular recesses (L 100 microm x W 50 microm x D 25 microm) arrayed within a 1 mm length on both sides of the middle section of the channel. Ketonic peroxyoxalate ester solution was filled in the recesses forming organic droplets, and keeping the aqueous sample solution flowing continuously in the extraction channel; analytes were transferred from the aqueous phase into the droplets through molecular diffusion. After liquid-liquid extraction preconcentration, catalyst and hydrogen peroxide solutions were introduced into the channel, and mixed with analytes and peroxyoxalate ester to emit chemiluminescence light. The performance of the system was tested using butyl rhodamine B, yielding a precision of 4% RSD (n = 5) and a detection limit of 10(-9) M. Within a 17 min analytical cycle, the consumptions of sample and peroxyoxalate solutions were 2.7 microL and 160 nL, respectively.     

Design of a multi-channel dropping segmenter for liquid-liquid extraction continuous flow-injection analysis

A simple dual-channel dropping segmenter was used for the simultaneous introduction of aqueous solutions of a sample and an organic analytical reagent directly into a continuous flow of an immiscible organic solvent. Droplets of precisely defined volume of the homogeneous reaction mixture are formed at the junction of the inlet capillary system. Reaction and extraction take place simultaneously in the individual segments of the aqueous phase during the transport through the reaction/extraction coil. An analytical signal is measured by an “on-tube” fast-reading spectrophotometric detector and processed mathematically. The applicability of the method is demonstrated with the determination of Cu(II) ions with tetramethylene-dithiocarbamate in neutral medium in 0.1 M ammonium acetate buffer.     

Ultrasound-assisted continuous liquid-liquid extraction without phase separation and hydrolysis of paracetamol in suppositories

An automated flow injection (FI) manifold based on iterative change of the flow direction has been designed to carry out continuous liquid-liquid extraction without phase separation and hydrolysis both with ultrasound-assistance. The dynamic approach has been applied to suppositories from which paracetamol has been extracted in this way into an aqueous phase and hydrolysed prior to reaction with o-cresol in the alkaline medium used as extractant. The three linked reactions, extraction-hydrolysis-derivatisation, cause displacement of the balance to completeness. The strategic location of the photometric flow-cell in the flow-injection manifold enables monitoring of the overall process and the obtaining of a characteristic multipeak recording. The influence of ultrasounds on the different steps was investigated. The indophenol blue dye formed was monitored at 620 nm. The limits of detection (LOD) and quantification (LOQ) of the method are 0.38 and 0.64 μg ml⁻¹, respectively, with a linear range from 0.64 to 50 μg ml⁻¹; a within-laboratory reproducibility between 2.07 and 4.66% and repeatability from 2.01 to 4.63%, both expressed as relative standard deviation. The results obtained with the proposed method are in excellent agreement with those provided by the official method, but with a shorter analysis time, lower sample and reagent consumption and less analyst involvement.     

Integrated microfluidic devices

“With the fundamentals of microscale flow and species transport well developed, the recent trend in microfluidics has been to work towards the development of integrated devices which incorporate multiple fluidic, electronic and mechanical components or chemical processes onto a single chip sized substrate. Along with this has been a major push towards portability and therefore a decreased reliance on external infrastructure (such as detection sensors, heaters or voltage sources).” In this review we provide an in-depth look at the “state-of-the-art” in integrated microfludic devices for a broad range of application areas from on-chip DNA analysis, immunoassays and cytometry to advances in integrated detection technologies for and miniaturized fuel processing devices. In each area a few representative devices are examined with the intent of introducing the operating procedure, construction materials and manufacturing technique, as well as any unique and interesting features.     

Solid-liquid separation after liquid-liquid extraction

A low-melting solid is used as organic solvent for liquid-liquid extraction at elevated temperatures followed by solidification and decantation of the aqueous phase.     

Preconcentration in multistage liquid-liquid extraction

Theoretical possibilities of the preconcentration of solutes in multistage static liquid-liquid extraction have been investigated. It was found that the preconcentration increases with increasing distribution ratio of the solutes between two phases as well as with the number of stages (n) and reaches its maximum value for n approaching infinity, i.e., in dynamic extraction. Comparison of the preconcentration in multistage (P_ns) and one-stage (p_1s) static operations shows that the relative preconcentration (q_ns=p_ns/p_1s) increases to infinity as the separation efficiency approaches 100%. Some of these theoretical considerations have been confirmed in extraction of radioiodine from aqueous solutions.Presented at the 2nd International Conference on the Separation of Ionic Solutes, SIS'87, Smolenice, Czechoslovakia, October 12–15, 1987.     

Determination of nitrate and nitrite by continuous liquid-liquid extraction with a flow-injection atomic-absorption detection system

Summary A flow injection system coupled on-line with a continuous liquid-liquid extractor is used for the indirect determination of nitrate and nitrite with an atomic-absorption detection system. These anions form ion-pairs with the copper(I)-neocuproine chelate which are extracted into methyl-isobutyl-ketone, the atomic-absorption signal of copper from the organic phase being proportional to the nitrate or nitrite concentration. The methods proposed herein are suitable for determining nitrate or nitrite at the g ml^–1 level with a sampling frequency of 35 ± 5 h^–1. The methods compare favourably with their batch counterparts with regard to sensitivity, selectivity, sample volume and sampling frequency.

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Bestimmung von nitrat und nitrit durch kontinuierliche flüssig-flüssig-extraction mit detektion durch ein fließinjektions-AAS-system

Zusammenfassung Ein Fließinjektionssytem, das on-line mit einem Flüssig-Flüssig-Extraktor gekoppelt ist, wird zur indirekten AAS-Bestimmung von Nitrat und Nitrit benutzt. Diese Anionen bilden mit Kupfer(I)-neocuproinchelat Ionenpaare, die mit Methylisobutylketon extrahiert werden. Das AAS-Signal des Kupfers aus der organischen Phase ist der Nitrat- bzw. Nitritkonzentration proportinal. Die vorgeschlagenen Verfahren eignen sich zur Nitrat- oder Nitritbestimmung im g/ml-Bereich mit einer Probenfrequenz von 35 ± 5 je Stunde. Diese Methoden sind den Batch-Verfahren in bezug auf Empfindlichkeit, Selektivität sowie Probevolumen und -frequenz überlegen.

     

Chiral separation by enantioselective liquid-liquid extraction

The literature on enantioselective liquid-liquid extraction (ELLE) spans more than half a century of research. Nonetheless, a comprehensive overview has not appeared during the past few decades. Enantioselective liquid-liquid extraction is a technology of interest for a wide range of chemists and chemical engineers in the fields of fine chemicals, pharmaceuticals, agrochemicals, fragrances and foods. In this review the principles and advances of resolution through enantioselective liquid-liquid extraction are discussed, starting with an introduction on the principles of enantioselective liquid-liquid extraction including host-guest chemistry, extraction and phase transfer mechanisms, and multistage liquid-liquid extraction processing. Then the literature on enantioselective liquid-liquid extraction systems is reviewed, structured on extractant classes. The following extractant classes are considered: crown ether based extractants, metal complexes and metalloids, extractants based on tartrates, and a final section with all other types of chiral extractants.     

A continuous liquid-liquid extraction system coupled on-line with capillary gas chromatography for environmental and ecotoxicological analysis

The applicability of a liquid-liquid extraction system which is coupled on-line with a capillary gas chromatograph was studied for environmental and ecotoxicological analyses. The optimized and automated system was used for the determination of apolar and rather non-volatile organic compounds in aqueous samples. Relevant aspects of sample introduction, phase separation and selection of extraction solvent are discussed. Three routine-tipe applications are described, viz. an improved method for the determination of hexachlorocyclohexanes in ground water and the determination of the so-called NCC-ether and ACC-ether in ecotoxicological studies. Depending on the application studied, the concentration levels varied from 0.1 to 6000 μg/I, using ECD and/or FID detection. Typical coefficients of variation obtained with the total extraction–GC procedure were 2–25%. The system was found to be rugged, it saves time compared with set-ups involving off-line liquid-liquid extraction and considerably reduces the manual work load.     

Speciation of mercury by continuous flow liquid-liquid extraction and inductively coupled plasma atomic emission spectrometry detection

An accurate, precise, sensitive and automated non-chromatographic method for methylmercury speciation based on a selective continuous liquid-liquid extraction of methylmercury, into xylene, as bromide and cold mercury vapour generation directly from the organic phase and final ICP-AES mercury detection is proposed. Both separation steps, liquid-liquid and gas-liquid are accomplished in a continuous mode and on line with ICP-AES as detector. The detection limit attained for methylmercury was 4ng·ml^–1 (as mercury). The precision of the determination at a concentration level around 20 times the detection limit was +-5%. The proposed methodology has been applied successfully to the speciation of methylmercury and inorganic mercury in spiked sea water and spiked urine samples.     

Electromembrane extraction in microfluidic formats

Electromembrane extraction is a microextraction technique where charged analytes are extracted across a supported liquid membrane and selectively isolated from the sample based on an electrical field. Since the introduction in 2006, there has been continuously increasing interest in electromembrane extraction, and currently close to 50 new articles are published per year. Electromembrane extraction can be performed in different technical configurations, based on standard laboratory glass vials or 96-well plate systems, and applications are typically related to pharmaceutical, environmental, and food and beverages analysis. In addition to this, conceptual research has developed electromembrane extraction into different milli- and microfluidic formats. These are much more early-stage activities, but applications among others related to organ-on-chip systems and smartphone detection indicate unique perspectives. To stimulate more research in this direction, the current article reviews the scientific literature on electromembrane extraction in milli- and microfluidic formats. About 20 original research articles have been published on this subject so far, and these are discussed critically in the following. Based on this and the authors own experiences with the topic, we discuss perspectives, challenges, and future research.