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%.     

Microfluidic liquid-liquid extraction system based on stopped-flow technique and liquid core waveguide capillary

In this work, a miniaturized liquid-liquid extraction system under stopped-flow manipulation mode with spectrometric detection was developed. A Teflon AF liquid-core waveguide (LCW) capillary was used to serve as both extraction channel for organic solvent flow and adsorption detection flow cell. Gravity induced hydrostatic pressure was used to drive the organic and aqueous phases through the extraction channels. During extraction process, a stable organic and aqueous phase interface was formed at the outlet of the capillary, through which the analyte in the flowing aqueous stream was extracted into the stationary organic solvent in capillary. The absorbance of the analyte extracted into the organic solvent was measured in situ by a spectrometric detection system with light emitting diode (LED) as light source and photodiode as absorbance detector. The performance of the system was demonstrated in the determination of sodium dodecyl sulfate (SDS) extracted as an ion pair with methylene blue into chloroform. The precision of the measured absorbance for a 5 mg L⁻¹ SDS standard was 6.1% R.S.D. (n = 5). A linear response range of 1-10 mg L⁻¹ SDS was obtained with 5 min extraction period. The limit of detection (LOD) for SDS based on three times standard deviation of the blank response was 0.25 mg L⁻¹.     

A simple method for preparation of macroporous polydimethylsiloxane membrane for microfluidic chip-based isoelectric focusing applications

A new, simple method was reported to prepare PDMS membranes with micrometer size pores for microfluidic chip applications. The pores were formed by adding polystyrene and toluene into PDMS prepolymer solution prior to spin-coating and curing. The resulting PDMS membrane has a thickness of around 10 μm and macropores with a diameter ranging from 1 to 2 μm measured using scanning electron microscope (SEM) imaging. This PDMS membrane was validated by integrating it with PDMS microfluidic chips for protein separation using isoelectric focusing mechanism coupled with whole channel imaging detection (IEF-WCID). It has been shown that five standard pI markers and a mixture of two proteins, myoglobin and β-lactoglobulin, can be separated using these chips. The results indicated that this macroporous PDMS membrane can replace the dialysis membrane in PDMS chips for the IEF-WCID technique. The preparation method of macroporous PDMS membrane may be potentially applied in other fields of microfluidic chips.     

Residence time model for assessing liquid-liquid extraction systems

A model based on the residence time of solvent in the extraction system may be used to describe the dynamic operation of a continuous liquid-liquid extractor. It is proposed that optimum performance occurs when the extract exiting from the contactor is near equilibrium with the solution being extracted. This approach was tested on two commercially available continuous extraction systems. The difference in their performance was found to be related to the level of agitation of the two contactor vessels: the stirred system was approximately six times more efficient than the simple column continuous extractor. The stirred system achieved a near equilibrium analyte distribution between the solvent and sample and could be described accurately in terms of residence time theory. This was in marked contrast to its unmixed counterpart where the analyte distribution between solvent and sample reached 14% of its equilibrium value during its residence in the contactor. The effect of dead volume of solvent within the extraction assembly on the extraction rate was also apparent; its main effect was to delay the extraction process.     

氯丙嗪分子印迹化学发光微流控传感器芯片的研究

以氯丙嗪分子印迹聚合物为识别物质,以鲁米诺-K3Fe(CN)6化学发光体系,建立了一种新型的氯丙嗪化学发光微流控分子印迹传感器芯片的检测方法。利用二氧化碳激光在聚甲基丙烯酸甲酯材质上刻蚀出200μm宽,150μm深的微通道,8 mm长,1 mm宽,0.5 mm深的微检测池。微检测池中填充50μm粒径大小的热聚合得到的氯丙嗪分子印迹聚合物作为识别物质,在线富集氯丙嗪,富集的氯丙嗪可以增强鲁米诺和K3Fe(CN)6的化学发光强度,以化学发光强度定量氯丙嗪量。该传感器的响应值与0.02~0.4μg/mL氯丙嗪呈良好的线性关系,检出限为8 ng/mL(3σ)。该微流控传感器芯片已用于测定人尿液中的氯丙嗪。     

An automated system for liquid-liquid extraction based on a new micro-batch extraction chamber with on-line detection: Preconcentration and determination of copper(II)

An automated system to perform liquid-liquid extraction is proposed, in which the effective mixture (the intimate contact) between the aqueous phase and the organic phase, as well as the separation of the phases, are carried out in a micro-batch glass extraction chamber. Sample, reagents and organic solvent are introduced into the glass extraction chamber by a peristaltic pump using air as carrier. The detection of the extracted species from the aqueous phase is made in a small volume (120-150 μl) of isobutyl methyl ketone (MIBK). The system allows enrichment factors of 2-10-fold. The proposed automatic system was evaluated for Cu(II) extraction based on complex formation between copper(II) and 1-(2′-pyridylazo)naphthol (PAN) in MIBK. When a volumetric ration of 2:1 (aqueous:organic) was implemented, copper was detected in the concentration range of 100-1600 μg l⁻¹ (r = 0.9995) with a relative standard deviation of 2% (200 μg l⁻¹, n = 5) and a detection limit of 20 μg l⁻¹. The analytical curve was linear over the concentration range 25-500 μg l⁻¹ (r = 0.9994) when a volumetric ratio of 10:1 was employed. With this ratio, the detection limit was 5.0 μg l⁻¹ and the relative standard deviation was 6% (50 μg l⁻¹, n = 5).     

Chemiluminescence microfluidic system sensor on a chip for determination of glucose in human serum with immobilized reagents

A chemiluminescence (CL) biosensor on a chip coupled to microfluidic system is described in this paper. The CL biosensor measured 25×45×5 mm in dimension, was readily produced in analytical laboratory. Glucose oxidase (GOD) was immobilized onto controlled-pore glass (CPG) via glutaraldehyde activation and packed into a reservoir. The analytical reagents, including luminol and ferricyanide, were electrostatically co-immobilized on an anion-exchange resin. The most characteristic of the biosensor was to introduce the air as the carrier flow in stead of the common solution carrier for the first. The glucose was sensed by the CL reaction between hydrogen peroxide produced from the enzymatic reaction and CL reagents, which were released from the anion-exchange resin. The proposed method has been successfully applied to the determination of glucose in human serum. The linear range of the glucose concentration was 1.1-110 mM and the detection limit was 0.1 mM (3σ).     

超声辅助液液萃取法提取烟用香精成分的研究

采用超声辅助液液萃取法(ULLE)提取某品牌烟用香精成分,GC-MS对其进行分析,研究了不同萃取剂、萃取时间和萃取温度对分析结果的影响,初步确定了最佳条件为:以二氯甲烷为萃取剂,饱和NaCl溶液作水相,室温下超声萃取5 min.又分别与同时蒸馏萃取法(SDE)和传统的液液萃取法(LLE)作以比较,对ULLE法和SDE法鉴定出的化学成分、重现性和定量值进行了对比.结果表明:超声辅助液液萃取具有操作简便、快速、节能、萃取效率高、重现性好等特点,适合于烟用香精成分的提取.     

Automatic flow procedure based on multicommutation exploiting liquid-liquid extraction for spectrophotometric lead determination in plant material

A not expensive automatic flow system based on multicommutation and exploiting the liquid-liquid extraction methodology for the determination of lead in plant material is described. The spectrophotometric procedure for lead determination was based on the reaction with dithizone followed by extraction using an organic solvent. The facilities afforded by the multicommutation approach allowed the use of an air stream as carrier, thus contributing to reduce the overall waste generation. The results obtained analysing plant materials compare very well with those obtained employing inductive coupled plasma optical emission spectrometry (ICP OES) at 90% confidence level. Others profitable features such as a linear response range between 50 and 200 μg l⁻¹ Pb (r = 0.999); a sampling rate of 15 determination per hour; a relative standard deviation of 1.8% (n = 12) for a typical sample containing 163 μg l⁻¹ Pb; a detection limit of 12 μg l⁻¹; a reagent consumption of 4.5 mg dithizone; and a waste generation of 225 μl organic solvent per determination were also achieved.     

Preparation of metal nanoband microelectrode on poly(dimethylsiloxane) for chip-based amperometric detection

We proposed herein a novel approach for fabricating nanoband microelectrodes for electrochemical detection on an electrophoresis microchip. The metal films were first obtained via region-selective electroless deposition of gold or copper films on PDMS substrates by selective region plasma oxidation through shadow masking. Both metal films show uniform surfaces with the thickness at the level of 100 nm. By casting another PDMS layer on the metal films, the cross section of the sandwich structures can be used as nanoband microelectrodes, which can be renewed just by cutting. These nanoband microelectrodes are successfully used as electrochemical detectors in microchip electrophoresis for the detection of amino acids, proteins and neurotransmitter molecules. Moreover, integrating an Au-Cu double-metal detector with a double-channel electrophoresis system, we can easily distinguish electroactive amino acids from that of non-electroactive amino acids.     

On-line liquid-liquid extraction system using a new phase separator for flame atomic absorption spectrometric determination of ultra-trace cadmium in natural waters

A robust flow injection (FI) on-line liquid-liquid extraction (LLE) preconcentration/separation system associated with a newly designed gravitational phase separator, coupled to flame atomic absorption spectrometry (FAAS) was developed. The performance of the system was illustrated for cadmium determination at the μg l⁻¹ level. The non-charged cadmium complex with ammonium pyrrolidine dithiocarbamate (APDC) was extracted on-line into isobutyl methyl ketone (IBMK). The organic phase was effectively separated from a large volume of aqueous phase and is led into a 100 μl loop of an injection valve before its introduction into the nebulizer. The system was optimized and offered good performance characteristics with unlimited life time of phase separator, greater flow rate ratios and improved flexibility, as compared with other solvent extraction preconcentration systems. With a sampling frequency of 33 h⁻¹, the enhancement factor was 155, the detection limit was 0.02 μg l⁻¹, the relative standard deviation was 3.2% at 2.0 μg l⁻¹ Cd concentration level and the calibration curve was linear over the concentration range 0.06-6.0 μg l⁻¹. The accuracy of the proposed method was evaluated by analyzing a certified reference material of water and by recovery measurements on spiked samples. Finally, it was successfully applied to the analysis of tapwater, river and seawater samples.     

Cloud point extraction: an alternative to traditional liquid-liquid extraction for lanthanides(III) separation

Cloud point extraction (CPE) was used to extract and separate lanthanum(III) and gadolinium(III) nitrate from an aqueous solution. The methodology used is based on the formation of lanthanide(III)-8-hydroxyquinoline (8-HQ) complexes soluble in a micellar phase of non-ionic surfactant. The lanthanide(III) complexes are then extracted into the surfactant-rich phase at a temperature above the cloud point temperature (CPT). The structure of the non-ionic surfactant, and the chelating agent-metal molar ratio are identified as factors determining the extraction efficiency and selectivity. In an aqueous solution containing equimolar concentrations of La(III) and Gd(III), extraction efficiency for Gd(III) can reach 96% with a Gd(III)/La(III) selectivity higher than 30 using Triton X-114. Under those conditions, a Gd(III) decontamination factor of 50 is obtained.     

Portable microfluidic system for determination of urinary creatinine

A simple, low cost and portable microfluidic system based on a two-point alkaline picrate kinetic reaction has been developed for the determination of urinary creatinine. The creatinine reacts with picric acid under alkaline conditions, forming an orange-red colour, which is monitored on PDMS microchip using a portable miniature fibre optic spectrometer at 510 nm. A linear range was displayed from 0 to 40 mg L⁻¹ creatinine (r² = 0.997) with a detection limit of 3.3 mg L⁻¹ (S/N = 3). On-chip absorbance signals are reproducible, with relative standard deviations (RSDs) of 7.1%, when evaluated with 20 mg L⁻¹ creatinine (n = 10). The standard curves in which the intra-run CVs (4.7-6.8%) and inter-run CVs (7.9%) obtained were performed on three different days and exhibited good reproducibility. The method was highly correlated with the conventional spectrophotometric method when real urine samples were evaluated (r² = 0.948; n = 15).     

Flow injection manifolds for liquid-liquid extraction without phase separation assisted by ultrasound

Flow injection (FI) manifolds based on iterative change of the flow direction have been designed to study the influence of auxiliary energy on continuous liquid-liquid extraction without phase separation and compare it with the non-assisted process in a single experiment. In order to demonstrate the utility of ultrasounds as auxiliary energy for the extraction of polyphenols from an organic phase, the approach has been applied to samples of extra virgin olive oil, using an alkaline aqueous phase as extractant and subsequent derivatization with the Folin-Ciocalteu reagent. The proposed method provides results similar to those from the official method-recoveries between 97 and 100%. The sensitivity of the proposed method is 3.5 times higher than that of the non-ultrasound-assisted method. The precision, expressed as relative standard deviation (R.S.D.) for n=5, was within 1-5% and the relative errors for the irradiated and non-irradiated method were within 3 and 5%, respectively. The repeatability and within-laboratory reproducibility, studied at two concentration levels (379 and 813 μg ml⁻¹) ranged between 0.7-4.4% and 0.6-4.8%, respectively. The proposed manifolds can also be applied to either other type of auxiliary energies—microwave, thermal—or two different types of auxiliary energies at the same time.     

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.     

Rapid determination of 95 pesticides in soybean oil using liquid-liquid extraction followed by centrifugation, freezing and dispersive solid phase extraction as cleanup steps and gas chromatography with mass spectrometric detection

A multi-residue method using liquid-liquid extraction (LLE) followed by centrifugation, freezing and dispersive solid phase extraction (dispersive SPE) as clean up steps and gas chromatography with mass spectrometric detection has been developed for the determination of trace levels of 95 pesticides in soybean oil. LLE has been optimized to extract these pesticide residues from soybean oil by studying the effect of different partitions between (i) acetonitrile (MeCN) saturated with petroleum ether and a soybean oil solution dissolved in petroleum ether saturated with MeCN, (ii) partition between MeCN and a soybean oil solution dissolved in petroleum ether saturated with MeCN, (iii) partition between MeCN and a soybean oil solution dissolved in petroleum ether, (iv) partition between MeCN saturated with n-hexane and a soybean oil solution dissolved in n-hexane saturated with MeCN, (v) partition between MeCN and a soybean oil solution, (vi) partition between MeCN and a soybean oil solution dissolved in n-hexane and (vii) partition between MeCN and a soybean oil solution dissolved in mixture of acetone and n-hexane (3:2) to the highest recovery yield of pesticides and the lowest co-extract fat residue in the final extract. Experiments were carried out in order to study the efficiency of using centrifugation and freezing steps as well as the used of primary secondary amine (PSA), florisil, graphite carbon black (GCB) and C18 for dispersive SPE on clean up stages to minimize the co-extract fat. The recoveries obtained ranged from 80 to 114% and the relative standard deviation (RSDs) from 2 to 14% for spiking levels of 0.040, 0.080 and 0.160 mg kg^− 1. The limits of quantification (LOQs) of almost all compounds were below the maximum residue limits (MRLs) established by the Korean legislations for soybean oil.     

Comparison of supercritical fluid extraction and liquid-liquid extraction for isolation of selected pesticides stored in freeze-dried water samples

Summary The stability of freeze-dried water samples spiked with eight agrochemicals (atrazine, simazine, linuron, carbaryl, propanil, fenitrothion, parathion and fenamiphos) were examined to evaluate their suitability as candidate reference materials for their determination in water samples. In addition, two different extraction procedures, liquid-liquid and supercritical fluid extraction, were compared for the isolation and trace enrichment of target analytes from freeze-dried water samples. Final analytical determinations were by gas chromatography-nitrogen phosphorus detection and electronic impact mass spectrometry, and by liquid chromatography-diode array detection. The whole methodology developed in this paper permitted the determination of pesticides spiked in water at levels varying from 0.03 to 6.9 g L^–1.     

Rapid, highly efficient extraction and purification of membrane proteins using a microfluidic continuous-flow based aqueous two-phase system

Membrane proteins play essential roles in regulating various fundamental cellular functions. To investigate membrane proteins, extraction and purification are usually prerequisite steps. Here, we demonstrated a microfluidic aqueous PEG/detergent two-phase system for the purification of membrane proteins from crude cell extract, which replaced the conventional discontinuous agitation method with continuous extraction in laminar flows, resulting in significantly increased extraction speed and efficiency. To evaluate this system, different separation and detection methods were used to identify the purified proteins, such as capillary electrophoresis, SDS-PAGE and nano-HPLC-MS/MS. Swiss-Prot database with Mascot search engine was used to search for membrane proteins from random selected bands of SDS-PAGE. Results indicated that efficient purification of membrane proteins can be achieved within 5-7s and approximately 90% of the purified proteins were membrane proteins (the highest extraction efficiency reported up to date), including membrane-associated proteins and integral membrane proteins with multiple transmembrane domains. Compared to conventional approaches, this new method had advantages of greater specific surface area, minimal emulsification, reduced sample consumption and analysis time. We expect the developed method to be potentially useful in membrane protein purifications, facilitating the investigation of membrane proteomics.     

Prediction of the detection ranges for HPLC-peroxyoxalate chemiluminescence detection system of fluorescent compounds

Summary A manual method for predicting the detection ranges of fluorescent compounds for the HPLC-peroxyoxalate chemiluminescence detection system is presented utilizing bis(4-nitro-2-(3,6,9-trioxadecyloxycarbonyl)phenyl) oxalate (TDPO) as a chemilumigenic reagent. The generated chemiluminescence decay curves were measured on a photomultiplier and extrapolated to zero time based on the first part of the decay curve. Dipyridamole, perylene, DNS-Ser, Rose Bengal, DNS-Asp, Trp-P-1, pyrencarboxylic acid methyl ester, perfenazine, alimemazine, oxypertine, Glu-P-2, benzydamine and doxorubicin gave chemiluminescence intensity (Icl) values of 3.2 × 10⁶, 2.8 × 10⁶, 2.3 × 10⁵, 2.1 × 10⁵, 1.9 × 10⁵, 1.4 × 10⁵, 9.4 × 10³, 6.2 × 10³, 4.2 × 10³, 3.3 × 10³, 2.3 × 10³, 9.7 × 10² and 3.1 × 10², respectively. The reaction conditions for the HPLC-CL detection system were investigated and optimum conditions obtained.