Phase separation of gas–liquid and liquid–liquid microflows in microchips

Phase separation of gas–liquid and liquid–liquid microflows in microchannels were examined and characterized by interfacial pressure balance. We considered the conditions of the phase separation, where the phase separation requires a single phase flow in each output of the microchannel. As the interfacial pressure, we considered the pressure difference between the two phases due to pressure loss in each phase and the Laplace pressure generated by the interfacial tension at the interface between the separated phases. When the pressure difference between the two phases is balanced by the Laplace pressure, the contact line between the two phases is static. Since the contact angle characterizing the Laplace pressure is restricted to values between the advancing and receding contact angles, the Laplace pressure has a limit. When the pressure difference between the two phases exceeds the limiting Laplace pressure, one of the phases leaks into the output channel of the other phase, and the phase separation fails. In order to experimentally verify this physical picture, microchips were used having a width of 215 μm and a depth of 34 μm for the liquid–liquid microflows, a width of 100 μm and a depth of 45 μm for the gas–liquid microflows. The experimental results of the liquid–liquid microflows agreed well with the model whilst that of the gas–liquid microflows did not agree with the model because of the compressive properties of the gas phase and evaporation of the liquid phase. The model is useful for general liquid–liquid microflows in continuous flow chemical processing.     

Determination of triazines in honey by dispersive liquid–liquid microextraction high-performance liquid chromatography

Dispersive liquid–liquid microextraction (DLLME) high-performance liquid chromatography (HPLC) was developed for extraction and determination of triazines from honey. A room temperature ionic liquid, 1-hexyl-3-methylimidazolium hexafluorophosphate [C₆MIM][PF_6.], was used as extraction solvent and Triton X 114 was used as dispersant. A mixture of 175 μL [C₆MIM][PF₆] and 50 μL 10% Triton X 114 was rapidly injected into the 20 mL honey sample by syringe. After extraction, phase separation was performed by centrifugation and the sedimented phase was analyzed by HPLC. Some experimental parameters, such as type and volume of extraction solvent, concentration of dispersant, pH value of sample solution, salt concentration and extraction time were investigated and optimized. The detection limits for chlortoluron, prometon, propazine, linuron and prebane are 6.92, 5.84, 8.55, 8.59 and 5.31 μg kg⁻¹, respectively. The main advantages of the proposed method are simplicity of operation, low cost, high enrichment factor and extraction solvent volume at microliter level. Honey samples were analyzed by the proposed method and obtained results indicated that the proposed method provides acceptable recoveries and precisions.     

Lipophilic ternary complexes in liquid–liquid extraction of trivalent lanthanides

The formation of ternary complexes between lanthanide ions [Nd(III) or Eu(III)], octyl(phenyl)-N,N-diisobutyl-carbamoylmethylphosphine oxide (CMPO), and bis-(2-ethylhexyl)phosphoric acid (HDEHP) was probed by liquid–liquid extraction and spectroscopic techniques. Equilibrium modeling of data for the extraction of Nd(III) or Eu(III) from lactic acid media into n-dodecane solutions of CMPO and HDEHP indicates the predominant extracted species are of the type [Ln(AHA)₂(A)] and [Ln(CMPO)(AHA)₂(A)], where Ln?=?Nd or Eu and A represents the DEHP^? anion. FTIR (for both Eu and Nd) and visible spectrophotometry (in the case of Nd) indicate the formation of the [Ln(CMPO)(A)₃] complexes when CMPO is added to n-dodecane solutions of the LnA₃ compounds. Both techniques indicate a stronger propensity of CMPO to complex Nd(III) versus Eu(III).     

Determination of non-steroidal anti-inflammatory drugs in urine by the combination of stir membrane liquid–liquid–liquid microextraction and liquid chromatography

A stir membrane liquid phase microextraction procedure working under the three-phase mode is proposed for the first time for the determination of six anti-inflammatory drugs in human urine. The target compounds are isolated and preconcentrated using a special device that integrates the extractant and the stirring element. An alkaline aqueous solution is used as extractant phase while 1-octanol is selected as supported liquid membrane solvent. After the extraction, all the analytes are determined by liquid chromatography (LC) with ultraviolet detection (UV). The analytical method is optimized considering the main involved variables (e.g., pH of donor and acceptor phases, extraction time, stirring rate) and the results indicate that the determination of anti-inflammatory drugs at therapeutic and toxic levels is completely feasible. The limits of detection are in the range from 12.6 (indomethacin) to 30.7 μg/L (naproxen). The repeatability of the method, expressed as relative standard deviation (RSD, n = 5) varies between 3.4% (flurbiprofen) and 5.7% (ketoprofen), while the enrichment factors are in the range from 35.0 (naproxen) to 72.5 (indomethacin).     

Alkylsulfate-based ionic liquids in the liquid–liquid extraction of aromatic hydrocarbons

The (liquid + liquid) equilibrium data (LLE) for the extraction of toluene from heptane with different ionic liquids (ILs) based on the alkylsulfate anion (R-SO₄) was determined at T = 313.2 K and atmospheric pressure. The effect of more complex R-SO₄ anions on capacity of extraction and selectivity in the liquid–liquid extraction of toluene from heptane was studied. The ternary systems were formed by {heptane + toluene + 1,3-dimethylimidazolium methylsulfate ([mmim][CH₃SO₄]), 1-ethyl-3-methylimidazolium hydrogensulfate ([emim][HSO₄]), 1-ethyl-3-methylimidazolium methylsulfate ([emim][CH₃SO₄]), or 1-ethyl-3-methylimidazolium ethylsulfate ([emim][C₂H₅SO₄])}. The degree of quality of the experimental LLE data was ascertained by applying the Othmer–Tobias correlation. The phase diagrams for the ternary systems were plotted, and the tie lines correlated with the NRTL model compare satisfactorily with the experimental data.     

Extraction of pesticides in water samples using vortex-assisted liquid–liquid microextraction

A simple solvent microextraction method termed vortex-assisted liquid–liquid microextraction (VALLME) coupled with gas chromatography micro electron-capture detector (GC-μECD) has been developed and used for the pesticide residue analysis in water samples. In the VALLME method, aliquots of 30 μL toluene used as extraction solvent were directly injected into a 25 mL volumetric flask containing the water sample. The extraction solvent was dispersed into the water phase under vigorously shaking with the vortex. The parameters affecting the extraction efficiency of the proposed VALLME such as extraction solvent, vortex time, volumes of extraction solvent and salt addition were investigated. Under the optimum condition, enrichment factors (EFs) in a range of 835–1115 and limits of detection below 0.010 μg L⁻¹ were obtained for the determination of target pesticides in water. The calculated calibration curves provide high levels of linearity yielding correlation coefficients (r²) greater than 0.9958 with the concentration level ranged from 0.05 to 2.5 μg L⁻¹. Finally, the proposed method has been successfully applied to the determination of pesticides from real water samples and acceptable recoveries over the range of 72–106.3% were obtained.     

Dispersive liquid–liquid microextraction based on ionic liquid in combination with high-performance liquid chromatography for the determination of bisphenol A in water

A method termed dispersive liquid–liquid microextraction (DLLME) coupled with high-performance liquid chromatography-variable wavelength detection (HPLC-VWD) was developed. DLLME-HPLC-VWD is a method for determination of bisphenol A (BPA) in water samples. In this microextraction method, several parameters such as extraction solvent volume, sample volume, disperser solvent, ionic strength, pH, and disperser volume were optimised with the aid of interactive orthogonal array and a mixed level experiment design. First, an orthogonal array design was used to screen the significant variables for the optimisation. Second, the significant factors were optimised by using a mixed level experiment. Under the optimised extraction conditions (extraction solvent: ionic liquid [C₆MIM][PF₆], 60 µL; dispersive solvent: methanol, 0.4 mL; and pH = 4.0), the performance of the established method was evaluated. The response linearity of the method was observed in a range of 0.002–1.0 mg L^?1 (three orders of magnitude) with correlation coefficient (R ²) of 0.9999. The repeatability of this method was 4.2–5.3% for three different BPA levels and the enrichment factors were above 180. The extraction recovery was about 50% for the three different concentrations with 3.4–6.4% of RSD. Limit of detection of the method was 0.40 µg L^?1 at a signal-to-noise ratio of 3. In addition, the relative recovery of sample of Songhua River, tap water and barrel-drain water at different spiked concentration levels was ranged 95.8–103.0%, 92.6–98.6% and 87.2–95.3%, respectively. Compared with other extraction technologies, there have been the following advantages of quick, easy operation, and time-saving for the present method.     

Optimization of parameters for the alcoholic-assisted dispersive liquid–liquid microextraction of estrogens in water

Extraction and determination of estrogens in water samples were performed using alcoholic-assisted dispersive liquid–liquid microextraction (AA-DLLME) and high-performance liquid chromatography (UV/Vis detection). A Plackett–Burman design and a central composite design were applied to evaluate the AA-DLLME procedure. The effect of six parameters on extraction efficiency was investigated. The factors studied were volume of extraction and dispersive solvents, extraction time, pH, amount of salt and agitation rate. According to Plackett–Burman design results, the effective parameters were volume of extraction solvent and pH. Next, a central composite design was applied to obtain optimal condition. The optimized conditions were obtained at 220 μL 1-octanol as extraction solvent, 700 μL ethanol as dispersive solvent, pH 6 and 200 μL sample volume. Linearity was observed in the range of 1–500 μg L^?1 for E2 and 0.1–100 μg L^?1 for E1. Limits of detection were 0.1 μg L^?1 for E2 and 0.01 μg L^?1 for E1. The enrichment factors and extraction recoveries were 42.2, 46.4 and 80.4, 86.7, respectively. The relative standard deviations for determination of estrogens in water were in the range of 3.9–7.2 % (n = 3). The developed method was successfully applied for the determination of estrogens in environmental water samples.     

Determination of four heterocyclic insecticides by ionic liquid dispersive liquid–liquid microextraction in water samples

A novel microextraction method termed ionic liquid dispersive liquid–liquid microextraction (IL-DLLME) combining high-performance liquid chromatography with diode array detection (HPLC-DAD) was developed for the determination of insecticides in water samples. Four heterocyclic insecticides (fipronil, chlorfenapyr, buprofezin, and hexythiazox) were selected as the model compounds for validating this new method. This technique combines extraction and concentration of the analytes into one step, and the ionic liquid was used instead of a volatile organic solvent as the extraction solvent. Several important parameters influencing the IL-DLLME extraction efficiency such as the volume of extraction solvent, the type and volume of disperser solvent, extraction time, centrifugation time, salt effect as well as acid addition were investigated. Under the optimized conditions, good enrichment factors (209–276) and accepted recoveries (79–110%) were obtained for the extraction of the target analytes in water samples. The calibration curves were linear with correlation coefficient ranged from 0.9947 to 0.9973 in the concentration level of 2–100 μg/L, and the relative standard deviations (RSDs, n = 5) were 4.5–10.7%. The limits of detection for the four insecticides were 0.53–1.28 μg/L at a signal-to-noise ratio (S/N) of 3.     

Facile synthesis of thiourea derivatives in ionic liquid

The synthesis of cinnamoyl thiourea derivatives from cinnamoyl isothiocyanate (CIT) with substituted aniline (RC6H4NH2) was investigated in the mostly used ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate, [Bmim][BF4]. Significant enhance-ments in reactivity, yield and reaction rate were achieved. The products could be recovered by simple filtration. [Bmim][BF4] couldbe recycled simply by removing water under vacuum and reused at least 9 times without significant decrease in activity.     

High-performance liquid chromatographic determination of diltiazem in human plasma after solid-phase and liquid–liquid extraction

A selective, sensitive, and accurate high-performance liquid chromatographic method for determination of diltiazem in plasma samples has been developed and validated. The effects of mobile phase composition, buffer concentration, mobile phase pH, and concentration of organic modifiers on retention of diltiazem and internal standard were investigated. Solid-phase and liquid–liquid extraction were examined and proposed for isolation of the drug and elimination of endogenous plasma interferences. A 5 m Lichrocart Lichrospher 60 RP-select B chromatographic column was used; the mobile phase was acetonitrile–0.025 mol L^–1 KH₂PO₄ (pH 5.5), 35:65 ( v / v) at a flow-rate of 1.5 mL min^–1. The detection wavelength was 215 nm. The calibration plots were linear in the concentration range 20.0–500.0 ng mL^–1. The method has been implemented to monitor diltiazem levels in patient samples.     

TXRF determination of mercury(II) in water in combination with liquid–liquid microextraction

A highly selective hybrid way of TXRF determination of mercury(II) in drinking water at the level of n(10^–2–10⁰) μg/L is developed. The technique of preconcentration of mercury(II) ions includes directly suspended droplet microextraction with benzene in the form of an iodide molecular complex. The proposed method of determination is characterized by its high degree of sensitivity and reproducibility (c _min = 8 ng/L, s _r = 0.12 (100 ng/L)). The accuracy of the analysis results is confirmed by the introduced–found method.     

Determination of priority pollutants in aqueous samples by dispersive liquid–liquid microextraction

A dispersive liquid–liquid microextraction (DLLME) method followed by high-performance liquid chromatography–triple quadrupole mass spectrometry has been developed for the simultaneous determination of linear alkylbenzene sulfonates (LAS C₁₀, C₁₁, C₁₂, and C₁₃), nonylphenol (NP), nonylphenol mono- and diethoxylates (NP₁EO and NP₂EO), and di-(2-ethylhexyl)phthalate (DEHP). The applicability of the method has been tested by the determination of the above mentioned organic pollutants in tap water and wastewater. Several parameters affecting DLLME, such as, the type and volume of the extraction and disperser solvents, sample pH, ionic strength and number of extractions, have been evaluated. Methanol (1.5 mL) was selected among the six disperser solvent tested. Dichlorobenzene (50 μL) was selected among the four extraction solvent tested. Enrichment factor achieved was 80. Linear ranges in samples were 0.01–3.42 μg L⁻¹ for LAS C₁₀–₁₃ and NP₂EO, 0.09–5.17 μg L⁻¹ for NP₁EO, 0.17–9.19 μg L⁻¹ for NP and 0.40–17.9 μg L⁻¹ for DEHP. Coefficients of correlation were higher than 0.997. Limits of quantitation in tap water and wastewater were in the ranges 0.009–0.019 μg L⁻¹ for LAS, 0.009–0.091 μg L⁻¹ for NP, NP₁EO and NP₂EO and 0.201–0.224 μg L⁻¹ for DEHP. Extraction recoveries were in the range from 57 to 80%, except for LAS C₁₀ (30–36%). The method was successfully applied to the determination of these pollutants in tap water and effluent wastewater from Seville (South of Spain). The DLLME method developed is fast, easy to perform, requires low solvent volumes and allows the determination of the priority hazardous substances NP and DEHP (Directive 2008/105/EC).     

Sensitive determination of nitrophenol isomers by reverse-phase high-performance liquid chromatography in conjunction with liquid–liquid extraction

A method for the highly sensitive determination of 2-, 3- and 4-nitrophenols was developed using reverse-phase high-performance liquid chromatography (RP-HPLC) with a UV photodiode array detector. Using a reverse-phase column and 40% aqueous acetonitrile as an eluent (i.e. isocratic elution), the integrated peak area of detector output was linear up to 300 mg/L and the detection limit was 150 µg/L. The sensitivity of this detection method was improved by pretreating the sample solutions with a solvent extraction procedure that makes use of the high partition coefficient of ethyl acetate (EA)/water system. To find an optimum condition for the extraction procedure, this process was simulated by plotting the concentration of nitrophenol extracted in organic solvent against the volume multiplication factor at various partition coefficient of solute. This simulation demonstrated that EA is a superior extractant to other organic solvents. With the newly developed method, the detection limit was extended to 0.3 µg/L. This method offers fast, reliable and more sensitive determination of nitrophenol isomers than any other HPLC method.     

On-line coupling of microporous membrane liquid–liquid extraction and gas chromatography in the analysis of organic pollutants in water

A method for the determination of hydrophobic pollutants in surface waters was developed. The pretreatment was done with microporous membrane liquid–liquid extraction, the extract was eluted to a sample loop in the large-volume injector valve of the gas chromatograph and the extract was injected on-line to the gas chromatograph. The method was optimised using standard compounds and the linearity, the limits of detection and quantification of the method were studied. The method allowed the determination of hydrophobic pesticides and PAHs at the ng L^–1 level. The RSD values for the repeatability of the method varied from 4.2% to 25.6%, being on average 9.5%. Surface water samples from Finnish lakes and rivers were analysed.     

Dispersive liquid–liquid–liquid microextraction combined with liquid chromatography for the determination of chlorophenoxy acid herbicides in aqueous samples

A novel sample preparation method “Dispersive liquid–liquid–liquid microextraction” (DLLLME) was developed in this study. DLLLME was combined with liquid chromatography system to determine chlorophenoxy acid herbicide in aqueous samples. DLLLME is a rapid and environmentally friendly sample pretreatment method. In this study, 25 μL of 1,1,2,2-tetrachloroethane was added to the sample solution and the targeted analytes were extracted from the donor phase by manually shaking for 90 s. The organic phase was separated from the donor phase by centrifugation and was transferred into an insert. Acceptor phase was added to this insert. The analytes were then back-extracted into the acceptor phase by mixing the organic and acceptor phases by pumping those two solutions with a syringe plunger. After centrifugation, the organic phase was settled and removed with a microsyringe. The acceptor phase was injected into the UPLC system by auto sampler. Fine droplets were formed by shaking and pumping with the syringe plunger in DLLLME. The large interfacial area provided good extraction efficiency and shortened the extraction time needed. Conventional LLLME requires an extraction time of 40–60 min; an extraction time of approximately 2 min is sufficient with DLLLME. The DLLLME technique shows good linearity (r² ≥ 0.999), good repeatability (RSD: 4.0–12.2% for tap water; 5.7–8.5% for river water) and high sensitivity (LODs: 0.10–0.60 μg/L for tap water; 0.11–0.95 μg/L for river water).     

Simultaneous determination of several phytohormones in natural coconut juice by hollow fiber-based liquid–liquid–liquid microextraction-high performance liquid chromatography

A simple, selective, sensitive and inexpensive method of hollow fiber-based liquid–liquid–liquid microextraction (HF-LLLME) combined with high performance liquid chromatography (HPLC)-ultraviolet (UV) detection was developed for the determination of four acidic phytohormones (salicylic acid (SA), indole-3-acetic acid (IAA), (±) abscisic acid (ABA) and (±) jasmonic acid (JA)) in natural coconut juice. To the best of our knowledge, this is the first report on the use of liquid phase microextraction (LPME) as a sample pretreatment technique for the simultaneous analysis of several phytohormones. Using phenetole to fill the pores of hollow fiber as the organic phase, 0.1 mol L⁻¹ NaOH solution in the lumen of hollow fiber as the acceptor phase and 1 mol L⁻¹ HCl as the donor phase, a simultaneous preconcentration of four target phytohormones was realized. The acceptor phase was finally withdrawn into the microsyringe and directly injected into HPLC for the separation and quantification of the target phytohormones. The factors affecting the extraction efficiency of four phytohormones by HF-LLLME were optimized with orthogonal design experiment, and the data was analyzed by Statistical Product and Service Solutions (SPSS) software. Under the optimized conditions, the enrichment factors for SA, IAA, ABA and JA were 243, 215, 52 and 48, with the detection limits (S/N = 3) of 4.6, 1.3, 0.9 ng mL⁻¹ and 8.8 μg mL⁻¹, respectively. The relative standard deviations (RSDs, n = 7) were 7.9, 4.9, 6.8% at 50 ng mL⁻¹ level for SA, IAA, ABA and 8.4% at 500 μg mL⁻¹ for JA, respectively. To evaluate the accuracy of the method, the developed method was applied for the simultaneous analysis of several phytohormones in five natural coconut juice samples, and the recoveries for the spiked samples were in the range of 88.3–119.1%.     

Development of an ionic liquid based dispersive liquid–liquid microextraction method for the analysis of polycyclic aromatic hydrocarbons in water samples

A simple, rapid and efficient method, ionic liquid based dispersive liquid–liquid microextraction (IL-DLLME), has been developed for the first time for the determination of 18 polycyclic aromatic hydrocarbons (PAHs) in water samples. The chemical affinity between the ionic liquid (1-octyl-3-methylimidazolium hexafluorophosphate) and the analytes permits the extraction of the PAHs from the sample matrix also allowing their preconcentration. Thus, this technique combines extraction and concentration of the analytes into one step and avoids using toxic chlorinated solvents. The factors affecting the extraction efficiency, such as the type and volume of ionic liquid, type and volume of disperser solvent, extraction time, dispersion stage, centrifuging time and ionic strength, were optimised. Analysis of extracts was performed by high performance liquid chromatography (HPLC) coupled with fluorescence detection (Flu). The optimised method exhibited a good precision level with relative standard deviation values between 1.2% and 5.7%. Quantification limits obtained for all of these considered compounds (between 0.1 and 7 ng L⁻¹) were well below the limits recommended in the EU. The extraction yields for the different compounds obtained by IL-DLLME, ranged from 90.3% to 103.8%. Furthermore, high enrichment factors (301–346) were also achieved. The extraction efficiency of the optimised method is compared with that achieved by liquid–liquid extraction. Finally, the proposed method was successfully applied to the analysis of PAHs in real water samples (tap, bottled, fountain, well, river, rainwater, treated and raw wastewater).     

Development of a dispersive liquid–liquid microextraction method for the determination of fluoroquinolones in chicken liver by high performance liquid chromatography

A simple and cost effective sample pre-treatment method, dispersive liquid–liquid microextraction (DLLME), has been developed for the extraction of six fluoroquinolones (FQs) from chicken liver samples. Clean DLLME extracts were analyzed for fluoroquinolones using liquid chromatography with diode array detection (LC-DAD). Parameters such as type and volume of disperser solvent, type and volume of extraction solvent, concentration and composition of phosphoric acid in the disperser solvent and pH were optimized. Linearity in the concentration range of 30–500 μg kg⁻¹ was obtained with regression coefficients ranging from 0.9945 to 0.9974. Intra-day repeatability expressed as % RSD was between 4 and 7%. The recoveries determined in spiked blank chicken livers at three concentration levels (i.e. 50, 100 and 300 μg kg⁻¹) ranged from 83 to 102%. LODs were between 5 and 19 μg kg⁻¹ while LOQs ranged between 23 and 62 μg kg⁻¹. All of the eight chicken liver samples obtained from the local supermarkets were found to contain at least one type of fluoroquinolone with enrofloxacin being the most commonly detected. Only one sample had four fluoroquinolone antibiotics (ciprofloxacin, difloxacin, enrofloxacin, norfloxacin). Norfloxacin which is unlicensed for use in South Africa was also detected in three of the eight chicken liver samples analyzed. The concentration levels of all FQs antibiotics in eight samples ranged from 8.8 to 35.3 μg kg⁻¹, values which are lower than the South African stipulated maximum residue limits (MRL).     

Extraction of vanadyl porphyrins in crude oil by inclusion dispersive liquid–liquid microextraction and nano-baskets of calixarene

The novelties of this approach are introducing the self-settled dispersive liquid–liquid microextraction technique to remove the centrifuging step, conducting the dispersive liquid–liquid microextraction in complex organic systems, applicability of water as disperser phase, and inclusion microextraction of charged porphyrins by nano-baskets of calix[4]arenes, which act as the settling agents as well as the inclusion ligands. Diacid p-tert-butylcalix[4]arene in the cone conformation was synthesized and used. The related parameters including ligand concentration, volume of water disperser, salt effect, and extraction time were optimized. The linear range, detection limit (S/N?=?3) and precision (RSD, n?=?6) were determined to be 0.2–50, 0.07?μg?L^?1 and 5.3%, respectively. The established method was applied to determine the target compound in five samples of live crude oil, were sampled from an Iranian offshore field. Owing to the overall differences (such as organic media, inclusion extraction, water-soluble ligands, etc.), the comparison of the proposed method with the traditional liquid–liquid microextraction was inapplicable. These results revealed that the new approach is competitive analytical tool and an alternative of the traditional methods in the crude oil and related systems. Moreover, in those systems that the inclusion separation is not requested, it is possible to use a tertiary system including a proper extraction agent/solvent and calixarene phase, as settling agent, along with the aqueous disperser in the organic systems.