Conventional Dispersive Liquid-liquid Microextraction Research Articles

Estimation of Some Useful Drugs in Water, Urine, and Medical Formulations Following Conventional and Modified Dispersive Microextraction Coupled with HPLC-UV

Dispersive Liquid-Liquid Microextraction (DLLME) coupled with high-performance liquid chromatography-ultraviolet spectroscopy was developed, as a fast and precise operation, for extractive recovery and estimation of two pharmaceuticals viz. moxifloxacin and galantamine, from water, urine, and medical formulations. The process was investigated for Extraction (ES) and Dispersive Solvent (DS) as well as pH, temperature, and salt concentration. Extraction was found effective using methanol (CH3OH), as the DS, employing 1,1,2,2-tetrachloroethane (C2H2Cl4) and chloroform (CHCl3), as the ES, for moxifloxacin and galantamine respectively. The optimum pH was found to be 6.9 for moxifloxacin and 10.2 for galantamine. Temperature and salt were found to have some influence on the extraction efficiency of moxifloxacin but insignificant for galantamine. An improvement of the operation in terms of the Extraction efficiency (ER %), Preconcentration Factor (PF), thermodynamic feasibility, and greenness were achieved during surfactant aided DLLME (SDS-DLLME), where anionic surfactant (Sodium Dodecyl Sulphate (SDS)) was employed and no DS was required. Interestingly, the volume requirement for ES was found less, compared to that in the conventional DLLME, without compromising the performance. Moreover, quantitative recovery of both the drugs was achieved using a single ES. Thus, mutual separation and simultaneous determination of moxifloxacin and galantamine may be designed. A two-phase separation with concomitant enrichment of the solute in the sediment phase occurred. The drugs in the sediment phase, on subsequent dilution with methanol, were determined using the High Performance Liquid Chromatography-Ultraviolet (HPLC-UV) system. The negative free energy changes for the operation indicated that the process was thermodynamically feasible. The process was found to be effective for the spiked recovery of the studied drugs from real samples viz, water, human urine, and commercial medical formulations.

Three phase dispersive liquid-liquid microextraction (DLLME) based on reverse micelles for the enrichment of Q-markers of cinnamic acids in traditional Chinese medicine

This work describes three phase dispersive liquid-liquid microextraction based on reverse micelles for the determination of Q-markers of cinnamic acids (caffeic acid, p-hydroxycinnamic acid, ferulic acid, and cinnamic acid) in traditional Chinese medicine followed by high performance liquid chromatography (HPLC) analysis. The variables influencing the procedure were optimized separately. Enrichment factors from 110 to 189, linearities from 1.2 to 960 ng mL−1 with r 2 exceeding 0.9943, detection limits from 0.1 to 0.6 ng mL−1, excellent precision with relative standard deviations below 5.6%, and good relative recoveries from 80.0% to 113.3% were achieved. In addition, the mechanism of the procedure was explored by comparison with conventional dispersive liquid-liquid microextraction at the optimum conditions. The results showed that the developed microextraction procedure improved the sensitivity and consumed less organic solvent and is a greener approach.

Dispersive liquid-liquid microextraction of zinc from environmental water samples using ionic liquid

In this work, the Dispersive Liquid-Liquid Microextraction (DLLME) method has intensified the extraction of Zinc from aqueous solution utilizing 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF6] and the retrieved metal was analyzed using UV-Vis spectrophotometer. Several extraction factors such as the volume of extraction solvent, centrifugation speed, pH, salt effect, the volume of dispersive solvent, sonication time, and temperature on extraction recovery using conventional DLLME, Temperature-controlled DLLME, and Ultrasound-assisted DLLME methods, respectively, were investigated. In the comparison of these three methods, the maximum extraction recovery was attained by the Ultrasound-assisted DLLME method with the optimum conditions of 60 µl extractant volume, 0.75 ml of dispersive solvent, 3000 rpm centrifugation speed at the pH of 6, and the temperature of 40 °C with 2 min of sonication. The ionic liquid used in the extraction process was completely recovered by sulfuric acid as a stripping agent and reused several times with less loss in its efficiency. The Ultrasound-assisted DLLME method was successfully applied to electroplating industrial effluent under the experimental optimum conditions and the extraction recovery was achieved by 87.4%.

Extraction of DNA with magnetic ionic liquids using in situ dispersive liquid-liquid microextraction.

A new class of magnetic ionic liquids (MILs) with metal-containing cations was applied in in situ dispersive liquid-liquid microextraction (DLLME) for the extraction of long and short double-stranded DNA. For developing the method, MILs comprised of N-substituted imidazole ligands (with butyl-, benzyl-, or octyl-groups as substituents) coordinated to different metal centers (Ni2+, Mn2+, or Co2+) as cations, and chloride anions were investigated. These water-soluble MILs were reacted with the bis[(trifluoromethyl)sulfonyl]imide anion during the extraction to generate a water-immiscible MIL capable of preconcentrating DNA. The feasibility of combining the extraction methodology with anion-exchange high-performance liquid chromatography with diode array detection (HPLC-DAD) or fluorescence spectroscopy was studied. The method with the Ni2+- and Co2+-based MILs was easily combined with fluorescence spectroscopy and provided a faster and more sensitive method than HPLC-DAD for the determination of DNA. In addition, the method was compared to conventional DLLME using analogous water-immiscible MILs. The developed in situ MIL-DLLME method required only 3min for DNA extraction and yielded 1.1-1.5 times higher extraction efficiency (EFs) than the conventional MIL-DLLME method. The in situ MIL-DLLME method was also compared to the trihexyl(tetradecyl)phosphonium tris(hexafluorocetylaceto)nickelate(II) MIL, which has been used in previous DNA extraction studies. EFs of 42-99% were obtained using the new generation of MILs, whereas EFs of only 20-38% were achieved with the phosphonium MIL. This new class of MILs is simple and inexpensive to prepare. In addition, the MILs present operational advantages such as easier manipulation in comparison to hydrophobic MILs, which can have high viscosities. These MILs are a promising new class of DNA extraction solvents that can be manipulated using an external magnetic field. Graphical abstract Magnetic ionic liquids with metal-containing cations are applied in in situ dispersive liquid-liquid microextraction for the extraction of long and short double-stranded DNA.

Salt-assisted dispersive liquid-liquid microextraction for enhancing the concentration of matrine alkaloids in traditional Chinese medicine and its preparations.

A fast, simple, and efficient salt-assisted dispersive liquid-liquid microextraction coupled with high-performance liquid chromatography was developed and introduced for the simultaneous enrichment, extraction, and determination of the trace levels of matrine alkaloids (sophoridine, matrine, and sophocarpine) in Sophorae Flavescentis Radix and Composite Kushen injection. Compared with conventional dispersive liquid-liquid microextraction, the proposed method, with added salt but without dispersant and centrifuging, makes the operation simpler, greener, and leads to a higher enrichment factor. The crucial parameters affecting the enrichment factors of target analytes, such as type and volume of extraction solvent, pH of sample phase, salt concentration, volume of sample phase, and extraction time, were investigated and optimized, meanwhile, the extraction mechanism of the method was analyzed and described. Under the optimized conditions, the enrichment factors of the three matrine alkaloids were 150, 178, and 227, respectively. Good linearities (r2 ≥0.9992) for all analytes, low limits of detection (less than 0.08ng/mL), satisfactory precisions (2.1-12.3%), and accuracies (recoveries, 99.3-103.9%) were achieved. The experimental results showed that the approach is a simple, fast, green, eco-friendly, and sensitive method and can be used for the preconcentration and determination of matrine alkaloids in traditional Chinese medicines and their preparations.

Improvement of dispersive liquid-liquid microextraction robustness by performing consecutive extractions: Determination of polycyclic aromatic hydrocarbons in Brazilian sugar cane spirits by GC-MS

This paper describes the development of a multiple dispersive liquid-liquid microextraction method for the determination of fifteen polycyclic aromatic hydrocarbons in samples of Brazilian sugar cane spirit (known as cachaça) with separation and detection by GC-MS. The results obtained with the multiple extraction approach were compared to those obtained with the conventional dispersive liquid-liquid microextraction method using the same sample. Sample dilution and solvent volume were optimized using the response surface methodology. The coefficient of determination (R2) for the multiple dispersive liquid-liquid microextraction method varied from 0.9939 to 0.9999. The limits of detection ranged from 0.06 to 1.5 μg L−1 and precision from 12 and 22%. The recovery values obtained with the proposed method ranged from 84 to 116%. The sum of the polycyclic aromatic hydrocarbons concentrations in six samples ranged from 0.65 to 12.2 μg L−1. Multiple dispersive liquid-liquid microextraction was shown to be efficient in relation to compensating the matrix effects due to variations in the sample composition and the extraction parameters showed greater robustness compared to the conventional dispersive liquid-liquid microextraction method, since it simulates an exhaustive extraction.

Overcoming the challenges of conventional dispersive liquid-liquid microextraction: analysis of THMs in chlorinated swimming pools.

A rapid, simple, and sensitive approach to the analysis of trihalomethanes (THMs) in swimming pool water samples has been developed. The main goal of this study was to overcome or to improve the shortcomings of conventional dispersive liquid-liquid microextraction (DLLME) and to maximize the realization of green analytical chemistry principles. The method involves a simple vortex-assisted microextraction step, in the absence of the dispersive solvent, followed by salting-out effect for the elimination of the centrifugation step. A bell-shaped device and a solidifiable solvent were used to simplify the extraction solvent collection after phase separation. Optimization of the independent variables was performed by using chemometric methods in three steps. The method was statistically validated based on authentic guidance documents. The completion time for extraction was less than 8 min, and the limits of detection were in the range between 4 and 72 ng L-1. Using this method, good linearity and precision were achieved. The results of THMs determination in different real samples showed that in some cases the concentration of total THMs was more than threshold values of THMs determined by accredited healthcare organizations. This method indicated satisfactory analytical figures of merit. Graphical Abstract A novel green microextraction technique for overcoming the challenges of conventional DLLME. The proposed procedure complies with the principles of green/sustainable analytical chemistry, comprising decreasing the sample size, making easy automation of the process, reducing organic waste, diminishing energy consumption, replacing toxic reagents with safer reagents, and enhancing operator safety.

Dispersive liquid-liquid microextraction for the determination of menthol residue in fish by GC–MS

Conventional dispersive liquid-liquid microextraction (DLLME) and low density solvent-based dispersive liquid-liquid microextraction (LDS-DLLME) were evaluated in the extraction of menthol (1R, 2S, 5R)-2-isopropyl-5-methylcyclohexanol from tilapia (Oreochromis niloticus) fillets. The nature of the extraction and disperser solvents underwent univariate analysis. The results indicated greater efficiency in the extraction of menthol when toluene was used as extraction solvent and acetone as the disperser solvent. Once the extraction and disperser solvents were set, the parameters: ionic strength and volumes of the extraction solvent and water were evaluated using the central composite design (CCD). The conditions determined as ideal were 0.1g of sodium sulfate, 100μL of toluene and 5mL of water. The enrichment factor of the LDS-DLLME technique was of 80 times, the limits of detection and quantification were of 0.0539 and 0.1190μgL−1, respectively. The methodology developed was applied to determine menthol residues in tilapia fillets killed at different times and at different anesthesia concentrations. The results showed that the time needed for the organism of the fish to completely eliminate the menthol was >24h. This methodology becomes promising for the obtaining of protocols which regulate the use of menthol as an anesthetic used in aquaculture.

Development of a dispersive liquid-liquid microextraction method with a new sequence of steps and its comparison with a conventional method.

In this paper, a dispersive liquid-liquid microextraction method with a new sequence of steps from the view of salt addition has been developed for the extraction and preconcentration of some organophosphorous pesticides from aqueous samples before analysis by gas chromatography with flame ionization detection. In this method, an appropriate mixture of extraction and disperser solvents is rapidly injected by a syringe into the aqueous sample. Then, sodium chloride is added into the solution to increase its ionic strength. The obtained results by the proposed method are compared with those of the conventional dispersive liquid-liquid microextraction in which the salt is added into the aqueous phase before dispersion of the extraction solvent. Some effective parameters on the method efficiency including type and volume of extraction and disperser solvents, type and percent of salt, etc. are investigated. Under the optimal conditions, limits of detection and quantification of the proposed method compared to conventional one were improved by a factor between 1.4-2.2 and 1.3-2.3, respectively. Extraction recoveries and enrichment factors of the proposed method with respect to conventional one enhanced from 43-60 to 72-99% and 1433-2000 to 2404-3285, respectively.

Application of Air-Assisted Liquid-Liquid Microextraction for Determination of Some Fluoroquinolones in Milk Powder and Egg Samples: Comparison with Conventional Dispersive Liquid-Liquid Microextraction

Herein, an air-assisted liquid-liquid microextraction (AALLME) has been described and compared to conventional dispersive liquid-liquid microextraction (DLLME) for the extraction/preconcentration of six fluoroquinolone compounds in milk powder and egg samples prior to high-performance liquid chromatography-UV detection (HPLC-UV). In order to compare the novel AALLME technique to the conventional DLLME technique, several parameters that influence the extraction efficiency were studied and optimized. Both methods have been validated for milk powder and egg analysis, obtaining limits of quantification lower than those usually permitted by legislation in food matrices, with precisions expressed as coefficients of variation lower than 8 % and recoveries between 72 and 115 % which were acceptable recoveries and repeatability. An AALLME method needs less organic solvent and shorter centrifugation time; therefore, it is more environmentally friendly and efficiently compared to DLLME.

Progress of Extraction Solvent Dispersion Strategies for Dispersive Liquid-liquid Microextraction

Abstract Dispersive liquid-liquid microextraction (DLLME) is a new sample preparation technique emerging recently. The dispersion of organic extraction solvent at micro-liter level in aqueous samples is the key step in DLLME. The published strategies of dispersion for DLLME are roughly classified into three types in terms of the instruments used and dispersion principles, namely physical dispersion method, in-situ chemical reaction-based dispersion method and new dispersion medium-based dispersion method. The physical dispersion method includes mechanical shaking method, ultrasound/microwave-assisted method and solubility-adjustment method. The in-situ chemical reaction method is referred to the two modes, in which either the dispersed extraction solvent is formed by in-situ chemical reaction or the dispersion of extraction solvent is achieved by the gas generated from chemical reactions. The new dispersion medium-based dispersion method uses some non-volatile substances, such as medium-chain saturated fatty acids, ionic liquid, surfactant and kapok fiber fragments, to substitute the dispersive solvent used in conventional DLLME. A total of 96 relevant literatures are cited in this review and the prospects of DLLME are highlighted.

Solid-based disperser liquid-liquid microextraction for the preconcentration of phthalate esters and di-(2-ethylhexyl) adipate followed by gas chromatography with flame ionization detection or mass spectrometry

A new approach for the development of a dispersive liquid-liquid microextraction followed by GC with flame ionization detection was proposed for the determination of phthalate esters and di-(2-ethylhexyl) adipate in aqueous samples. In the proposed method, solid and liquid phases were used as the disperser and extractant, respectively, providing a simple and fast mode for the extraction of the analytes into a small volume of an organic solvent. In this method, microliter levels of an extraction solvent was added onto a sugar cube and it was transferred into the aqueous phase containing the analytes. By manual shaking, the sugar was dissolved and the extractant was released into the aqueous phase as very tiny droplets to provide a cloudy solution. Under optimized conditions, the proposed method showed good precision (RSD less than 5.2%), high enrichment factors (266-556), and low LODs (0.09-0.25 μg/L). The method was successfully applied for the determination of the target analytes in different samples, and good recoveries (71-103%) were achieved for the spiked samples. No need for a disperser solvent and higher enrichment factors compared with conventional dispersive liquid-liquid microextraction and low cost and short sample preparation time are other advantages of the method.

Development of on-line spectroscopic determination approach of dispersive liquid–liquid microextraction based on an effective device

A novel, rapid, simple, and low-cost on-line determination approach of dispersive liquid–liquid microextraction (DLLME) with low-density solvents was developed with the support of a specially designed effective homemade device. The proposed method surmounted the drawbacks of conventional DLLME of the need of high-density solvents as extractants, and the requirement of centrifugation operation to obtain phase separation, and the difficulties to realize on-line determination. The amount of sample utilized can conveniently change according to practical needs by varying the volume of the extraction tube of the device to perform a more effective DLLME. A case study was carried out to assess this method utilizing the dye rhodamine B as the model analyte. The experiment parameters influencing the extraction were systematically investigated. Under optimum conditions, the linearity was obtained in the range of 0.015–1.000μg/mL with the correlation coefficient (r2) of 0.9980. The limit of detection and quantification were 6.1 and 20.4μg/L, respectively. Good repeatability was achieved with the relative standard deviations (RSD) for five replicate measurements of different concentration samples less than 4.06%, and the presented method was successfully employed to quantify rhodamine B in three real samples.

A novel hydrogel based microextraction of analytes

We report on a new method for the preconcentration and microextraction of analytes from aqueous samples using a pH-sensitive hydrogel. It is referred to as semisolid–liquid dispersive microextraction (SSLDM) and has the advantages of both dispersive liquid–liquid microextraction (DLLME) and solid-phase extraction (SPE). The surface area of the droplets is large, so the equilibrium state is quickly reached. The high density of the gel facilitates phase separation, and disadvantages of existing methods are overcome in that there is no need for extraction and dispersive solvents (as in conventional DLLME) and no need for desorption (as in SPE). The SSLDM method integrates sampling, extraction and concentration into one single and solvent-free step. The method was exemplarily applied to the preconcentration of malachite green (MG) and crystal violet (CV) which then were quantified by spectrophotometry. Specifically, poly (styrene-alt-maleic acid), a pH-sensitive hydrogel, was used to extract MG and CV from water samples. The linear analytical range is from 0.01 to 1μmolL−1 for MG, and from 0.05 to 1μmolL−1 for CV. The correlation coefficient for MG and CV is 0.999 and 0.993, respectively. The limit of detection for MG and CV is 0.011 and 0.014μmolL−1, respectively.

Magnetic nanoparticle assisted dispersive liquid–liquid microextraction for the determination of 4-n-nonylphenol in water

A fast extraction technique involving dispersive liquid–liquid microextraction (DLLME) coupled with magnetic nanoparticle-based dispersive solid-phase microextraction (D-μ-SPE) was developed. For preliminary study, this method was applied for the extraction of 4-n-nonylphenol (4-NP) in water. In this method, n-octyl-triethoxysilane surface-modified magnetic iron oxide nanoparticles (C8MNPs) were first synthesized. The DLLME was performed by injecting 1 mL of methanol (disperser) containing 10 μL of 1-octanol (extraction solvent) into 15 mL of water sample. To this solution, C8MNPs were immediately added for the retrieval of the extraction solvent and of the extracted 4-NP by sonication. Subsequently, a magnet was held next to the vial to attract and isolate the C8MNPs. Then, the water sample was decanted, the nanoparticles were freeze-dried, and the 4-NP was extracted from nanoparticles by sonication with methanol. The detection of 4-NP was performed using a HPLC coupled with a fluorescence detector. Under optimal extraction conditions, a low method of detection limit (13.9 ng L−1), good linearity (R2 = 0.9958), and repeatability (1.7–2.2%) were achieved during 4-NP extraction. This method was also successfully used to analyze the real water samples such as drinking water and secondary wastewater. Generally, this sample preparation method offered an alternative to the conventional DLLME, because, in this method, centrifugation is not required and the retrieval of the extraction solvent is based on the adsorption process by magnetic nanoparticles (MNPs). Also, this two-step method improved the versatility of DLLME because the selection of the extraction solvent was no longer limited to the high density solvents. Because MNPs can be surface-modified for the extraction of different organic solvents, this method could have great prospects in the future.

Selective preconcentration of silver by one-step displacement dispersive liquid–liquid microextraction and determination by graphite furnace atomic absorption spectrometry

A simple and rapid one-step displacement dispersive liquid–liquid microextraction method (D-DLLME) was developed for the selective preconcentration of silver followed by graphite furnace atomic absorption spectrometry determination. In the proposed method, Cu was reacted with diethyldithiocarbamate (DDTC) to form a Cu–DDTC complex, and it was used as a chelating agent instead of DDTC for dispersive liquid–liquid microextraction (DLLME) of silver. Because the stability of Ag–DDTC is higher than that of Cu–DDTC, Ag can displace Cu from the Cu–DDTC complex and be preconcentrated in a single DLLME procedure. Potential interference from co-existing metal ions with lower DDTC complex stability was largely eliminated as they cannot displace Cu from the Cu–DDTC complex, and the tolerance limits for these ions were improved by a long way compared with the conventional DLLME method. Under the optimal conditions, the limit of detection of this method was 16 ng L−1 (3σ) for silver, and an enhancement factor of 82 was achieved with a sample volume of 5.0 mL. The proposed method was successfully applied for the determination of trace silver in some environmental and biological samples with satisfactory results.

Development of a new dispersive liquid–liquid microextraction method in a narrow-bore tube for preconcentration of triazole pesticides from aqueous samples

In the present work a new, simple, rapid and environmentally friendly dispersive liquid–liquid microextraction (DLLME) method has been developed for extraction/preconcentration of some triazole pesticides in aqueous samples and in grape juice. The extract was analyzed with gas chromatography–flame ionization detection (GC–FID) or gas chromatography–mass spectrometry (GC–MS). The DLLME method was performed in a narrow-bore tube containing aqueous sample. Acetonitrile and a mixture of n-hexanol and n-hexane (75:25, v/v) were used as disperser and extraction solvents, respectively. The effect of several factors that influence performance of the method, including the chemical nature and volume of the disperser and extraction solvents, number of extraction, pH and salt addition, were investigated and optimized. Figures of merit such as linearity ( r 2 > 0.995), enrichment factors (EFs) (263–380), limits of detection (0.3–5 μg L −1) and quantification (0.9–16.7 μg L −1), and relative standard deviations (3.2–5%) of the proposed method were satisfactory for determination of the model analytes. The method was successfully applied for determination of target pesticides in grape juice and good recoveries (74–99%) were achieved for spiked samples. As compared with the conventional DLLME, the proposed DLLME method showed higher EFs and less environmental hazards with no need for centrifuging.

Dispersive liquid–liquid microextraction using a surfactant as disperser agent

A novel and efficient surfactant-assisted dispersive liquid-liquid microextraction combined with high-performance liquid chromatography-photodiode array detection was developed for the determination of phenylurea herbicides in water samples. Based on this procedure, which is a dispersive-solvent-free technique, the extractant is dispersed in the aqueous sample using methyltrialkylammonium chloride. Compared with the conventional dispersive liquid-liquid microextraction, the new extraction method has many advantages such as higher extraction efficiency, low cost, reduced environmental hazards, and consumption of less extracting solvent. A few microliters of chloroform containing an appropriate amount of methyltrialkylammonium chloride (mixture of C8-C10) was used to extract the analytes from water samples. The main parameters relevant to the extraction process (namely, type of surfactant, selection of extractant solvent, extractant volume, surfactant concentration, ionic strength, and extraction time) were investigated. The performed analytical procedure showed limits of detection ranging from 2.3 to 18 ng/L, and precision ranges from 0.6% to 2.0% (as intra-day relative standard deviation, RSD) and from 1.3% to 8.3% (as inter-day RSD) depending on the analyte. The method showed good linearity between 0.04 and 40 microg/L with squared correlation coefficients better than 0.9920. This newly established approach was successfully applied to spiked real water samples.

Displacement-dispersive liquid–liquid microextraction coupled with graphite furnace atomic absorption spectrometry for the selective determination of trace silver in environmental and geological samples

A novel displacement-dispersive liquid–liquid microextraction method was developed for the selective determination of trace silver in complicated samples by graphite furnace atomic absorption spectrometry. This method involves two steps of dispersive liquid–liquid microextraction (DLLME). Firstly, copper ion reacted with diethyldithiocarbamate (DDTC) to form Cu-DDTC complex and extracted with DLLME procedure using carbon tetrachloride (extraction solvent) and methanol (dispersive solvent); then, the sedimented phase was dispersed into the sample solution containing silver ion with methanol and another DLLME procedure was carried out. Because the stability of Ag-DDTC is larger than that of Cu-DDTC, Ag + can displace Cu 2+ from the pre-extracted Cu-DDTC and thus the preconcentration of Ag + was achieved. Potential interference from co-existing transition metal ions with lower DDTC complex stability was largely eliminated as they cannot displace Cu 2+ from Cu-DDTC complex. The tolerance limits for the co-existing ions were increased by a long way compared with conventional DLLME. Under the optimal conditions, the limit of detection was 20 ng L −1 (3 σ) for silver with a sample volume of 5.0 mL, and an enhancement factor of 72 was achieved. The proposed method was successfully applied to determine of trace silver in some environmental and geological samples with satisfactory results.