Liquid-phase Microextraction Method Research Articles

Combination of online hollow fiber liquid phase microextraction with smartphone-based sensing for in situ formaldehyde assay in fabric and wastewater samples.

A miniaturized analytical methodology was introduced based on the combination of a direct and online hollow fiber microextraction method with smartphone color detection. The method was used for the determination of formaldehyde (target analyte) in fabric and wastewater samples. In this regard, two reagents including ammonium acetate buffer and acetylacetone were added to the formaldehyde samples to create a colored compound. The colored compound was extracted from the sample by using the hollow fiber liquid-phase microextraction method, the extracted phase was not taken out of the extraction box and was directly transferred into a specially designed detection cell, and a smartphone was applied forin-situ color sensing and data readout. This combination gathered the advantages of both state-of-the-art microextraction techniques and smartphone sensing. Formaldehyde, as a carcinogenic compound widely used in paint and clothing industries, was selected as a model test. Factors affecting extraction efficiency were investigated and optimized, including the type of organic solvents, reagent concentration, salt, pH, stirring speed, reaction temperature, and extraction time. The linear region of the method under optimal conditions was 40-1500µg L-1 for wastewater samples and 0.3-11.2mg kg-1 for fabrics. The limit of detection and limit of qualification were 13 and 40µg L-1, respectively. The relative standard deviations for concentrations of 100 and 1000µg L-1 were 6% and 4%, respectively. To evaluate the application of the method for real samples, types of fabric and two samples of oil refinery wastewater were selected. The relative recovery in real samples was 84-98%. The results of the analytical parameters of the method show that the developed method can be used as an efficient method to determine formaldehyde in real samples.

Preparation and investigation of green and cheap deep eutectic solvents for determination of essential and toxic metal ions at trace levels in different coffee products

In this research, a vortex-assisted hydrophobic deep eutectic solvent-based dispersive liquid phase microextraction (VA-HDES-DLPME) method was developed to extract some essential (Fe, Mn and Zn) and toxic (Cd and Pb) metal ions from coffee products. After the VA-HDES-DLPME method, the amounts of the metal ions in the HDES-phase were determined by flame atomic absorption spectrophotometry (FAAS). For selective extraction of metal ions, five HDESs (as extraction solvent) were prepared and tested according to the ultrasonic-assisted procedure. Some dispersive solvents were investigated to ensure the dispersion of HDES in the sample solution. In the VA-HDES-DLPME method, heating and centrifugation steps were not required to separate the HDES-phase from the sample solution. Key factors were investigated and optimized to achieve selective and rapid extraction of metal ions. Under optimized conditions, the working range of the VA-HDES-DLPME method for metal ions ranged from 0.03 to 280 μg kg−1. The detection limits of Fe(II), Mn(II), Zn(II), Cd(II), and Pb(II) ions were 0.01, 0.27, 0.02, 0.015, and 0.18 μg kg−1, respectively. Relative standard deviation and extraction recovery for five replicate runs of 5 μg kg−1 of metal ions were in the range of 1.3%–1.9% and 94 ± 4%-98 ± 2%, respectively. Validation of the VA-HDES-DLPME method was tested by studies on three reference materials. In the final step, the VA-HDES-DLPME method was successfully applied to microwave digestion of coffee samples using a standard addition method. The obtained quantitative recoveries showed the good accuracy of the method.

In-syringe homogeneous liquid-phase microextraction followed by filtration-based phase separation for on-site extraction of chloroanilines from water samples.

This study introduces a new in-syringe homogeneous liquid-phase microextraction method for the rapid on-site extraction of chloroanilines from water samples. Extraction was performed using a plastic syringe, eliminating the use of any electrical power source. Di-(2-ethylhexyl) phosphoric acid (DEHPA) served as the extractant. The process initially involved dissolving DEHPA in an alkaline solution to obtain a homogeneous solution. Subsequently, the sodium salt of DEHPA was precipitated by salting-out, and the resulting heterogeneous mixture was filtered using a syringe filter. The precipitate containing the analytes was then dissolved in methanol for analysis by high-performance liquid chromatography. Under optimal conditions, extraction recovery for chloroanilines ranged from 26% to 71%. Method linearity was evaluated within a concentration range of 1.0-100µg/L, resulting in coefficients of determination exceeding 0.9987 for all analytes. Method detection limits ranged from 0.28 to 0.41µg/L. Intra and inter-day precision values were below 9.5% and 10.8%, respectively. The developed method was applied to determine chloroanilines in real waters, yielding acceptable recoveries ranging from 80% to 109% for spiked tap, rain, and stream waters. Additionally, the method was successfully employed for on-site extraction of target contaminants, demonstrating no statistically significant differences compared to laboratory results.

Determination of phenytoin at trace levels in domestic wastewater and synthetic urine samples by gas chromatography-mass spectrometry after its preconcentration by simple liquid-phase microextraction.

This work presents a sensitive and accurate analytical method for the determination of phenytoin at trace levels in domestic wastewater and synthetic urine samples by gas chromatography-mass spectrometry (GC-MS) after the metal sieve-linked double syringe liquid-phase microextraction (MSLDS-LPME) method. A metal sieve was produced in our laboratory in order to disperse water-immiscible extraction solvents into aqueous media. Univariate optimization studies for the selection of proper extraction solvent, extraction solvent volume, mixing cycle, and initial sample volume were carried out. Under the optimum MSLDS-LPME conditions, mass-based dynamic range, limit of quantitation (LOQ), limit of detection (LOD), and percent relative standard deviation (%RSD) for the lowest concentration in calibration plot were figured out to be 100.5-10964.2 μg kg-1, 150.6 μg kg-1, 45.2 μg kg-1, and 9.4%, respectively. Detection power was improved as 187.7-folds by the developed MSLDS-LPME-GC-MS system while enhancement in calibration sensitivity was recorded as 188.0-folds. In the final step of this study, the accuracy and applicability of the proposed system were tested by matrix matching calibration strategy. Percent recovery results for domestic wastewater and synthetic urine samples were calculated as 95.6-110.3% and 91.7-106.6%, respectively. These results proved the accuracy and applicability of the proposed preconcentration method, and the obtained analytical results showed the efficiency of the lab-made metal sieve apparatus.

Alkanediol–hexafluoroisopropanol amphiphilic supramolecular solvent: Fabrication, characterization, and application potential for doping control of hormones and metabolic modulators in human urine

A novel amphiphilic supramolecular solvent (SUPRAS) was developed by hexafluoroisopropanol (HFIP)-induced self-assembly of 1,2-hexanediol in an aqueous matrix. Its application potential in multiclass determination was assessed by extracting from urine 10 prohibited hormones and metabolic modulators (log P from 2.38 to 7.57) listed by the World Anti-Doping Agency (WADA). This SUPRAS is stably formed across a wide pH range (2–12) and is unaffected by salt concentrations (<10 % g mL−1 of NaCl), and it has a higher density than water. The dehydration and hydrogen bonding ability of HFIP, as well as hydrophobic interactions between alkanediols, dominates the formation of the SUPRAS. The nanostructure of the SUPRAS, composed of 1,2-hexanediol, HFIP, and a high content of water (>25 %, w/w), forms large spherical micellar aggregates (10–100 μm) that exhibit amphiphilic properties. A 1,2-hexanediol-HFIP SUPRAS-based liquid-phase microextraction (LPME) method for detection of selected prohibited drugs in urine coupled with liquid chromatography–tandem mass spectrometry (LC-MS/MS) was established, optimized, and validated. The method showed fast extraction time (30 s of vortex) and low solvent consumption (160 μL of organic solvent). Under the optimal conditions (7 % g mL−1 of 1,2-hexanediol, 10 % v/v of HFIP), the SUPRAS achieved high extraction efficiencies (>80 %) and an enrichment factor of 6.0, with minimal matrix effects for all analytes due to its high amphiphilicity and large surface area. The method demonstrated excellent linearity (R ≥0.9909), with method limits of detection ranging from 0.018 to 0.18 ng mL−1 and method limits of quantitation ranging from 0.060 to 0.60 ng mL−1, which are well below the minimum required performance levels set by authorities. Furthermore, the intra- and inter-day relative recoveries for spiked human urine samples varied in the ranges of 90.3–121 % and 88.1–119 %, respectively, with relative standard deviations less than 13 % and 19 %, respectively. This SUPRAS-based LPME method proves to be simple, highly efficient, and eco-friendly, and it has promising potential for multiclass determination in doping control.

Development of a vortex-assisted switchable-hydrophilicity solvent-based liquid phase microextraction for fast and reliable extraction of Zn (II), Fe (II), Pb (II), and Cd (II) from various baby food products

This manuscript describes the development of a novel liquid phase microextraction (LPME) method for the extraction and determination of Zn (II), Fe (II), Pb (II), and Cd (II) in various infant/baby food and supplements products. The method is based on vortex-assisted extraction combined with a switchable-hydrophilicity solvent (SHS) sample preparation. The SHS, which undergoes reversible phase changes triggered by pH change, enables selective extraction and easy phase separation. A flame atomic absorption spectroscopy was used in the final determination step. Optimization studies revealed, that the optimal pH of the sample solution (after digestion) during analytes extraction is 5.5. A l-proline is added to the sample (375 mM) to ensure the complexation of the target metal cations. After the complexation step, 750 µL of SHS - a N, N-Dimethylcyclohexylamine along with 0.9 mL of 2 M of acetic acid solution is added (hydrophilicity switch-on stage) and mixed manually to obtain a homogeneous solution. In the last stage, 0.45 mL of 10 M NaOH solution (hydrophilicity switch-off stage) is added to the sample solution and a vortex for 100 s is applied to ensure the effective extraction and separation of the complex containing the analytes. At this stage, a cloudy solution is immediately obtained. Finally, the effective phase separation is obtained at the centrifugation step (4000 rpm for 2 mins). The method limit of detection was as 0.03, 0.009, 0.6, and 0.2 ng/L for Zn (II), Fe (II), Cd (II), and Pb (II) respectively with RSD% below 2.0 %. The analysis of certified reference materials and real samples proved the full applicability of the method for routine analysis, contributing to the field of heavy metal analysis and ensuring the safety of baby products. According to the AGREE methodology, this method can be named as green analytical chemistry method with a score of 0.77.

Development of a hollow fiber–liquid phase microextraction method using tissue culture oil for the extraction of free metoprolol from plasma samples

In this research, a method known as a hollow fiber-liquid-phase microextraction was employed to extract and concentrate free metoprolol from plasma samples. The extracted analyte was subsequently determined using high-performance liquid chromatography coupled with a diode-array detector. Several parameters, including hollow fiber length, sonication time, extraction temperature, and salt addition, were investigated and optimized to enhance extraction efficiency. After extracting the analyte under optimum conditions from plasma samples, the enrichment factor and extraction recovery were 50 and 86 %, respectively. Moreover, the method exhibited detection and quantification limits of 0.41 and 1.30 ng mL−1, respectively. The analysis of real samples demonstrated satisfactory relative recoveries in the range of 91–99 %.

Removal of two antidepressant active pharmaceutical ingredients from hospital wastewater by polystyrene-coated magnetite nanoparticles-assisted batch adsorption process.

This study employed simple polystyrene-coated magnetite nanoparticles (PS@MNPs)-assisted batch adsorption process for the removal of two antidepressant active ingredients (amitriptyline HCl and sertraline HCl) from hospital wastewater. Dominant parameters of the adsorption process including pH, adsorbent amount, and contact period were optimized through the univariate approach to enhance the adsorption efficiency. Upon reaching optimum adsorption conditions, equilibrium experiments were performed by spiking the adsorbates in hospital wastewater in the concentration range of 100-2000 μg/L. The concentrations of the adsorbates in the effluent were calculated using the matrix-matching calibration strategy to enhance the accuracy of quantification. A validated switchable solvent-based liquid phase microextraction (SS-LPME) method was employed to enrich the two active pharmaceutical ingredients (APIs) prior to sensitive determination with GC-MS (gas chromatography-mass spectrometry). The equilibrium data were mathematically modeled employing the Langmuir and Freundlich adsorption isotherm models. The isotherm constants were calculated, and the results showed that both the isotherm models fitted well with the experimental data. The efficient and simple batch adsorption strategy reported in this study was successfully employed to remove amitriptyline HCl and sertraline HCl from hospital wastewater at low concentrations.

Development of a new method for determination of bisphenol A based on stirrer-assisted switchable hydrophilic solvent-based liquid phase microextraction coupled with electrochemical sensor

In this work, a novel stirrer-assisted liquid-phase microextraction method using switchable hydrophilic solvents was developed for the extraction and preconcentration of bisphenol A from real samples prior to electrochemical analysis. For the first time, the effect of stirring while switching the extraction solvent (N,N-dipropylamine, DPA) was investigated, and the use of stirring instead of temperature change, which is a time-consuming process, hazardous acids (e.g., HCl), and dry ice was used for bisphenol A extraction based on switchable solvents. Various parameters such as solvent type, solvent volume, stirring time, and stirring speed were optimized. The optimized conditions were 100 μl DPA, 2 min extraction time, 30 s stirring time, 700 rpm stirring speed, and solution pH of 7.0. A theoretical study was also conducted to show the effects of stirring on the homogenization of the phases. The proposed method offers some advantages, such as simplicity, use of a small amount of inexpensive and less hazardous reagents, rapid extraction, and shorter analysis time. Under the optimized conditions for the developed method, LOQ and LOD were obtained to be 0.01 and 0.003 μM, respectively. Moreover, the calibration curves were linear in the range of 0.01–250 μM. The proposed method was used for the determination of bisphenol A in food and water samples.

Deep eutectic solvents for the determination of endocrine disrupting chemicals

The harmful effects of endocrine disrupting chemicals (EDCs) to humans and other organisms in the environment have been well established over the years, and more studies are ongoing to classify other chemicals that have the potential to alter or disrupt the regular function of the endocrine system. In addition to toxicological studies, analytical detection systems are progressively being improved to facilitate accurate determination of EDCs in biological, environmental and food samples. Recent microextraction methods have focused on the use of green chemicals that are safe for analytical applications, and present very low or no toxicity upon disposal. Deep eutectic solvents (DESs) have emerged as one of the viable alternatives to the conventional hazardous solvents, and their unique properties make them very useful in different applications. Notably, the use of renewable sources to prepare DESs leads to highly biodegradable products that mitigate negative ecological impacts. This review presents an overview of both organic and inorganic EDCs and their ramifications on human health. It also presents the fundamental principles of liquid phase and solid phase microextraction methods, and gives a comprehensive account of the use of DESs for the determination of EDCs in various samples.

Deep eutectic solvent liquid phase microextraction, powered by ultrasonic system, for determination of β-carotene in food samples

The research work is mainly concerned with the extraction of β-carotene, which is a terpenoid compound, from food and fruit samples using deep eutectic solvent based liquid phase extraction. Deep eutectic solvent liquid phase microextraction method, powered by ultrasonic mixing, (DES-UP-LPME) was carried out with deep eutectic solvent (DES) consisting of tetrabutylammoniumbromide (TBAB) and decanoic acid (DA). Key parameters such as pH, sample volume, tetrahydrofuran (THF) volume, DES type and volume, matrix effect, ultrasonication/centrifugation time were optimized to increase the extraction efficiency of β-carotene. Quantitative recoveries were obtained when pH, TBAB:DA ratio and sample volume were 3, 1:3 and 30, respectively. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.005 µg/mL and 0.015 µg/mL, respectively. Various food samples were analyzed spectrophotometrically by using the developed DES-UP-LPME at 450 nm. The addition/recovery studies were also performed on water samples to evaluate the accuracy of the method.

Optimization of vortex-assisted hydrophobic magnetic deep eutectic solvent-based dispersive liquid phase microextraction for quantification of niclosamide in real samples.

In this manuscript, a green and fast vortex-assisted hydrophobic magnetic deep eutectic solvent-based dispersive liquid phase microextraction (VA-HMDES-DLPME) method was developed for the selective extraction and determination of niclosamide in read samples, including rice, medicine tablets, and water samples. Here, hydrophobic magnetic deep eutectic solvents were used as the extracting solvent without requiring any centrifugation step. In the light of preliminary experiments, important parameters, such as volume of extraction solvent, pH, acetonitrile volume and vortex time, affecting the extraction efficiency of niclosamide were optimized using a Box-Behnken design. The linear dynamic range (0.25-120 µg/L), the limit of detection (0.08 µg/L), the limit of quantitation (0.25 µg/L), preconcentration factor (180), and enrichment factor (130) of the method were determined using optimized data. In particular, the validation parameters of the optimized VA-HMDES-DLPME, including robustness, matrix effect accuracy, and precision, were investigated. In addition to this, intra- and inter-day precisions were determined as≤3.5 % and≤4.1%, respectively. Finally, the optimized method was successfully used for the extraction of niclosamide in the selected samples prior to spectrophotometric analysis.

An air-assisted dispersive liquid phase microextraction method based on a hydrophobic magnetic deep eutectic solvent for the extraction and preconcentration of melamine from milk and milk-based products.

In the current research, a fast and sustainable air-assisted hydrophobic magnetic deep eutectic solvent-based dispersive liquid phase microextraction followed by UV-Vis spectrophotometry measurements was optimized for the extraction and determination of melamine in milk and milk-based products. The central composite design was applied for the optimization of factors affecting the recovery of melamine. Quantitative extraction of melamine was achieved using hydrophobic magnetic deep eutectic solvents prepared from a mixture of octanoic acid, aliquat-336, and cobalt(II) chloride. The optimum conditions for extraction were found as follows: 6 extraction cycles, pH 8.2, extraction solvent volume 260µL, and acetone volume 125µL.Interestingly, a centrifugation step was not required to achieve phase separation. Under the optimum conditions, melamine was determined in the linear range of 3-600ngmL-1, the limit of detection (3Sblank/m) of 0.9ngmL-1, and the enrichment factor of 144. The validation of the method was investigated by the analysis of reference materials. Consequently, the method was successfully applied for the analysis of melamine residues in milk and milk-based products.

Extraction of Novichoks from aqueous samples for verification analysis of Chemical Weapons Convention

ABSTRACT The study was undertaken with the objective of evaluating the different procedures for the extraction of the Novichok class of chemicals from aqueous samples for the verification of Chemical Weapons Convention (CWC). These classes of chemicals are recently added to the scheduled list of CWC, which necessitates the optimisation of analytical protocols for their verification analyses in different environmental samples. Three analytes, namely N-(1-(diethylamino)ethylidene)-P-methylphosphonamidic fluoride (A230), methyl N-(1-(diethylamino)ethylidene)phosphoramidofluoridate (A232) and ethyl N-(1-(diethylamino)ethylidene)phosphoramidofluoridate (A234), were taken as representative chemicals in aqueous samples and extracted with established protocols, such as liquid–liquid extraction (LLE), solid phase extraction (SPE), solid-supported liquid extraction (SLE) and liquid phase microextraction (LPME) techniques. The extraction efficacies were evaluated in terms of the recoveries of analytes as well as the removal of background interferences. Amongst the extraction techniques, SLE offered the least (43.2–66.7%) and LLE and SPE-HLB offered the best recoveries (79.1–92.9%) of the analytes with adequate sample clean-up. LPME techniques produced much better detection limits, going down to 7.6 ng/mL for A234. LPME methods were also found advantageous in terms of high enrichment factors, ease of operation, minimal waste generation and individual safety for handling the toxic chemicals.

Application of instantaneous nebulization dispersive liquid-phase microextraction combined with HPLC for the determination of chalcone and isoflavone in traditional Chinese medicines.

A simple and rapid instantaneous nebulization dispersive liquid-phase microextraction method was developed, and combined with high-performance liquid chromatography for determination of the contents of seven analytes in traditional Chinese medicines. In this study, using the sprinkler device to achieve instantaneous synchronous dispersion and extraction, only one spray can rapidly achieve the concentration and enrichment of seven kinds of chalcone and isoflavones. The key factors affecting the extraction efficiency were optimized including the type and volume of extractant, the pH and salt concentration of the sample phase, and the number of dispersion. Under the optimal conditions, the enrichment factor of the target analytes ranged from 103.1 to 180.9, with good linearity and correlation coefficients above 0.9970. The limits of detection ranged from 0.02 to 0.15ng/mL, with good accuracy (recoveries 91.1 to 108.9%) and precision (relative standard deviations 1.5-7.1%). This method has short extraction time (2 s), low organic solvent consumption and high enrichment effect, so it has a wide application prospects.

Spray assisted preconcentration method combined with HPLC – Continuous flow hydride generation – FAAS for inorganic arsenic speciation in olive oil samples

Speciation analysis of arsenic in edible oils is an important topic in terms of the assessment of its risks for human health and the quality of edible oils. In this study, high performance liquid chromatography – continuous flow hydride generation – flame atomic absorption spectrometry (HPLC-CFHG-FAAS) system after vortex assisted reverse phase spray-based fine droplet formation liquid phase microextraction (VA-RP-SFDF-LPME) method was proposed to qualify/quantify arsenite and total arsenic. Limit of detection (LOD) and limit of quantification (LOQ) for arsenite were calculated as 2.86 µg kg–1 (as As) and 9.52 µg kg–1 (as As), respectively. After the extraction/preconcentration process, a prereduction was carried out in the presence of 0.010 mol/L HCl (containing 0.39% L-cysteine) with heat (90 ± 5 oC) for the determination of total arsenic content while arsenite was directly determined via the developed system. Recovery for arsenite and total inorganic arsenic were in the range of 91.5 – 120.4% and 90.0 – 104.4%, respectively. The developed method is proposed for the analysis of olive oil samples containing inorganic arsenic species. This is the first study to carry out the inorganic arsenic speciation in olive oil by HPLC-CFHG-FAAS system after the preconcentration of the species by the VA-RP-SFDF-LPME system. For the matrix including arsenite and arsenate, the developed method can be safely used to find the concentration of both species accurately.

Optimization and Validation of Liquid Phase Microextraction Method Based on Oil Droplets to Quantify Algal Metabolites (2-Methylisoborneol, Geosmin, etc.) in Drinking Water Supplies

Optimization and Validation of Liquid Phase Microextraction Method Based on Oil Droplets to Quantify Algal Metabolites (2-Methylisoborneol, Geosmin, etc.) in Drinking Water Supplies

Development of A Liquid-Phase Microextraction Method for Simultaneous Determination of Parabens in Lipstick Samples at Trace Levels by High-Performance Liquid Chromatography.

The endocrine-disrupting potential of parabens, as well as their relation to cancer, has sparked significant discussions over their impact. Consequently, analyses of cosmetic products are an essential necessity, particularly in terms of human health and safety. In this study, a highly accurate and sensitive liquid-phase-based microextraction method was developed to determine the five parabens at trace levels by high-performance liquid chromatography. All prominent parameters of the method such as extraction solvent type and amount (1,2-dichloroethane/250μL), and dispersive solvent type and amount (isopropyl alcohol/2.0mL) were optimized to enhance the extraction efficiency of the analytes. The mobile phase consisting of 50mM ammonium formate aqueous solution (pH4.0) and acetonitrile (60:40, v/v) was used to elute the analytes at a flow rate of 1.2mLmin-1 in the isocratic mode. Analytical performance of the optimum method for methyl, ethyl, propyl, butyl and benzyl parabens were determined and the analytes recorded detection limit values of 0.78, 0.75, 0.34, 0.33 and 0.75μgkg-1, respectively. Four different lipstick samples were analyzed under optimum conditions of the developed method, and the amount of parabens quantified in the samples using matrix matched calibration standards was in the range of 0.11-1.03%.

Determination of trimethoprim in milk, water and plasma using protein precipitation combined with liquid phase microextraction method

A simple and effective microextraction method based on protein precipitation and continuous sample drop flow microextraction (CSDF-ME) for the extraction of trimethoprim from milk, water and plasma is reported. The precipitation with zinc acetate was used to appreciably separate trimethoprim (TMP) from the complex matrix of milk samples. After protein precipitation, TMP which was present in the upper phase was extracted and pre-concentrated using CSDF-ME. To this end, the pH of the upper phase was adjusted to 10.0 and filtered. Afterwards, the extracted TMPs were concentrated by pumping the aqueous solution into a conical vial containing 35.0 μL of chloroform and 7.5 μL of DMSO (as co-solvent) at a flow rate of 0.45 mL min-1. Finally, the concentrated TMPs were determined by HPLC-UV. This is the first report on the extraction and quantification of TMP from milk samples using protein precipitation coupled with CSDF-ME-HPLC-UV. Having optimized the experimental conditions, the proposed method was thoroughly validated for milk. plasma and water. The results showed that the method was linear between 10.0 and 1200.0 µg L-1. The LOD and LOQ for TMP in different matrices were 3.0–8.0 and 10.0–25.0 µg L− 1, respectively. The relative recovery and the enrichment factor were 81.6–101.3% and 19.0–40.0, respectively. The relative standard deviations for intraday precision and between-day precision at a concentration level of 200.0 μg L-1 were 3.3–6.0 and 2.6–8.3, respectively. The resulting LOQ with trueness over 81.6%, indicates the method's applicability for TMP analysis in complicated matrices such as milk with a considerable reduction in chemicals and reagents required for the determination.

Development of a Liquid-Phase Microextraction Method Prior to HPLC Analysis of Quercetin in Food Samples.

In this research, an efficient, fast, low-cost and easy-to-use liquid-phase microextraction method was established to measure quercetin in onion and tomato before analysis by HPLC instrument. Herein, a rotatable central composite design-response surface methodology and artificial neural network were applied to model, optimize and predict the affecting factors on the microextraction procedure. Here, a minimal level of extractant was applied in the absence of a disperser. The cloudy state was formed by repeatedly suctioning and injecting the mixture of the aqueous solution and extractant with a glass syringe. Due to this procedure, a turbid solution composed of the very fine droplets of extractant dispersed in the aqueous solution was created, the contact surface was significantly enlarged and the quercetin was promptly extracted. The optimum values for the proposed method included 284μL of 1-undecanol as the organic extractive solvent, pH of sample 3.3, the number of air injected nine times and speed and duration of centrifugation 4,000rpm and 5min. The linear range and detection of limit were achieved at 20-4,000 and 6μgL-1, respectively. RSD% was obtained ˂4.93% (n = 5). This model was applied to monitor quercetin in tomato and onion samples.