Sodium dodecyl sulfate sensitized switchable solvent liquid‐phase microextraction for the preconcentration of protoberberine alkaloids in Rhizoma coptidis

A sodium dodecyl sulfate sensitized switchable solvent liquid‐phase microextraction method was developed and applied to the preconcentration of active alkaloids in Rhizoma coptidis followed by high performance liquid chromatography determination. Before extraction, nonionic triethylamine was converted to its cationic form in the presence of carbon dioxide. Then, the ionic solvent carrying target analytes was once more reverted to its nonionic form by adding sodium hydroxide, as well as phase separation and analytes enrichment were realized simultaneously. Several parameters affecting the approach, such as concentration of sodium dodecyl sulfate, extraction solvent volume, sodium hydroxide concentration, sample phase pH, injection solvent type, and extraction time, were investigated and optimized. The possible microextraction mechanism of double micelle supramolecular inclusion was explored. Under the optimum conditions, the enrichment factors of four protoberberine alkaloids were from 101.8 to 152.0. The linear ranges (with r² ≥ 0.990) were 0.032–4.23, 0.031–4.33, 0.0026–10.04, and 0.0013–4.13 μg/mL for epiberberine, coptisine, palmatine, and berberine, respectively. The detection limits were in the range of 0.16–0.32 ng/mL. Satisfactory accuracies (recoveries 98.8–104.6%) and precisions (RSDs 1.9–10.9%) were also obtained. The results showed that the approach is rapid, effective, eco‐friendly, and easy‐to‐handle for the enrichment and detection of active alkaloids in Rhizoma coptidis.     

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 0.08 ng/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.     

Development of a novel hollow‐fiber liquid‐phase microextraction based on oil‐in‐salt and its comparison with conventional one

A novel hollow‐fiber liquid‐phase microextraction based on oil‐in‐salt was proposed and introduced for the simultaneous extraction and enrichment of the main active compounds of hesperidin, honokiol, shikonin, magnolol, emodin, and β,β′‐dimethylacrylshikonin in a formula of Zi‐Cao‐Cheng‐Qi decoction and the single herb, Fructus Aurantii Immaturus , Cortex Magnoliae Officinalis , Radix et Rhizoma , and Lithospermum erythrorhizon , composing the formula prior to their analysis by high‐performance liquid chromatography. The results obtained by the proposed procedure were compared with those obtained by conventional hollow‐fiber liquid‐phase microextraction, and the proposed procedure mechanism was described. In the procedure, a hollow‐fiber segment was first immersed in organic solvent to fill the solvent in the fiber lumen and wall pore, and then the fiber was again immersed into sodium chloride solution to cover a thin salt membrane on the fiber wall pore filling organic solvent. Under the optimum conditions, the enrichment factors of the analytes were 0.6–109.4, linearities were 0.002–12 μg/mL with r ² ≥ 0.9950, detection limits were 0.6–12 ng/mL, respectively. The results showed that oil‐in‐salt hollow‐fiber liquid‐phase microextraction is a simple and effective sample pretreatment procedure and suitable for the simultaneous extraction and concentration of trace‐level active compounds in traditional Chinese medicine.     

Ballpoint connector‐protected salt‐oil‐salt liquid phase microextraction for concentration and enrichment of trace anthraquinone compounds in rhubarb

This study proposed a new ballpoint connector‐protected salt‐oil‐salt liquid phase microextraction for extraction and enrichment of trace rhein and chrysophanol in rhubarb prior to determination of the analytes by high performance liquid chromatography. In this study, a handy ballpoint connector (between ballpoint tip and ink chamber) was used as extraction device, in which its cavity was filled with n‐octanol, and the bare n‐octanol in its two opening ends was covered with a thin layer of sodium chloride film. The design subtly assembled salt film onto ballpoint connector for extraction and enrichment, which greatly improved the enrichment factors of the target analytes. Moreover, the novel procedure and its extraction mechanism were described and analyzed, and several crucial parameters reflecting the extraction effect were investigated and optimized. Under optimum conditions, high enrichment factors (247 and 127), good linearities with r ≥ 0.9998, limits of detection (0.6–1.1 ng/mL), relative standard deviations of intra‐ and interday (2.2–8.8% and 4.3–8.9%), and average recoveries (97.6–98.1%), were obtained, respectively. The proposed method can not only eliminate the negative effects from viscosity and ion strength at high salt concentration of sample phase, but also make salting‐out effect be focused on small area so as to maximize the extraction effect.     

Three‐phase hollow‐fiber liquid‐phase microextraction based on deep eutectic solvent as acceptor phase for extraction and preconcentration of main active compounds in a traditional Chinese medicinal formula

A three‐phase hollow‐fiber liquid‐phase microextraction based on deep eutectic solvent as acceptor phase was developed and coupled with high‐performance capillary electrophoresis for the simultaneous extraction, enrichment, and determination of main active compounds (hesperidin, honokiol, shikonin, magnolol, emodin, and β,β′‐dimethylacrylshikonin) in a traditional Chinese medicinal formula. In this procedure, two hollow fibers, impregnated with n‐heptanol/n‐nonanol (7:3, v/v) mixture in wall pores as the extraction phase and a combination (9:1, v/v) of methyltrioctylammonium chloride/glycerol (1:3, n/n) and methanol in lumen as the acceptor phase, were immersed in the aqueous sample phase. The target analytes in the sample solution were first extracted through the organic phase, and further back‐extracted to the acceptor phase during the stirring process. Important extraction parameters such as types and composition of extraction solvent and deep eutectic solvent, sample phase pH, stirring rate, and extraction time were investigated and optimized. Under the optimal conditions, detection limits were 0.3–0.8 ng/mL with enrichment factors of 6–114 for the analytes and linearities of 0.001–13 μg/mL (r² ≥ 0.9901). The developed method was successfully applied to the simultaneous extraction and concentration of the main active compounds in a formula of Zi‐Cao‐Cheng‐Qi decoction with the major advantages of convenience, effectiveness, and environmentally friendliness.     

Ultrapreconcentration and determination of organophosphorus pesticides in water by solid‐phase extraction combined with dispersive liquid–liquid microextraction and high‐performance liquid chromatography

Solid‐phase extraction coupled with dispersive liquid–liquid microextraction was developed as an ultra‐preconcentration method for the determination of four organophosphorus pesticides (isocarbophos, parathion‐methyl, triazophos and fenitrothion) in water samples. The analytes considered in this study were rapidly extracted and concentrated from large volumes of aqueous solutions (100 mL) by solid‐phase extraction coupled with dispersive liquid–liquid microextraction and then analyzed using high performance liquid chromatography. Experimental variables including type and volume of elution solvent, volume and flow rate of sample solution, salt concentration, type and volume of extraction solvent and sample solution pH were investigated for the solid‐phase extraction coupled with dispersive liquid–liquid microextraction with these analytes, and the best results were obtained using methanol as eluent and ethylene chloride as extraction solvent. Under the optimal conditions, an exhaustive extraction for four analytes (recoveries >86.9%) and high enrichment factors were attained. The limits of detection were between 0.021 and 0.15 μg/L. The relative standard deviations for 0.5 μg/L of the pesticides in water were in the range of 1.9–6.8% (n = 5). The proposed strategy offered the advantages of simple operation, high enrichment factor and sensitivity and was successfully applied to the determination of four organophosphorus pesticides in water samples.     

Ionic liquid for single‐drop microextraction followed by high‐performance liquid chromatography‐ultraviolet detection to determine carbonyl compounds in environmental waters

A sensitive method based on ionic liquid for single‐drop liquid microextraction coupled with HPLC‐UV was developed for the determination of carbonyl compounds in environmental waters using 1‐octyl‐3‐methylimidazolium hexafluorophosphate [C₈min][PF₆] as extraction solvent and 2,4‐dinitrophenylhydrazine as derivatizing agent. The extraction parameters affecting the enrichment factors such as solvent volume, pH, extraction time and salt concentration were investigated. A homemade funnel form polytetrafluoroethylene sleeve was fixed at the tip of the syringe needle and this allowed the use of 10 μL drop of ionic liquid for direct immersion extraction. Under the optimal conditions, the remarkable enrichment factors up to 150‐fold were obtained depending on the target analytes. The method has been validated when rectilinear relationship was obtained between the concentrations of analytes and peak area in the range of 5–100 ng/mL, the correlation coefficients were from 0.995 to 0.998, and the limit of detection was in the range of 0.04–2.03 ng/mL. The method was applied to monitor the concentration of carbonyl compounds in environmental waters with spiked recovery in the range of 84.2–106.9%.     

Determination of 3,5,6‐trichloro‐2‐pyridinol,phoxim and chlorpyrifos‐methyl in water samples using a new pretreatment method coupled with high‐performance liquid chromatography

A novel low‐density solvent‐based vortex‐assisted surfactant‐enhanced‐emulsification liquid–liquid microextraction with the solidification of floating organic droplet method coupled with high‐performance liquid chromatography was developed for the determination of 3,5,6‐trichloro‐2‐pyridinol, phoxim and chlorpyrifos‐methyl in water samples. In this method, the addition of a surfactant could enhance the speed of the mass transfer from the sample solution into the extraction solvent. The extraction solvent could be dispersed into the aqueous by the vortex process. The main parameters affecting the extraction efficiency were investigated and the optimum conditions were established as follows: 80 μL 1‐undecanol as extraction solvent, 0.2 mmol/L of Triton X‐114 selected as the surfactant, the vortex time was fixed at 60 s with the vortex agitator set at 3000 rpm, the concentration of acetic acid in sample solution was 0.4% v/v and 1.0 g addition of NaCl. Under the optimum conditions, the enrichment factors were from 172 to 186 for the three analytes. The linear ranges were from 0.5 to 500 μg/L with a coefficient of determination (r²) of between 0.9991 and 0.9995. Limits of detections were varied between 0.05 and 0.12 μg/L. The relative standard deviations (n = 6) ranged from 0.26 to 2.62%.     

Analysis of isoquinoline alkaloids using chitosan‐assisted liquid–solid extraction followed by microemulsion liquid chromatography employing a sub‐2‐micron particle stationary phase

A simple, efficient, and green chitosan‐assisted liquid–solid extraction method was developed for the sample preparation of isoquinoline derivative alkaloids followed by microemulsion LC. The optimized mobile phase consisted of 0.8% w/v of ethyl acetate, 1.0% w/v of SDS, 8.0% w/v of n‐butanol, 0.1% v/v acetic acid, and 10% v/v ACN. Compared to pharmacopoeia method and organic solvent extraction, this new approach avoided the use of volatile organic solvents, replacing them with relatively small amounts of chitosan. Under the optimum conditions, good linearity (r² > 0.9980) for all calibration curves and low detection limits between 0.05 and 0.10 μg/mL were achieved. The presented procedure was successfully applied to determine alkaloids in Rhizoma coptidis with satisfactory recoveries (81.3–106.4%).     

Comparison of three‐phase hollow fiber liquid‐phase microextraction based on reverse micelle with conventional two‐phase hollow fiber liquid‐phase microextraction and their applications for analysis of cinnamic acids in traditional Chinese medicines

A novel three‐phase hollow fiber liquid‐phase microextraction was developed based on reverse micelle as extraction solvent and acceptor phase, and compared with conventional two‐phase hollow fiber liquid‐phase microextraction. Both procedures were used in the extraction and concentration of four cinnamic acids (caffeic acid, p‐hydroxycinnamic acid, ferulic acid, and cinnamic acid) in traditional Chinese medicines prior to high‐performance liquid chromatography analysis. Parameters affecting the two procedures were investigated and optimized to obtain the optimum enrichment factors. The mechanism of the developed procedure was explored and elucidated by comparison with conventional two‐phase hollow fiber liquid‐phase microextraction. Under the optimized conditions, the analytes’ enrichment factors were between 50 and 118 for the proposed procedure, and 31–96 for conventional two‐phase mode. Satisfactory linear ranges (r² ≥ 0.99), detection limits (0.1–0.6 ng/mL), precisions (<9.2%), and accuracies (recoveries: 80–123.1%) were observed for the two procedures. The results showed that the enrichment capacity of the proposed procedure for the cinnamic acids is better than that of conventional two‐phase procedure, and both are eco‐friendly, simple, and effective for the enrichment and detection of cinnamic acids in traditional Chinese medicines.     

Solid‐phase microextraction based on an agarose‐chitosan‐multiwalled carbon nanotube composite film combined with HPLC–UV for the determination of nonsteroidal anti‐inflammatory drugs in aqueous samples

We describe the preparation, characterization, and application of a composite film adsorbent based on blended agarose‐chitosan‐multiwalled carbon nanotubes for the preconcentration of selected nonsteroidal anti‐inflammatory drugs in aqueous samples before determination by high performance liquid chromatography with ultraviolet detection. The composite film showed a high surface area (4.0258 m²/g) and strong hydrogen bonding between the multiwalled carbon nanotubes and agarose/chitosan matrix, which prevent adsorbent deactivation and ensure long‐term stability. Several parameters, such as sample pH, addition of salt, extraction time, desorption solvent, and concentration of multiwalled carbon nanotubes in the composite film were optimized using a one‐factor‐at‐time approach. The optimum extraction conditions obtained were as follows: isopropanol as conditioning solvent, 10 mL of sample solution at pH 2, extraction time of 30 min, stirring speed of 600 rpm, 100 μL of isopropanol as desorption solvent, desorption time of 5 min under ultrasonication, and 0.4% w/v of composite film. Under the optimized conditions, the calibration curve showed good linearity in the range of 1–500 ng/mL (r² = 0.997–0.999), and good limits of detection (0.89–8.05 ng/mL) were obtained with good relative standard deviations of < 4.59% (n = 3) for the determination of naproxen, diclofenac sodium salt, and mefenamic acid drugs.     

Salt‐assisted liquid–liquid extraction in microchannel

In this study, for the first time, salt‐assisted liquid–liquid extraction was performed in a microchannel system. The proposed design is based on the increase of contact surface area between target analytes and extracting phase during the sample and extracting phase transfer in microchannel. In this method, first sample solution, extracting solvent, and salt were mixed by stirrer and simultaneously delivered into a microchannel using a syringe pump. In order to optimize the influential parameters on the extraction efficiency of the proposed method, zidovudine and tenofovir disoproxil fumarate were selected as model analytes. The main parameters such as extracting solvent and its volume, salt amount, pH of sample solution, and microchannel shape, length, and its inner diameter were investigated and optimized. Under the optimized conditions, the proposed method was linear in the range of 0.1–30 µg/mL and R² coefficients were equal to 0.9922 and 0.9947 for zidovudine and tenofovir disoproxil fumarate, respectively. Extraction efficiency of the proposed method was compared with conventional salt‐assisted liquid–liquid extraction. The results show that the proposed design has higher extraction efficiency than conventional salt‐assisted liquid–liquid extraction. Finally, the proposed method was successfully applied for the determination of zidovudine and tenofovir disoproxil fumarate in plasma samples.     

Separation of cucurbitane triterpenoids from bitter melon drinks and determination of partition coefficients using vortex‐assisted dispersive liquid‐phase microextraction followed by UHPLC analysis

A rapid, effective method applying vortex‐assisted liquid–liquid microextraction before ultra‐high performance liquid chromatography with mass spectrometry and evaporative light scattering detection was developed for the analysis of four cucurbitane triterpenoids (momordicoside L, momordicoside K, momordicoside F₂, and 3β,7β,25‐trihydroxy cucurbita‐5,23(E )‐dien‐19‐al) in bitter melon juices. Variables affecting the extraction efficiency including different extraction solvents, volume of extraction solvent, salt amount, acid condition, vortex speed and time were optimized thoroughly. Under the optimum conditions, precision was determined by the intra‐ and inter‐day tests in a range of 1.1–5.7% and 2.9–4.0% (RSD), respectively, with recoveries between 95.7 and 106.1%. The calibration curves showed good linearity with square correlation coefficient of 0.9936–0.9991 (evaporative light scattering detection) and 0.9858–0.9989 (MS). The detection limits ranged from 0.8–1.9 ng/mL (MS) to 3–10 ng/mL (evaporative light scattering detection) for these compounds. Enrichment factors of four target compounds were between 27 and 63 times. The proposed method was also used to determine the apparent solvent/water partition coefficients of analytes within the range of 53–120. The developed method can effectively enrich and quantify cucurbitane triterpenoids from bitter melon drinks.     

Simultaneous derivatization and lighter‐than‐water air‐assisted liquid–liquid microextraction using a homemade device for the extraction and preconcentration of some parabens in different samples

Simultaneous derivatization and air‐assisted liquid–liquid microextraction using an organic that is solvent lighter than water has been developed for the extraction of some parabens in different samples with the aid of a newly designed device for collecting the extractant. For this purpose, the sample solution is transferred into a glass test tube and a few microliters of acetic anhydride (as a derivatization agent) and p‐xylene (as an extraction solvent) are added to the solution. After performing the procedure, the homemade device consists of an inverse funnel with a capillary tube placed into the tube. In this step, the collected extraction solvent and a part of the aqueous solution are transferred into the device and the organic phase indwells in the capillary tube of the device. Under the optimal conditions, limits of detection and quantification for the analytes were obtained in the ranges of 0.90–2.7 and 3.0–6.1 ng/mL, respectively. The enrichment and enhancement factors were in the ranges of 370–430 and 489–660, respectively. The method precision, expressed as the relative standard deviation, was within the range of 4–6% (n = 6) and 4–9% (n = 4) for intra‐ and interday precisions, respectively. The proposed method was successfully used for the determination of methyl‐, ethyl‐, and propyl parabens in cosmetic, hygiene and food samples, and personal care products.     

Vortex‐ and CO2‐gas‐assisted liquid–liquid microextraction with salt addition for the high‐performance liquid chromatographic determination of furanic compounds in concentrated juices and dried fruits

A novel microextraction method based on vortex‐ and CO₂‐assisted liquid–liquid microextraction with salt addition for the isolation of furanic compounds (5‐hydroxymethyl‐2‐furaldehyde, 5‐methyl‐2‐furaldehyde, 2‐furaldehyde, 3‐furaldehyde, 2‐furoic and 3‐furoic acids) was developed. Purging the sample with CO₂ was applied after vortexing to enhance the phase separation and mass transfer of the analytes. The optimum extraction conditions were: extraction solvent (volume), propyl acetate (125 μL); sample pH, 2.4; vortexing time, 45 s; salt concentration, 25% w/v and purging time, 5 min. The analytes were separated using an ODS Hypersil C₁₈ column (250×4.6 mm i.d, 5 μm) under gradient flow. The proposed method showed good linearities (r² >0.999), low detection limits (0.08–1.9 μg/L) and good recoveries (80.7–122%). The validated method was successfully applied for the determination of the furanic compounds in concentrated juice (mango, date, orange, pomegranate, roselle, mangosteen and soursop) and dried fruit (prune, date and apricot paste) samples.     

Dispersive liquid–liquid microextraction as an effective preanalytical step for the determination of estradiol in human urine

In this work, a fast and effective dispersive liquid–liquid microextraction was developed for the isolation and preconcentration of free 17 β‐estradiol, the main human estrogen, from real human urine samples. To optimize the extraction technique, few important parameters such as type and volume of extraction and dispersive solvents, centrifugation conditions, effect of salt addition, and extraction time were studied. Optimal conditions were obtained when injecting 600 μL mixture of tetrachloromethane as extraction solvent and ethanol as dispersive solvent (1:5, v/v) into 2 mL of urine containing 8% NaCl and following centrifugation at 10 000 rpm, thus reaching enrichment factor 28 and extraction recovery 98% for estradiol. Procedure was evaluated by means of high‐performance liquid chromatography with UV detection (λ = 280 nm) using a C‐18 column and methanol/water (60:40, v/v) as the mobile phase. The method was linear within the concentration range 1.0–250.0 mg/L (r  = 0.9997) and provided a limit of detection of 0.25 mg/L. The proposed method was applied to the determination of free estradiol in real human pregnancy urine.     

Determination of N‐nitrosamines in cosmetic products by vortex‐assisted reversed‐phase dispersive liquid–liquid microextraction and liquid chromatography with mass spectrometry

A new analytical method for the simultaneous determination of trace levels of seven prohibited N‐nitrosamines (N‐nitrosodimethylamine, N‐nitrosoethylmethylamine, N‐nitrosopyrrolidine, N‐nitrosodiethylamine, N‐nitrosopiperidine, N‐nitrosomorpholine, and N‐nitrosodiethanolamine) in cosmetic products has been developed. The method is based on vortex‐assisted reversed‐phase dispersive liquid–liquid microextraction, which allows the extraction of highly polar compounds, followed by liquid chromatography with mass spectrometry. The variables involved in the extraction process were studied to obtain the highest enrichment factor. Under the selected conditions, 75 μL of water as extraction solvent was added to 5 mL of n‐hexane sample solution and assisted by vortex mixing during 30 s to form the cloudy solution. The method was successfully validated showing good linearity (0.5–50 ng/mL), enrichment factors up to 65 depending on the target compound, limits of detection values of 1.8–50 ng/g, and good repeatability (RSD < 9.8%). Finally, the proposed method was applied to different cosmetic samples. Quantitative relative recovery values (80–113%) were obtained, thus showing that matrix effects were negligible. The achieved analytical features of the proposed method, besides of its simplicity and affordability, make it useful to perform the quality control of cosmetic products to ensure the safety of consumers.     

Simple and rapid determination of zaltoprofen in human plasma by manual‐shaking‐assisted dispersive liquid–liquid microextraction followed by liquid chromatography with ultraviolet detection

A readily applicable method was developed to determine the concentration level of zaltoprofen, a non‐steroidal antiinflammatory drug from the propionic acid family, in human plasma. This method is based on manual‐shaking‐assisted dispersive liquid–liquid microextraction coupled with liquid chromatography with ultraviolet detection. Factors affecting the extraction efficiency were screened and optimized by experimental design using fractional factorial and central composite designs, respectively. Optimal conditions were: 220 μL of C₂H₄Cl₂ (extraction solvent), 5 mL of 3.75% w/v NaCl aqueous solution at pH 2.0, and manual shaking for 13 s (65 times). The resulting extraction method yielded a reasonable enrichment factor of 18.0 (±0.6, n  = 3) and extraction recovery of 86.0% (±3.3%, n  = 3). The established method was validated for selectivity, linearity, precision, accuracy, matrix effect, recovery, dilution integrity, and stability, and it met the acceptable criteria for all of the tested parameters. Specifically, the method was linear in the range of 0.16–50.0 mg/L, precise (< 8.8% RSD), accurate (–7.5–5.6% deviation), and showed negligible matrix effects (96.1–106.4%) with high absolute recovery (94.5–97.7%). Compared with previous methods involving labor‐intensive liquid–liquid extraction or non‐specific protein precipitation, our method allows the simple, rapid, and efficient determination of zaltoprofen using the most affordable analytical instrument, liquid chromatography with ultraviolet detection.     

Pressurized Liquid Extraction Combined with Dispersive Liquid‐liquid Micro‐extraction as an Efficient Sample Preparation Method for Determination of Volatile Components in Tobacco

The pressurized liquid extraction (PLE) followed by dispersive liquid–liquid micro‐extraction (DLLME) has been developed for extraction of volatile components in tobacco. 35 volatile components were detected by gas chromatography mass spectrometry (GC‐MS). Methanol–methyl tert‐butyl ether (MTBE) (8:2, v/v) was selected as PLE extraction solvent. The optimized DLLME procedure, 3 mL of pure water and 1.0 mL tobacco extract solution, 40 μL of chloroform as extraction solvent, 0.5 mL of acetonitrile as disperser solvent, was validated. Under the optimum conditions, the enrichment factors were in the range of 96‐159. The limits of detection were between 0.14 and 0.33 μg/kg. The repeatability of the proposed method, expressed as relative standard deviation, varied between 4.3 and 7.5% (n = 6). The recoveries of the analytes evaluated by fortification of tobacco samples were in the range of 84.7‐96.4%. Compared with the conventional sample preparation method for determination of volatile components in tobacco, the proposed method was quick and easy to operate, and had high‐enrichment factors and low consumption of organic solvent.     

Determination of four sulfonylurea herbicides in tea by matrix solid‐phase dispersion cleanup followed by dispersive liquid–liquid microextraction

Matrix solid‐phase dispersion combined with dispersive liquid–liquid microextraction has been developed as a new sample pretreatment method for the determination of four sulfonylurea herbicides (chlorsulfuron, bensulfuron‐methyl, chlorimuron‐ethyl, and pyrazosulfuron) in tea by high‐performance liquid chromatography with diode array detection. The extraction and cleanup by matrix solid‐phase dispersion was carried out by using CN‐silica as dispersant and carbon nanotubes as cleanup sorbent eluted with acidified dichloromethane. The eluent of matrix solid‐phase dispersion was evaporated and redissolved in 0.5 mL methanol, and used as the dispersive solvent of the following dispersive liquid–liquid microextraction procedure for further purification and enrichment of the target analytes before high‐performance liquid chromatography analysis. Under the optimum conditions, the method yielded a linear calibration curve in the concentration range from 5.0 to 10 000 ng/g for target analytes with a correlation coefficients (r²) ranging from 0.9959 to 0.9998. The limits of detection for the analytes were in the range of 1.31–2.81 ng/g. Recoveries of the four sulfonylurea herbicides at two fortification levels were between 72.8 and 110.6% with relative standard deviations lower than 6.95%. The method was successfully applied to the analysis of four sulfonylurea herbicides in several tea samples.