Dispersive Liquid-liquid Microextraction for Simultaneous Determination of Six Parabens in Aqueous Cosmetics

A simple and rapid sample preparation method of dispersive liquid-liquid microextraction（DLLME） was applied in the simultaneous determination of six parabens in the aqueous cosmetics. The analysis was performed on gas chromatography coupled with a flame ionization detection（GC-FID）. The mixed solution containing 30 μL of chloroform（extraction solvent） and 300 μL of tetrahydrofuran（dispersive solvent） was rapidly injected into the sample solution for the purpose of microextraction. After that, the solution mentioned above was centrifuged at 4000 r/min for 10 min, and then the organic sediment phase was detected by GC-FID. The effects of experimental parameters, such as the extraction solvent and the volume of it, and the dispersive solvent and the volume of it, on the yield of the extraction were studied in detail. Under the optimum conditions, the enrichment factors of the target analytes range from 87 to 214. Linearity ranges are 0.05-10.0μg/mL for methylparaben and 0.025--5.0 μg/mL for the other five parabens. The relative standard deviations（RSDs） are lower than 8.2%（n=6）. The proposed method was applied to the analysis of six parabens in eleven aqueous cosmetics. The recoveries of the target analytes in the spiked real samples are in the range of 81.0%-103%.     

Valorization of Fermented Shrimp Waste with Supercritical CO2 Conditions: Extraction of Astaxanthin and Effect of Simulated Gastrointestinal Digestion on Its Antioxidant Capacity

Lactic acid fermentation increases the bioactive properties of shrimp waste. Astaxanthin is the principal carotenoid present in shrimp waste, which can be found esterified in the liquid fraction (liquor) after its lactic acid fermentation. Supercritical CO₂ technology has been proposed as a green alternative to obtain astaxanthin from fermented shrimp waste. This study aimed to optimize astaxanthin extraction by supercritical CO₂ technology from fermented liquor of shrimp waste and study bioaccessibility using simulated gastrointestinal digestion (GD) of the optimized extract. A Box–Behnken design with three variables (pressure, temperature, and flow rate) was used to optimize the supercritical CO₂ extraction. The optimized CO₂ extract was obtained at 300 bar, 60 °C, and 6 mL/min, and the estimated characteristics showed a predictive extraction yield of 11.17%, antioxidant capacity of 1.965 mmol of Trolox equivalent (TE)/g, and astaxanthin concentration of 0.6353 µg/g. The experiment with optimal conditions performed to validate the predicted values showed an extraction yield of 12.62%, an antioxidant capacity of 1.784 mmol TE/g, and an astaxanthin concentration of 0.52 µg/g. The astaxanthin concentration decreased, and the antioxidant capacity of the optimized extract increased during gastrointestinal digestion. In conclusion, our optimized supercritical CO₂ process is suitable for obtaining astaxanthin from shrimp by-products after lactic acid fermentation.     

Development of a Sensitive Method for the Determination of 4‐(Methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanol in Human Urine Using Solid‐phase Extraction Combined with Ultrasound‐assisted Dispersive Liquid–liquid Microextraction and LC‐MS/MS Detection

An efficient and sensitive analytical method based on molecularly imprinted solid‐phase extraction (MISPE) and reverse‐phase ultrasound‐assisted dispersive liquid–liquid microextraction (USA‐DLLME) coupled with LC–MS/MS detection was developed and validated for the analysis of urinary 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanol (NNAL), a tobacco‐specific nitrosamine metabolite. The extraction performances of NNAL on three different solid‐phase extraction (SPE) sorbents including the hydrophilic‐lipophilic balanced sorbent HLB, the mixed mode cationic MCX sorbent and the molecularly imprinted polymers (MIP) sorbent were evaluated. Experimental results showed that the analyte was well retained with the highest extraction recovery and the optimum purification effect on MIP. Under the optimized conditions of MIP and USA‐DLLME, an enrichment factor of 23 was obtained. Good linearity relationship was obtained in the range of 5‐1200 pg/mL with a correlation coefficient of 0.9953. The limit of detection (LOD) was 0.35 pg/mL. The recoveries at three spiked levels ranged between 88.5% and 93.7%. Intra‐ and inter‐day relative standard deviations varied from 3.6% to 7.4% and from 5.4% to 9.7%, respectively. The developed method combing the advantages of MISPE and DLLME significantly improves the purification and enrichment of the analyte and can be used as an effective approach for the determination of ultra‐trace NNAL in complex biological matrices.     

分散液-液微萃取-气相色谱法快速检测番茄中3种拟除虫菊酯类农药

建立了快速(quick)、简单(easy)、便宜(cheap)、有效(effective)、可靠(rugged)和安全(safe)(QuEChERS)的分散液-液微萃取(DLLME)-气相色谱快速测定番茄中拟除虫菊酯类农药残留的方法。样品经乙腈提取,N-丙基乙二胺(PSA)净化,采用DLLME富集,用气相色谱法分析。考察了联苯菊酯、甲氰菊酯和氟氰菊酯在番茄中的残留测定,同时考察了萃取剂种类与体积、分散剂体积以及萃取时间等因素对萃取效率的影响,以40 μL氯仿为萃取剂,1000 μL乙腈为分散剂,萃取时间为60 s。结果表明: 3种拟除虫菊酯类农药在番茄中的检出限分别为0.5、0.5、0.3 μg/kg。在1、10和50 μg/kg添加水平下,联苯菊酯、甲氰菊酯和氟氰菊酯在番茄中的平均回收率分别为89%～109%、92.5%～105%和90%～108%,相对标准偏差分别为2.5%～7.6%、2.8%～5.7%、3.8%～9.1%。该方法简便、快速、安全、价格低廉,重现性好,可用于番茄中拟除虫菊酯类农药的快速检测。     

分散液液微萃取-反相液液微萃取-扫集-胶束电动色谱法测定红酒中的3种氯酚类物质

建立了分散液液微萃取（DLLME）-反相液液微萃取（RP-LLME）-扫集-胶束电动色谱富集模型,并用于红酒中五氯酚（PCP）、2,4,6-三氯酚（TCP）和2,4-二氯酚（DCP）3种氯酚的测定。实验考察了两步微萃取的萃取参数对氯酚萃取率的影响和样品分离富集的电泳条件。最佳萃取条件DLLME为：3.5 mL红酒（pH 3.0,120 g/L NaCl）,300 μL正己烷（萃取剂）;RP-LLME为：25 μL 0.16 mol/L NaOH（萃取剂）。最佳电泳条件：25 mmol/L NaH₂PO₄,100 mmol/L十二烷基硫酸钠（SDS）,30%（v/v）乙腈,pH 2.3;分离电压-15 kV;样品基质为80 mmol/L NaH₂PO₄;压力进样20 s×20.67 kPa（3 psi）。PCP和TCP的线性范围为0.5~100 μg/L（r≥0.9910）,DCP的线性范围为1.5~80 μg/L（r=0.9851）。3种分析物的检出限（S/N=3）为0.035~0.114 μg/L,加标回收率为75.2%~104.7%,相对标准偏差≤6.17%。该方法富集倍数高、灵敏度高、重现性好、分析速度快,可为不同样品基质中痕量氯酚污染物及某些弱酸性有机污染物测定提供参考。     

Dispersive liquid-liquid microextraction followed by reversed phase HPLC for the determination of decabrominated diphenyl ether in natural water

A simple, rapid, and efficient method, dispersive liquid-liquid microextraction (DLLME), has been developed for the extraction and preconcentration of decabrominated diphenyl ether (BDE-209) in environmental water samples. The factors relevant to the microextraction efficiency, such as the kind and volume of extraction and dispersive solvent, the extraction time, and the salt effect, were optimized. Under the optimum conditions (extraction solvent: tetrachloroethane, volume, 22.0 microL; dispersive solvent: THF, volume, 1.00 mL; extraction time: below 5 s and without salt addition), the most time-consuming step is the centrifugation of the sample solution in the extraction procedure, which is about 2 min. In this method, the enrichment factor could be as high as 153 in 5.00 mL water sample, and the linear range, correlation coefficient (r(2)), detection limit (S/N = 3), and precision (RSD, n = 6) were 0.001-0.5 microg/mL, 0.9999, 0.2 ng/mL, and 2.1%, respectively. This method was successfully applied to the extraction of BDE-209 from tap, East Lake, and Yangtse River water samples; the relative recoveries were 95.8, 92.9, and 89.9% and the RSD% (n = 3) were 1.9, 2.7, and 3.5%, respectively. Comparison of this method with other methods, such as solid-phase microextraction (SPME), and single-drop microextraction (SDME), indicates that DLLME is a simple, fast, and low-cost method for the determination of BDE-209, and thus has tremendous potential in polybrominated diphenyl ethers (PBDEs) residual analysis in environmental water samples.     

基于分子络合的分散液液微萃取与高效液相色谱联用检测环境水样中2种苯氧羧酸类除草剂

建立了基于分子络合的分散液液微萃取（DLLME）方法,以磷酸三丁酯为萃取剂,以甲醇为分散剂,与高效液相色谱联用检测了环境水样中麦草畏和2,4-二氯苯氧乙酸（2,4-D酸）2种苯氧羧酸类除草剂,对影响前处理效果的因素（包括水样的pH值、萃取剂的种类和体积、分散剂的种类和体积、反萃液的pH值、反萃液的体积和盐浓度等）进行了详细考察,在最佳萃取条件下（水样体积10 mL,水样的pH值为0~1.0、100 μL磷酸三丁酯萃取剂、1000 μL甲醇分散剂、0.01 mol/L的氢氧化钾反萃液的体积为80 μL）,2种苯氧羧酸类除草剂在0.50~1000 μg/L范围内具有良好的线性,相关系数不小于0.9985,麦草畏和2,4-D酸的检出限分别为0.44 μg/L和0.49 μg/L,富集倍数分别为85和90,在实际样品中的加标回收率为75.7%~104.0%。该方法基于分子络合反应机理,将新型萃取剂磷酸三丁酯应用于分散液液微萃取,与HPLC联用实现了麦草畏和2,4-D酸的富集与检测,为环境水样中苯氧羧酸类除草剂的检测提供了新的前处理方法。     

对羟基苯甲酸印迹聚合物微粒的制备及其固相萃取应用

以对羟基苯甲酸(p-HBA)为模板分子,丙烯酰胺(AM)为功能单体,乙二醇二甲基丙烯酸酯为交联剂,采用沉淀聚合法在乙腈溶剂中制备了p-HBA印迹聚合物微粒,研究了p-HBA加入量及聚合反应体系的总浓度对印迹聚合物结合性能的影响,采用色谱法对其进行了评价。结果表明,p-HBA的加入量及反应体系的总浓度对结合性能均有影响,当p-HBA加入量为1.0 mmol(与AM物质的量比为1:2)时,在37.5 mL乙腈中制得印迹聚合物P₂对p-HBA具有高的亲和力(k'=4.01)和选择性。将印迹聚合物P₂作为固相萃取填料,研究了分子印迹固相萃取p-HBA的方法,测得2种不同载样模式下p-HBA的柱容量分别为6.91 μg/100 mg和1.93 μg/100 mg,测得天麻样品中p-HBA的加标回收率为76.8%~86.6%(RSD=3.4%~6.2%)(n=3)。结果表明,采用沉淀聚合法以AM为功能单体制备的p-HBA印迹聚合物微粒适宜作为固相萃取填料,可实现天麻样品中p-HBA的选择性分离净化。     

Synthesis and in vitro Antimycobacterial Activity of Moxifloxacin Methylene and Ethylene Isatin Derivatives

A series of novel moxifloxacin methylene and ethylene isatin derivatives with remarkable improvement in lipophilicity, compared to the parent moxifloxacin, was designed, synthesized and characterized by 1H NMR, MS and HRMS. These derivatives were initially evaluated for their in vitro antimycobacterial activity against M. smegmatis CMCC 93202. Compounds 3a―3f, 5a, 5f and 5j were chosen for the further evaluation of their in vitro activity against Mycobacterium tuberculosis(MTB) H37Rv ATCC 27294 and MDR-MTB 09710. All the target compounds[ minimum inhibitory concentration(MIC): 0.39―>16 μg/mL] were far more active than rifampin(MIC: 2.0―>256 μg/mL), but less active than moxifloxacin(MIC: 0.1―1.0 μg/mL) against the three tested strains. The most active compounds 3a and 3c were found to be 2―64 fold more potent than isoniazid and rifampin against M. smegmatis CMCC 93202, 2 fold more potent than rifampin against MTB H37Rv ATCC 27294, and 16―>64 fold more potent than ethambutol, isoniazid and rifampin against MDR-MTB 09710.     

Selective solid-phase extraction of tebuconazole in biological and environmental samples using molecularly imprinted polymers

Molecularly imprinted polymers (MIPs) were prepared by precipitation polymerization using tebuconazole (TBZ) as a template. Frontal chromatography and selectivity experiments were used to determine the binding capabilities and binding specificities of different MIPs. The polymer that had the highest binding selectivity and capability was used as the solid-phase extraction (SPE) sorbent for the direct extraction of TBZ from different biological and environmental samples (cabbage, pannage, shrimp, orange juice and tap water). The extraction protocol was optimized and the optimum conditions were: conditioning with 5 mL methanol:acetic acid (9:1), 5 mL methanol and 5 mL water respectively, loading with 5 mL aqueous samples, washing with 1.2 mL acetonitrile (ACN):phosphate buffer (5:5, pH3), and eluting with 3 mL methanol. The MIPs were able to selectively recognize, effectively trap and preconcentrate TBZ over a concentration range of 0.5–15 μmol/L. The intraday and interday RSDs were less than 9.7% and 8.6%, respectively. The limit of quantification was 0.1 μmol/L. Under optimum conditions, the MISPE recoveries of spiked cabbage, pannage, shrimp, orange juice and tap water were 62.3%, 75.8%, 71.6%, 89% and 93.9%, respectively. MISPE gave better HPLC separation efficiencies and higher recoveries than C18 SPE and strong cation exchange (SCX) SPE. Figure HPLC analysis of spiked pannage after MISPE (A) and after C18 SPE (B). HQ (1), E3 (2), p-NP (3), FTF (4), TBZ (5), PNZ (6), HXZ (7) Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Simultaneous determination of tetrahydropalmatine and tetrahydroberberine in rat urine using dispersive liquid-liquid microextraction coupled with high-performance liquid chromatography

Dispersive liquid-liquid microextraction (DLLME) coupled with high-performance liquid chromatography (HPLC)-UV detection was applied in rat urine for the extraction and determination of tetrahydropalmatine (THP) and tetrahydroberberine (THB), both active components in Rhizoma corydalis. Various parameters affecting the extraction efficiency, such as the type and volume of extraction and dispersive solvent, pH, etc. were evaluated. Under the optimal conditions (extraction solvent: 37 μL of chloroform, dispersive solvent: 100 μL of methanol, alkaline with 100 μL of 1 mol/L NaOH, and without salt addition), the enrichment factors of THP and THB were more than 30. The extraction recoveries were 69.8-75.8% and 72.7-77.6% for THP and THB in rat urine, respectively. Both THP and THB showed good linearity in the range of 0.025-2.5 μg/mL, and the limit of quantification was 0.025 μg/mL (S/N=10, n=6). The intra-day and inter-day precision of THP and THB were <12.6%. The relative recoveries ranged from 95.5 to 107.4% and 96.8 to 100.9% for THP and THB in rat urine, respectively. The method has been successfully applied to rat urine samples. The results demonstrated that DLLME is a very simple, rapid and efficient method for the extraction and preconcentration of THP and THB from urine samples.     

Quantification of astaxanthin in shrimp waste hydrolysate by HPLC

In the present study, a simple and rapid reversed-phase HPLC method for the determination of astaxanthin in shrimp waste hydrolysate has been developed and validated. The analytical procedure involves the direct extraction of astaxanthin from the lipid fraction with methanol. The analytical column, SS Exil ODS, was operated at 25C. The mobile phase consisted of a mixture of water:methanol:dichloromethane:acetonitrile (4.5:28:22:45.5 v/v/v/v) at a flow rate of 1.0 mL/min. Detection and identification were performed using a photodiode array detector (lambda(detection) = 476 nm). The proposed HPLC method showed adequate linearity, repeatability and accuracy.     

Purification of Astaxanthin from Laminaria japonica by Ionic Liquid-based Monolithic Cartridge

An effective and accurate method was developed for the extraction of astaxanthin from Laminaria japonica with subsequent separation by ionic liquid-based monolithic cartridge. The optimized extraction conditions including extraction solvent(ethanol), extraction time(90 min) and ultrasonic power(75 W) were obtained by systematical investigation. Chromatographic analysis was performed on a C₁₈ column with ultraviolet(UV) detection at 476 nm, and a solution consisting of methanol/acetonitrile/H₂O/dichloromethane(83:6:6:5, volume ratio) was used as the mobile phase at a flow rate of 0.7 mL/min. After ionic liquid-based monolithic solid phase extraction, 17.82 μg/g astaxanthin was obtained from Laminaria japonica. This ionic liquid-based monolithic cartridge exhibits high affinity and selectivity for astaxanthin, and it can be potentially used as the stationary phase of high performance liquid chromatography(HPLC).     

分子印迹固相萃取-超高效液相色谱-串联质谱法测定鸡肉中9种氟喹诺酮药物残留

建立了分子印迹固相萃取（MISPE）-超高效液相色谱-串联质谱（UPLC-MS/MS）同时测定鸡肉中9种氟喹诺酮药物残留的分析方法。样品经均质处理后,采用磷酸盐缓冲液提取,提取液经MISPE柱净化后,采用BEH C₁₈柱分离,以乙腈-0.1%（v/v）甲酸水溶液为流动相,梯度洗脱,采用电喷雾正离子多反应监测模式,外标法定量。考察了MISPE柱对9种氟喹诺酮药物的吸附特异性;9种药物在0.25~100 μg/L范围内线性关系良好,相关系数（r）>0.9965;检出限和定量限分别为0.08 μg/kg和0.25 μg/kg;在0.25、2.5、5.0 μg/kg添加水平下,9种药物的回收率为65.8%~112.2%,批内、批间RSD分别为0.6%~13.5%和0.5%~14.9%;MISPE的最大柱容量为464.7~932.4 μg/L。该方法灵敏度好、操作简单、快速。     

Liquid-liquid Microextraction Based on Solidification of Floating Organic Drops Coupled with Gas Chromatography for Analyzing Trace Benzene,Toluene and Xylene in Water Samples

A new liquid-liquid microextraction method based on the solidification of floating organic drops coupled with gas chromatography was developed for the determination of trace benzene, toluene and xylene(BTX) in water samples. In the microextraction procedure, a microdrop of n-decanol was delivered to the surface of the analytes’ solution, and stirred for a desired time. Following the absolute extraction, the sample vial was cooled in an ice bath for 10 min. The solidified n-decanol was then transferred into a plastic tube and melted naturally; and 1 μL of it was injected into gas chromatography for analysis. Factors relevant to the extraction efficiency were studied and optimized. The optimal experimental conditions were: 15 μL of n-decanol as extractive solvent, 30 mL of solution containing analytes, no salt, the stirring rate 400 r/min, the extraction temperature 30 °C, and the extraction time 30 min. Under those optimized conditions, the detection limit(LOD) of analytes was in a range of 0.05―0.10 ng/mL by the developed method. A good linearity(r>0.99) in a calibration range of 0.01―100 μg/mL was obtained. The recoveries of the real samples at different spiked levels of BTX were in the range from 92.2% to 103.4%.     

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.     

Molecularly imprinted solid-phase extraction combined with ultrasound-assisted dispersive liquid-liquid microextraction for the determination of four Sudan dyes in sausage samples

A simple and highly selective molecularly imprinted solid-phase extraction (MISPE) combined with ultrasound-assisted dispersive liquid-liquid microextraction (DLLME) was developed for the determination of four Sudan dye (I, II, III, and IV) residues in sausage products. The novel molecularly imprinted microspheres (MIMs) synthesized by aqueous suspension polymerization using phenylamine-naphthol as the dummy template show high affinity to the four Sudan dyes and were applied as selective sorbents of MISPE-DLLME to overcome the drawbacks of template leakage in quantitative analysis. Good linearity was obtained in a range of 0.005-2.0 μg g(-1) and the average recoveries of the four Sudan dyes at three spiked levels ranged from 86.3 to 107.5%. The MISPE-DLLME-HPLC protocol significantly improved the purification and enrichment of the analytes and eliminated the template leakage of the conventional MISPE on quantitative analysis.     

Extraction of Astaxanthin from Shrimp Waste Using Pressurized Hot Ethanol

An efficient and environmentally sustainable extraction method is proposed for the enrichment of a high-value pigment, astaxanthin, from a low-value raw material, shrimp waste. Ethanol at elevated temperature and pressure was used as a “green” extraction solvent. An experimental design approach based on central composite design was used to investigate the dependence of pressurized liquid extraction (PLE) operating variables (pressure, temperature, extraction time) on the recovered astaxanthin concentration from shrimp waste. The results show that at a 95% confidence level, the most significant PLE operating variables were extraction temperature and time. Extraction pressure had only a minor effect on the astaxanthin recovery in the studied experimental conditions. The maximum astaxanthin recovery obtainable by PLE was calculated from the chemometrics results and then appraised by experiments. Our results show astaxanthin yields of around 24 mg kg^?1 shrimp waste. The reproducibility of the developed PLE method is good, showing a relative standard deviation of 3.5% (n = 6) for astaxanthin.     

Determination of triazine herbicides in environmental samples by dispersive liquid-liquid microextraction coupled with high performance liquid chromatography

A simple, rapid, efficient, and environmentally friendly method for the determination of five triazine herbicides in water and soil samples was developed by using dispersive liquid-liquid microextraction (DLLME), coupled with high performance liquid chromatography-diode array detection (HPLC-DAD). The water samples were directly used for DLLME extraction. For soil samples, the target analytes were first extracted by water-methanol (99:1, v/v). In the DLLME extraction method, chloroform was used as an extraction solvent, and acetonitrile as a dispersive solvent. Under the optimum conditions, the enrichment factors of DLLME were in the range between 183-221. The linearity of the method was obtained in the range of 0.5-200 ng/mL for the water sample analysis, and 1-200 ng/g for the soil samples, respectively. The correlation coefficients ranged from 0.9968 to 0.9999. The limits of detection were 0.05-0.1 ng/mL for the water samples, and 0.1-0.2 ng/g for the soil samples. The proposed method has been successfully applied to the analysis of target triazine herbicides (simazin, atrazine, prometon, ametryn, and prometryn) in water and soil samples with satisfactory results.     

Application of dispersive liquid-liquid microextraction combined with high-performance liquid chromatography for the determination of methomyl in natural waters

A new method was developed for determination of methomyl in water samples by combining a dispersive liquid-liquid microextraction (DLLME) technique with HPLC-variable wavelength detection (VWD). In this extraction method, 0.50 mL of methanol (as dispersive solvent) containing 20.0 microL of tetrachloroethane (as extraction solvent) was rapidly injected by syringe into a 5.00-mL water sample containing the analyte, thereby forming a cloudy solution. After phase separation by centrifugation for 2 min at 4000 rpm, the enriched analyte in the settled phase (8 +/- 0.2 microL) was at the bottom of the conical test tube. A 5.0-microL volume of the settled phase was analyzed by HPLC-VWD. Parameters such as the nature and volume of the extraction solvent and the dispersive solvent, extraction time, and the salt concentration were optimized. Under the optimum conditions, the enrichment factor could reach 70.7 for a 5.00-mL water sample and the linear range, detection limit (S/N = 3), and precision (RSD, n = 6) were 3-5000 ng/mL, 1.0 ng/mL, and 2.6%, respectively. River and lake water samples were successfully analyzed by the proposed method. Comparison of this method with solid-phase extraction, solid-phase microextraction, and single-drop microextraction, indicates that DLLME combined with HPLC-VWD is a simple, fast, and low-cost method for the determination of methomyl, and thus has tremendous potential in trace analysis of methomyl in natural waters.