Songqing Li

Comparison of the performance of conventional, temperature-controlled, and ultrasound-assisted ionic liquid dispersive liquid-liquid microextraction combined with high-performance liquid chromatography in analyzing pyrethroid pesticides in honey samples.

This research paper presents a comparative study of the performance of conventional, ultrasound-assisted (UA), and temperature-controlled (TC) ionic liquid (IL) dispersive liquid-phase microextraction (IL-DLLME). Various parameters that affect extraction efficiency, such as type and volume of extraction and disperser solvent, centrifugation time, salt addition, effect of temperature on TC-IL-DLLME, and effect of sonication time on UA-IL-DLLME, were evaluated. UA-IL-DLLME was found to provide the best extraction efficiency. Under optimized conditions, great enrichment factors (506-515) and good recoveries (101.2-103.0%) were obtained by analyte extraction in real samples. The limit of detections (LODs) ranged from 0.21 to 0.38 μg L(-1). Good linearity was obtained in the range of 0.5-200 μg L(-1) for ethofenprox and tetramethrin, and 1-200 μg L(-1) for meperfluthrin and alpha-cypermethrin. Based on optimized conditions, the UA-IL-DLLME method was applied and combined with high-performance liquid chromatography with diode array detection (HPLC-DAD) to determine the presence of ethofenprox, tetramethrin, meperfluthrin, and alpha-cypermethrin in honey samples.

In-situ metathesis reaction combined with ultrasound-assisted ionic liquid dispersive liquid-liquid microextraction method for the determination of phenylurea pesticides in water samples.

A novel microextraction technique, named in-situ metathesis reaction, combined with ultrasound-assisted ionic liquid dispersive liquid-liquid microextraction was developed for the determination of five phenylurea pesticides (i.e., diuron, diflubenzuron, teflubenzuron, flufenoxuron, and chlorfluazuron) in environmental water samples. In the developed method, 360 μL LiNTf(2) aqueous solution (0.162 g/mL) was added to the sample solution containing a small amount of [C(6)MIM]Cl (0.034 g) to form a water-immiscible ionic liquid, [C(6)MIM]NTf(2), as extraction solution. The mixed solutions were placed in an ultrasonic water bath at 150 W for 4min and centrifuged at 3500 rpm for 10 min to achieve phase separation. After centrifugation, fine droplets of the extractant phase settled to the bottom of the centrifuge tube and were directly injected into the high-performance liquid chromatography system for analysis. The quantity of [C(6)MIM]Cl, the molar ratio of [C(6)MIM]Cl and LiNTf(2), ionic strength, ultrasound time, and centrifugation time, were optimized using a Plackett-Burman design. Significant factors obtained were optimized by employing a central composite design. The optimized technique provides good repeatability (RSD 2.4 to 3.5%), linearity (0.5 μg/L to 500 μg/L), low LODs (0.06 μg/L to 0.08 μg/L) and great enrichment factor (244 to 268). The developed method can be applied in routine analysis for the determining of phenylurea pesticides in environmental samples.

Determination of insecticides in water using in situ halide exchange reaction‐assisted ionic liquid dispersive liquid–liquid microextraction followed by high‐performance liquid chromatography

A dispersive liquid-liquid microextraction (DLLME) method using in situ halide exchange reaction to form ionic liquid (IL) extraction phase was developed to determine four insecticides (i.e. methoxyfenozide, tetrachlorvinphos, thiamethoxam, and diafenthiuron) in water samples. The preconcentration procedure, followed by high-performance liquid chromatography and variable wavelength detectors (VWD), enabled the formation of the immiscible IL extraction phase; the insecticides were transferred into the IL phase simultaneously, which enhanced the efficiency and sufficiency, greatly shortening the operation time. The experimental parameters affecting the extraction efficiency including volume of extraction IL, extraction and centrifugation times, volume of the sample solution and exchanging reagent, and addition of organic solvent and salt were investigated and optimized. Under optimized conditions, the extractions yielded recoveries of the target analytes from 82 to 102%. The calibration curves were linear, and the correlation coefficient ranged from 0.9990 to 0.9999 under the concentration levels of 5-200 μg/L. The relative standard deviation (n=6) was 2.9-4.6%. The limits of detection (LODs) for the four insecticides were between 0.98 and 2.54 μg/L.

Sequential dispersive liquid-liquid microextraction for the determination of aryloxyphenoxy-propionate herbicides in water.

A novel dispersive liquid-liquid microextraction (DLLME) method followed by HPLC analysis, termed sequential DLLME, was developed for the preconcentration and determination of aryloxyphenoxy-propionate herbicides (i.e. haloxyfop-R-methyl, cyhalofop-butyl, fenoxaprop-P-ethyl, and fluazifop-P-butyl) in aqueous samples. The method is based on the combination of ultrasound-assisted DLLME with in situ ionic liquid (IL) DLLME into one extraction procedure and achieved better performance than widely used DLLME procedures. Chlorobenzene was used as the extraction solvent during the first extraction. Hydrophilic IL 1-octyl-3-methylimidazolium chloride was used as a dispersive solvent during the first extraction and as an extraction solvent during the second extraction after an in situ chloride exchange by bis[(trifluoromethane)sulfonyl]imide. Several experimental parameters affecting the extraction efficiency were studied and optimized with the design of experiments using MINITAB® 16 software. Under the optimized conditions, the extractions resulted in analyte recoveries of 78-91%. The correlation coefficients of the calibration curves ranged from 0.9994 to 0.9997 at concentrations of 10-300, 15-300, and 20-300 μg L(-1). The relative SDs (n = 5) ranged from 2.9 to 5.4%. The LODs for the four herbicides were between 1.50 and 6.12 μg L(-1).

Simultaneous determination of four synthesized metabolites of mequindox in urine samples using ultrasound-assisted dispersive liquid-liquid microextraction combined with high-performance liquid chromatography.

A novel pretreatment method termed ultrasound-assisted dispersive liquid-liquid microextraction (UADLLME) coupled with high-performance liquid chromatography-ultraviolet detector (HPLC-UV) was applied for the detection of four synthesized metabolites of mequindox in pig urine samples. A total volume of 200 μL of methanol (dispersant) and 60 μL of 1,1,2,2-tetrachloroethane (extract) were injected into 5.0 mL of urine sample and then emulsified by ultrasound treatment for 4 min to form a cloudy solution. The effect of several factors on the recovery of each metabolite was investigated by a fitting derivation method for the first time. Under optimum conditions, the method yields a linear calibration curve in the concentration range from 0.5 to 500 μg/L and a limit of detection (LOD) of 0.16-0.28 μg/L for target analytes. The recoveries ranged from 72.0% to 91.3% with a relative standard deviation (RSD) of less than 5.2%. The enrichment factors for the four compounds ranged from 75 to 95. Two pig urine samples were successfully analyzed using the proposed method.

In situ metathesis reaction combined with liquid-phase microextraction based on the solidification of sedimentary ionic liquids for the determination of pyrethroid insecticides in water samples.

A novel dispersion liquid-liquid microextraction method based on the solidification of sedimentary ionic liquids (SSIL-DLLME), in which an in situ metathesis reaction forms an ionic liquid (IL) extraction phase, was developed to determine four pyrethroid insecticides (i.e., permethrin, cyhalothrin, fenpropathrin, and transfluthrin) in water followed by separation using high-performance liquid chromatography. In the developed method, in situ DLLME was used to enhance the extraction efficiency and yield. After centrifugation, the extraction solvent, tributyldodecylphosphonium hexafluorophosphate ([P44412][PF6]), was easily collected by solidification in the bottom of the tube. The effects of various experimental parameters, the quantity of tributyldodecylphosphonium bromide ([P44412]Br), the molar ratio of [P44412]Br to potassium hexafluorophosphate (KPF6), the ionic strength, the temperature of the sample solution, and the centrifugation time, were optimized using a Plackett-Burman design to identify the significant factors that affected the extraction efficiency. These significant factors were then optimized using a central composite design. Under the optimized conditions, the recoveries of the four pyrethroid insecticides at four spiked levels ranged from 87.1% to 101.7%, with relative standard deviations (RSDs) ranging from 0.1% to 5.5%. At concentration levels between 1 and 500 µg/L, good linearity was obtained, with coefficients of determination greater than 0.9995. The limits of detection (LODs) for the four pyrethroid insecticides were in the range of 0.71-1.54 µg/L. The developed method was then successfully used for the determination of pyrethroid insecticides in environmental samples.

Optimization of dispersive liquid–liquid microextraction based on the solidification of floating organic droplets using an orthogonal array design and its application for the determination of fungicide concentrations in environmental water samples

A dispersive liquid-liquid microextraction method based on the solidification of floating organic droplets was developed as a simple and sensitive method for the simultaneous determination of the concentrations of multiple fungicides (triazolone, chlorothalonil, cyprodinil, and trifloxystrobin) in water by high-performance liquid chromatography with variable-wavelength detection. After an approach varying one factor at a time was used, an orthogonal array design [L25 (5(5))] was employed to optimize the method and to determine the interactions between the parameters. The significance of the effects of the different factors was determined using analysis of variance. The results indicated that the extraction solvent volume significantly affects the efficiency of the extraction. Under optimal conditions, the relative standard deviation (n = 5) varied from 2.3 to 5.5% at 0.1 μg/mL for each analyte. Low limits of detection were obtained and ranged from 0.02 to 0.2 ng/mL. In addition, the proposed method was applied to the analysis of fungicides in real water samples. The results show that the dispersive liquid-liquid microextraction based on the solidification of floating organic droplets is a potential method for detecting fungicides in environmental water samples, with recoveries of the target analytes ranging from 70.1 to 102.5%.

Determination of triazole pesticides in rat blood by the combination of ultrasound-enhanced temperature-controlled ionic liquid dispersive liquid–liquid microextraction coupled to high-performance liquid chromatography

This paper presents a study of the performance of ultrasound-enhanced temperature-controlled (UETC) ionic liquid dispersive liquid–liquid microextraction (IL-DLLME). The use of ultrasonication and heating can enhance the ability of the ionic liquid to extract the analytes. Various parameters that would affect the extraction efficiency, such as the type and volume of the extraction and dispersing solvents, salt concentration, pH value, centrifugation time, effect of temperature on UETC-IL-DLLME, were investigated and optimized. Under the optimal extraction conditions, good enrichment factors (178–197) and recoveries (88.9–98.5%) were obtained. Good linearity was obtained in the range of 4–500 μg L−1 for myclobutanil and in the range of 6–500 μg L−1 for uniconazole, penconazole, tebuconazole and hexaconazole. Based on the optimized conditions, the UETC-IL-DLLME method was applied and combined with high-performance liquid chromatography with diode array detection (HPLC-DAD) to determine the presence of five triazole fungicides. The results showed that the method we proposed could effectively determine the target fungicides in rat blood samples.

Extensible automated dispersive liquid–liquid microextraction

In this study, a convenient and extensible automated ionic liquid-based in situ dispersive liquid-liquid microextraction (automated IL-based in situ DLLME) was developed. 1-Octyl-3-methylimidazolium bis[(trifluoromethane)sulfonyl]imide ([C8MIM]NTf2) is formed through the reaction between [C8MIM]Cl and lithium bis[(trifluoromethane)sulfonyl]imide (LiNTf2) to extract the analytes. Using a fully automatic SPE workstation, special SPE columns packed with nonwoven polypropylene (NWPP) fiber, and a modified operation program, the procedures of the IL-based in situ DLLME, including the collection of a water sample, injection of an ion exchange solvent, phase separation of the emulsified solution, elution of the retained extraction phase, and collection of the eluent into vials, can be performed automatically. The developed approach, coupled with high-performance liquid chromatography-diode array detection (HPLC-DAD), was successfully applied to the detection and concentration determination of benzoylurea (BU) insecticides in water samples. Parameters affecting the extraction performance were investigated and optimized. Under the optimized conditions, the proposed method achieved extraction recoveries of 80% to 89% for water samples. The limits of detection (LODs) of the method were in the range of 0.16-0.45 ng mL(-1). The intra-column and inter-column relative standard deviations (RSDs) were <8.6%. Good linearity (r>0.9986) was obtained over the calibration range from 2 to 500 ng mL(-1). The proposed method opens a new avenue for automated DLLME that not only greatly expands the range of viable extractants, especially functional ILs but also enhances its application for various detection methods. Furthermore, multiple samples can be processed simultaneously, which accelerates the sample preparation and allows the examination of a large number of samples.

Comparison of GIAO and CSGT for calculating (13) C and (15) N nuclear magnetic resonance chemical shifts of substituent neutral 5-aminotetrazole and 5-nitrotetrazole compounds.

The comparison of the gauge‐including atomic orbital (GIAO) and the continuous set of gauge transformation methods for calculating nuclear magnetic chemical shifts (CSs) mainly at density functional levels of theory are presented. Isotropic 13 C and 15 N magnetic CS for 14 compounds of tetrazoles are reported. Compared with establishing a convenient and consistent protocol to be employed for confirming the experimental 13 C and 15 N NMR spectra of tetrazole compounds, different combinations of functionals and basis sets were considered. The most reliable results were obtained at GIAO/B3LYP/aug‐cc‐pVDZ with integral equation formulation for the polarizable continuum model (PCM), which has the smallest root mean square errors and can be used to calculate 13 C and 15 N NMR CS with a very high accuracy for tetrazoles. These results show that the accurately calculated 15N NMR CS of tetrazoles could be used for the evaluation of the intrinsic relationship between structure and explosive properties. Copyright