Lijun He

Ionic liquid-based dispersive liquid-liquid microextraction followed high-performance liquid chromatography for the determination of organophosphorus pesticides in water sample.

Using 1-octyl-3-methylimidazolium hexafluorophosphate ([C(8)MIM][PF(6)]) ionic liquid as extraction solvent, organophosphorus pesticides (OPPs) (parathion, phoxim, phorate and chlorpyifos) in water were determined by dispersive liquid-liquid microextraction (DLLME) combined with high-performance liquid chromatography (HPLC). The extraction procedure was induced by the formation of cloudy solution, which was composed of fine drops of [C(8)MIM][PF(6)] dispersed entirely into sample solution with the help of disperser solvent (methanol). Parameters including extraction solvent and its volume, disperser solvent and its volume, extraction time, centrifugal time, salt addition, extraction temperature and sample pH were investigated and optimized. Under the optimized conditions, up to 200-fold enrichment factor of analytes and acceptable extraction recovery (>70%) were obtained. The calibration curves were linear in the concentration range of 10.5-1045.0 microg L(-1) for parathion, 10.2-1020.0 microg L(-1) for phoxim, 54.5-1089.0 microg L(-1) for phorate and 27.2-1089.0 microg L(-1) for chlorpyifos, respectively. The limits of detection calculated at a signal-to-noise ratio of 3 were in the range of 0.1-5.0 microg L(-1). The relative standard deviations for seven replicate experiments at 200 microg L(-1) concentration level were less than 4.7%. The proposed method was applied to the analysis of four different sources water samples (tap, well, rain and Yellow River water) and the relative recoveries of spiked water samples are 99.9-115.4%, 101.8-113.7% and 87.3-117.6% at three different concentration levels of 75, 200 and 1000 microg L(-1), respectively.

A new 1,3-dibutylimidazolium hexafluorophosphate ionic liquid-based dispersive liquid-liquid microextraction to determine organophosphorus pesticides in water and fruit samples by high-performance liquid chromatography.

The paper described a new ionic liquid, 1,3-dibutylimidazolium hexafluorophosphate, as extraction solvent for extraction and preconcentration of organophosphorus pesticides (fenitrothion, parathion, fenthion and phoxim) from water and fruit samples by dispersive liquid-liquid microextraction combined with high-performance liquid chromatography. The effects of experimental parameters, such as extraction solvent volume, disperser solvent and its volume, extraction and centrifugal time, sample pH, extraction temperature and salt addition, on the extraction efficiency were investigated. An extraction recovery of over 75% and enrichment factor of over 300-fold were obtained under the optimum conditions. The linearity relationship was also observed in the range of 5-1000 microgL(-1) with the correlation coefficients (r(2)) ranging from 0.9988 to 0.9999. Limits of detection were 0.01-0.05 microgL(-1) for four analytes. The relative standard deviations at spiking three different concentration levels of 20, 100 and 500 microgL(-1) varied from 1.3-2.7, 1.4-1.9 and 1.1-1.7% (n=7), respectively. Three real samples including tap water, Yellow River water and pear spiked at three concentration levels were analyzed and yielded recoveries ranging from 92.7-109.1, 95.0-108.2 and 91.2-108.1%, respectively.

Poly(ionic liquid) immobilized magnetic nanoparticles as new adsorbent for extraction and enrichment of organophosphorus pesticides from tea drinks

New poly(ionic liquid) immobilized magnetic nanoparticles (PIL-MNPs) were synthesized via co-polymerization of 1-vinyl-3-hexylimidazolium-based ionic liquid and vinyl-modified magnetic particles and were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, and magnetic measurements. The PIL-MNPs were utilized as adsorbent phases in magnetic solid-phase extraction (MSPE). The extraction and enrichment efficiency were evaluated by using four organophosphorus pesticides (parathion, fenthion, phoxim and temephos) as test analytes. Various parameters, such as amount of adsorbent, adsorption time, desorption solvent and time, and ionic strength were investigated. The proposed method showed good linearity for the analytes in the concentration range of 1-200μgL(-1) with a correlation coefficient (R)>0.9963. Low limit of detection of 0.01μgL(-1) and high enrichment factors ranging from 84 to 161 were achieved. The proposed method has been successfully used to determine organophosphorus pesticides from three tea drink samples with satisfactory recovery of 81.4-112.6% and RSDs of 4.5-11.3%. The PIL-MNP adsorbent can be reused for 20 times without a noticeable decrease in extraction efficiency.

Effective indirect enrichment and determination of nitrite ion in water and biological samples using ionic liquid-dispersive liquid–liquid microextraction combined with high-performance liquid chromatography

An ionic liquid dispersive liquid-liquid microextraction high-performance liquid chromatography (IL-DLLME-HPLC) method for effective enrichment and determination of nitrite ion in water and biological samples was developed. The method was based on the reaction of nitrite ion with p-nitroaniline in the presence of diphenylamine in acid media and IL-DLLME of azo product. The optimization of reaction and extraction conditions, such as kind and concentration of acid, reaction time, volume of reaction solvent, temperature, kind of extraction and dispersive solvent, volume of extraction and dispersive solvent, addition of salt, extraction and centrifugal time were studied. Under the optimal conditions, 1-octyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide IL-DLLME procedure provided high enrichment factor of 430 and good extraction recovery of 91.7% for nitrite ion. The linearity was observed in the range of 0.4-500.0 μg L⁻¹ with good correlation coefficient (r²=0.9996). The relative standard deviations (RSDs) for five replicate measurements varied between 1.5% and 4.8%. The limit of detection of the method (S/N=3) was 0.05 μg L⁻¹. The interference effect of some anions and cations was also tested. The developed method allowed achieving an excellent enrichment factor, yielding a lower LOD in comparison with other methods. Moreover, the proposed method was able to analyze nitrite ion in water and biological samples with satisfactory recovery ranged from 96.5% to 107.3%.

Dispersive liquid–liquid microextraction followed by high-performance liquid chromatography for the determination of three carbamate pesticides in water samples

A simple, rapid and efficient method, dispersive liquid–liquid microextraction (DLLME) in conjunction with high-performance liquid chromatography (HPLC), has been developed for the determination of three carbamate pesticides (methomyl, carbofuran and carbaryl) in water samples. In this extraction process, a mixture of 35 µL chlorobenzene (extraction solvent) and 1.0 mL acetonitrile (disperser solvent) was rapidly injected into the 5.0 mL aqueous sample containing the analytes. After centrifuging (5 min at 4000 rpm), the fine droplets of chlorobenzene were sedimented in the bottom of the conical test tube. Sedimented phase (20 µL) was injected into the HPLC for analysis. Some important parameters, such as kind and volume of extraction and disperser solvent, extraction time and salt addition were investigated and optimised. Under the optimum extraction condition, the enrichment factors and extraction recoveries ranged from 148% to 189% and 74.2% to 94.4%, respectively. The methods yielded a linear range in the concentration from 1 to 1000 µg L−1 for carbofuran and carbaryl, 5 to 1000 µg L−1 for methomyl, and the limits of detection were 0.5, 0.9 and 0.1 µg L−1, respectively. The relative standard deviations (RSD) for the extraction of 500 µg L−1 carbamate pesticides were in the range of 1.8–4.6% (n = 6). This method could be successfully applied for the determination of carbamate pesticides in tap water, river water and rain water.

Tetraazacalix[2]arene[2]triazine modified silica gel: A novel multi-interaction stationary phase for mixed-mode chromatography

A novel multi-interaction and mixed-mode stationary phase based on tetraazacalix[2]arene[2]triazine modified silica (NCS) was synthesized and characterized by infrared spectra, elemental analysis and thermogravimetric analysis. Mechanism involved in the chromatographic separation is the multi-interaction including hydrophobic, π-π, hydrogen-bonding, inclusion and anion-exchange interactions. Based on these interactions, successful separation could be achieved among polycyclic aromatic hydrocarbons, aromatic position isomers, organic bases and phenols in reversed-phase chromatography. Inorganic anions were also shown to be individually separated in anion-exchange chromatography by using the same column. Moreover, the results here also demonstrated that NCS based stationary phase could effectively reduce the adverse effect of residual silanol in the separation process. Such stationary phase with characteristics of multi-interaction mechanism and mixed-mode separation is potential for the analysis of complex samples.

New oxo-bridged calix[2]arene[2]triazine stationary phase for high performance liquid chromatography

A new oxo-bridged calix[2]arene[2]triazine bonded stationary phase (OCATS) for high performance liquid chromatography (HPLC) was prepared using 3-aminopropyltriethoxysilane as coupling reagent. The structure of new material was characterized by infrared spectroscopy, elemental analysis and thermogravimetric analysis. The chromatographic performance and retention mechanism of the new stationary phase were evaluated in reversed-phase mode compared with ODS using different solute probes including polycyclic aromatic hydrocarbons (PAHs), mono-substituted benzenes, disubstituted benzene isomers. The new OCATS stationary phase could provide various interactions for different solutes, such as hydrophobic, hydrogen bonding, ππ and inclusion interactions. The synergistic effects resulting from aromatic rings, bridging oxygen atoms and triazine nitrogen atoms and alkyl linkers in the new material improved the separation selectivity by multiple retention mechanisms. The retention behaviors of the analytes on OCATS column were explained with the assistance of quantum chemistry calculation results using DFT-B3LYP/STO-3G* base group. The OCATS column was successfully employed for the analysis of melamine in infant formula.

Macrocyclic polyamine‐functionalized silica as a solid‐phase extraction material coupled with ionic liquid dispersive liquid–liquid extraction for the enrichment of polycyclic aromatic hydrocarbons

In this study, silica modified with a 30-membered macrocyclic polyamine was synthesized and first used as an adsorbent material in SPE. The SPE was further combined with ionic liquid (IL) dispersive liquid-liquid microextraction (DLLME). Five polycyclic aromatic hydrocarbons were employed as model analytes to evaluate the extraction procedure and were determined by HPLC combined with UV/Vis detection. Acetone was used as the elution solvent in SPE as well as the dispersive solvent in DLLME. The enrichment of analytes was achieved using the 1,3-dibutylimidazolium bis[(trifluoromethyl)sulfonyl]imide IL/acetone/water system. Experimental conditions for the overall macrocycle-SPE-IL-DLLME method, such as the amount of adsorbent, sample solution volume, sample solution pH, type of elution solvent as well as addition of salt, were studied and optimized. The developed method could be successfully applied to the analysis of four real water samples. The macrocyclic polyamine offered higher extraction efficiency for analytes compared with commercially available C18 cartridge, and the developed method provided higher enrichment factors (2768-5409) for model analytes compared with the single DLLME. Good linearity with the correlation coefficients ranging from 0.9983 to 0.9999 and LODs as low as 0.002 μg/L were obtained in the proposed method.

Determination of Trace Acrylamide in Starchy Foodstuffs by HPLC Using a Novel Mixed-Mode Functionalized Calixarene Sorbent for Solid-Phase Extraction Cleanup

In this paper, a rapid and effective HPLC method, using tetraazacalix[2]arene[2]triazine-modified silica gel (NCSi) as solid-phase extraction (SPE) sorbent, was developed for the purification and determination of trace acrylamide in starchy foodstuffs. The main influence factors of SPE including amount of NCSi sorbent, sample flow rate, and volume and composition of washing solution were investigated and evaluated in the sample pretreatment step. The optimized purification effect was achieved at the sample flow rate of 3 mL/min with 100 mg of NCSi and 2 mL of washing solution (water, 100%). The HPLC separation was carried out on a C18 column (250×4.6 mm i.d., 5 μm) with a mobile phase of methanol/water (10:90, v/v). The linear range of the calibration curve was 4-4000 ng/mL with s correlation coefficient of >0.9999. The intraday and interday RSDs (n=5) of peak areas of acrylamide were 0.22 and 0.90% and the intraday and interday RSDs (n=5) of retention times were 0.50 and 1.63%, respectively. In addition, overall recoveries through the extraction and NCSi-SPE purification ranged from 73.13 to 98%. Compared with the commercial SPE sorbents, NCSi featured excellent selectivity to retain polar and nonpolar interferences in the sample matrices. The improved method was simple, rapid, accurate, and promising for the determination of trace acrylamide in starchy foods with a complex matrix.

A new 14-membered tetraazamacrocycle-bonded silica stationary phase for reversed-phase high-performance liquid chromatography.

A new high-performance liquid chromatography stationary phase has been prepared by covalently bonding 14-membered tetraazamacrocycle to silica gel using γ-chloropropyltrimethoxylsilane as coupling agent. The structure of the new material was characterized by infrared spectroscopy and elemental analysis. With 32 solutes including aromatic and aliphatic compounds, the linear solvation energy relationship method was successfully used to chromatographically evaluate the new phase in reversed phase mode. The retention property of the new phase shows evident similarity with that of ODS stationary phase, as well as distinctive, unique retention characteristics. The separations of n-alkylbenzene, carbamate and organophosphorus pesticides with diversified functional groups as well as phenolic compounds demonstrate that in addition to hydrophobic interaction, dipole-dipole interaction and hydrogen bonding interaction plus acid-base equilibrium could also be simultaneously offered by this new stationary phase, as a result excellent chromatographic performances are guaranteed.