Determination of nicotinyl pesticide residues in vegetables by micellar electrokinetic capillary chromatography with quantum dot indirect laser-induced fluorescence

A new assay was developed by use of micellar electrokinetic capillary chromatography with indirect LIF fluorescence for the determination of thiamethoxam, acetamiprid, and imidacloprid residues in vegetables, in which the cadmium telluride quantum dots (QDs) synthesized in aqueous phase were used as fluorescent background substance and their excitation and emission wavelengths matched with LIF detector by engineering their size. The factors that affected the peak height and the resolution were optimized. The running buffer was composed of 4.4 μM cadmium telluride QDs as fluorescent background substance, 40 mM borate and 60 mM SDS, and its pH was adjusted to 8.0. The separation voltage was 25 kV. Under the optimum conditions, the detection limits were 0.05, 0.01, and 0.009 mg/kg; the linear dynamic ranges were 0.5-30, 0.1-30, and 0.1-30 mg/L; and the average recoveries of spiked samples were 72.0-101.2, 74.0-106.7, and 77.8-105.1% for thiamethoxam, acetamiprid, and imidacloprid, respectively. The assay can meet the requirement of maximum residue limits to these three pesticides in the regulations of European Union and Japan, and has been applied for determining their residues in vegetables.     

Rapid determination of NSAIDs by capillary and microchip electrophoresis with capacitively coupled contactless conductivity detection in wastewater

A simple, rapid method using CE and microchip electrophoresis with C⁴D has been developed for the separation of four nonsteroidal anti-inflammatory drugs (NSAIDs) in the environmental sample. The investigated compounds were ibuprofen (IB), ketoprofen (KET), acetylsalicylic acid (ASA), and diclofenac sodium (DIC). In the present study, we applied for the first time microchip electrophoresis with C⁴D detection to the separation and detection of ASA, IB, DIC, and KET in the wastewater matrix. Under optimum conditions, the four NSAIDs compounds could be well separated in less than 1 min in a BGE composed of 20 mM His/15 mM Tris, pH 8.6, 2 mM hydroxypropyl-beta-cyclodextrin, and 10% methanol (v/v) at a separation voltage of 1000–1200 V. The proposed method showed excellent repeatability, good sensitivity (LODs ranging between 0.156 and 0.6 mg/L), low cost, high sample throughputs, portable instrumentation for mobile deployment, and extremely lower reagent and sample consumption. The developed method was applied to the analysis of pharmaceuticals in wastewater samples with satisfactory recoveries ranging from 62.5% to 118%.     

CE‐ESI‐MS coupled with dynamic pH junction online concentration for analysis of peptides in human urine samples

In this article, an approach has been developed for the analysis of some small peptides with similar pI values by CE‐ESI‐MS based on the online concentration strategy of dynamic pH junction. The factors affected on the separation, detection and online enrichment, such as BGE, injection pressure, sheath flow liquid and separation voltage have been investigated in detail. Under the optimum conditions, i.e. using 0.5 mol/L formic acid (pH 2.15) as the BGE, preparing the sample in 50 mM ammonium acetate solution (pH 7.5), 50 mbar of injection pressure for 300 s, using 7.5 mM of acetic acid in methanol–water (80% v/v) solution as the sheath flow liquid and 20 kV as the separation voltage, four peptides with similar pI values, such as L ‐Ala‐L ‐Ala (pI=5.57), L ‐Leu‐D ‐Leu (pI=5.52), Gly‐D ‐Phe (pI=5.52) and Gly‐Gly‐L ‐Leu (pI=5.52) achieved baseline separation within 18.3 min with detection limits in the range of 0.2–2.0 nmol/L. RSDs of peak migration time and peak area were in the range of 1.45–3.57 and 4.93–6.32%, respectively. This method has been applied to the analysis of the four peptides in the spiked urine sample with satisfactory results.     

Establishment of pressurized liquid extraction followed by HPLC–MS/MS method for the screening of adrenergic drugs,steroids, sedatives,colorants and antioxidants in swine feed

A facile and sensitive multi‐residue detection approach of pressurized liquid extraction following high‐performance liquid chromatography tandem mass spectrometry was established to detect the residues of adrenergic drugs, steroids, sedative, colorant and antioxidant in feed. The conditions employed for pressurized liquid extraction involved acetonitrile/ethyl acetate (1:1, v/v) as the extracting solvent, the temperature 80°C, two cycles and a static time of 10 min. The extraction was followed by a solid‐phase extraction clean‐up step. The separation of samples was done by C₁₈ column with the mobile phase of 5 mM ammonium acetate solution and acetonitrile with 0.1% formic acid. The limits of quantification ranged from 0.03 to 1 μg/kg, limits of detection were in a range of 0.01–0.5 μg/kg, and average recoveries were 70.4–98.6%. The pressurized liquid extraction procedure was optimized and overall method was validated in terms of sensitivity, linearity, selectivity, matrix effect, accuracy, recovery and stability of the target drugs in the pressurized liquid extraction extracts solution. The screening method was proved to be fast, selective, accurate and sensitive for screening drugs.     

Separation and simultaneous determination of seven bioactive components in Tripterygium wilfordii Hook. F. and Tripterygium preparations by micellar electrokinetic capillary chromatography

A simple, comprehensive, and highly selective MEKC method has been developed for simultaneous analysis of seven bioactive components (triptolide, wilfortrine, wilfordine, wilforgine, wilforine, triptophenolide, and triptonide) in the root extracts of Tripterygium wilfordii Hook. F. (TWHF) and Tripterygium preparations (TPs). Optimal BGE consisted of 10 mM sodium tetraborate, 30 mM SDS, and 30% v/v methanol. The separation voltage was 20 kV and the temperature was 25°C. A DAD was used and the detection wavelength was at 218 nm. Under the optimum conditions, the baseline separation of seven components was achieved in less than 26 min. Excellent precision, good stability, and accuracy were obtained. For all analytes, linear calibrations were established within 10–100 μg/mL. The LOD and LOQ were within 1.2–4.2 μg/mL and 4.0–14 μg/mL, respectively. The developed method was suitable for the determination of key components in TWHF and TPs.     

Capillary electrophoresis-acid barrage stacking online enrichment method for highly sensitive determination of four isoflavones

A capillary electrophoresis-acid barrage stacking online enrichment method has been established to detect the four isoflavones which are Daidzein, Genistein, Formononetin, and Biochanin A. The proposed method was optimized using a single factor alternative method, and the optimal conditions obtained from the optimization were: the BGE was 25 mM borax and 2 mM β-cyclodextrin, the applied separation voltage was 20 kV, and the detection wavelength was 260 nm. The time ratio of the injection of sample and the injection of acid was 150 s:20 s, and the acid used was 250 mM acetic acid. The sample solvent used was 60% v/v acetonitrile. The established method had the enrichment factor of these four isoflavones at 24.5, 32.0, 29.2, and 33.7, respectively, LOD and LOQ are as low as nanograms per milliliter. Finally, the CE-acid barrage stacking method was successfully applied to the determination of four isoflavones in rat plasma and red clover extract, verifying the applicability and feasibility of the method.     

Ultrafast synthesis of near-infrared-emitting aqueous CdTe/CdS quantum dots with high fluorescence

The traditional aqueous route to synthesis CdTe/CdS Core/shell (c/s) quantum dots (QDs) via decomposition of Cd-thiol complexes is usually time consuming. Herein, an ultrafast and facile aqueous synthetic approach under atmospheric pressure for CdTe/CdS c/s QDs with emission from the green to the near-infrared window (535–820 nm) is reported. With purified CdTe core QDs diluted in solution of Cd-3-mercaptopropionic acid (MPA) complexes, CdTe/CdS c/s QDs with emission wavelengths at 700 and 800 nm can be obtained within 20- and 45-min refluxing under the optimized experimental conditions, respectively. This is the most rapid way to prepare CdTe/CdS c/s QDs in aqueous phase, and the obtained QDs were highly luminescent without postsynthesis treatment. The influences of various experimental factors, including Cd²⁺ concentration, MPA-to-Cd ratio, pH value, and dilution ratio on the growth rate and luminescent properties of the obtained CdTe/CdS c/s QDs, have been taken into consideration. The three processes “purification-dilution-addition” ensure the synthesis environment with high pH value and low core concentration and have a marked impact on the rapid synthesis rate and the resulting high fluorescence of CdTe/CdS c/s QDs.     

Chiral separation and quantitation of cetirizine and hydroxyzine by maltodextrin-mediated CE in human plasma: effect of zwitterionic property of cetirizine on enantioseparation

In the present study, a very simple CE method for chiral separation and quantitation of zwitterionic cetirizine (CTZ), as the main metabolite of hydroxyzine (HZ), and HZ has been developed. In addition, the effect of zwitterionic property of CTZ on enantioseparation was investigated. Maltodextrin, a linear polysaccharide, as a chiral selector was used and several parameters affecting the separation such as pH of BGE, concentration of chiral selector and applied voltage were studied. The best BGE conditions for CTZ and HZ enantiomers were optimized as 75 mM sodium phosphate solution at pH of 2.0, containing 5% w/v maltodextrin. Results showed that, compared to HZ, pH of BGE was an effective parameter in enantioseparation of CTZ due to the zwitterionic property of CTZ. The linear range of the method was over 30-1200 ng/mL for all enantiomers of CTZ and HZ. The quantification and detection limits (S/N=3) of all enantiomers were 30 and 10 ng/mL, respectively. The method was used to quantitative enantioseparation of CTZ and HZ in spiked human plasma.     

Simultaneous determination of weakly ionizable analytes in urine and plasma samples by transient pseudo-isotachophoresis in capillary zone electrophoresis

A rapid method for the simultaneous determination of several non-steroidal anti-inflammatory drugs (NSAIDs) in human plasma and urine was developed using transient pseudo-isotachophoresis (ITP) in capillary zone electrophoresis (CZE). The influence of different parameters on resolution and preconcentration efficiency, such as background electrolyte (BGE) composition, sample injection, sample matrix composition, and pH, were studied to optimize the transient pseudo-ITP performance. Optimized conditions were a BGE consisting of 100 mM Na₂B₄O₇ in 10% aqueous MeOH solution and hydrodynamic injection of the sample at 50 mbar for 90 s. The sample was prepared in a solution mixture of 1% NaCl/ethanol (30:70 v/v) at pH 10. Our results show that this simple strategy offers improved sensitivity compared to conventional CZE analysis, reaching a 45-fold preconcentration factor. The detection limits (LODs) were as low as 0.07 mg/L for standard samples with good repeatability (values of relative standard deviation, %RSD < 11%). The method was applied to the analysis of NSAIDs in biological samples. Validation for human plasma and urine samples demonstrated good linearity, low detection limits, and satisfactory repeatability values.     

Development and Validation of Nonaqueous Capillary Electrophoresis Method for Simultaneous Estimation of Icariin,Icariside II,and Epimedin K in Epimedium Leaves

This paper describes a novel nonaqueous capillary electrophoresis method for the separation and determination of Icariin, Icariside II, and Epimedin K in Epimedium leaves. Three flavonoids were extracted by ultrasonication with EtOH-H₂O (70:30) followed by a HP 20 resin column cleanup procedure. The optimized electrophoretic conditions were obtained with the running solution of 8 mM borate MeCN/H₂O (60:40, v/v) (pH 11.40), separation voltage of +20 kV and detection wavelength of 270 nm. The limits of quantification ranged from 0.24 to 0.84 mg/kg (signal/noise = 3) for three flavonoids. Three flavonoids in 10 Epimedium leaves were successfully measured and evaluated.     

Efficient sample clean‐up and online preconcentration for sensitive determination of melamine in milk samples by capillary electrophoresis with contactless conductivity detection

Based on an efficient sample clean‐up and field‐amplified sample injection online preconcentration technique in capillary electrophoresis with contactless conductivity detection, a new analytical method for the sensitive determination of melamine in milk samples was established. In order to remove the complex matrix interference, which resulted in a serious problem during field‐amplified sample injection, liquid–liquid extraction was utilized. As a result, liquid–liquid extraction provides excellent sample clean‐up efficiency when ethyl acetate was used as organic extraction by adjusting the pH of the sample solution to 9.5. Both inorganic salts and biological macromolecules are effectively removed by liquid–liquid extraction. The sample clean‐up procedure, capillary electrophoresis separation parameters and field‐amplified sample injection conditions are discussed in detail. The capillary electrophoresis separation was achieved within 5 min under the following conditions: an uncoated fused‐silica capillary, 12 mM HAc + 10 mM NaAc (pH = 4.6) as running buffer, separation voltage of +13 kV, electrokinetic injection of +12 kV × 10 s. Preliminary validation of the method performance with spiked melamine provided recoveries >90%, with limits of detection and quantification of 0.015 and 0.050 mg/kg, respectively. The relative standard deviations of intra‐ and inter‐day were below 6%. This newly developed method is sensitive and cost effective, therefore, suitable for screening of melamine contamination in milk products.     

Determination of the enantiomeric and diastereomeric impurities of RS‐glycopyrrolate by capillary electrophoresis using sulfated‐β‐cyclodextrin as chiral selectors

A practical chiral CE method, using sulfated‐β‐CD as chiral selector, was developed for the enantioseparation of glycopyrrolate containing two chiral centers. Several parameters affecting the separation were studied, including the nature and concentration of the chiral selectors, BGE pH, buffer type and concentration, separation voltage, and temperature. The separation was carried out in an uncoated fused‐silica capillary of (effective length 40 cm) × 50 μm id with a separation voltage of 20 kV using 30 mM sodium phosphate buffer (pH 7.0, adjusted with 1 M sodium hydroxide) containing 2.0% w/v sulfated‐β‐CD at 25°C. Finally, the method for determining the enantiomeric impurities of RS‐glycopyrrolate was proposed. The method was further validated with respect to its specificity, linearity range, accuracy and precision, LODs, and quantification in the expected range of occurrence for the isomeric impurities (0.1%).     

Separation and determination of alkyl sulfate surfactants in wastewater by capillary electrophoresis coupled with contactless conductivity detection after preconcentration by simultaneous adsorption using alumina beads

The aim of the present study is to determine four anionic alkyl sulfate (AS) surfactants with different alkyl chains, namely, C8, C10, C12, and C14, in wastewater by CE with capacitively coupled contactless conductivity detection (CE-C⁴D). The conditions effective for the separation of the four AS surfactants were systematically optimized and found to be in a Tris-His (50 mM/20 mM) BGE solution at a pH of 8.95, using a separation voltage of +15 kV, hydrodynamic injection by siphoning using a 20 cm injection height and an injection time of 20 s. The LODs for C8, C10, C12, and C14 were 2.58, 2.30, 2.08, and 3.16 mg/L, respectively. The conditions used to achieve the simultaneous adsorption and preconcentration of the AS surfactants using Al₂O₃ beads were pH of 3 and 0.1 mM NaCl. The adsorption efficiencies were found to be 45.6, 50.8, 81.7, and 99.9%, while the desorption efficiencies reached 66.1, 70.4, 83.9, and 100.0% for C8, C10, C12, and C14, respectively. The concentrations of the AS surfactants in wastewater samples were quantified by CE-C⁴D after preconcentration by simultaneous adsorption using Al₂O₃ beads. The results obtained from the proposed method were consistent with those obtained by HPLC-MS/MS, with a deviation of less than 15%. Our results indicate that the CE-C⁴D performed after preconcentration by an adsorption technique using Al₂O₃ beads is a new, inexpensive, and suitable method for quantifying AS surfactants in wastewater samples.     

Separation and quantification of the urinary enantiomers of 2-hydroxyglutaric acid by capillary electrophoresis with capacitively coupled contactless conductivity detection: Application to the diagnosis of D- and L-2-hydroxyglutaric aciduria

2-hydroxyglutaric aciduria is an inherited neurometabolic disorder with two major types: D-2-hydroxyglutaric aciduria and L-2-hydroxyglutaric aciduria. An easy and fast capillary electrophoresis system combined with a capacitively coupled contactless conductivity detection method was developed for the enantioseparation and determination of D- and L-2-hydroxyglutaric acid in urine. D- and L-2-hydroxyglutaric acids were separated using vancomycin as the chiral selector. The optimal separation conditions for enantiomers were achieved by the use of a buffer containing 50 mM 4-(N-morpholino) butane sulfonic acid solution (pH 6.5), an electroosmotic flow modifier (0.001% [w/v] polybrene), and 30 mM vancomycin as chiral selector. The analysis time was 6 min under optimal conditions. The optimized and validated method was successfully implemented for quantifying D- and L-2-hydroxyglutaric aciduria in patients’ urine, without any pretreatment step. The linearity of the method was determined to be in the range of 2–100 mg/L for D- and L-2-hydroxyglutaric acid in urine. The precision (relative standard deviation%) was obtained at about 7%. For D- and L-2-hydroxyglutaric acids, the limits of detection were 0.567 and 0.497 mg/L, respectively.     

Use of high‐conductivity sample solution with sweeping‐micellar electrokinetic capillary chromatography for trace‐level quantification of paliperidone in human plasma

Paliperidone is a new antipsychotic drug with a relatively low therapeutic concentration of 20–60 ng/mL. We established an accurate and sensitive CE method for the determination of paliperidone concentrations in human plasma in this study. To minimize matrix effect caused by quantification errors, paliperidone was extracted from human plasma using Oasis HLB SPE cartridges with three‐step washing procedure. To achieve sensitive quantification of paliperidone in human plasma, a high‐conductivity sample solution with sweeping‐MEKC method was applied for analysis. The separation is performed in a BGE composed of 75 mM phosphoric acid, 100 mM SDS, 12% acetonitrile, and 15% tetrahydrofuran. Sample solution consisted of 10% methanol in 250 mM phosphoric acid and the conductivity ratio between sample matrix and BGE was 2.0 (γ, sample/BGE). The results showed it able to detect paliperidone in plasma samples at concentration as low as 10 ng/mL (S/N = 3) with a linear range between 20 and 200 ng/mL. Compared to the conventional MEKC method, the sensitivity enhancement factor of the developed sweeping‐MEKC method was 100. Intra‐ and interday precision of peak area ratios were less than 6.03%; the method accuracy was between 93.4 and 97.9%. This method was successfully applied to the analysis of plasma samples of patients undergoing paliperidone treatment.     

Glutathione-capped CdTe quantum dots for the sensitive detection of glucose

A simple and sensitive assay system for glucose based on the glutathione (GSH)-capped CdTe quantum dots (QDs) was developed. GSH-capped CdTe QDs exhibit higher sensitivity to H₂O₂ produced from the glucose oxidase catalyzed oxidation of glucose, and are also more biocompatible than other thiols-capped QDs. Based on the quenching of H₂O₂ on GSH-capped QDs, glucose can be detected. The detection conditions containing reaction time, the concentration of glucose oxidase and the sizes of QDs were optimized and the detection limits for glucose was determined to be 0.1 μM; two detection ranges of glucose from 1.0 μM to 0.5 mM and from 1.0 mM to 20 mM, respectively were obtained. The detection limit was almost a 1000 times lower than other QDs-based optical glucose sensing systems. The developed glucose detection system was simple and facile with no need of complicated enzyme immobilization and modification of QDs.     

Determination of pharmaceuticals in drinking water by CD-modified MEKC: separation optimization using experimental design

A suite of 12 widely used pharmaceuticals (ibuprofen, diclofenac, naproxen, bezafibrate, gemfibrozil, ofloxacin, norfloxacin, carbamazepine, primidone, sulphamethazine, sulphadimethoxine and sulphamethoxazole) commonly found in environmental waters were separated by highly sulphated CD-modified MEKC (CD-MEKC) with UV detection. An experimental design method, face-centred composite design, was employed to minimize run time without sacrificing resolution. Using an optimized BGE composed of 10 mM ammonium hydrogen phosphate, pH 11.5, 69 mM SDS, 6 mg/mL sulphated beta-CD and 8.5% v/v isopropanol, a separation voltage of 30 kV and a 48.5 cm x 50 microm id bare silica capillary at 30 degrees C allowed baseline separation of the 12 analytes in a total analysis time of 6.7 min. Instrument LODs in the low milligram per litre range were obtained, and when combined with offline preconcentration by SPE, LODs were between 4 and 30 microg/L.     

Determination of multiple antibiotics in leafy vegetables using QuEChERS–UHPLC–MS/MS

A modified quick, easy, cheap, effective, rugged, and safe method was established for simultaneous extraction and cleanup of multiple antibiotics in leafy vegetables, and ultra‐high performance liquid chromatography with tandem mass spectrometry was used for analysis. Antibiotics in leafy vegetables were extracted with citric acid/sodium citrate in mixed solvents consisting of acetonitrile/methanol (85:15, v/v) from 10 g of vegetables. Octadecylsilyl and graphitized carbon black were used as dispersant adsorbents. This method was able to effectively extract all of the target antibiotics from leafy vegetables. The average recoveries of 20 antibiotics ranged from 57 to 91%. The limits of detection were 0.33–2.92 μg/kg. The developed method subsequently demonstrated its selectivity, sensitivity, and reliability for detecting multiple antibiotics in 15 samples. Antibiotic residues in vegetables have attracted great concern with respect to human health. It is recommended that standards should be established for antibiotic residues in vegetables to ensure food safety.     

Preparative and scaled‐up separation of high‐purity α‐linolenic acid from perilla seed oil by conventional and pH‐zone refining counter current chromatography

α‐Linolenic acid is an essential omega‐3 fatty acid needed for human health. However, the isolation of high‐purity α‐linolenic acid from plant resources is challenging. The preparative separation methods of α‐linolenic acid by both conventional and pH‐zone refining counter current chromatography were firstly established in this work. The successful separation of α‐linolenic acid by conventional counter current chromatography was achieved by the optimized solvent system n‐heptane/methanol/ water/acetic acid (10:9:1:0.04, v/v), producing 466 mg of 98.98% α‐linolenic acid from 900 mg free fatty acid sample prepared from perilla seed oil with linoleic acid and oleic acid as by‐products. The scaled‐up separation in 45× is efficient without loss of resolution and extension of separation time. The separation of α‐linolenic acid by pH‐zone refining counter current chromatography was also satisfactory by the solvent system n‐hexane/methanol/water (10:5:5, v/v) and the optimized concentration of trifluoroacetic acid 30 mM and NH₄OH 10 mM. The separation can be scaled up in 180× producing 9676.7 mg of 92.79% α‐linolenic acid from 18 000 mg free fatty acid sample. pH‐zone refining counter current chromatography exhibits a great advantage over conventional counter current chromatography with 20× sample loading capacity on the same column.     

CE‐MS method development for peptides analysis,especially hepcidin,an iron metabolism marker

A method for the resolution of a peptides mixture including hepcidin‐25, an iron metabolism marker, was developed by CE‐ESI‐MS. Several strategies were tested to optimize peptide separation, such as the addition of cyclodextrins or organic solvents in the BGE or the use of coated capillaries. Best results in terms of resolution, symmetry and efficiency were obtained with a BGE made of 500 mM ammonium acetate pH 4.5/ACN 70:30 v/v. Using the methodology of experimental design, BGE concentration, sheath liquid composition and MS‐coupling parameters were then optimized in order to obtain the best signal intensity for hepcidin. Finally, a 225 mM BGE and a sheath liquid composed of isopropanol/water 80:20 v/v containing 0.5% v/v formic acid were selected as it constitutes the best compromise for selectivity, peak shape and sensitivity.