Multiresidue determination of (fluoro)quinolone antibiotics in chicken by polymer monolith microextraction and field-amplified sample stacking procedures coupled to CE-UV

Simultaneous determination of 9 (fluoro)quinolone antibiotics (FQs) was accomplished by capillary electrophoresis-ultraviolet (CE-UV) based on poly(methacrylic acid-co-ethylene glycol dimethacrylate) (MAA-EGDMA) monolith microextraction (PMME) coupled with on-line preconcentration technique of field-amplified sample stacking (FASS). The effects of composition of the acid and organic solvent in the sample solution, sampling time, and voltage on the efficiency of the sample stacking have been systematically investigated. Several parameters that influence extraction efficiency for PMME such as pH of sample solution, extraction volume, and wash and desorption conditions were optimized. In the proposed method, a substantial increase in sensitivity for all the FQs tested was achieved by the combination of PMME procedure with on-line preconcentration of FASS prior to CE analysis. Good linearities were obtained for the 9 tested FQs with the correlation coefficients (R) above 0.9954. The limits of detection (S/N = 3) were found to be 2.4-34.0 ng g⁻¹ and the recoveries ranged from 81.2 to 100% with relative standard deviations less than 11.3%. The proposed PMME-FASS-CE method was applied to the determination of FQs residues in chicken samples.     

聚合物整体柱微萃取-高效液相色谱法检测鸡蛋中的磺胺嘧啶和磺胺二甲嘧啶残留

建立了鸡蛋中磺胺嘧啶和磺胺二甲嘧啶残留量的聚合物整体柱微萃取和高效液相色谱检测方法。以聚(甲基丙烯酸-乙二醇二甲基丙烯酸酯)毛细管整体柱作为萃取装置。为了得到较高的萃取效率,优化了影响萃取效率的参数(萃取流速、萃取体积、样品基质pH值)。样品经过匀浆、乙醇提取、磷酸盐缓冲溶液稀释、离心等步骤后直接进行萃取。鸡蛋中磺胺嘧啶和磺胺二甲嘧啶的检出限分别为11.2 ng/g和8.8 ng/g,在50～5000 ng/g的浓度范围内具有良好的线性关系。加标回收率大于65%,日内、日间测定的相对标准偏差不高于8.2%。结果表明,方法简单、快速、灵敏度高,适用于鸡蛋中磺胺嘧啶和磺胺二甲嘧啶的常规分析。     

Multiresidue analysis of beta-agonists in pork by coupling polymer monolith microextraction to electrospray quadrupole time-of-flight mass spectrometry

A novel method of polymer monolith microextraction (PMME) using poly(methacrylic acid-co-ethylene glycol dimethacrylate) monolith combined with electrospray ionization quadrupole time-of-flight mass spectrometry (ESI-QTOF MS) was developed for the rapid and sensitive determination of beta-agonists in pork samples. The conditions of PMME were optimized for the improvement of extraction efficiency and reduction of the matrix interferences from pork. Under the optimal condition, the eluate solution allowed direct analysis by mass spectrometry. In the positive ion mode and in the multiple reaction monitoring (MRM) mode, the limits of detection (LODs) for beta-agonists were found to be 0.08 ng/g (clenbuterol, CLB), 0.18 ng/g (salbutamol, SBTM) and 0.26 ng/g (terbutaline, TBTL) in pork, respectively, with good inter- and intra-day precisions (2-10% for CLB, 11-23% for SBTM and 4-16% for TBTL). The proposed PMME/ESI-QTOF MS method was successfully applied to the determination of beta-agonist residues in thirteen real samples, and the positive samples were confirmed according to the identification points (IPs) system defined by Commission Decision 2002/657/EC. To investigate the matrix effect, the proposed method was compared with PMME-HPLC/ESI-QTOF MS and the slight decrease in sensitivity of PMME/ESI-QTOF MS was ascribed to the inter-analyte ion suppression.     

Capillary electrophoresis‐laser‐induced fluorescence detection of rat brain catecholamines with microwave‐assisted derivatization

In this study, a rapid and sensitive method is described for the catecholamines detection in rat brain. CE with LIF detection for the determination of FITC derivatized catecholamines (dopamine, epinephrine, and norepinephrine) was demonstrated. Conventional water bath and microwave‐assisted derivatization methods were employed and a significant reduction in the derivatization time from 2 h for the conventional water bath at room temperature (ca. 25°C) to 2 min for the microwave‐assisted derivatization was achieved. Online sample concentration of field‐amplified sample stacking (FASS) method was employed to achieve higher sensitivities (the detection limits obtained in the normal injection mode ranged from 2.6 to 4.5 ng L^?1 and in the FASS mode ranged from 22 to 34 pg L^?1). Furthermore, this microwave‐assisted derivatization CE–LIF method successfully determined catecholamines in rat brain with as low as 100 ng L^?1 (FASS mode) to 10 μg L^?1 (normal injection mode). This CE–LIF method provided better detection ability when compared to the best reports on catecholamines analyses.     

Sensitive analysis of donepezil in plasma by capillary electrophoresis combining on-column field-amplified sample stacking and its application in Alzheimer's disease

Field-amplified sample stacking (FASS) in capillary electrophoresis (CE) was used to determine the concentration of donepezil, an acetylcholinesterase inhibitor, in human plasma. A sample pretreatment by liquid-liquid extraction with isopropanol/n-hexane (v/v 3:97) and subsequent quantification by FASS-CE was used. Before sample loading, a water plug (0.5 psi, 6 s) was injected to permit FASS. Electrokinetic injection (7 kV, 90 s) was used to introduce sample cations. The separation condition for donepezil was performed in electrolyte solutions containing Tris buffer (60 mM, pH 4.0) with sodium octanesulfonate 40 mM and 0.01% polyvinyl alcohol as a dynamic coating to reduce analytes' interaction with capillary wall. The separation was performed at 28 kV and detected at 200 nm. Using atenolol as an internal standard, the linear ranges of the method for the determination of donepezil in human plasma were over a range of 1-50 ng/mL. The limit of detection was 0.1 ng/mL (S/N=3, sampling 90 s at 7 kV). One female volunteer (54 years old) was orally administered a single dose of 10 mg donepezil (Aricept, Eisai), and blood samples were drawn over a 60 h period for pharmacokinetic study. The method was also applied successfully to monitor donepezil in sixteen Alzheimer's disease patients' plasmas.     

An online field-amplification sample stacking method for the determination of diuretics in urine by capillary electrophoresis-amperometric detection

A simple and sensitive online field-amplification sample stacking (FASS) pre-enrichment method following by capillary electrophoresis with amperometric detection has been developed for the determination of diuretics, such as indapamide (IDP), hydrochlorothiazide (HCT) and bumetanide (BMTN) in urine. Under the optimum conditions, it was found that the low concentration buffer solution could be used as the diluents for simultaneous field-amplification injection of three diuretics after electrokinetically injecting a short water plug (15 kV, 3 s). Three analytes could be well separated within 10 min in an uncoated fused-silica capillary with H(3)BO(3)-Na(2)B(4)O(7) (BB) buffer solution (pH 8.98). The detection limits (S/N=3) were 9.0 ng/mL for IDP, 20 ng/mL for HCT and 1.5 ng/mL for BMTN, respectively. The detection limits of three diuretics were much lower by FASS than that by conventional sample injection, of which the detection limits were 340, 890 and 330 ng/mL for IDP, HCT and BMTN, respectively. Especially, for bumetanide the detection limit was 220-time lower by FASS. The linear ranges of three diuretics were all over three orders of magnitude. The proposed method has been successfully applied to analyze the diuretics in human urine samples without off-column sample pre-concentration.     

On-line sample stacking and short-end injection CE for the determination of fluoxetine and norfluoxetine in plasma: Method development and validation using experimental designs

A short-end injection CE method combining field-amplified sample stacking (FASS) is presented for the analysis of fluoxetine (FL) and norfluoxetine in plasma. In this study, FASS enhanced the sensitivity about 1100-fold, while short-end injection reduced the analysis time to less than 4 min. Parameters involved in the separations were investigated using a central composite design (CCD) and response surface methodology to optimize the separation conditions in a total of only 32 runs. Samples injected into the capillary for 99.9 s at a voltage of -5 kV were stacked in a water plug (0.5 psi, 9 s). Baseline resolution of FL and its major metabolite was achieved using a BGE formulation consisting of phosphate-triethanolamine at low pH, and a separation voltage of -10 kV. Five percent methanol was added as organic modifier to enhance selectivity and resolution. The linear range was between 10 and 500 ng/mL (r >0.9946), covering the expected plasma therapeutic ranges. The LOD in plasma were 4 ng/mL (S/N = 3), a value comparable to that obtained using LC-MS, showing the success of the on-line stacking technique. Our method was also successfully validated in quantification and pharmacokinetic studies with three volunteer plasma samples and could be applied to pharmacogenetic studies.     

Trace analysis of zotepine and its active metabolite in plasma by capillary electrophoresis with solid phase extraction and head-column field-amplified sample stacking

A sensitive high-performance capillary zone electrophoresis (CZE) with head-column field-amplified sample stacking (FASS) in binary system has been developed for the simultaneous determination of zotepine and its active metabolite, norzotepine, in human plasma. The separation of zotepine and norzotepine was performed using a background electrolyte consisting of 50% ethylene glycol-borate buffer (20mM, pH 8.0) solution with 20% methanol as the running buffer and on-column detection at 200 nm. Under the optimal FASS-CZE condition, good separation with high efficiency and short analysis time is achieved. Several parameters affecting the separation and sensitivity of the drug were studied, including sample matrix, pH and concentrations of the borate buffer, ethylene glycol and methanol. Using clozapine as an internal standard, the linear ranges of the method for the determination of zotepine and norzotepine in human plasma were over 3-100 ng/mL; the detection limits of zotepine and norzotepine in plasma were 2 and 1 ng/mL, respectively. A sample pretreatment by means of solid-phase extraction (SPE) with subsequent quantitation by FASS-CZE was used. The application of the proposed method for determination of zotepine and norzotepine in plasma collected after oral administration of 125 mg zotepine in one schizophrenic patient was demonstrated.     

Extraction of clenbuterol from urine using hydroxylated poly(glycidyl methacrylate-co-ethylene dimethacrylate) monolith microextraction followed by high-performance liquid chromatography determination

A hydroxylated poly(glycidyl methacrylate-co-ethylene dimethacrylate) (GMA-co-EDMA) monolithic capillary was prepared for polymer monolith microextraction (PMME). Coupled to HPLC with UV detection, this extraction medium was successfully applied to establish a simple and fast method for the analysis of clenbuterol (CLB) in urine. To obtain optimum extraction performance, the effects of pH value and ionic strength of the sample matrix on extraction efficiency were investigated. The linearity of the method was evaluated over a concentration range of 10-2000 ng/mL and the correlation coefficient (R2 value) was 0.9985. The detection limit and quantification limit were 2.3 and 7.7 ng/mL, respectively. Good reproducibility of the method was obtained, yielding the intra- and interday RSDs less than 5.1 and 9.1%, respectively. Moreover, the hydroxylated poly(GMA-co-EDMA) monolithic capillary exhibited good preparation reproducibility and long-term extraction life. When applied to the determination of CLB in urine samples, an effective removal of interfering compounds was achieved and recoveries were in the range of 87.6-106%. The determination of CLB from one real sample including pretreatment, extraction, and analysis could be finished within 30 min.     

Determination of quinolone residues in chicken and fish by capillary electrophoresis-mass spectrometry

A specific pressure-assisted CE-MS method is described for the analysis of five quinolone residues. MS using a single quadrupole is compared with multiple-stage MS using a quadrupole IT (QIT-MS(n)). The procedure involves a common sample preparation by SPE on disposable cartridges. The most suitable electrolyte is 60 mM (NH(4))(2)CO(3) at pH 9.2. Single quadrupole does not provide enough fragmentation to confirm identities according to the current legislation. However, QIT-MS(n) achieves selective fragmentation. Using this method, danofloxacin, enrofloxacin, flumequine, ofloxacin, and pipemidic acid are analyzed in fortified samples of chicken and fish. Recoveries at levels of 50 ng/g were 62-99%, except for flumequine, which gives recoveries > or =45%. RSDs are from 9 to 16% and the LOD is equal (20 ng/g) for the five analytes. Confirmation of the quinolones' identity is achieved using QIT-MS(3). Forty samples of chicken and fish taken from different local markets are analyzed. Enrofloxacin is also determined in incurred chicken muscle using this method.     

Rapid determination of Δ-Tetrahydrocannabinol in saliva by polymer monolith microextraction combined with gas chromatography-mass spectrometry

A method was developed for the determination of Δ⁹-Tetrahydrocannabinol (THC) in saliva by polymer monolith microextraction (PMME) combined with gas chromatography-mass spectrometry. The poly(methacrylic acid-co-ethylene glycol dimethacrylate) (p(MAA-co-EGDMA)) monolithic capillary column was selected as the extraction medium of PMME, which showed high extraction capacity towards THC in saliva. To reach optimum PMME extraction performance, several PMME parameters were investigated, including matrix pH, flow rate for extraction, sampling volume and elution solvent. Under the optimal conditions, good extraction efficiency was obtained with no matrix interference in the process of extraction and the subsequent GC-MS analysis. In the selected-ion monitoring (SIM) mode, the limit of detection (LOD) for THC was 0.68 ng/mL. The linearity range of the method was 3-300 ng/mL. Excellent reproducibility of the method was exhibited by intra- and inter-day precisions, yielding the relative standard deviations (R.S.D.s) less than 12%; recoveries higher than 89%. The proposed method was proved to be rapid, sensitive, and competently applied to the determination of THC in saliva samples.     

On-line sample enrichment for the determination of proteins by capillary zone electrophoresis with poly(vinyl alcohol)-coated bubble cell capillaries

Field-amplified sample stacking (FASS) is used to separate basic proteins in a poly-(vinyl alcohol)-coated bubble cell capillary. To our knowledge, this is the first paper describing the on-column stacking of proteins (as cations) using FASS in bubble cell capillary. The bubble cell capillary is fabricated using a one-step method. Cetyltrimethylammonium chloride is added into the running buffer to reverse the EOF and, thus, to pump the water plug out during the sample stacking step. The effect of the water plug lengths and sample injection durations were investigated and optimized. The results obtained were compared with those for the normal capillary without bubble cell in terms of resolution and sensitivity enhancement. Under the optimal condition, this method can improve the sensitivity of the peak areas ranging from 5000- to 26 000-fold. The RSDs (n = 5) of the migration time and peak area are satisfactory (less than 0.6 and 12%, respectively). Application of the capillary electrophoresis method with bubble cell, FASS, and UV detection thereby leads to the determination of these proteins at concentrations ranging from 3 to 10 ng/mL, based on a signal-to-noise ratio of 3:1.     

Preparation and application of trimethylamine amination polychloromethyl styrene nanolatex coated capillary column for the determination of bromate by field‐amplified sample stacking open‐tubular capillary electrochromatography

A new trimethylamine amination polychloromethyl styrene nanolatex (TMAPL) and TMAPL coated capillary column (ccc‐TMAPL) were successfully prepared. The TMAPL coating was characterized with reversed steady EOF values of ca. ?16.8 × 10^?5 cm² V^?1 s^?1. It was applied to establish open‐tubular (OT) CEC and field‐amplified sample stacking (FASS) OT‐CEC methods for the determination of bromate in tap water. Compared to OT‐CEC, the LOD with FASS‐OT‐CEC was improved from 80 to 8 ng/mL. The developed FASS‐OT‐CEC method was practically used for the analysis of bromate in tap water samples with recoveries ranging from 93.6 to 103.5%.     

Automatic sample preparation of sulfonamide antibiotic residues in chicken breast muscle by using dynamic microwave-assisted extraction coupled with solid-phase extraction

In the work, a rapid, simple and high-throughput sample preparation method was developed for the determination of sulfonamide (SA) antibiotic residues in chicken breast muscle. The extraction and clean-up were online combined and up to 20 samples can be treated simultaneously in 6 min. The SAs were first extracted with acetonitrile under the action of microwave energy, and then the extract was directly introduced into the SPE column for on-line clean-up and concentration. Subsequently, the SAs eluted from the SPE column were determined by liquid chromatography-tandem mass spectrometry. The precisions of extraction results of 20 samples were in the range of 4.9-7.4%. The limits of detection and quantification obtained were in the range of 2.4-3.6 ng/g and 8.6-11.3 ng/g for SAs, respectively. The recoveries of SAs obtained by analyzing chicken muscles at three fortified levels (10, 50 and 500 ng/g) were in the range of 82.6-93.2%. The results of the validation process prove that the proposed method is suitable for treating numbers of complex samples simultaneously in a short time.     

Rapid analysis of melamine in infant formula by sweeping-micellar electrokinetic chromatography

In the present study, an analytical method using capillary electrophoresis with on-line preconcentration technique was developed for rapid determination of melamine in infant formula. Both stacking and sweeping preconcentration techniques had been investigated for the comparison of their effectiveness in melamine analysis. The limit of detection of melamine standard was 0.5 ng/mL for the field amplified sample stacking (FASS) technique and 9.2 ng/mL for the sweeping technique. Although the FASS technique provided better concentration efficacy than the sweeping technique, the matrix effect was more profound with the former. Matrix effect was evaluated by comparing the enhancement factor (EF) of melamine standard and post-extraction spiked infant formula solution. The EF was changed from 429.86 ± 9.81 to the level less than 133.31 with significant peak distortion in the FASS system, and it was remained unchanged in the sweeping system. Sweeping-micellar electrokinetic chromatography (sweeping-MEKC) was demonstrated to be most suitable for real sample analysis. Under optimum sweeping-MEKC conditions, melamine content in infant formulas could be determined within 6 min. The developed solid phase extraction (SPE) procedures coupled with the sweeping-MEKC method was subjected to method validation. Run-to-run repeatability (n = 3) and day-to-day reproducibility (n = 3) of peak area were within 3.6% and 4.8% RSD, respectively. The accuracy was tested by spiking 0.5 and 2 μg/mL of melamine standard in the melamine contaminated milk powder provided by the European Commission, and the recoveries were 93.4 ± 0.5% and 98.7 ± 0.4%, respectively. Results of this study show a great potential for the sweeping-MEKC method as a tool for the fast screening of melamine in infant formulas.     

Rapid and sensitive determination of strychnine and brucine in human urine by capillary electrophoresis with field‐amplified sample stacking

A simple, rapid, sensitive and low‐cost method using capillary electrophoresis (CE) coupled with field‐amplified sample stacking (FASS) has been developed and validated for the simultaneous determination of strychnine and brucine residues in human urine. Before sample loading, a water plug (3.5 kPa, 3 s) was injected to contain sample cations and to permit FASS. Electrokinetic injection at a voltage (20 kV, 25 s) was then used to introduce cations. Separation was performed using 20 mM acetate buffer (pH 3.8) with an applied voltage of 20 kV. The calibration curves were linear over a range of 8.00–2.56 ∞ 10² ng/mL (r = 0.9995) for strychnine and 10.0–3.20 × 10² ng/mL (r = 0.9999) for brucine. Extraction recoveries in urine were greater than 79.6 and 82.8% for strychnine and brucine, respectively, with an RSD of less than 4.9%. The detection limits (signal‐to‐noise ratio 3) for strychnine and brucine were 2.00 and 2.50 ng/mL, respectively. A urine sample from one healthy female volunteer (26 years old, 50 kg) was pretreated and analyzed. Strychnine and brucine levels in urine could be detected 24 h after administration. On these grounds, this method was feasible for application to preliminary screening of trace levels of abused drugs for both doping control and forensic analysis. Copyright © 2009 John Wiley & Sons, Ltd.     

Polymer Monolith Microextraction Coupled with HPLC for Determination of Jasmonates in Wintersweet Flowers

A simple, fast, and effective method has been presented for the determination of jasmonates in plant samples by polymer monolith microextraction (PMME). A poly (methacrylic acid-ethylene glycol dimethacrylate) (MAA-EGDMA) monolith-based device was developed for extraction, purification, and concentration; HPLC-UV was used for evaluation. To realize the best microextraction efficiency, parameters such as sample pH value, flow rate, and sample volume were systematically examined and optimized. Aqueous solution (5 mL) of jasmonates at pH 3.0 was selected as sample solution, and loaded onto the monolith at flow rate of 0.15 mL/min; finally, 50 μL of acetonitrile was used for elution. The proposed method exhibited impressive enrichment efficiency (almost 100-fold) and the limits of detection for jasmonic acid and methyl jasmonate obtained 0.5 and 2 ng/mL by using UV detection. Wide linear ranges were also observed (2–2000 and 5–2000 ng/mL) for both jasmonic acid and methyl jasmonate, with R² > 0.999. The developed PMME-HPLC method was successfully applied to the determination of jasmonates in fresh wintersweet flowers with recoveries in the range of 91.9–97.2%. The result was confirmed by an HPLC-MS method. The PMME method was also compared with a conventional C18-SPE method and exhibited better clean-up efficiency.     

Microwave-assisted extraction and in situ clean-up for the determination of fluoroquinolone antibiotics in chicken breast muscle by LC-MS/MS

A new method was developed for the determination of six fluoroquinolone antibiotics including fleroxacin, levofloxacin, ciprofloxacin, lomfloxacin, enrofloxacin, and sparfloxacin in chicken breast muscle, in which the extraction and clean-up were performed in one step by microwave irradiation. The mixture of ACN containing 0.3% v/v phosphoric acid/water pH 3 (70:30, v/v) was used as the extraction solution and hexane was used as the clean-up solution. The extract was analyzed by liquid chromatography-tandem mass spectrometry system. The RSDs of intra- and inter-day obtained are in the range of 1.0-10.4 and 3.8-13.6%, respectively. In the three fortified levels of chicken breast muscle (20, 100, and 500 ng/g), the recoveries of fluoroquinolone antibiotics ranging from 66.0 to 97.2% are obtained. The LODs are in the range of 2.7-6.7 ng/g. This method simplifies the process of the sample preparation and reduces the operation errors.     

Determination of lasalocid with sensitized terbium(III) luminescence detection

The luminescence of the lasalocid-terbium(III) system in the presence of Triton X-100 and trioctylphosphine oxide has been studied by obtaining kinetic and equilibrium measurements and using the stopped-flow mixing technique. The initial rate and luminescence signal of this system are directly proportional to the lasalocid concentration, which allows one to develop very simple, fast, automatic methods for the determination of this analyte. Kinetic and equilibrium data can be obtained in only 0.1 and 10 s, respectively. The calibration graphs were linear over the range 0.004-5.0 mug ml(-1) (kinetic method) and 0.01-5.0 mug ml(-1) (equilibrium method) and the detection limits achieved were 1 and 3 ng ml(-1), respectively, equivalent to 2 and 6 ng g(-1) lasalocid in a chicken liver sample, which are similar to those afforded by the chromatographic methods described for this determination. The relative standard deviation of both methods was close to 2%. The analytical recoveries obtained by applying the kinetic and equilibrium methods to drinking water, poultry feed and chicken liver samples ranged from 95.6 to 102.1% and from 95.9 to 104.9%, respectively.     

Quality evaluation of six bioactive constituents in goji berry based on capillary electrophoresis field amplified sample stacking

Goji berry, fruits of the plant Lycium barbarum L., has long been used as traditional medicine and functional food in China. In this work, a simple and easy‐operation on‐line concentration capillary electrophoresis (CE) for detection flavonoids in goji berry was developed by coupling of field amplified sample stacking (FASS) with an electroosmotic (EOF) pump driving water removal process. Due to the EOF pump and electrokinetic injection showing different influence on the concentration, the analytes injection condition should be systemically studied. Thereafter, the verification of the analytes injection conditions was achieved using response surface experimental design. Under the optimum conditions, 86–271 folds sensitivity enhancement upon normal capillary zone electrophoresis (CZE, 50 mbar × 5 s) were achieved for six flavonoids, and the detection limits ranged from 0.35 to 1.82 ng/mL; the LOQ ranged from 1.20 to 6.01 ng/mL. Eventually, the proposed method was applied to detect flavonoids in 30 goji berry samples from different habitats of China; and the results indicated that the flavonoids were rich in the eluent of 30–60% methanol, which provided a reference for extraction of goji berry flavonoids.