Application of poly(methacrylic acid-ethylene glycol dimethacrylate) monolith microextraction coupled with capillary zone electrophoresis to the determination of opiates in human urine

A novel poly(methacrylic acid-ethylene glycol dimethacrylate) (MAA-EGDMA) monolith microextraction method coupled with CZE was proposed for rapidly determining a mixture of opiates comprising heroin, 6-monoacetylmorphine, morphine, codeine, papaverine, and narcotine in human urine. The extraction device contained a regular plastic syringe, the poly(MAA-EGDMA) monolithic capillary tube (530 microm id x 3 cm) and a plastic pinhead, which connected the monolithic capillary tube and the syringe without leakage. In the polymer monolith microextraction, the sample solution was ejected via the monolithic capillary tube by a programmable syringe pump, followed by desorption with an aliquot of appropriate solution, which was collected into a vial for the subsequent analysis by CZE. The best separation was achieved using a buffer composed of 0.1 M disodium hydrogen phosphate (adjusted to pH 4.5 with 1 M hydrochloric acid) and 20% methanol v/v with temperature and voltage of 25 degrees C and 25 kV, respectively. By applying electrokinetic injection with field-enhanced sample stacking, detection limits of 6.6-19.5 ng/mL were achieved. Excellent method of reproducibility was found over a linear range of 80-2000 ng/mL.     

Poly(methacrylic acid-ethylene glycol dimethacrylate) monolith in-tube solid-phase microextraction applied to simultaneous analysis of some amphetamine derivatives in urine by capillary zone electrophoresis

A method based on in-tube solid-phase microextraction and capillary zone electrophoresis (CZE) was proposed for simultaneously determining four amphetamines (amphetamine, methamphetamine, 3,4-methylenedioxyamphetamine, and 3,4-methylenedioxymethamphetamine) in urine. A poly(methacrylic acid-ethylene glycol dimethacrylate) monolithic capillary column, which can provide sufficient extraction efficiency, was introduced for the extraction of amphetamines from urine samples. The hydrophobic main chains and acidic pendant groups of the monolithic column make it a superior material for extraction of basic analytes from aqueous matrix. After extraction, the samples were analyzed by CZE. The best separation was achieved using a buffer composed of 0.1 M disodium hydrogen phosphate (adjusted to pH 4.5 with 1 M hydrochloric acid) and 20% methanol v/v, with a temperature and voltage of 25 degrees C and 20 kV, respectively. By applying electrokinetic injection with field-amplified sample stacking, detection limits of 25-34 microg/L were achieved. Excellent method of reproducibility was found over a linear range of 0.1-5 mg/L. Determination of these analytes from abusers' urine sample was also demonstrated.     

In-tube solid-phase microextraction with poly(methacrylic acid-ethylene glycol dimethacrylate) monolithic capillary for direct high-performance liquid chromatographic determination of ketamine in urine samples

Ketamine was used for anaesthesia originally but has emerged as an abused drug in recent years. The prevalence of ketamine abuse demands a direct and rapid determination method. It is known that in-tube solid phase microextraction (in-tube SPME) can perform extraction with a capillary linked directly to a HPLC system, providing an automated and accurate extraction procedure. In this paper, an in-tube SPME coupled to HPLC method was developed for the determination of ketamine in urine samples with a poly(methacrylic acid-ethylene glycol dimethacrylate) monolithic capillary column as the extraction phase, which is expected to provide higher extraction efficiency than open tubular capillaries. After optimizing the extraction conditions, ketamine was extracted directly from urine samples in a wide dynamic linear range of 50-10,000 ng mL(-1), with the detection limit obtained as 6.4 ng mL(-1). The intra-day and inter-day precision for the method was 1.6% and 1.7%, respectively. The urine samples from suspect addicts have been successfully analyzed within 20 min. The re-usability of the monolithic column was also confirmed as no decrease of the extraction efficiency was shown after urine extraction.     

Poly(methacrylic acid-ethylene glycol dimethacrylate) monolith in-tube solid phase microextraction coupled to high performance liquid chromatography and analysis of amphetamines in urine samples

In-tube solid-phase microextraction (SPME) based on a poly(methacrylic acid-ethylene glycol dimethacrylate) monolithic capillary column was investigated for the extraction of amphetamine, methamphetamine and their methylenedioxy derivatives. The monolithic capillary column showed high extraction efficiency towards target analytes, which could be attributed to its larger loading amount of extraction phase than conventional open-tubular extraction capillaries and the convective mass transfer procedure provided by its monolithic structure. The extraction mechanism was studied, and the results indicated that the extraction process of the target analytes was involved with hydrophobic interaction and ion-exchange interaction. The polymer monolith in-tube SPME-HPLC system with UV detection was successfully applied to the determination of amphetamine, methamphetamine and their methylenedioxy derivatives in urine samples, yielding the detection limits of 1.4 - 4.0 ng/mL. Excellent method reproducibility (RSD < 2.9%) was found over a linear range of 0.05-5 microg/mL, and the time for the whole analysis was only approximately 25 min. The monolithic capillary column was reusable in coping with the complicated urine samples.     

Poly (methacrylic acid-ethylene glycol dimethacrylate) monolithic capillary for in-tube solid phase microextraction coupled to high performance liquid chromatography and its application to determination of basic drugs in human serum

A poly (methacrylic acid-ethylene glycol dimethacrylate) monolithic capillary column was prepared for in-tube solid-phase microextraction. Comparing with the commonly used open tubular extraction capillary, which cannot provide sufficient extraction efficiency since the ratio of its coating volume to that of the capillary void volume is relatively small, the monolithic column with greater phase ratio combined with convective mass transfer provides the possibility to improve the extraction efficiency with shorter capillary. As to poly (methacrylic acid-ethylene glycol dimethacrylate), its hydrophobic main chains and acidic pendant groups make it a superior material for extraction of basic analytes from aqueous matrix.An on-line monolithic capillary column solid phase microextraction (SPME) method was developed for determination of theobromine, theophylline and caffeine in serum samples. The high extraction efficiency was obtained for all the three analytes, yielding the detection limits of 12, 8 and 6.5 ng/mL by UV detection, respectively. Excellent method reproducibility (R.S.D. < 2.9%) was found over a linear dynamic range of 0.05-2 μg/mL in serum sample. The monolithic capillary column was proved to be reusable in coping with serum samples, which would facilitate practical determination of basic drugs.     

Application of capillary zone electrophoresis to the screening of some angiotensin II receptor antagonists

A capillary zone electrophoretic (CZE) method was optimized for the separation of five angiotensin II receptor antagonists (Losartan, Irbesartan, Valsartan, Telmisartan and Eprosartan) and two of their metabolites (EXP 3174 and Candesartan M1) by means of experimental design methodologies. The aim of this study was to define rapidly experimental conditions under which the analytes can be resolved for quantitation. The effects of the buffer (pH, concentration and composition), the organic modifier and voltage were studied. Critical factors were identified in a screening design (fractional factorial design) and sequentially an optimization design (central composite design) was used to choose optimal conditions for separation. The most favorable electrophoretic conditions were found by setting the resolution at a threshold value (Rs < or = 1.5) and minimizing, if possible, analysis time. Successful results were obtained with a 50 mM potassium dihydrogen phosphate:boric acid (25:75 v/v) buffer at pH 5.5 in the presence of 5% methanol and application of a 25 kV voltage. Analysis time was 8 min in a conventional fused-silica capillary (50 cm effective length) in a normal cationic mode (anode at the inlet and cathode at the outlet) after hydrostatical sample injection for 30 s.     

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.     

Development of a solid phase extraction procedure for HPLC-DAD determination of several angiotensin II receptor antagonists in human urine using mixture design

The optimisation of a solid phase extraction procedure involves several variables whose influence has been widely studied. However, in most cases, only process variables are taken into account. In this work, the influence of those process variables together with the fact of using mixtures of solvents during the elution step of the solid phase extraction of four angiotensin II receptor antagonist drugs has been studied. Since the influence on the extraction efficiency of several process variables were simultaneously tested, a D-optimal design was constructed. The composition of the elution solvent (a mixture of methanol, acetonitrile, ethanol and acetone at different proportions from 0 to 100% each solvent), the percentage and pH of the buffer solution added to the urine samples at the beginning of the extraction procedure; the percentage of the organic component and the volume of the washing solution, the drying time and the volume of the elution solvent were the studied variables. The chromatographic separation was carried out by gradient elution mode with 0.026% trifluoroacetic acid (TFA) in the organic phase and 0.031% TFA in the aqueous phase using an Atlantis dC18, 100 mm × 3.9 mm I.D. chromatographic column at a flow rate of 1 mL/min and a column temperature of 35 ± 0.2 °C. For detection a diode array detector set at 232 nm was used. The extraction procedure for spiked human urine samples was developed using C8 cartridges, phosphate buffer pH 6.8 as conditioning agent, a drying step of 10 min, a washing step with methanol-phosphate buffer (20:80, v/v) and methanol as eluent. Recovery percentages obtained: 84% for eprosartan, 74% for telmisartan, 74% for irbesartan and 89% for valsartan allow the determination of these drugs concentration levels in urine.     

Combining poly (methacrylic acid‐co‐ethylene glycol dimethacrylate) monolith microextraction and octadecyl phosphonic acid‐modified zirconia‐coated CEC with field‐enhanced sample injection for analysis of antidepressants in human plasma and urine

A method based on poly (methacrylic acid‐co‐ethylene glycol dimethacrylate) monolith microextraction and octadecylphosphonic acid‐modified zirconia‐coated CEC followed by field‐enhanced sample injection preconcentration technique was proposed for sensitive CE‐UV analysis of six antidepressants (doxepin, clozapine, imipramine, paroxetine, fluoxetine and chlorimipramine) in human plasma and urine. A poly(methacrylic acid‐co‐ethylene glycol dimethacrylate) monolithic capillary column was introduced for the extraction of antidepressants from urine and plasma samples. The hydrophobic main chains and acidic pendant groups of the monolithic column make it a superior material for extraction of basic analytes from aqueous matrix. After extraction, the desorption solvent, which normally provided an excellent medium to ensure direct compatibility for field‐enhanced sample injection in CE, was analyzed by CE directly. By the use of alkylphosphonate‐modified zirconia‐coated CEC for separation of the basic compounds of antidepressants, high separation efficiency and resolution were achieved because that both hydrophobic interaction between analytes and alkylphosphonate‐modified zirconia coat and electrophoretic effect work on the separation of antidepressants. The best separation was achieved using a buffer composed of 0.3 M ammonium acetate (adjusted to pH 4.5 with 1 M acetic acid) and 35% ACN v/v, with a temperature and voltage of 20°C and 20 kV, respectively. By applying both preconcentration procedures, LODs of 11.4–51.5 and 3.7–17.0 μg/L were achieved for the six antidepressants in human plasma and urine, respectively. Excellent method of reproducibility was found over a linear range of 50–5000 μg/L in plasma and urine sample.     

Determination of mercury(II) in water samples using dispersive liquid-liquid microextraction and back extraction along with capillary zone electrophoresis

We have developed a method for the determination of mercury in water samples that combines dispersive liquid-liquid microextraction (DLLME) with back-extraction (BE) and detection by capillary zone electrophoresis. DLLME is found to be a simple, cost-effective and rapid method for extraction and preconcentration. The BE procedure is based on the fact that the stability constant of the hydrophilic chelate of Hg(II) with L-cysteine is much larger than that of the respective complex with 1-(2-pyridylazo)-2-naphthol. Factors affecting complex formation and extraction efficiency (such as pH value, concentration of the chelating agent, time of ultrasonication and extraction, and type and quantity of disperser solvent) were optimized. Under the optimal conditions, the enrichment factor is 625, and the limit of detection is 0.62???g?L^?1. The calibration plot is linear in the range between 1 and 1,000???g?L^?1 (R ²?=?0.9991), and the relative standard deviation (RSD, for n?=?6) is 4.1%. Recoveries were determined with tap water and seawater spiked at levels of 10 and 100???g?L^?1, respectively, and ranged from 86.6% to 95.1%, with corresponding RSDs of 3.95?C5.90%.

Development of a solid‐phase microextraction fiber coated with poly(methacrylic acid‐ethylene glycol dimethacrylate) and its application for the determination of chlorophenols in water coupled with GC

A solid‐phase microextraction (SPME) fiber coated with poly(methacrylic acid‐ethylene glycol dimethacrylate) coupled to GC with a micro electron‐capture detector was developed for the determination of four chlorphenols in water samples for the first time. A novel and simple method for the preparation of this novel SPME fiber was proposed by copolymerization of methacrylic acid and ethylene glycol dimethacrylate in an appropriate solvent using a glass capillary as a “mold”. The factors affecting the polymerization were optimized in detail. Furthermore, the extraction performance of the poly(methacrylic acid‐ethylene glycol dimethacrylate) fiber was evaluated. Moreover, experimental headspace‐SPME parameters, such as extraction temperature, extraction time, salt concentration, stirring speed, and pH, were optimized by orthogonal array experimental designs. Under the optimized conditions, the target analytes were linear in the range of 0.2–50 ng/mL, and the correlation coefficients were all greater than 0.99. RSD was less than 8.9%, and the detection limits were in the range of 0.1–10 ng/L. Four cholorphenols were detected from tap and lake water samples using the proposed method, with the recoveries of spiked natural water samples were ranged from 91.8 to 110.8, and 90.6 to 111.4% for tap and lake water samples, respectively.     

聚(甲基丙烯酸-乙二醇二甲基丙烯酸酯)搅拌棒吸附萃取与液相色谱-质谱联用检测牛奶中的磺胺类药物

将聚(甲基丙烯酸-乙二醇二甲基丙烯酸酯) (poly(MAA-co-EDMA))聚合物原位聚合于玻璃内插管外表面上,得到一种多孔聚合物涂层;将其作为搅拌棒吸附萃取的萃取介质,考察了其对磺胺类药物的萃取性能;最后将其与高效液相色谱-电喷雾质谱(HPLC-ESI-MS)联用,建立了一种牛奶中4种磺胺类药物的检测方法。在最佳条件下,牛奶中4种磺胺类药物的检出限(S/N=3)和定量限(S/N=10)分别为0.11～0.52 μg/L和0.35～1.72 μg/L。在1～500 μg/L的范围内峰面积与质量浓度具有良好的线性关系,日内、日间测定的相对标准偏差不高于11.3%。结果表明,该方法简便、灵敏度高且成本低,适合于牛奶中磺胺类药物的检测。     

Surface modification of poly(dimethylsiloxane) microfluidic devices and its application in simultaneous analysis of uric acid and ascorbic acid in human urine

A novel and simple method based on layer-by-layer (LBL) technique has been developed for the modification of the channel in PDMS electrophoresis microchip to create a hydrophilic surface with a stable EOF. The functional surface was obtained by sequentially immobilizing chitosan and deoxyribonucleic acid (DNA) onto the microfluidic channel surface using the LBL assembly technique. Compared to the native PDMS microchips, the contact angle of the chitosan-DNA modified PDMS microchips decreased and the EOF increased. Experimental conditions were optimized in detail. The chitosan-DNA modified PDMS microchips exhibited good reproducibility and long-term stability. Separation of uric acid (UA) and ascorbic acid (AA) performed on the modified PDMS microchip generated 43,450 and 46,790 N/m theoretical plates compared with 4048 and 19,847 N/m with the native PDMS microchip. In addition, this method has been successfully applied to real human urine samples, without SPE, with recoveries of 97-105% for UA and AA.     

Construction of a portable sample preparation device with a magnetic poly(methacrylic acid‐co‐ethylene dimethacrylate) monolith as the extraction medium and its application in the enrichment of UV filters in water samples

A portable sample preparation device with a magnetic polymer monolith as the extraction medium was constructed. The monolith was synthesized by polymerizing methacrylic acid and ethylene dimethacrylate around a cylindrical magnet. In this way, the monolith with a magnetic core could be readily attached to the extraction device by magnetism. The constructed device was evaluated for the enrichment of UV filters in water samples, followed by high‐performance liquid chromatographic analysis. The extraction efficiency for the targets was satisfactory with no matrix interference. Good linearities were obtained for the UV filters with the correlation coefficients >0.9986. The limits of detection and quantification for the UV filters were 0.3–0.8 and 1.0–2.4 ng/mL, respectively. The recoveries of the UV filters from the spiked water samples at the concentration of 100 ng/mL were 95.3–101.7%, with relative standard deviations <10%. Accordingly, the proposed portable device was demonstrated to be suitable for on‐site simultaneous sampling, purification, and preconcentration within a single step.     

A poly (4‐vinylpridine‐co‐ethylene glycol dimethacrylate) monolithic concentrator for in‐line concentration‐capillary electrophoresis analysis of phenols in water samples

A poly(4‐vinylpridine‐co‐ethylene glycol dimethacrylate) monolith was synthesized in a capillary and constructed as a concentrator for the in‐line polymeric monolith microextraction coupling with capillary electrophoresis. The integrated system was then used for the simultaneous determination of five trace phenols (2‐nitrophenol, 3‐nitrophenol, 4‐nitrophenol, 2‐chlorophenol, and 2,4‐dichlorophenol) in water samples. The experimental parameters for in‐line solid‐phase extraction, such as composition and volume of the elution plug, pH of sample solution, and the time for sample loading were optimized. The sensitivity for the mixture of phenols (2‐nitrophenol, 3‐nitrophenol, 4‐nitrophenol, 2‐chlorophenol, and 2,4‐dichlorophenol) enhanced to 615–2222 folds at the optimum condition was compared to the sensitivity for a normal hydrodynamic injection in capillary electrophoresis. Linearity ranged from concentration of 10–500 ng mL^?1(R² > 0.999) for all five phenols with the detection limits of 1.3–3.3 ng mL^?1. In tap, snow and Yangtze River water spiked with 20 ng mL^?1 and 200 ng mL^?1, respectively, the recoveries of 84–105% were obtained. It has been demonstrated that this work has great potential for the analysis of phenols in genuine water samples.     

Assembly of poly(dopamine)/poly(acrylamide) mixed coatings by a single‐step surface modification strategy and its application to the separation of proteins using capillary electrophoresis

In this work, a facile approach was developed to modify a fused‐silica capillary inner surface based on poly(dopamine) and poly(acrylamide) mixed coatings for protein separation by capillary electrophoresis. The surface morphology, thickness, and chemical components of poly(dopamine)/poly(acrylamide) mixed coatings on glass slides and silicon wafers were studied by atom force microscopy, ellipsometry, and X‐ray photoelectron spectroscopy, respectively. The hydrophilicity and stability of the mixed coatings on glass slides were investigated by static water contact angle measurements. A comparative study of electroosmotic flow showed that the poly(dopamine)/poly(acrylamide) mixed coatings could provide effective suppression of electroosmotic flow. Meanwhile, the fast and efficient separations of the mixture of four alkaline proteins, the mixture of acidic, basic, and neutral proteins and egg white proteins were obtained by capillary electrophoresis. Furthermore, the consecutive protein separation runs and low RSDs of migration time demonstrated that these poly(dopamine)/poly(acrylamide) mixed coatings were capable of minimizing protein adsorption during the protein separation by using capillary electrophoresis.     

Synthesis of poly(N,N‐dimethylacrylamide)‐block‐poly(ethylene oxide)‐block‐poly(N,N‐dimethylacrylamide) and its application for separation of proteins by capillary zone electrophoresis

A series of well‐defined triblock copolymers, poly(N, N‐dimethylacrylamide)‐block‐poly(ethylene oxide)‐block‐poly(N, N‐dimethylacrylamide) (PDMA‐b‐PEO‐b‐PDMA) synthesized by atom transfer radical polymerization, were used as physical coatings for protein separation. A comparative study of EOF showed that the triblock copolymer presented good capillary coating ability and EOF efficient suppression. The effects of the M_r of PDMA block in PDMA‐b‐PEO‐b‐PDMA triblock copolymer and buffer pH on the separation of basic protein for CE were investigated. Moreover, the influence of the copolymer structure on separation of basic protein was studied by comparing the performance of PDMA‐b‐PEO‐b‐PDMA triblock copolymer with PEO‐b‐PDMA diblock copolymer. Furthermore, the triblock copolymer coating showed higher separation efficiency and better migration time repeatability than fused‐silica capillary when used in protein mixture separation and milk powder samples separation, respectively. The results demonstrated that the triblock copolymer coatings would have a wide application in the field of protein separation.