Determination of tetracyclines in food samples by molecularly imprinted monolithic column coupling with high performance liquid chromatography

A novel solid phase extraction (SPE) method for determination of tetracyclines (TCs) in milk and honey samples by molecularly imprinted monolithic column was developed. Using tetracycline (TC) as the template, methacrylic acid (MAA) as the functional monomer, ethylene glycol dimethacrylate (EGDMA) as the cross-linker, methanol as the solvent, cyclohexanol and dodecanol as the mixed porogenic solvents, a TC imprinted monolithic column was prepared by in situ molecular imprinting technique for the first time, and the optimal synthesis conditions and the selectivity of TC imprinted monolithic column were investigated. The interfering substances in food samples and TCs can be separated successfully on imprinted column. Molecularly imprinted solid phase extraction (MISPE) coupling with C18 column was used to determinate the TCs in milk and honey. The recoveries of this method for six tetracyclines antibiotics such as tetracycline (TC), oxytetracycline (OTC), minocycline (MINO), chlortetracycline (CTC), metacycline (MTC) and doxycycline (DTC) were investigated, and high recoveries of 73.3-90.6% from milk samples and 62.6-82.3% from honey samples were obtained. A method for determination of TCs at low concentration level in milk and honey samples was successfully developed by using the monolithic column as the precolumn for solid phase extraction of six TCs compounds.     

Magnetic solid phase extraction based on phenyl silica adsorbent for the determination of tetracyclines in milk samples by capillary electrophoresis

A magnetic solid phase extraction method coupled to capillary electrophoresis is proposed for the determination of tetracycline, oxytetracycline, chlortetracycline and doxycycline in milk samples. Five different magnetic phenyl silica adsorbents covered with magnetite were synthesized by varying the molar ratio of phenyltrimethylsilane and tetramethylorthosilicate; these adsorbents were evaluated in terms of their pH and degree of hydrophobicity for tetracycline retention. The optimal, selected combination of conditions was a pH of 10.0 and a magnetic sorbent ratio of 4:1; under these conditions, the retention capacity ranged from 99.7% to 101.2% for the four tetracyclines analyzed. The elution conditions and initial sample volume of the proposed extraction method were also optimized, and the best results were obtained with 1×10(-3) M acetic acid in methanol as eluent and a 200 ml of sample volume. Under optimal conditions, average recoveries ranged from 94.2% to 99.8% and the limits of detection ranged from 2 to 9 μg l(-1) for the four tetracyclines. After the proposed method was optimized and validated, 25 milk samples of different brands were analyzed, oxytetracycline residues were detected in five samples, in concentrations ranging from 98 to 213 μg l(-1). Subsequent analysis of positive samples by SPE-CE and magnetic solid phase extraction-HPLC revealed than no significant differences were found from results obtained by the proposed methodology. Thus, the developed magnetic extraction is a robust pre-concentration technique that can be coupled to other analytical methods for the quantitative determination of tetracyclines.     

Application of mercapto‐silica polymerized high internal phase emulsions for the solid‐phase extraction and preconcentration of trace lead(II)

A new class of solid‐phase extraction column prepared with grafted mercapto‐silica polymerized high internal phase emulsion particles was used for the preconcentration of trace lead. First, mercapto‐silica polymerized high internal phase emulsion particles were synthesized by using high internal phase emulsion polymerization and carefully assembled in a polyethylene syringe column. The influences of various parameters including adsorption pH value, adsorption and desorption solvents, flow rate of the adsorption and desorption procedure were optimized, respectively, and the suitable uploading sample volumes, adsorption capacity, and reusability of solid phase extraction column were also investigated. Under the optimum conditions, Pb²⁺ could be preconcentrated quantitatively over a wide pH range (2.0–5.0). In the presence of foreign ions, such as Na⁺, K⁺, Ca²⁺, Zn²⁺, Mg²⁺, Cu²⁺, Fe²⁺, Cd²⁺, Cl^? and NO₃^?, Pb²⁺ could be recovered successfully. The prepared solid‐phase extraction column performed with high stability and desirable durability, which allowed more than 100 replicate extractions without measurable changes of performance. The feasibility of the developed method was further validated by the extraction of Pb²⁺ in rice samples. At three spiked levels of 40.0, 200 and 800 μg/kg, the average recoveries for Pb²⁺ in rice samples ranged from 87.3 to 105.2%.     

Fabrication of boron‐rich multiple monolithic fibers for the solid‐phase microextraction of carbamate pesticide residues in complex samples

To enrich carbamate pesticides from complex matrices, an adsorbent based on poly (vinylboronic anhydride pyridine complex‐co‐ethylenedimethacrylate) monolith was fabricated and utilized as the extraction phase of multiple monolithic fiber solid‐phase microextraction. Due to the abundant boron atoms in the monolith, the B–N coordination interaction between adsorbent and analytes play a key role in the efficient extraction of analytes. Under the optimized conditions, the monolithic fibers were combined with high‐performance liquid chromatography for the quantify trace levels of carbamate pesticides in environmental water and orange juice samples. For water sample, the limit of detection and limit of quantification were in the range of 0.017–0.29 and 0.057–0.96 μg/L, respectively. The related values in orange juice samples were 0.038–0.39 and 0.12–1.36 μg/kg, respectively. Besides, the proposed method also exhibits wide linearity, satisfactory coefficients of determination, and good precision. The introduced approach was successfully applied to determine trace target analytes in real‐life samples. The spiked recoveries with different fortified concentrations were in the range of 80.4–117% for water samples and 83.7–119% for fruit juice samples. The relative standard deviations were below 10%. The results evidence that the suggested method was convenient, reliable, and eco‐friendly for the monitoring of trace levels of carbamate pesticides in complex samples such as waters and juices.     

Facile preparation of a polydopamine‐based monolith for multiple monolithic fiber solid‐phase microextraction of triazine herbicides in environmental water samples

A new multiple monolithic fiber solid‐phase microextraction using a polydopamine‐based monolith as the extraction medium is proposed. The monolith was synthesized by facile in situ copolymerization of N‐methacryldopamine and dual cross‐linkers (divinylbenzene/ethylenedimethacrylate) in the presence of N ,N‐dimethylformamide. The effect of the contents of N‐methacryldopamine and porogen in the polymerization mixture on the extraction performance was investigated thoroughly. A series of characterization studies was performed to validate the structure and properties of the monolith. The prepared multiple monolithic fibers were used for the extraction of triazine herbicides in environmental water samples. After the optimization of the extraction parameters, a convenient, sensitive, cost‐effective, and environmentally friendly method for the determination of trace triazine herbicides in water samples was developed by coupling multiple monolithic fibers solid‐phase microextraction with high‐performance liquid chromatography and diode array detection. The results indicated that the limits of detection and quantification for the target compounds were 0.031–0.14 and 0.10–0.45 μg/L, respectively. Good precision and reproducibility were obtained with the relative standard deviations below 10%. The developed method was applied to the analysis of the triazine herbicides in different water samples (lake, river, and farmland waters). The recoveries of the method were in the range between 79.6 and 117%.     

Boronate affinity monolithic column incorporated with graphene oxide for the in‐tube solid‐phase microextraction of glycoproteins

A poly(vinylphenylboronic acid–ethylene glycol dimethacrylate) monolithic material incorporated with graphene oxide was synthesized inside a poly(ether ether ketone) tube. This tube with boronate affinity monolith was coupled with a high‐performance liquid chromatography system through a six‐port valve to construct an online solid‐phase microextraction with high‐performance liquid chromatography system. The performance of this solid‐phase microextraction with high‐performance liquid chromatography system was demonstrated by standard glycoprotein in aqueous samples, namely, horseradish peroxidase. Some parameters that affect the extraction performance were investigated, including sampling rate, pH of sample solution, and sampling volume. Under the optimized conditions, the developed method showed high extraction efficiency toward horseradish peroxidase. The addition of graphene oxide greatly increased the extraction efficiency of boronate affinity monolith for horseradish peroxidase. The limit of detection of the proposed method was as low as 0.01 μg/mL by using ultraviolet detection. The recognition specificity was also evaluated by analyzing the mixture of bovine serum albumin (nonglycoprotein) and horseradish peroxidase. The results showed that this material could selectively extract horseradish peroxidase from the mixture, indicating its good specificity toward glycoproteins. The proposed method was further applied for analyzing rat plasma samples spiked with horseradish peroxidase. Good recovery and repeatability were obtained.     

Determination of urinary 8‐hydroxy‐2′‐deoxyguanosine by a combination of on‐line molecularly imprinted monolithic solid phase microextraction with high performance liquid chromatography–ultraviolet detection

8‐Hydroxy‐2′‐deoxyguanosine (8‐OHdG) is a sensitive biomarker for DNA oxidative damage. However, its determination in human urine is confounded by trace level and complex matrix. In this study, a new configuration of on‐line solid phase microextraction coupled to high performance liquid chromatography‐ultraviolet detection was established with molecularly imprinted monolithic column as extraction sorbent. The tailor made monolith exhibited high extraction efficiency with the enrichment factor 101.84 for 8‐OHdG owing to its special porous structure and inherent selectivity. Under optimal condition, appreciable sensitivity had been achieved for this incorporation with limit of detection 2.04 nmol/L (S/N = 3) and limit of quantification 7.12 nmol/L (S/N = 10), respectively. Precise determination with wide range linearity (0.007–5.00 μmol/L) afforded a practical alternative in urinary 8‐OHdG analysis and 107 different subjects had been successfully analyzed. This newly developed method embodied useful prospect for the investigation of DNA oxidative damage with less expense, convenient maintenance and ease of operation     

Efficiency of a miniaturized silica monolithic cartridge in reducing matrix ions as demonstrated in the simultaneous extraction of morphine and codeine from urine samples for quantification with liquid chromatography-tandem mass spectrometry (LC-MS/MS)

Presence of matrix ions could negatively affect the sensitivity and selectivity of liquid chromatography‐tandem mass spectrometer (LC‐MS/MS). In this study, the efficiency of a miniaturized silica monolithic cartridge in reducing matrix ions was demonstrated in the simultaneous extraction of morphine and codeine from urine samples for quantification with LC‐MS. The miniaturized silica monolith with hydroxyl groups present on the largely exposed surface area function as a weak cation exchanger for solid phase extraction (SPE). The miniaturized silica cartridge in 1 cm diameter and 0.5 cm length was housed in a 2‐ml syringe fixed over a SPE vacuum manifold for extraction. The cleaning effectiveness of the cartridge was confirmed by osmometer, atomic absorption spectrometer, LC‐MS and GC‐TOFMS. The drugs were efficiently extracted from urine samples with recoveries ranging from 86% to 114%. The extracted analytes, after concentration and reconstitution, were quantified using LC‐MS/MS. The limits of detection for morphine and codeine were 2 ng/ml and 1 ng/mL, respectively. The relative standard deviations of measurements ranged from 3% to 12%. The monolithic sorbent offered good linearity with correlation coefficients > 0.99, over a concentration range of 50–500 ng/ml. The silica monolithic cartridge was found to be more robust than the particle‐based packed sorbent and also the commercial cartridge with regards to its recyclability and repeated usage with minimal loss in efficiency. Our study demonstrated the efficiency of the miniaturized silica monolith for removal of matrix ions and extraction of drugs of abuse in urinary screening. Copyright © 2011 John Wiley & Sons, Ltd.     

Development of multiple monolithic fiber solid‐phase microextraction and liquid chromatography–tandem mass spectrometry method for the sensitive monitoring of aminoglycosides in honey and milk samples

A simple and sensitive method for the simultaneous extraction and determination of six aminoglycosides in honey and milk samples was developed using multiple monolithic fiber solid‐phase microextraction and liquid chromatography with tandem mass spectrometry. The multiple monolithic fibers based on poly(methacrylic acid‐co‐ethylenedimethacrylate) monolith as the extraction medium was used to concentrate target analytes. Because there were abundant carboxyl groups in the monolith, the monolithic fibers could extract aminoglycosides effectively through cation‐exchange and hydrophobic interactions. To obtain optimum extraction performance, several extraction parameters including desorption solvent, adsorption and desorption time, pH value and ionic strength in sample matrix, were investigated in detail. Under the optimized extraction conditions, the limits of detection of the proposed method were 0.10–0.30 and 0.23–0.59 μg/kg for honey and milk samples, respectively. Satisfactory linearity was achieved for analytes with the coefficients of determination above 0.99. At the same time, the developed method showed acceptable method repeatability and reproducibility. Finally, the proposed method was successfully applied to the determination of aminoglycosides in real honey and milk samples. Recoveries obtained for the determination of six target analytes in spiking samples ranged from 67.9 to 110%, and the relative standard deviations were in the range of 1.2–11%.     

Determination of trace hydroxyl polycyclic aromatic hydrocarbons in urine using graphene oxide incorporated monolith solid‐phase extraction coupled with LC‐MS/MS

The biomonitoring of hydroxy polycyclic aromatic hydrocarbons in urine, as a direct way to access multiple exposures to polycyclic aromatic hydrocarbons, has raised great concerns due to their increasing hazardous health effects on humans. Solid‐phase extraction is an effective and useful technique to preconcentrate trace analytes from biological samples. Here, we report a novel solid‐phase extraction method using a graphene oxide incorporated monolithic syringe for the determination of six hydroxy polycyclic aromatic hydrocarbons in urine coupled with liquid chromatography‐tandem mass spectrometry. The effect of graphene oxide amount, washing solvent, eluting solvent, and its volume on the extraction performance were investigated. The fabricated monoliths gave higher adsorption efficiency and capacity than the neat polymer monolith and commercial C₁₈ sorbent. Under the optimum conditions, the developed method provided the detection limits (S/N = 3) of 0.02–0.1 ng/mL and the linear ranges of 0.1–1500 ng/mL for six analytes in urine sample. The recoveries at three spiked levels ranged from 77.5 to 97.1%. Besides, the intra column‐to‐column (n = 3) and inter batch‐to‐batch (n = 3) precisions were ≤ 9.8%. The developed method was successfully applied for the determination of hydroxy polycyclic aromatic hydrocarbons in urine samples of coke oven workers.     

Efficient sample preparation method based on solvent‐assisted dispersive solid‐phase extraction for the trace detection of butachlor in urine and waste water samples

In this work, an efficient sample preparation method termed solvent‐assisted dispersive solid‐phase extraction was applied. The used sample preparation method was based on the dispersion of the sorbent (benzophenone) into the aqueous sample to maximize the interaction surface. In this approach, the dispersion of the sorbent at a very low milligram level was achieved by inserting a solution of the sorbent and disperser solvent into the aqueous sample. The cloudy solution created from the dispersion of the sorbent in the bulk aqueous sample. After pre‐concentration of the butachlor, the cloudy solution was centrifuged and butachlor in the sediment phase dissolved in ethanol and determined by gas chromatography with flame ionization detection. Under the optimized conditions (solution pH = 7.0, sorbent: benzophenone, 2%, disperser solvent: ethanol, 500 μL, centrifuged at 4000 rpm for 3 min), the method detection limit for butachlor was 2, 3 and 3 μg/L for distilled water, waste water, and urine sample, respectively. Furthermore, the preconcentration factor was 198.8, 175.0, and 174.2 in distilled water, waste water, and urine sample, respectively. Solvent‐assisted dispersive solid‐phase extraction was successfully used for the trace monitoring of butachlor in urine and waste water samples.     

Preparation of l‐phenylalanine‐imprinted solid‐phase extraction sorbent by Pickering emulsion polymerization and the selective enrichment of l‐phenylalanine from human urine

A novel l‐ phenylalanine molecularly imprinted solid‐phase extraction sorbent was synthesized by the combination of Pickering emulsion polymerization and ion‐pair dummy template imprinting. Compared to other polymerization methods, the molecularly imprinted polymers thus prepared exhibit a high specific surface, large pore diameter, and appropriate particle size. The key parameters for solid‐phase extraction were optimized, and the result indicated that the molecularly imprinted polymer thus prepared exhibits a good recovery of 98.9% for l‐ phenylalanine. Under the optimized conditions of the procedure, an analytical method for l‐ phenylalanine was well established. By comparing the performance of the molecularly imprinted polymer and a commercial reverse‐phase silica gel, the obtained molecularly imprinted polymer as an solid‐phase extraction sorbent is more suitable, exhibiting high precision (relative standard deviation 3.2%, n = 4) and a low limit of detection (60.0 ± 1.9 nmol·L^?1) for the isolation of l‐ phenylalanine. Based on these results, the combination of the Pickering emulsion polymerization and ion‐pair dummy template imprinting is effective for preparing selective solid‐phase extraction sorbents for the separation of amino acids and organic acids from complex biological samples.     

Preparation of restricted‐access material precolumns by grafting δ‐gluconolactone onto a hybrid silica monolithic column for on‐line solid‐phase extraction of tetracycline residues from milk

A restricted‐access material–hybrid monolithic column was prepared based on single‐component organosiloxane and dynamic grafting of δ‐gluconolactone for on‐line solid phase extraction of tetracycline antibiotic residues from milk. The hybrid monolithic column was prepared in a stainless‐steel chromatographic column using methyltrimethoxysilane as the single precursor. δ‐Gluconolactone was covalently coupled to aminopropyl derivatized hybrid monolithic column, which formed hydrophilic structures on the surface of the pore of the restricted‐access material–hybrid monolithic column. The columns were characterized by scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, nitrogen adsorption, contact angle analysis, dynamic adsorption, and chromatographic performance evaluation. The restricted‐access material–hybrid monolithic column was applied to the on‐line extraction of tetracycline residues from milk. An enrichment factor of 15.8 and a good sample clean‐up effect were obtained under the optimized conditions. The recoveries of the three spiked milk samples were between 81.7 and 102.5% with relative standard deviations (n = 3) in the range of 2–5%. The limits of detection (S/N = 3) for target compounds were in the range of 3.80–9.03 μg/kg. The results show that the on‐line extraction using the restricted‐access material–hybrid monolithic column was powerful for food sample pretreatment with high selectivity and good clean‐up effect.     

Determination of tetracycline antibiotics in fatty food samples by selective pressurized liquid extraction coupled with high‐performance liquid chromatography and tandem mass spectrometry

For the determination of trace residues of tetracycline antibiotics in fatty food samples, selective pressurized liquid extraction coupled with high‐performance liquid chromatography and tandem mass spectrometry was applied in this study. Copper(II) isonicotinate was first used as online cleanup adsorbent in the selective pressurized liquid extraction process. The adsorbent to sample ratio, extraction temperature, extraction time, and recycle times, etc. were optimized. The tetracyclines in food samples of pork, chicken meat, and clam meat were detected by liquid chromatography with tandem mass spectrometry. Tetracycline was found at levels of 0.32 and 0.53 μg/g and oxytetracycline was found at 0.14 and 0.21 μg/g in chicken meat and clam meat, respectively, while chlorotetracycline and deoxytetracycline were below the detection limit. The detection limit (S/N = 3) for these four tetracyclines were from 0.2 to 3.3 ng/g, the recoveries were from 75.8 to 110.5%, and relative standard deviations were from 5.5 to 13.6%. Copper(II) isonicotinate showed a higher purification capacity than other cleanup adsorbents for extraction of antibiotics in fatty food and the recovery showed predominance compared with a pressurized liquid extraction method without adsorbent. The study demonstrated that copper(II) isonicotinate would be a promising cleanup adsorbent in pressurized liquid extraction for the analysis of trace organic pollutants in complicated samples.     

Determination of Tetracyclines in Honey Using Liquid Chromatography with Ultraviolet Absorbance Detection and Residue Confirmation by Mass Spectrometry

A determination method has been optimized and validated for the simultaneous analysis of tetracycline （TC）, oxytetracycline （OTC）, chlortetracycline （CTC） and doxycycline （DC） in honey. Tetracyclines （TCs） were removed from honey samples by chelation with metal ions bound to small Chelating Sepharose Fast Flow columns and eluted with Na2EDTA-Mcllvaine pH 4.0 buffers. Extracts were further cleaned up by Oasis HLB solid-phase extraction （SPE）, while other solid-phase extraction cartridges were compared. Chromatographic separation was achieved using a polar end-capped C 18 column with an isocratic mobile phase consisting of oxalic acid, acetonitrile and methanol. LC with ultraviolet absorbance at 355 nm resulted in the quantitation of all four tetracycline residues from honey samples fortified at 15, 50, and 100 ng/g, with liner ranges for tetracyclines of 0.05 to 2 μg/mL. Mean recoveries for tetracyclines were greater than 50% with R.S.D. values less than 10% （n= 18）. Detection limits of 5, 5, 10, 10 ng/g for oxytetracycline, tetracycline, chlortetracycline and doxycycline, respectively and quantitation limits of 15 ng/g for all the four tetracyclines were determined. Direct confirmation of the four residues in honey （2-50 ng/g） was realized by liquid chromatography-tandem mass spectrometry （LC/MS/MS）. The linear ranges of tetracyclines determined by LC/MS/MS were between 5 to 300 ng/mL, with the linear correlation coefficient r〉 0.995. The limits of detection of 1 to 2 ng/g were obtained for the analysis of the TCs in honey.     

Microwave‐assisted extraction and high‐throughput monolithic‐polymer‐based micro‐solid‐phase extraction of organophosphorus,triazole, and organochlorine residues in apple

A high‐throughput micro‐solid‐phase extraction device based on a 96‐well plate was constructed and applied to the determination of pesticide residues in various apple samples. Butyl methacrylate and ethylene glycol dimethacrylate were copolymerized as a monolithic polymer and placed in the cylindrically shaped stainless‐steel meshes of 96‐micro‐solid‐phase extraction device and used as an extracting unit. Before the micro‐solid‐phase extraction, microwave‐assisted extraction was employed to facilitate the transfer of the pesticide residues from the apple matrix to liquid media. Then, 1 mL of the aquatic samples was transferred into the 96‐well plate and the 96‐micro‐solid‐phase extraction device was applied for the extraction of the selected pesticides. Influential parameters, such as sorbent‐to‐sorbent reproducibility, microwave‐assisted extraction time, ionic strength and micro‐solid‐phase extraction time, were optimized. The limits of quantitation were below 120 μg/kg, which are lower than the maximum residue limits. The developed method was successfully implemented for the extraction and determination of the selected pesticides from 20 different apple samples gathered from local markets. Phosalone was identified and quantified at the concentration level of 147 (±16.4) μg/kg in one of the samples.     

Selective and sensitive determination of protoberberines by capillary electrophoresis coupled with molecularly imprinted microextraction

In this work, we developed a novel molecularly imprinted solid‐phase microextraction with capillary electrophoresis method for the selective extraction and determination of protoberberines in complicated samples. The imprinted monolith was prepared in a micropipette tip‐based device by using acrylamide as the functional monomer, ethyleneglyoldimethacrylate as the cross‐linker and dimethylsulfoxide as the porogen, and exhibited an imprinting factor of 2.41 to berberine, 2.36 to palmatine and 2.38 to jatrorrhizine. Good capillary electrophoresis separation was achieved by using 20 mM phosphate buffer at pH 7 as running buffer with the addition of organic modifier of 10% methanol. Parameters such as sample pH value, sample flow rate and sample volume were investigated for imprinted monolith‐based solid‐phase microextraction. An imprinted solid‐phase microextraction with capillary electrophoresis method was developed, the method showed a wide linear range (0.3–50 μg/mL), good linearity (R² ≥ 0.9947) and good reproducibility (relative standard deviations ≤ 0.73%), the limit of detection was as low as 0.1 μg/mL, which was lower than some reported methods based on capillary electrophoresis for protoberberines. The method has been applied for determination of three common protoberberines in Cortex Phellodendri Chinensis, by using a molecularly imprinted monolith as the selective sorbent, most of the matrices in the Cortex Phellodendri Chinensis sample were removed and three protoberberines were selectively enriched and well determined.     

Direct preparation of a graphene oxide modified monolith in a glass syringe as a solid‐phase extraction cartridge for the extraction of quaternary ammonium alkaloids from Chinese patent medicine

Packed cartridges have been widely used in solid‐phase extraction. However, there are still some drawbacks, such as they are blocked easily and the method is time‐consuming. In view of the advantages of monoliths, a monolithic extraction material has been directly synthesized in a glass syringe without any gap between the monolith and syringe inner wall. The monolithic syringe was modified with graphene oxide by loading graphene oxide dispersion onto it. The content of graphene oxide and the surface topography of the monolith have been evaluated by elemental analysis and scanning electron microscopy, respectively, which confirmed the successful modification. This prepared graphene oxide‐modified monolithic syringe was directly used as a traditional solid‐phase extraction cartridge. As expected, it shows good permeability and excellent capability for the extraction of quaternary ammonium alkaloids. The sample loading velocity (1–6 mL/min) does not affect the recovery. Under the optimal conditions, good linearities (R  = 0.9992–0.9998) were obtained for five quaternary ammonium alkaloids, and the limits of detection and quantification were 0.5‐1 and 1–2 μg/L, respectively. The proposed method was successfully applied for the analysis of quaternary ammonium alkaloids in Chinese patent medicine.     

Extraction and preconcentration of formaldehyde in water by polypyrrole‐coated magnetic nanoparticles and determination by high‐performance liquid chromatography

In this study, a simple and rapid extraction method based on the application of polypyrrole‐coated Fe₃O₄ nanoparticles as a magnetic solid‐phase extraction sorbent was successfully developed for the extraction and preconcentration of trace amounts of formaldehyde after derivatization with 2,4‐dinitrophenylhydrazine. The analyses were performed by high‐performance liquid chromatography followed by UV detection. Several variables affecting the extraction efficiency of the formaldehyde, i.e., sample pH, amount of sorbent, salt concentration, extraction time and desorption conditions were investigated and optimized. The best working conditions were as follows: sample pH, 5; amount of sorbent, 40 mg; NaCl concentration, 20% w/v; sample volume, 20 mL; extraction time, 12 min; and 100 μL of methanol for desorption of the formaldehyde within 3 min. Under the optimal conditions, the performance of the proposed method was studied in terms of linear dynamic range (10–500 μg/L), correlation coefficient (R² ≥ 0.998), precision (RSD% ≤ 5.5) and limit of detection (4 μg/L). Finally, the developed method was successfully applied for extraction and determination of formaldehyde in tap, rain and tomato water samples, and satisfactory results were obtained.     

On-chip solid phase extraction and enzyme digestion using cationic PolyE-323 coatings and porous polymer monoliths coupled to electrospray mass spectrometry

We evaluate the compatibility and performance of polymer monolith solid phase extraction beds that incorporate cationic charge, with a polycationic surface coating, PolyE-323, fabricated within microfluidic glass chips. The PolyE-323 is used to reduce protein and peptide adsorption on capillary walls during electrophoresis, and to create anodal flow for electrokinetically driven nano-electrospray ionization mass spectrometry. A hydrophobic butyl methacrylate-based monolithic porous polymer was copolymerized with an ionizable monomer, [2-(methacryloyloxy)ethyl] trimethylammonium chloride to form a polymer monolith for solid phase extraction that also sustains anodal electroosmotic flow. Exposure of the PolyE-323 coating to the monolith forming mixture affected the performance of the chip by a minor amount; electrokinetic migration times increased by ～5%, and plate numbers were reduced by an average of 5% for proteins and peptides. 1-mm long on-chip monolithic solid phase extraction columns showed reproducible, linear calibration curves (R(2)=0.9978) between 0.1 and 5 nM BODIPY at fixed preconcentration times, with a capacity of 2.4 pmol or 0.92 mmol/L of monolithic column for cytochrome c. Solution phase on-bed trypsin digestion was conducted by capturing model protein samples onto the monolithic polymer bed. Complete digestion of the proteins was recorded for a 30 min stop flow digestion, with high sequence coverage (88% for cytochrome c and 56% for BSA) and minimal trypsin autodigestion product. The polycationic coating and the polymer monolith materials proved to be compatible with each other, providing a high quality solid phase extraction bed and a robust coating to reduce protein adsorption and generate anodal flow, which is advantageous for electrospray.