Sensitive amperometric detection for capillary electrophoresis of phenol carbamates with in-line thermal hydrolysis strategy.

A strategy on amperometric detection for CZE of phenol carbamates as model analytes with a facile in-line thermal hydrolysis was presented, in which a thermal hydrolysis, subsequent CZE separation and final column-end amperometric detection were accomplished in an intact capillary. Key parameters of hydrolysis dynamics of carbamates and electrochemical detection of the hydrolysates were studied, as well as electrophoretic conditions. Under the optimal conditions, the capillary was utilized as chambers for in situ hydrolysis, CZE separation, and electrochemical detection. The successive separation of hydrolysates of five carbamates (propoxur, carbofuran, 3-OH-carbofuran, carbaryl and bendiocarb) were achieved within 17 min. Applied to vegetable samples, the recoveries of carbamates fortified at 0.02 and 0.05 mg/kg were ranging in 88-107.2 and 86.3-107.3%, respectively. The success in the implementation of such a scheme resulted in a simple instrument as compared with those current analytical methods with post-column derivization or pre-column hydrolysis, or online enrichment in chip, respectively. This protocol might possess a potential utility for the sensitive amperometric detection of phenol carbamates.

Ultrasound-assisted dispersive liquid-liquid microextraction followed by ion mobility spectrometry for the simultaneous determination of bendiocarb and azinphos-ethyl in water, soil, food and beverage samples.

A sensitive and fast ultrasound-assisted dispersive liquid-liquid microextraction procedure combined with ion mobility spectrometry has been developed for the simultaneous extraction and determination of bendiocarb and azinphos-ethyl. Experimental parameters affecting the analytical performance of the method were optimized: type and volume of extraction solvent (chloroform, 150 µL), pH (9.0), type and volume of buffer (ammonium buffer pH = 9.0, 4.5 mL) and extraction time (3.0 min). Under optimum conditions, the linearity was found to be in the range of 2-40 and 6-100 ng/mL and the limits of detection (LOD) were 1.04 and 1.31 ng/mL for bendiocarb and azinphos-ethyl, respectively. The method was successfully validated for the analysis of bendiocarb and azinphos-ethyl in different samples such as waters, soil, food and beverage samples.

Determination of Meserine, a new candidate for Alzheimer's disease in mice brain by liquid chromatography-tandem mass spectrometry and its application to a pharmacokinetic and tissue distribution study.

A rapid and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for determination of Meserine ((-)-meptazinol phenylcarbamate), a novel potent inhibitor of acetylcholinesterase (AChE), was developed, validated, and applied to a pharmacokinetic study in mice brain. The lower limit of quantification (LLOQ) was 1 ng mL(-1) and the linear range was 1-1,000 ng mL(-1). The analyte was eluted on a Zorbax SB-Aq column (2.1 × 100 mm, 3.5 µm) with the mobile phase composed of methanol and water (70:30, v/v, aqueous phase contained 10 mM ammonium formate and 0.3% formic acid) using isocratic elution, and monitored by positive electrospray ionization in multiple reaction monitoring (MRM) mode. The flow rate was 0.25 mL min(-1). The injection volume was 5 µL and total run time was 4 min. The relative standard deviation (RSD) of intraday and interday variation was 2.49-7.81 and 3.01-7.67%, respectively. All analytes were stable after 4 h at room temperature and 6 h in autosampler. The extraction recoveries of Meserine in brain homogenate were over 90%. The main brain pharmacokinetic parameters obtained after intranasal administration were T max = 0.05 h, C max = 462.0 ± 39.7 ng g(-1), T 1/2 = 0.4 h, and AUC(0-∞) = 283.1 ± 9.1 ng h g(-1). Moreover, Meserine was distributed rapidly and widely into brain, heart, liver, spleen, lung, and kidney tissue. The method is validated and could be applied to the pharmacokinetic and tissue distribution study of Meserine in mice.

Review of the validated HPLC and LC-MS/MS methods for determination of drugs used in clinical practice for Alzheimer's disease.

Alzheimer's disease (AD) is a neurological disorder and is the most frequent type of dementia among elderly people. Donepezil, rivastigmine, galantamine, tacrine and memantine are the US Food and Drug Administration approved oral drugs used in the treatment of AD. Quantitation of these drugs in various biological matrices and monitoring them in long-term treatment is essential to titer the dose of these drugs and ensure patient compliance. This review provides a comprehensive account of various HPLC and LC-MS/MS assays, which have been successfully employed to measure the drug levels in various biological matrices arising from preclinical and clinical studies. In addition, this review collates various considerations such as internal standard selection, extraction schemes, matrix effect, selectivity evaluation and optimization of mass spectrometric conditions to enable the development of sound bioanalytical methods for quantitation of Alzheimer's drugs. Overall LC-MS/MS methods have proven to be the choice of bioanalytical method for the quantification of Alzheimer's drugs in both preclinical and clinical studies. In conclusion, important features of LC-MS/MS methodology for Alzheimer's drugs include shortened analysis time, increased throughput, selectivity and lower cost of analysis.

Determination of metolcarb in food by capillary electrophoresis immunoassay with a laser-induced fluorescence detector.

A capillary electrophoresis immunoassay (CEIA) was developed for the determination of trace metolcarb (MTMC) in food. The method was based on the competitive reactions between fluorescently labeled MTMC tracer and free MTMC with a limited amount of anti-MTMC antibody and the separation and determination by CE with LIF detector. A fluorescent reagent, FITC was labeled on MTMC to construct an immunofluorescent probe. CEIA experimental parameters such as the pH value and concentration of the running buffer and separation voltage as well as incubation time were systematically investigated. Under the optimized conditions, fluorescently labeled antigen and antibody bound could be well separated within 3 min using Na2B4O7/NaH2PO4 buffer (20:10 mmol/L, pH 9.0) for background electrolyte, 20 kV for the separation voltage, and 20°C for the column temperature. The linear range of the method was 0.25-50.0 µg/L with LOD 0.07 µg/L. The RSD for relative migration time and relative fluorescence intensity ratio were 2.90% (intraday) and 4.73% (intraday), respectively. The proposed method has been applied to determine the residue of MTMC in food samples with the satisfactory recovery.

Dispersive liquid-liquid microextraction based on the solidification of a floating organic droplet for simultaneous analysis of diethofencarb and pyrimethanil in apple pulp and peel.

A method for analysis of diethofencarb and pyrimethanil in apple pulp and peel was developed by using dispersive liquid-liquid microextraction based on solidification of a floating organic droplet (DLLME-SFO) and high-performance liquid chromatography with diode-array detection (HPLC-DAD). Acetonitrile was used as the solvent to extract the two fungicides from apple pulp and peel, assisted by microwave irradiation. When the extraction process was finished, the target analytes in the extraction solvent were rapidly transferred from the acetonitrile extract to another extraction solvent (1-undecanol) by using DLLME-SFO. Because of the lower density of 1-undecanol than that of water, the finely dispersed droplets of 1-undecanol collected on the top of aqueous sample and solidified at low temperature. Meanwhile, the tiny particles of apple cooled and precipitated. Recovery was tested for a concentration of 8 µg kg⁻¹. Recovery of diethofencarb and pyrimethanil from apple pulp and peel was in the range 83.5-101.3%. The repeatability of the method, expressed as relative standard deviation, varied between 4.8 and 8.3% (n = 6). Detection limits of the method for apple pulp and peel varied from 1.2-1.6 µg kg⁻¹ for the two fungicides. Compared with conventional sample preparation, the method has the advantage of rapid speed and simple operation, and has high enrichment factors and low consumption of organic solvent.

Chiral separation of neonicotinoid insecticides by polysaccharide-type stationary phases using high-performance liquid chromatography and supercritical fluid chromatography.

The enantiomeric separations of three neonicotinoid insecticides (identified as compounds 1, 2, and 3) were performed on three polysaccharide-type chiral columns, that is, Chiralcel OD-H, Chiralpak AD-H, and Chiralpak IB, by high-performance liquid chromatography (HPLC) and supercritical fluid chromatography (SFC). Effects of the modifier percentage and column temperature on chiral recognitions of chiral stationary phases were also studied. Both 1 and 2 could be resolved on all three columns selected, with the highest R(s) values obtained on Chiralpak AD-H and Chiralcel OD-H, respectively. However, satisfactory separation of the four stereoisomers of 3 was only achieved on Chiralcel OD-H. Considering the effects of ethanol on the values of k, α, and R(s), we concluded that hydrogen bonding, π-π, and/or dipole-dipole interactions might be all responsible for the chiral separation. In comparison to HPLC, a shorter run time was achieved for 1 and 2 by SFC. However, 3 could not be stereoselectively resolved using SFC. On the basis of the calculated thermodynamic parameters, we found that the separation processes of enantiomers of 1 and 2 were entropy controlled and enthalpy controlled, respectively.

Analysis of positional isomers of 2-3-4-alkoxyphenylcarbamic acid derivatives by a combination of TLC and IMS.

In this study, we have demonstrated a separation of positional isomers of some derivatives of alkoxyphenylcarbamic acid. These compounds belong to drugs with local anesthetics activity. The low volatility compounds were analysed by a Thin Layer Chromatography (TLC) and Ion Mobility Spectrometry (IMS) using diode laser desorption for sample introduction to IMS. This combined approach allowed the identification of compounds. Also, we have carried out IMS studies of all compounds and determined their ion mobilities The ion mobilities were increasing with the geometry change from position ortho to para of alkoxy chain, which is in agreement with their different collision cross section (CCS).

Exposure to pesticides in utero impacts the fetal immune system and response to vaccination in infancy.

The use of pesticides to reduce mosquito vector populations is a cornerstone of global malaria control efforts, but the biological impact of most pesticides on human populations, including pregnant women and infants, is not known. Some pesticides, including carbamates, have been shown to perturb the human immune system. We measure the systemic absorption and immunologic effects of bendiocarb, a commonly used carbamate pesticide, following household spraying in a cohort of pregnant Ugandan women and their infants. We find that bendiocarb is present at high levels in maternal, umbilical cord, and infant plasma of individuals exposed during pregnancy, indicating that it is systemically absorbed and trans-placentally transferred to the fetus. Moreover, bendiocarb exposure is associated with numerous changes in fetal immune cell homeostasis and function, including a dose-dependent decrease in regulatory CD4 T cells, increased cytokine production, and inhibition of antigen-driven proliferation. Additionally, prenatal bendiocarb exposure is associated with higher post-vaccination measles titers at one year of age, suggesting that its impact on functional immunity may persist for many months after birth. These data indicate that in utero bendiocarb exposure has multiple previously unrecognized biological effects on the fetal immune system.

Preparation and application of a molecularly imprinted polymer for the determination of trace metolcarb in food matrices by high performance liquid chromatography.

In this article, for the first time, a molecularly imprinted polymer (MIP) for the metolcarb was prepared by bulk polymerization using metolcarb as the template, methacrylic acid as the functional monomer and ethylene glycol dimethacrylate as the cross-linker. The prepared polymer was characterized by FT-IR, static and kinetic adsorption experiments, and the results showed that it has been successfully synthesized and had good selective ability for metolcarb. The MIP was applied as a sorbent in molecularly imprinted SPE coupled with HPLC-UV for separation and determination of trace metolcarb in three kinds of food matrices at three concentration levels. Under the optimal conditions, the LODs (S/N=3) of cabbage, cucumber and pear were 7.622, 6.455 and 13.52 microg/kg, respectively, and recoveries were in the range of 68.80-101.31% with RSD (n=3) below 3.78% in all cases. To demonstrate further the selectivity of the MIP obtained, a comparison with commercially available C(18) SPE was performed. The results indicated that molecularly imprinted SPE showed better chromatography, better selectivity and higher recoveries for metolcarb than commercially available C(18) SPE.

Identification and characterization of new impurities in rivastigmine.

Rivastigmine is a drug against Alzheimer's disease, and is a non-pharmacopoeial compound. During the preparation of rivastigmine in our laboratory, two impurities were detected and identified with a simple and sensitive reversed-phase liquid chromatography coupled with electrospray-mass spectrometry. The same impurities were also observed in commercial batches. These impurities were isolated by preparative HPLC and co-injected with rivastigmine sample to confirm the retention times in HPLC. These impurities were characterized as N,N-dimethyl-3-[1-dimethylaminoethyl]phenylcarboxylate (dimethyl-rivastigmine) and N,N-diethyl-3-[1-dimethylaminoethyl]phenylcarboxamide (diethyl-rivastigmine). Structural elucidation of these impurities by spectral data (1H NMR, 13C NMR and MS) is discussed.

[Therapeutic drug monitoring of felbamate]. / Suivi thérapeutique pharmacologique du felbamate.

Felbamate is a derivative of meprobamate used in second-line partial epilepsy and in the Lennox-Gastaut syndrome. Felbamate is well absorbed and has linear kinetics: C(max) and AUC increasing linearly with dose. The metabolism takes place in the liver. Metabolites represent 40 to 60% of excretion and are eliminated via the urine. The half-life is between 15 and 23 hours. Clearance is dependent on renal function. There is a concentration - efficacy and concentration - toxicity relationship. These arguments are in favour of a TDM but the therapeutic range is not clearly established. Potentially fatal side effects can be caused by felbamate (aplastic anemia, acute liver failure), which limits its use because they are dose-independant.

Graphitic carbon nitride/graphene oxide(g-C3N4/GO) nanocomposites covalently linked with ferrocene containing dendrimer for ultrasensitive detection of pesticide.

We report herein the design of a novel electrochemical sensing strategy for sensitive detection of pesticide based on graphitic carbon nitride (g-C3N4)/graphene oxide(GO) nanocomposite covalently bound to a ferrocene containing dendrimer(Fc-TED). The g-C3N4 with sufficient N atoms for providing lone pairs of electrons to an electron acceptor so as to enhance the adsorption towards organic molecules. The Fc-TED dendrimers with the native redox signaling center (Fe3+/Fe2+) can increase the electron transition of g-C3N4 from valence to conduction band. While GO can accelerate the electron transfer from g-C3N4 surface and Fc-TED to glassy carbon electrode(GCE), which would amplify the electrochemical signal of g-C3N4/GO/Fc-TED/GCE sensor and then improve the sensing performance. It is found that the fabricated electrode demonstrated an admirable electrochemical sensing performance towards metolcarb in terms of low detection limit (8.3 nM), wide concentration range (0.045-213 µM) and rapid response time (2s). The proposed sensor can selectively detect the metolcarb and easily discriminated metolcarb from the possible interfering species. The practical applicability of the sensor was successfully evaluated in real vegetable sample and achieved satisfactory recoveries with good precision and accuracy.

Characterization of chemical profiles of pH-sensitive cleavable D-gluconhydroximo-1, 5-lactam hydrolysates by LC-MS: A potential agent for promoting tumor-targeted drug delivery.

Currently, controllable linker cleavage at the target site will facilitate the clinical treatment of cancer. Dual-functional prodrugs in combination of carbohydrate as targeting group and pH-sensitive cleavable linker are desired in clinical development. Here, a qualified structure of N-phenylcarbamate-d-gluconhydroximo-1,5-lactam was employed and proved to be a potential candidate prodrug in the drug design. To proof this concept, the possible mechanism of Beckmann rearrangement and the degraded products were confirmed by HPLC and LC-MS under the acid condition mimic lysosome. Hence, the strategy of d-gluconhydroximo-1,5-lactam as a prodrug carrier fabricated with interested drugs will provide a great potential approach for chemotherapy.

Development of an enzyme-linked immunosorbent assay for metolcarb residue analysis and investigation of matrix effects from different agricultural products.

The development of a direct competitive enzyme-linked immunosorbent assay based on polyclonal antibodies for N-methylcarbamate insecticide metolcarb is described. Two new haptens for the metolcarb were designed and synthesized. Both haptens were conjugated with keyhole limpet hemocyanin to form the immunogens. Four rabbits were immunized with the immunogens for production of polyclonal antibodies against metolcarb. Antisera titers were tested on the homologous coating antigens using a noncompetitive indirect enzyme-linked immunosorbent assay. The high titer antisera were used to develop the direct competitive enzyme-linked immunosorbent assay for the detection of metolcarb. The antibody-antigen combination with the highest selectivity for metolcarb was further optimized and its tolerance to changes in chemical conditions (ionic strength, pH value, and organic solvent) was studied. Under optimum conditions, the sensitivity and the limit of detection were determined to be 22 microg L(-1) and 1.2 microg L(-1) respectively. Determination of metolcarb in fruit juices and vegetables was accomplished by simple, rapid, and efficient extraction methods. Recoveries of metolcarb from spiked samples ranged from 80.5% to 109.5%. Validation of the developed immunosorbent assay was conducted by comparison of results from high-performance liquid chromatography. The correlation between the data obtained using developed immunosorbent assay and high-performance liquid chromatography was high (R2 = 0.9884). Therefore, the developed immunosorbent assay in this study was suitable for the rapid quantitative determination of metolcarb in agricultural products.

Temperature-controlled ionic liquid-dispersive liquid-phase microextraction for preconcentration of chlorotoluron, diethofencarb and chlorbenzuron in water samples.

This article describes a new, rapid and sensitive method for the determination of chlorotoluron, diethofencarb and chlorbenzuron from water samples with temperature-controlled ionic liquid-dispersive liquid-phase microextraction. In the preconcentration procedure, ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate [C(6)MIM] [PF(6)] was employed as the extraction solvent. The parameters, such as volume of [C(6)MIM] [PF(6)], sample pH, extraction time, centrifuging time, temperature and salting-out effect, were investigated in detail. Under the optimal extraction conditions, it has been found that three analytes had excellent LODs (S/N=3) in the range of 0.04-0.43 microg/L. The RSDs (n=6) were in the range of 1.3-4.7%. The proposed method was evaluated with lake water, tap water and melted snow water samples. The experimental results indicated that the proposed method had excellent prospect and would be widely used in the future.

Analysis of phenoxyl-type N-methylcarbamate pesticide residues in vegetables by capillary zone electrophoresis with pre-column hydrolysis and amperometric detection.

With systematic studies of pre-column thermalhydrolysis, a method is described for the determination of fivephenoxyl-type N-methylcarbamates (NMCs) (viz., propoxur, carbofuran, 3-hydroxy-carbofuran, carbaryl, and bendiocarb) in vegetables by capillary zone electrophoresis with amperometric detection. Effects of hydrolysis parameters such as alkali medium, temperature, and hydrolysis time, as well as separation conditions, are investigated. Under the optimum conditions, baseline separation of five hydrolysates is achieved within 16 min. Good calibration curves of propoxur, carbofuran, 3-hydroxy-carbofuran, carbaryl, and bendiocarb are obtained from 1.20x10(-7) to 5.00x10(-5) mol/L, and their detection limits (S/N=3) are 1.80x10(-8), 1.50x10(-8), 1.80x10(-8), 2.50x10(-8), and 1.80x10(-8) mol/L, respectively, which is approximately 20 approximately 50-fold more sensitive than those previously reported with a UV method. In the application of vegetable samples, the five NMCs are well determined. Average recoveries of 75 approximately 89% and 86 approximately 100% at fortified levels of 0.05 and 0.80 mg/kg are achieved with relative standard deviations of 2 approximately 6%, respectively. The method is sensitive, reproducible, and provides an alternative means for the analysis of phenoxyl-type NMC pesticide residues.

Determination of metolcarb and diethofencarb in apples and apple juice by solid-phase microextraction-high performance liquid chromatography.

A method for the determination of metolcarb and diethofencarb in apples and apple juice is developed using solid-phase microextraction (SPME) coupled with high-performance liquid chromatography (HPLC). The experimental conditions of SPME, such as the kind of extraction fiber, extraction time, stirring rate, pH of the extracting solution, and desorption conditions are optimized. The SPME is performed on a 60 microm polydimethylsiloxane/divinylbenzene fiber for 40 min at room temperature with the solution being stirred at 1100 rpm. The extracted pesticides on the SPME fiber are desorbed in the mobile phase into SPME-HPLC interface for HPLC analysis. Separations are carried out on a Baseline C18 column (4.6 i.d. x 250 mm, 5.0 microm) with acetonitrile-water (55/45, v/v) as the mobile phase at a flow rate of 1.0 mL/min, and photodiode-array detection at 210 nm. For apple samples, the method is linear for both metolcarb and diethofencarb in the range of 0.05-1.0 mg/kg (r > 0.99), with a detection limit (S/N = 3 ) of 15 and 5 microg/kg, respectively. For apple juice, the method is linear for both metholcarb and diethofencarb over the range of 0.05-1.0 mg/L (r > 0.99) with the detection limit (S/N = 3 ) of 15 and 3 microg/L, respectively. Excellent recovery and reproducibility values are achieved. The proposed method is shown to be simple, sensitive, and organic solvent-free, and is suitable for the determination of the two pesticides in apples and apple juice.

Dissipation of insect growth regulators in fresh orange and orange juice.

It was studied the dissipation rates of fenoxycarb, Lufenuron, flufenoxuron and pyriproxyfen from their application on navelina orange crops to the production of orange juice. Supervised trials were carried out for the phytosanitary treatments under two situations, one according to Good Agricultural Practices (GAP) and the other one with Critical Agricultural Practices (CAP). Samples of both situations were transformed into orange juice according to the current industrial process. The analytical methodology included acetone and dichloromethane/petroleum ether extraction and aminopropyl-based cleanup. Method validation followed SANCO Guidelines. The final objective was the determination of the exposure to the residues in raw and processed orange when good and critical agricultural conditions are used in the field.

A simple approach for a spatial terrestrial exposure assessment of the insecticide fenoxycarb, based on a high-resolution landscape analysis.

BACKGROUND: The objective was to refine the standard regulatory exposure scenario used in plant protection product authorisations by developing a more realistic landscape-related GIS-based exposure assessment for terrestrial non-target arthropods. We quantified the proportion of adjacent off-target area in agricultural landscapes potentially exposed to insecticide drift from applications of the active substance fenoxycarb. High-resolution imagery, landscape classification and subsequent stepwise analysis of a whole landscape using drift and interception functions were applied to selected areas in representative fruit-producing regions in Germany. RESULTS: Even under worst-case assumptions regarding treated area, use rate and drift, less than 12% of the non-agricultural habitat area would potentially be exposed to fenoxycarb drift above regulatory acceptable concentrations. Additionally, if the filtering effect of tall vegetation were taken into account, this number would decrease to 6.6%. Further refinements to landscape elements and application conditions indicate that less than 5% of the habitat area might be exposed above regulatory acceptable concentrations, meaning that 95% of the non-agricultural habitat area will be unimpacted (i.e. no unacceptable effects) and can serve as refuge for recolonisation. CONCLUSION: Approaches and tools are proposed for standardisable and transparent refinements in regulatory risk assessments on the landscape level. © 2016 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.