Yahong Liu

Novel cyromazine imprinted polymer applied to the solid-phase extraction of melamine from feed and milk samples

A water compatible molecularly imprinted polymer (MIP) using cyromazine as a mimic template, methacrylic acid as the functional polymer and ethylene glycol dimethacrylate as the cross-linker was synthesized and used to extract melamine from feed and milk samples via a molecularly imprinted solid-phase extraction (MISPE) protocol. Optimum retention of melamine on the MISPE cartridge was achieved using methanol, and the interferences in the samples were effectively washed out. The binding capacity of the polymer toward melamine was found to be about 500 microg of melamine/g of polymer. The recoveries of 2 microg and 20 microg melamine standard spiked into water extract of blank feeds and milk samples were between 83.4% and 103%, with relative standard deviation <5.6%. The cyromazine-MIP demonstrated high cross-reactivity for melamine and low affinity to cyanuric acid. The ionic bond interaction was regarded as the main factors that dominated the retention of the melamine on the MISPE cartridge.

Determination of 26 veterinary antibiotics residues in water matrices by lyophilization in combination with LC–MS/MS

A sensitive, simple and reliable multi-residue method was developed for the determination of 26 widely used veterinary antibiotics including 6 macrolides, 2 pleuromutilins, 4 tetracyclines, 2 lincosamides, 6 fluoroquinolones and 6 sulfonamides in different water matrices using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Water samples were lyophilized to dryness. Target compounds were separated on Zorbax SB-Aq column (150mm×2.1mm i.d., 3.5μm) and determined by LC-MS/MS operating in positive electrospray ionization mode. Spiked at concentration levels of 0.02, 0.4 and 4μgL(-1), recoveries of all target compounds were over 70% except sulfaquinoxaline (59.0% at 0.02μgL(-1)) with relative standard deviations below 20%. Limits of detection (LOD) and limits of quantification (LOQ) of 26 drugs ranged from 0.1 to 6.5ngL(-1) and from 0.3 to 19ngL(-1), respectively. The developed method was successfully applied to the analysis of 26 antibiotics residues in fish pond water, groundwater, biogas digester water, and lagoon wastewater samples collected from local pig farms.

Development of a multi-residue method for fast screening and confirmation of 20 prohibited veterinary drugs in feedstuffs by liquid chromatography tandem mass spectrometry

A simple multiresidue method was developed for detecting and quantifying twenty analytes from 5 classes of prohibited veterinary drugs (β-agonists (9), anabolic hormones (4), quinoxalines (4), tranquilizers (1), cyproheptadine, and clonidine in animal feeds using a QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) approach. Feed samples were extracted by ultrasonic-assisted extraction with a mixture of methanol-acetonitrile (50:50, v/v), followed by a cleanup using a dispersive solid-phase extraction with PSA (primary secondary amine). Target compounds were separated and determined by a liquid chromatography tandem quadrupole mass spectrometer operating in positive electrospray ionization mode, using multiple reaction monitoring (MRM). The recoveries of these compounds were between 56.7% and 103% at three spiked levels. The repeatability was lower than 10%, whereas reproducibility was no more than 15% except for nandrolone (17% at 10μgkg(-1)) and diazepam (19% at 10μgkg(-1)). Decision limits (CCαs) and detection capabilities (CCβs) ranged from 0.42 to 5.74μgkg(-1) and 5.70-9.81μgkg(-1), respectively. The method was successfully applied to screening of real samples obtained from local feed markets and confirmation of the suspected target analytes.

Molecularly imprinted solid-phase extraction for determination of tilmicosin in feed using high performance liquid chromatography.

A simple, sensitive and reproducible molecularly imprinted solid-phase extraction (MISPE) coupled with high performance liquid chromatographic method was developed for monitoring tilmicosin in feeds. The polymers were prepared using tylosin as mimic template molecule, methacrylic acid as functional monomer and ethylene glycol dimethacrylate as cross-linking monomer, and chloroform as a solvent by bulk polymerization. Under the optimum MISPE conditions, the novel polymer sorbent can selectively extract and enrich tilmicosin from variety of feeds. The MISPE cartridge was better than non-imprinted, C(18) and HLB cartridges in terms of both recovery and precision. Mean recoveries of tilmicosin from five kinds of feeds spiked at 1, 10 and 50 mg kg(-1) ranged from 76.9% to 95.6%, with intra-day and inter-day relative standard deviation less than 7.6%. The linearity was ranged from 1.0 to 100 mg L(-1) for matrix standard solution (r=0.9990). The limit of detection was approximately 0.35 mg kg(-1) and the limit of quantification was approximately 0.98 mg kg(-1). There was cleaner chromatogram by using MISPE than C(18) and HLB SPE.

Development of a modified QUick, Easy, CHeap, Effective, Rugged and Safe method for the determination of multi-class antimicrobials in vegetables by liquid chromatography tandem mass spectrometry.

A modified quick, easy, cheap, efficient, rugged and safe (QuEChERS) method coupled with liquid chromatography tandem mass spectrometry (LC-MS/MS) was developed for rapid determination of 26 veterinary antimicrobials in vegetables. Samples were extracted by single-phase extraction with acetonitrile-methanol (85:15, v/v) and citric buffer solution, followed by liquid-liquid partitioning with the addition of anhydrous magnesium sulfate and sodium chloride. A dispersive solid-phase extraction with primary secondary amine was applied for cleanup. Concentration and solvent exchange was performed prior to LC-MS/MS analysis. All matrix-matched calibration curves were linear with correlation coefficients (r) over 0.99. Recoveries for all the analytes spiked at 0.5 (1 or 1.5), 5 and 50 ng/mL were in the range of 60.0-98.0%, except for sulfaquinoxaline, sulfaclozine and doxycycline, with relative standard deviations below 25% for the low concentration level, 20% for the medium and 15% for the high. The decision limits and the detection capabilities of the analytes ranged from 0.005 to 0.5 μg/kg and from 0.02 to 1.5 μg/kg, respectively. The method was developed and validated in accordance with romaine lettuce matrix, and higher recovery rates were obtained from the other five kinds of vegetables including white radish, Chinese cabbage, cucumber, string bean and green pepper. Matrix effects of different vegetables were evaluated and signal suppression effect was observed for the majority of 26 analytes. Finally, the method was applied to the analysis of real samples collected from the agricultural areas in the vicinity of local pig farms, and the phenomenon of vegetables contaminated by antimicrobials residues is provoking.

Molecularly imprinted solid-phase extraction for the selective determination of valnemulin in feeds with high performance liquid chromatography

A simple, sensitive and reproducible high performance liquid chromatographic method was developed for determining valnemulin in feeds. Feed samples were extracted with ethyl acetate under alkaline condition, cleaned up by molecularly imprinted solid-phase extraction, and analyzed by high performance liquid chromatography with ultraviolet detection. The characteristics of the synthesized polymer were evaluated and the loading capacity of the polymer was about 1000 μg analyte/g imprinted polymer. The new procedure for the feed sample cleanup using the prepared polymer cartridge gave higher recoveries and fewer matrix interferences. The assay exhibited a linear dynamic range of 5.0-200 mg kg(-1) with the correlation coefficient above 0.9993. Recoveries of valnemulin from feed samples spiked at 5.0, 20 and 50 mg kg(-1) ranged between 76.0% and 94.4% with relative standard deviations of less than 9%. The limit of detection for valnemulin in feeds was 1 mg kg(-1).

Simultaneous determination of cyadox and its metabolites in plasma by high-performance liquid chromatography tandem mass spectrometry

Cyadox is a novel antimicrobial growth-promoter of the quinoxalines. For food safety and pharmacokinetic studies, a convenient, sensitive and reproducible LC-ESI-MS/MS method was developed for the simultaneous determination of cyadox and its major metabolites, quinoxaline-2-carboxylic acid, 1,4-bisdesoxycyadox, cyadox-1-monoxide and cyadox-4-monoxide in chicken plasma. Plasma sample was subjected to a simple deproteinisation with acetonitrile. Analysis was performed on a C18 column by detection with mass spectrometry in multiple reaction monitoring mode. A gradient elution program with 0.2% formic acid, methanol and acetonitrile was performed at a flow rate of 0.2 mL/min. The decision limits (CCαs) of five analytes in plasma ranged from 1.0 to 4.0 μg/L, and the detection capabilities (CCβs) were <10 μg/L. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. The extraction recoveries of five analytes were between 87.4 and 93.9% in plasma at the spiked levels of 5 (10)-200 μg/L with the relative standard deviations <10% for each analyte. The developed method demonstrated a satisfactory applicability in real plasma samples.

Toxicokinetics of T-2 toxin and its major metabolites in broiler chickens after intravenous and oral administration.

T-2 toxin, one of the most toxic trichothecene mycotoxins, causes economic losses in animal production. Little information is available on the toxicokinetic parameters of T-2 toxin and its major metabolites (i.e., HT-2 toxin and T-2 triol) in broiler chickens. In this study, toxicokinetics of T-2 toxin and its major metabolites were evaluated in broiler chickens after a single intravenous (0.5 mg/kg b.w.) and multiple oral administrations (2.0 mg/kg b.w., every 12 h for 2 days). Plasma concentration profiles of T-2 toxin and its metabolites were analyzed by a noncompartmental model method. Following intravenous administration, the terminal elimination half-lives (t(1/2λz)) of T-2 toxin, HT-2 toxin, and T-2 triol were 17.33 ± 1.07 min, 33.62 ± 3.08 min, and 9.60 ± 0.50 min, respectively. Following multiple oral administrations, no plasma levels above the limit of quantification were observed for HT-2 toxin. The t(1/2λz) of T-2 toxin and T-2 triol was 23.40 ± 2.94 min and 87.60 ± 29.40 min, respectively. Peak plasma concentrations (Cmax ) of 53.10 ± 10.42 ng/mL (T-2 toxin) and 47.64 ± 9.19 ng/mL (T-2 triol) were observed at Tmax of 13.20 ± 4.80 min and 38.40 ± 15.00 min, respectively. T-2 toxin had a low absolute oral bioavailability (17.07%). Results showed that the T-2 toxin was rapidly absorbed and most of the T-2 toxin was extensively transformed to metabolites in broiler chickens.

Simultaneous determination of quinocetone and its major metabolites in chicken tissues by high-performance liquid chromatography tandem mass spectrometry

A convenient, rapid and sensitive liquid chromatography-tandem mass spectrometry method was firstly established for the simultaneous determination of quinocetone and its 4 major metabolites: 1-desoxyquinocetone, di-deoxyquinocetone, carbonyl reduced metabolite from di-deoxyquinocetone and 3-methyl-quinoxaline-2-carboxylic acid in chicken muscle, liver, kidney and fat. Sample was extracted with acetonitrile and chloroform, and further purified by Oasis MAX SPE cartridge. Analysis was performed on a C(18) column by detection with mass spectrometry in multiple reaction monitoring mode and using a gradient elution program with 0.1% formic acid solution and acetonitrile. The correlation coefficients (r) for each calibration curves are higher than 0.99 within the experimental concentration range. The recoveries of the five target analytes at three spiking levels were between 77.1% and 95.2%, with relative standard deviations less than 15%. The decision limits of the five analytes in chicken edible tissues ranged from 0.24 to 0.76 μg kg(-1), and the detection capabilities were below 2.34 μg kg(-1). The developed method demonstrated a satisfactory applicability in incurred chicken tissue samples.

Determination of multi-class antimicrobial residues in soil by liquid chromatography-tandem mass spectrometry

Antimicrobial residues in environmental matrices may result in the occurrence of antimicrobial-resistant bacteria in soil. In this paper, a new analytical method based on liquid chromatography-tandem mass spectrometry for multiresidue analysis of 24 antimicrobials of a wide polarity range and variable physicochemical properties, including sulfonamides, tetracyclines, fluoroquinolones, macrolides, lincosamides and pleuromutilins in soil was developed. Samples were extracted with an acetonitrile: Na2EDTA–McIlvaine buffer (pH 4.0, 5 : 5, v/v) system and then re-extracted with a 0.2 M sodium hydroxide solution. The extracts were purified using an HLB solid phase extraction cartridge. Chromatographic separation of the components was performed on a Zorbax SB-Aq column using acetonitrile–0.1% formic acid as mobile phase. The method developed was linear in a concentration range from the limits of quantification to 200 μg kg−1, with correlation coefficients higher than 0.99. The limits of detection and limits of quantification ranged from 0.01 to 2 μg kg−1 and 0.04 to 5 μg kg−1, respectively. The overall average recoveries for target analytes were more than 60% except for tetracycline (59.3%) in three spiked levels of 1, 4 and 20 μg kg−1 with relative standard deviations less than 20%. The method was further applied for the determination of residual antimicrobials in real samples. Some target antimicrobials were detected at different levels and tetracycline residues were dominant. 163.6 μg kg−1 of chlortetracycline was detected in a soil sample. The results indicate that the proposed method has good feasibility.