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Milk is an important consumer product with high nutritional value. The presence of veterinary drug residues in milk owing to the indiscriminate use of veterinary drugs may affect consumer health. In the mass spectrometric analysis of trace compounds, chromatographic co-eluting components easily interfere with the mass spectral signals obtained, affecting the accuracy of qualitative and quantitative analyses. Matrix purification is a promising method to reduce the matrix effect. Chitosan is a natural biopolymer with numerous active functional groups such as amino, acetyl, and hydroxyl groups; these groups can adsorb lipids through hydrophobic and electrostatic interactions. Chitosan also has the advantages of low production cost, stable chemical properties, and convenient modification. Novel chitosan-based materials are promising candidates for lipid purification. In this study, a chitosan membrane was modified with trimethoxyoctadecylsilane (C 18 -CSM). C 18 -CSM was prepared through one-step hydrolysis and used as a dispersive solid phase extraction (DSPE) adsorbent to purify the matrix during milk pretreatment. We combined C 18 -CSM with ultra-high performance liquid chromatography-quadrupole/electrostatic field orbitrap mass spectrometry (UHPLC-Q/Exactive Orbitrap MS) to develop an effective method for the extraction and determination of ofloxacin, enrofloxacin, ciprofloxacin, diazepam, and metronidazole in milk. C 18 -CSM was characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, and water contact angle testing. The results indicated that the material has a rough surface and uniformly dense cross-section. The water contact angle of C 18 -CSM was 104°, indicating its good hydrophobicity. The pretreatment conditions (extraction solvent, dosage of NaCl, extraction frequency, and dosage of C 18 -CSM) that influenced the recoveries of the five veterinary drugs were investigated in detail. The optimal conditions were established as follows: 5% formic acid in acetonitrile, 1 g NaCl, extraction 1 time, 20 mg C 18 -CSM. Separation was performed on a Hypersil GOLD VANQUISH column (100 mm×2.1 mm, 1.9 μm). The mobile phase consisted of 0.1% formic acid aqueous solution and 0.1% formic acid in acetonitrile, and was flowed at a rate of 0.3 mL/min. The sample injection volume was 1 μL, and the column temperature was maintained at 25 ℃. Mass spectrometric analysis was performed in positive electrospray ionization mode. To verify the necessity of the purification material, the matrix effect was investigated using the matrix-matched standard curve method. The use of C 18 -CSM reduced the matrix effects of the five necessity drugs from the range of -22%-8.8% to the range of -13%-3.6%, indicating that C 18 -CSM is a highly efficient DSPE material. Under optimal conditions, the developed method showed good linearities within the range of 0.5-100 μg/L, with correlation coefficients ( r 2 )≥0.9970. The limits of detection(LODs) and quantification (LOQs) were 0.2 μg/L and 0.5 μg/L, respectively. To assess the accuracy and precision of the method, we prepared milk samples with three spiked levels (low, medium, and high). The recoveries of the five veterinary drugs were ranged from 79.5% to 115%, and the intra-day and inter-day relative standard deviations were 7.0%-13% ( n =6) and 1.3%-11% ( n =3), respectively. This study provides a simple, accurate, and reliable method for the rapid and simultaneous determination of the five veterinary drug residues in milk.

A method was established for the simultaneous detection of 12 prohibited veterinary drugs, including β 2 -receptor agonists, nitrofuran metabolites, nitroimidazoles, chlorpromazine, and chloramphenicol, in pig urine. The sample was pretreated by enzymolysis, acid hydrolysis/derivatization, and liquid-liquid extraction combined with solid-phase extraction. Detection was performed using ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). Ammonium acetate solution (0.2 mol/L, 4.5 mL) and β -glucuronidase/aryl sulfatase (40 μL) were added to the sample, which was subsequently enzymolized at 37 ℃ for 2 h. Then, 1.5 mL of 1.0 mol/L hydrochloric acid solution and 100 μL of 0.1 mol/L o -nitrobenzaldehyde solution were added to the sample. The mixture was incubated at 37 ℃ for 16 h, and the analytes were extracted with 8 mL of ethyl acetate by liquid-liquid extraction. The lower aqueous phase obtained after extraction was extracted and purified using a mixed cation-exchange solid-phase extraction column. The extracts were combined, the extraction solution was blow-dried with nitrogen, and the residue was redissolved for determination. The samples were analyzed under multiple-reaction monitoring mode with both positive and negative electrospray ionization, and quantified using an isotope internal standard method. The correlation coefficients ( r ) of the 12 compounds were >0.99. The limits of detection (LODs) and quantification (LOQs) of chloramphenicol were 0.05 and 0.1 μg/L, respectively, and the LODs and LOQs of the other compounds were 0.25 and 0.5 μg/L, respectively. The mean recoveries and RSDs at 1, 2, and 10 times the LOQ were 83.6%-115.3% and 2.20%-12.34%, respectively. The proposed method has the advantages of high sensitivity, good stability, and accurate quantification; thus, it is suitable for the simultaneous determination of the 12 prohibited veterinary drug residues in pig urine.

The consumption of poultry eggs has increased in recent years owing to the abundance of production and improvements in living standards. Thus, the safety requirements of poultry eggs have gradually increased. At present, few reports on analytical methods to determine banned veterinary drugs during egg-laying period in poultry eggs have been published. Therefore, establishing high-throughput and efficient screening methods to monitor banned veterinary drugs during egg-laying period is imperative. In this study, an analytical method based on ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) combined with QuEChERS-based techniques was developed for the simultaneous determination of 31 banned veterinary drugs encompassing nine drug classes (macrolides, antipyretic and analgesic drugs, sulfonamides, antibacterial synergists, anticoccidials, antinematodes, quinolones, tetracyclines, amphenicols) in different types of poultry eggs. The main factors affecting the response, recovery, and sensitivity of the method, such as the extraction solvent, purification adsorbent, LC separation conditions, and MS/MS parameters, were optimized during sample pretreatment and instrumental analysis. The 31 veterinary drug residues in 2.00 g eggs were extracted with 2 mL of 0.1 mol/L ethylene diamine tetraacetic acid disodium solution and 8 mL 3% acetic acid acetonitrile solution, and salted out with 2 g of sodium chloride. After centrifugation, 5 mL of the supernatant was cleaned-up using the QuEChERS method with 100 mg of octadecylsilane-bonded silica gel (C 18 ), 50 mg of N -propylethylenediamine (PSA), and 50 mg of NH 2 -based sorbents. After nitrogen blowing and redissolution, the 31 target analytes were separated on a Waters CORTECS UPLC C 18 analytical chromatographic column (150 mm×2.1 mm, 1.8 μm) at a flow rate, column temperature, and injection volume of 0.4 mL/min, 30 ℃, and 5 μL, respectively. Among these analytes, 26 analytes were acquired in dynamic multiple reaction monitoring (MRM) mode under positive electrospray ionization (ESI + ) conditions using (A) 5 mmol/L ammonium acetate (pH 4.5) and (B) acetonitrile as mobile phases. The gradient elution program was as follows: 0-2.0 min, 12%B-30%B; 2.0-7.5 min, 30%B-50%B; 7.5-10.0 min, 50%B; 10.0-10.1 min, 50%B-100%B; 10.1-12.0 min, 100%B; 12.0-12.1 min, 100%B-12%B; The five other target analytes were acquired in MRM mode under negative electrospray ionization (ESI - ) conditions using (A) H 2 O and (B) acetonitrile as mobile phases. The gradient elution program was as follows: 0-2.0 min, 12%B-40%B; 2.0-6.0 min, 40%B-80%B; 6.0-6.1 min, 80%B-100%B; 6.1-8.0 min, 100%B; 8.0-8.1 min, 100%B-12%B. Matrix-matched external standard calibration was used for quantification. The results showed that all the compounds had good linear relationships within their respective ranges, with correlation coefficients of >0.99. The limits of detection (LODs) and quantitation (LOQs) were 0.3-3.0 μg/kg and 1.0-10.0 μg/kg, respectively. The average recoveries of the 31 banned veterinary drugs spiked at three levels (LOQ, maximum residue limit (MRL), and 2MRL) in poultry eggs ranged from 61.2% to 105.7%, and the relative standard deviations (RSDs) ranged from 1.8% to 17.6%. The developed method was used to detect and analyze banned veterinary drugs in 30 commercial poultry egg samples, including 20 eggs, 5 duck eggs, and 5 goose eggs. Enrofloxacin was detected in one egg with a content of 12.3 μg/kg. The proposed method is simple, economical, practical, and capable of the simultaneous determination of multiple classes of banned veterinary drugs in poultry eggs.

Chloramphenicols, nitroimidazoles, lincosamides, and macrolides are common antibiotics used in veterinary medicine. Overdoses of these drugs will lead to residual substances in animal-derived foods and accumulate in the body through the food chain, thereby exerting adverse effects on human health. Therefore, regulation of veterinary drug levels is imperative to ensure the quality of animal-derived foods and safeguard the health of consumers. In this study, a method based on ultra performance liquid chromatography-tandem mass spectrometry coupled with solid phase extraction (SPE-UPLC-MS/MS) was developed for the simultaneous determination of eight prohibited and restricted veterinary drugs and three metabolite residues across four categories (chloramphenicols, nitroimidazoles, lincosamides, and macrolides) in eggs, liquid milk, chicken, and freshwater fish. The main factors affecting the response, recovery, and sensitivity of the method, such as the type and pH values of the extraction solvent, dilution solution for the analytes, type of chromatographic column, and type and proportion of the mobile phase, were optimized during sample pretreatment and instrument analysis. The samples were hydrolyzed and dispersed in 0.1 mol/L phosphate buffer solutions (pH 9.0) and extracted with acetonitrile. The extract was further extracted using ethyl acetate. After centrifugation, the supernatant ethyl acetate was concentrated to near dryness in nitrogen below 40 ℃. The residue was dissolved in 0.3 mL methanol, followed by the addition of 5.7 mL phosphate buffer solution. After shaking, the solutions were purified and enriched on an Oasis HLB SPE column. The target analytes were separated on an ACQUITY UPLC BEH C18 chromatographic column (100 mm×2.1 mm, 1.7 μm) at a column temperature of 40 ℃ with a flow rate of 0.4 mL/min. The injection volume was 10 μL. Gradient elution was carried out with methanol and 0.1% formic acid aqueous solution as the mobile phases. Multiple reaction monitoring (MRM) was conducted in the positive and negative electrospray ionization modes. The isotope internal standard method was used for quantitative analysis. Under optimal conditions, each analyte showed a good linear relationship in each range, and the correlation coefficient ( R 2 ) was greater than 0.99. The limits of detection (LODs) ranged from 0.050 to 0.50 μg/kg, and the limits of quantification (LOQs) ranged from 0.20 to 1.5 μg/kg. With eggs, freshwater fish, chicken, and liquid milk as the matrix samples, the recoveries in spiked blank samples were determined at different addition levels in compliance with the current legislation. The average recoveries of the 11 analytes were 65.3% to 108%. The relative standard deviations (RSDs) were between 0.40% and 21%. The matrix effects of the analytes were between 0.0124% and 46.80% in four different samples after purification on the Oasis HLB column. The practicality of the proposed approach for routine analyses of the eight prohibited and restricted veterinary drugs, and three metabolite residuals was evaluated by applying it to the determination of these compounds in animal-derived food samples. The samples, including 80 eggs, 80 chicken, 40 liquid milk, and 32 freshwater fish, were procured from a supermarket and a farm product market. The results of the positive samples were consistent with those observed with the standard methods. The method described herein is easy to operate, sensitive, and accurate. It is suitable for the simultaneous and rapid determination of various prohibited and restricted veterinary drug residues and metabolites in animal-derived foods.

Hazardous chemicals in food are an important cause of food safety problems. Mass spectrometry is an effective tool for the qualitative and quantitative analysis of these substances. In this paper, the fragmentation mechanisms for several chemical hazardous substances, including pesticides, veterinary drugs, mycotoxins, and other chemical pollutants classified by structural analogs, are reviewed. For each class of compounds, we summarize the characteristic fragments and neutral loss generated by cleavage in the mass spectrometry analysis. We also summarize the mechanisms applied to screen and discover new structural analogs in food. This review can help researchers analyze and confirm the structure of compounds and provide a theoretical basis for the discovery of new structural analogs in food.

A method was established for the rapid determination of 28 prohibited and restricted veterinary drugs of five classes (sulfonamides, quinolones, chloramphenicols, nitrofurans metabolites and triphenylmethane) in fish and shrimp by ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) coupled with simultaneous extraction and purification. After optimizing the sample pretreatment methods and chromatographic conditions, the samples were hydrolyzed with hydrochloric acid. The five kinds of residual drugs were simultaneously extracted with acetonitrile after nitrofuran metabolites derivatized with 2-nitrobenzaldehyde. The extraction solutions were dehydrated with sodium chloride and salted out. The acetonitrile layer was purified with n -hexane and concentrated to near dryness. The residues were dissolved in 1.0 mL methanol. Then, the solutions were purified by dispersive solid phase extraction with C18, N -( n -propyl)ethylenediamine (PSA) and amino bonded silica gel (NH2) sorbents. The residues were separated on a ZORBAX C18 chromatographic column (50 mm×2.1 mm, 1.8 μm). The MS data were acquired in positive and negative multiple reaction monitoring (MRM) modes, and quantitated by the isotope internal standard method. With this approach, the linear relationships of the 28 veterinary drugs were good. The linear correlation coefficients were greater than 0.99. The limits of detection and limits of quantification were in the range of 0.1-0.8 μg/kg and 0.3-2.7 μg/kg, respectively. The average recoveries at three spiked levels (1, 5, and 20 fold of the LOQs) were 70.0%-120% with relative standard deviations of 0.9%-10.0%. The method is simple, rapid, accurate and sensitive, and it is suitable for the rapid determination of various prohibited and restricted drugs in fish and shrimp.

A method was established to rapidly determine 20 kinds of veterinary drug residues including three catagories of antibiotics (sulfonamides, quinolones, and chloramphenicols) and two kinds of triphenylmethanes (malachite green (MG) and leucomalachite green (LMG)) in fish and shrimp, based on dispersive solid phase extraction purification-ultra high performance liquid chromatography-tandem mass spectrometry. The samples were first hydrolyzed using a dipotassium hydrogen phosphate solution, and then extracted using acetonitrile. Afterward, the extraction solution was dehydrated and salted out with sodium chloride and condensed to nearly dry using a rotating evaporator. This residue was dissolved in 1.0 mL methanol. The resulting solution was purified by dispersive solid phase extraction method with C18 and PSA sorbents, and filtered through a filter. The target compounds were separated employing a ZORBAX C18 column. The mass spectrometer datas were acquired by multiple reaction monitoring (MRM) of positive and negative modes and quantitated applying the isotope internal standard method. The 20 veterinary drugs showed a good linear relationship in the range of 0.2-300 μg/L. The limits of detection and the limits of quantification were 0.1-0.6 and 0.3-1.8 μg/kg, respectively, while the correlation coefficients were greater than 0.99. The average recoveries at the three spiked levels (1, 5, and 20 times of quantitative limits) ranged between 72.5%-118%, with the relative standard deviations of 1.9%-9.8%. The advantages of method include a simple pretreatment, a high detection efficiency, and a low cost. Moreover, it is suitable for the simultaneous determination of multiple veterinary drug residues in fish and shrimp.

The analysis of veterinary drugs in organic fertilizers is crucial for an assessment of their potential risks to microbial communities in soils and to human health. A method has been developed for the simultaneous determination of ten fluoroquinolones in organic fertilizers by using the QuEChERS method coupled with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The sample was extracted with disodium ethylenediaminetetraacetic acid (Na 2 EDTA)-McIlvaine buffer (pH=4.0) and acetonitrile. The target compounds were separated on an Atlantis T3 C18 column (250 mm×4.6 mm, 5 μm) with a mobile phase of 0.2% (v/v) formic acid in acetonitrile and analyzed in the multiple reaction monitoring (MRM) mode via electrospray ionization (ESI). Ten fluoroquinolones were quantified by an internal standard method. The calibration curves of the ten fluoroquinolones exhibited good linearity over the range of 10-500 μg/kg, and the correlation coefficients were above 0.9930. The limits of detection were 0.5-2.5 μg/kg; the limits of quantification were 1.7-8.3 μg/kg. The analytical method was successfully applied in a survey of veterinary drug contamination in nine compost samples. The average recoveries were 82.5%-117.1%, with relative standard deviations of 3.4%-10.2%. The method is accurate, reliable, and sensitive and supports the simultaneous detection of various veterinary drug residues. Therefore, this method can provide a basis for the risk assessment of veterinary drugs in organic fertilizers.

A comprehensive pretreatment system was developed to simultaneously extract and purify 120 veterinary antibiotics, possessing various physicochemical properties in eight categories. This system was coupled with ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) for the detection of the antibiotics. The samples were dissolved and dispersed by a Na 2 EDTA-Mcllvaine buffer, extracted with acetonitrile containing 1.5% (v/v) formic acid, and cleaned using an Oasis PRiME HLB SPE system followed by n -hexane liquid purification. The separation of residue targets was performed on an Atlantis ® T3 column (100 mm×2.1 mm, 3 μm) with a gradient elution of 0.1% (v/v) formic acid aqueous solution and acetonitrile as mobile phases and detected by UPLC-MS/MS with the multiple reaction monitoring (MRM) mode via ESI + ionization. The pH of the extraction solvent and the purification method were optimized to promote the target recoveries. All targets showed good linear ranges from 1.0 to 50.0 μg/L, while all their correlation coefficients ( r 2 ) were higher than 0.9953, including r 2 values of 89 targets being over 0.9990. The limits of quantification (LOQs) of seven targets were 10.0 μg/kg; 21 targets, 5.0 μg/kg; and the remaining 92 targets, not higher than 2.0 μg/kg. The average recoveries on three spiked levels (low, medium, and high) for all targets ranged from 71.5%-109.2%, with RSD ranging from 0.6%-15.3%. The combined system, exhibiting satisfying recovery and stable repeatability, can be suitably employed for the simultaneous determination of multiple veterinary antibiotics in animal-derived meat products.

A method was established for the determination of 50 kinds of antibiotic residues (macrolides, quinolones, sulfonamides, tetracyclines, nitroimidazoles, lincomycin and chloramphenicol) in drone pupa powder by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The samples were extracted with perchloric acid and lead acetate solution, and the protein was precipitated. The extraction solution was adjusted to pH 8 using dipotassium hydrogen phosphate, then the solution was purified by solid phase extraction (SPE) and analyzed by LC-MS/MS. The target compounds in the drone pupa powder were determined quantitatively and quantitatively by using multiple reaction monitoring and positive ion or negative ion modes. The recoveries of the 50 antibiotics were in the range of 70.2%-118.3%, and the relative standard deviations (RSDs) were 1.8%-13.6%. The method is simple, selective, and can be suitable for the analysis and confirmation of veterinary drug residues in drone pupa powder.

An ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF-MS) method was developed for determination of 39 veterinary drugs in Procambarusclarkii. Samples were extracted with acidified acetonitrile and purified with enhanced matrix removal-lipid (EMR-Lipid) adsorbent and graphitized multi-walled carbon nanotubes (GMWNTs). Extracts were analyzed by UHPLC-Q-TOF-MS. Target compounds were screened according to accurate mass, isotopic ratio, and retention time, and confirmed by library search. Target analytes were quantified using the chromatographic peak area of each compound. For each of the drugs of interest, calibration curves were linear in their respective ranges with correlation coefficients greater than 0.99. The limits of quantification (LOQs) were 3-15 μg/kg. The recoveries for target compounds spiked in Procambarusclarkii ranged from 62.4% to 105.8%, with relative standard deviations (RSDs) ranging from 2.5% to 13.5%. This method is simple, rapid, accurate, and suitable for simultaneous determination of 39 veterinary drugs, including sulfonamides, quinolones, and triphenylmethane, extracted from Procambarusclarkii.

To establish a method for the determination of veterinary drug residues in eggs by ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS), samples were extracted and purified using frozen lipid filtration combined with the QuEChERS method taking advantage of dispersive solid-phase extraction (DSPE). A total of 125 veterinary drug residues in eggs were analyzed, encompassing 11 classes of drugs (nitroimidazoles, benzimidazoles, sulfonamides, quinolones, macrolides, tetracyclines, androgens, progestational hormones, glucocorticoids, estrogens, and chloramphenicols). The drugs were extracted in acetonitrile/water (70:30, v/v) containing 0.1 mol/L EDTA. The precipitation of lipids and proteins was promoted by performing the extractions at very low temperature (-20℃) for 2 h. Further purification was carried out using dispersive solid-phase extraction (DSPE) followed by dilution of the supernatant. Detection and analysis of veterinary drug residues by UHPLC-MS/MS was conducted and quantified by the external standard method. Our results showed that this method gave good linearity within a certain concentration range (relative coefficient, R 2 ≥ 0.99), and the acceptable limits of quantification were determined to be 2.0-60 μg/kg for the 125 veterinary drugs. Good recovery values (60.4%-119.3%) were achieved for all the 125 veterinary drugs with RSD values ranging from 0.3% to 16.1%. This method proved suitable for the rapid determination of veterinary drug residues in eggs with a simple, accurate, and low-cost procedure.

A liquid chromatography-tandem mass spectrometry method, coupled with a dispersive solid phase extraction (DSPE) procedure for sample preparation, was developed to determine 13 classes of 42 veterinary drugs in four representative animal-derived foods. The analytes were dispersed with water, extracted with acetonitrile containing 5% (v/v) formic acid, salted out by salts, and purified by DSPE. The analytes were separated on a C18 column (100 mm×2.1 mm, 2 μ m) with gradient elution using the mobile phase containing methanol and 0.1% (v/v) formic acid aqueous solution. Electrospray ionization-mass spectrometry was performed in multiple reaction monitoring mode for analysis of the 42 compounds. The correlation coefficients of the standard calibration curves for the 42 veterinary drugs were all above 0.995. Most recoveries at three spiked levels in the four representative matrixes ranged from 65.8% to 135.5%, with relative standard deviations of 0.5%-14.2% ( n =6). The limits of detection (LODs, S/N =3) and the limits of quantification (LOQs, S/N =10) were 0.01-1.68 μ g/kg and 0.01-5.62 μ g/kg, respectively. The method is simple, rapid, sensitive, and suitable for the simultaneous determination of the 42 veterinary drugs in animal-derived food.

We established a system for the simultaneous extraction and cleaning of 99 veterinary drugs from food by ultra-performance liquid chromatography coupled with quadrupole electrostatic field-orbital trap-high-resolution mass spectrometry (UHPLC-Q-Orbitrap HRMS). The system is based on the supported liquid-liquid extraction technology through one-off pretreatment, which covers the common eight categories of physical and chemical properties, and the extraction and purification of 99 different veterinary drug residues. At the same time, the one-step multi residue screening of 99 veterinary drug residues has been realized using HRMS. The results showed that the method was suitable for extraction from milk, pork, and fish. The 99 veterinary drugs showed a good linear relationship in the concentration range of 0.001-0.1 μg/mL, the limit of quantification was 0.5-20.0 μg/kg, the average recoveries were 60%-120%, and the relative standard deviations (RSDs) were not more than 15%. The pre-processing and instrumental analysis of this method have high detection efficiency, strong maneuver ability, and strong compatibility with different physical and chemical compounds. Moreover, the detection limit can meet all the objects of the test and greatly reduce the detection cost.

A method has been developed for the simultaneous determination of 64 veterinary drugs in aquatic products using ultra-high performance liquid chromatography-quadrupole/electrostatic field orbitrap high-resolution mass spectrometry. The samples were extracted with an acetonitrile/water mixture (80/20, v/v), cleaned up by normal hexane saturated with acetonitrile and primary secondary amine (PSA) adsorbent, quantified with external standard method. The drugs were analyzed in full scan/data dependent mass spectrum 2 (Full MS/ddMS 2 ) Top 1 mode. The calibration curves of the 64 drugs were linear with the correlation coefficients more than 0. 9967. The average recoveries of the 64 analytes ranged from 56.2% to 124.6%, and the relative standard deviations (RSDs) were 1.3%-29.8% in the three kinds of matrixes (fish, shrimp and shell) at three levels. The limits of quantification were 0.2-10 μg/kg. The method is simple, rapid, sensitive, reliable and suitable for the screening of residues in aquatic products.

A method has been developed for the simultaneous determination of the 10 kinds of 121 veterinary drugs (including chloramphenicols, β-agonists, sulfonamides, 4-quinolones, nitroimidazoles, macrolides, avermections, polyether antibiotics, tetracycline antibiotics, cephalosporins, etc.) in pork using QuEChERS method coupled with ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The drugs were extracted with Na2EDTA-McIlvaine buffer solution (pH = 4) and acetonitrile. Anhydrous sodium sulfate was used for the salting-out process. The solutions divided into two groups were cleaned-up by different mixed sorbents. The drugs were analyzed by UPLC-MS/MS in multiple reaction monitoring (MRM) mode via electrospray ionization. Among the 121 drugs, 5 drugs were quantified by internal standard method, and the other 116 drugs were quantified by external standard method. The calibration curves of the 121 drugs were linear in the range of 0.02-40 μg/L with the correlation coefficients more than 0.99. The limits of quantification (LOQs, S/N = 10) were 0.05-10 μg/kg. The average recoveries of 8 drugs at LOQ level in pork ranged from 41.7% to 59.6% with the relative standard deviations (RSDs) of 1.7% - 13.5%. The average recoveries of 10 drugs at LOQ level in pork ranged from 122.6% to 163.2% with the RSDs of 0.6% -14.8%. The average recoveries of 103 drugs at LOQ level in pork ranged from 60.3% to 118.3% with the RSDs of 0.4% - 16.7%. The proposed method is rapid, simple, sensitive, reliable and cost-effective.

An analytical method was established for the simultaneous determination of six classes of 33 veterinary drug residues in pork by ultra performance liquid chromatography coupled with quadrupole-time of flight mass spectrometry (UPLC-Q-TOF MS). The QuEChERS method has been validated for the extraction. In this method, the sample was extracted by acetonitrile containing 5% (v/v) acetic acid and cleaned-up with C18 and NH2 adsorbents. The extract was measured directly by UPLC-Q-TOF MS with electrospray ionization in positive mode. The compounds were separated on a ZORBAX SB-C18 column (100 mm x 2.1 mm, 3.5 µm) with acetonitrile-0.1% formic acid containing 5 mmol/L ammonium acetate as mobile phases under gradient elution. The confirmatory analysis was carried out by determining the retention times and accurate masses of all the compounds and fragment ions upon Target MS/MS. The correlation coefficients of the 33 veterinary drugs were more than 0. 99 within their linear ranges. The limits of quantification (LOQs) were 2.5-100 µg/kg. The recoveries ranged from 67.0% to 109.0% with the relative standard deviations (RSDs, n = 6) not more than 15.1%. The method is rapid, sensitive, and suitable for the simultaneous determination of multi-classes of veterinary drugs in pork.

A novel multiresidue analytical method has been developed and validated for the determination of five classes of veterinary drugs including 18 β-lactams, 15 quinolones, 21 sulfonamides, 3 sulfonamide potentiators and 6 antiparasitics in meat using dispersive solid-phase extraction (dispersive-SPE) and high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The analytes were extracted with a vortex mixer by 0.1 mol/L Na2 EDTA solution and acetonitrile containing 1% (v/v) acetic acid, and then the extracts were purified using dispersive-SPE with C18 sorbent. Electrospray ionization mass spectrometry was operated in positive mode using dynamic multiple reaction monitoring (DMRM) for the qualitative and quantitative analysis of the 63 analytes after the separation on a Poroshell EC-C18 column (100 mm x 2.1 mm, 2.4 µm). The correlation coefficients of linear calibration curves were over 0.99 in the corresponding concentration ranges. The average recoveries of the 63 analytes ranged from 62.2% to 112.0%, and the relative standard deviations (RSDs) were 3.1%-16.3% in spiked meat (pork, beef and chicken muscle) at three levels. The limits of detection (LODs, S/N ≥ 3) and the limits of quantification (LOQs, S/N ≥ 10) were 0.1-3.0 µg/kg and 0.5-10.0 µg/kg, respectively. The method is simple, rapid, sensitive, reliable and suitable for the determination of residues in animal products.

A rapid and sensitive method has been developed for the simultaneous determination of 50 veterinary drugs (including macrolides, quinolones, sulfonamides, and tetracyclines) in cheese using a modified QuEChERS method coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS). After adding Na2EDTA buffer solution and ceramic homogenizer, the cheese sample was extracted by 5% (v/v) acetic acid-acetonitrile, sodium chloride and anhydrous sodium sulfate were used for salting-out process. The resulting supernatant solution was purified by C18 sorbent and the re-dissolved solution was analyzed by LC-MS/MS under dynamic multi-reaction monitoring (dynamic MRM) mode via positive electrospray ionization with a ZORBAX-SB-C18 column. The limits of quantification (LOQ, S/N= 10) of the target compounds ranged from 0. 05 µg/kg to 20 µg/kg in cheese. At spiked levels of 20, 50, 100 µg/kg (n =6) , the percentages of drug with a recovery between 70% and 120% were 94%, 92%, and 96%, respectively. The relative standard deviations (RSDs) were between 1% and 14%. This method has been applied to determine seven real samples from markets. Roxithromycin and flumequine have been detected in two samples separately. The results demonstrated that this simple, rapid and accurate method is suitable for the detection of multi-class veterinary drugs in cheese.

An ultra performance liquid chromatography-tandem mass spectrometric method, with modified QuEChERS method for sample preparation, was developed for the determination of the 4 kinds of 29 banned and restricted veterinary drugs in chicken muscle, chicken liver, porcine muscle and porcine liver samples. The drugs were extracted with McIlvaine buffer solution and acetonitrile, then cleaned-up by modified QuEChERS method, and finally analyzed by ultra performance liquid chromatography-tandem mass spectrometry in multiple reaction monitoring mode via positive electrospray ionization. The method was validated at three fortification levels (LOQ level, 20 µg/kg and 50 µg/kg) in chicken muscle, chicken liver, porcine muscle and porcine liver samples. The validation results were as follows. The correlation coefficients of the standard calibration curves for the 29 veterinary drugs were all between 0. 993 and 0. 999 over their own concentration ranges. The average recoveries of the 29 drugs were between 71. 5% and 93. 2%, with the relative standard deviations (RSDs) between 0. 8% and 7. 7%. The limits of determination (S/N=3) of the drugs were between 0. 3 and 3. 0 µg/kg. The limits of quantification (S/N≥10) were 1. 0 µg/kg for amantadine, 10.0 µg/kg for the tetracycline drugs, and 5. 0 µg/kg for all the other drugs. It was indicated that the method developed is easy, sensitive, and has a good purification effect. The sensitivity, accuracy and precision of the method were all acceptable, and it can meet the requirements of the multiple residue analysis. So, this method can be further applied to investigate the veterinary drug residues in animal derived foods.

Matrix effect is an important interfering factor in LC-MS quantitative analysis. In this paper, matrix effects and retention efficiencies of 33 veterinary drugs spiked in river water were studied on hydrophilic-lipophilic balance (HLB) cartridges of 3 brands (Waters, Supelco, and CNW), using LC-MS/MS for detection and reverse osmosis (RO) water as the control under 500-fold concentration. In RO water, only the exogenous matrix effects were observed on three brands of HLB cartridges. Most quinolones and tetracyclines showed positive matrix effects. Estrogens showed negative matrix effects on two brands of HLB cartridges. Sulfonamides were not obviously affected by matrix effects. Chloramphenicols showed negative matrix effects on one brand of HLB cartridge. In river water, matrix effects were different from those of the RO water due to the combined exogenous and endogenous interfering substances. Sulfonamides showed slight matrix effects as those in RO water. Most quinolones and tetracyclines showed positive matrix effects. Chloramphenicols and estrogens showed negative matrix effects. Compared to the external standard method, matrix matched calibration method effectively overcame the matrix effects with better quantitative results. The recoveries of 33 target veterinary drugs spiked in river water at 50 ng/L and 200 ng/L levels were in the ranges of 40.3%-146.0% (Waters), 37.8%-104.2% (Supelco), and 52.9%-150.1% (CNW) with RSDs (n = 4) of 0.2%-14.6%. The results indicated that there was no significant difference in the retention efficiency between the 3 HLB cartridges with the matrix matched calibration method. This study provided supporting data for the HLB cartridge selection in multi-residual determination of the veterinary drugs in river water samples.

An ultra performance liquid chromatography with electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS) method was developed for the simultaneous determination of 29 veterinary drugs of quinolones, sulfonamides, macrolides and nitrofurans in compound feeds. The sample was extracted with methanol-acetonitrile ( 1 : 1, v/v), and then cleaned up using solid phase extraction with an Oasis HLB column, detected by UPLC-ESI-MS/ MS. The UPLC separation was performed on a C18 column (100 mm x 2.1 mm, 1.7 microm) using a gradient elution with the mobile phases of methanol and 0. 1% (v/v) formic acid aqueous solution. The ESI-MS/MS detection was achieved in positive mode under multiple reaction monitoring (MRM) mode. The linear ranges were from 0.01 to 5.0 mg/L with the correlation coefficients above 0. 99 for all the 29 veterinary drugs. The average recoveries of the 29 veterinary drugs spiked in three feed matrixes (the compound premix feed, the complete formula feed and the concentrated feed) at four spiked levels were 61.2% - 94.3% with the relative standard deviations (RSDs) of 2.2% - 15.0%. The limits of detection were 0. 01 mg/kg or 0.05 mg/kg. The method is rapid, accurate, reproducible, sensitive and easy to apply, and suitable for the simultaneous determination of diverse veterinary drugs in compound feeds.

An analytical method was established for the simultaneous determination of 42 pesticides and veterinary drugs in milk by ultra performance liquid chromatography coupled with quadrupole-time of flight mass spectrometry (UPLC-Q-TOF-MS). The target compounds are the commonly used drugs including 13 pesticides and 29 veterinary drugs. The QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) method was used for sample preparation. The analytes in milk samples were extracted with acetonitrile containing 1.0% (v/v) formic acid, and were salted out by adding anhydrous sodium sulfate and potassium chloride. After that, the extract solution was purified by dispersive solid phase extraction with C18 sorbent. In the chromatographic analysis of 42 target compounds were separated on an ACQUITY UPLC BEH C18 column with the gradient elution using the mobile phases of acetonitrile and water containing 0.1% formic acid. MS(E) (where E represents collision energy) acquisition under positive ion mode was performed to obtain accurate relative molecular masses and fragment ions. As a result, the limits of quantification (LOQ, S/N = 10) of the target compounds were from 1 microg/kg to 100 microg/kg in milk. The average recoveries of the 42 analytes spiked at three concentration levels were ranged from 68.2% to 129.1% with the relative standard deviations of 2.8% - 30.8%. This method can be applied to the analysis of the 42 pesticides and veterinary drugs in milk due to its fastness, simplicity and relatively high sensitivity.

A liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI MS/MS) method for the determination of 5 polyether antibiotics (lasalocid, salinomycin, monensin, narasin and maduramicin) in chicken tissues was developed. The polyether antibiotics were extracted from chicken tissues with methanol. The extract was evaporated to dry, and redissolved in hexane, then cleaned up on a Sep-Pak Silica solid-phase extraction cartridge. The target drugs were eluted with 6 mL methylene chloride-methanol (90:10, v/v), and the eluate was collected and dried under a gentle stream of nitrogen gas, then the residue was dissolved with 1 mL acetonitrile (containing 0.1% formic acid) and analyzed by LC-MS/MS. The LC separation was performed on a Symmetry Shield reversed phase C18 bonded silica column with acetonitrile (containing 0.1% formic acid)-0.1% formic acid (97:3, v/v) as mobile phase. The quantification was carried out by positive electrospray ionization and multiple reaction monitoring (MRM) mode. The validation was carried out on spiked chicken muscle (spiked at 0.1 -1500 microg/kg) and chicken liver (spiked at 0.2-4500 microg/kg), the average recoveries of target drugs ranged from 71.6%-99.1% with intra-day relative standard deviations (RSDs) of 3.2%-10.7% and inter-day RSDs of 4.6%-14.7%. The limits of quantification (LOQs) in chicken muscle and liver were 0.1-1.0 kg/kg. The results demonstrated that the sensitivity, accuracy and precision of this method meet the requirements of veterinary drug residue analysis. The method is applicable to detect 5 polyether antibiotics in chicken muscle and liver.

Molecularly imprinted polymers (MIPs) have already appeared as new selective sorbents for solid phase extraction (SPE) of organic compounds in different samples by extracting certain analytes selectively from complex matrices without matrix interference. This review aims to present a summary of the application of MIPs in the solid phase extraction and enrichment of analytes from the environmental samples. The target analytes include pesticides, herbicides, toxins, veterinary drugs, heavy metal ions, endocrine disruptor compounds and other environmental hazards.

Nitrofurans are a group of widely used veterinary antibiotics that have been banned in many countries. This has generated a great deal of interests and demands for assay of nitrofurans in animal food products. To our knowledge, this is the first time that a high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method has been successfully developed for simultaneously analyzing the metabolites of four nitrofuran antibiotics (furazolidone, furaltadone, nitrofurazone and nitrofurantoin) in royal jelly. Trichloroacetic acid solution was used both to precipitate proteins and to provide acidic reaction condition. Four isotope internal standards were utilized to improve the quantitative precision. The limits of detection (LODs) were 0.03 microg/kg for the metabolite of furaltadone and 0.05 microg/kg for the other three metabolites. The limits of quantitation were 0.20 microg/kg for the metabolite of furaltadone and 0.25 microg/kg for the other three metabolites. The linear range was 0.4-20 ng/mL for all the target analytes. The recoveries calibrated by internal standard were in the range of 97.7%-104.8 with the relative standard deviations (RSDs) of 2.7-9.7. It showed that this method could meet the requirements of national monitoring plan in China and the Minimum Required Performance Limits (MRPL) set by the European Union.

A sensitive and selective method is presented for simultaneous determination of tetracycline antibiotics (TCs) veterinary drugs. Oxytetracycline (OTC), tetracyclines (TC) and chlortetracycline (CTC) in the chicken muscle were extracted, and then solid-phase cleaned-up on a C18 reversed-phase column to obtain an extract suitable for analysis by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Electrospray ionization was applied and operated in the positive ion mode. The calibration curves were good linear between the peak areas and the mass concentrations of TCs from 25 to 500 microg/L with the correlation coefficient more than 0.99. The average recoveries from spiked chicken muscle at the three concentrations of 50, 100 and 200 microg/kg were from 72.4% to 94.9% with relative, standard deviation less than 11%. The detection limits of TCs were 10 microg/kg. The method was successfully validated for chicken muscle in compliance with the requirements set by Document No. 1 of 2003 dispatched by the Bureau of Animal Husbandary of Ministry of Agriculture. This method is suitable for the determination of OTC, TC and CTC in chicken muscle.

A method for rapid determination of oxolinic acid residues in baked eels and fresh eels by high performance liquid chromatography without derivatization was studied. The samples were triturated, and extracted with methylene dichloride. The extracted solutions were evaporated to dryness, and then was dissolved by using the mobil phase. The solutions were cleaned-up by partition with n-hexane before analysis. The components were analysed on a Nova-Pak C18 column (150 mm x 3.9 mm i.d., 5 microm), with methanol-diluted phosphoric acid (pH 2.5) (40:60, V/V) as the mobile phose at a flow rate of 0.8 mL/min and detected by a fluorescence detector at the excitation wavelength (lambdaex) 254 nm and the emission wavelength (lambdaem) 375 nm. The detection limit was 0.01 mg/kg (S/N = 3). The recoveries were over 80 %, and the relative standard deviations (RSDs) were less than 3.8%.