Quantitative analysis of polypeptide antibiotic residues in a variety of food matrices by liquid chromatography coupled to tandem mass spectrometry

Analysing polypeptide antibiotics residues in animal muscle tissues: The crucial role of HRMS

A confirmatory method for the determination of polypeptide antibiotics (bacitracin, colistin, and polymyxin B) in muscle samples has been developed. Extraction is performed with acidified methanol, and a clean-up step by solid-phase extraction with polymeric cartridges is applied. Separation by ultra-high performance liquid chromatography (UHPLC) is carried out using a solid core C18 column and gradient elution with water/acetonitrile containing 0.2% formic acid. High-resolution mass spectrometry (HRMS) (Q-Orbitrap) detection using different working modes has proved to be highly advantageous in eliminating interfering signals from endogenous matrix components. The analytical method has been successfully validated according to Commission Regulation 2021/808/EU and is currently used in a public health laboratory involved in veterinary medicines residue surveillance activities.

Multiresidues Multiclass Analytical Methods for Determination of Antibiotics in Animal Origin Food: A Critical Analysis

Veterinary drugs are widely used to prevent and treat diseases. The European Union has forbidden the use of antibiotics as growth promoters since 2006. Its abusive use leads to the presence of antibiotic residues (AR) in foods of animal origin which is associated with antibiotic resistance. The monitoring of AR in food intended for human consumption is of utmost importance to assure Food Safety. A systematic bibliographic review was carried out on the analytical methodologies, published in 2013, for the determination of AR in foods of animal origin. The food processing effect in the AR detected in animal products is also addressed. However, there is a preference for multiresidues multiclass methods, i.e., methodologies that allow determining simultaneously different classes of antibiotics, which is still a challenge for researchers. The wide diversity of physico-chemical properties of these drugs is an obstacle to achieving excellent analytical performance for a vast number of molecules analyzed concurrently. New techniques in sample preparation continue to be developed in order to obtain a compromise between good recoveries and extracts without interferences (clean extracts). The most widely used analytical methodology for the determination of AR is liquid chromatography coupled with mass spectrometry. However, the current trend is focused on the use of powerful high-resolution MS detectors such as Time of Flight and Orbitrap with modern chromatographic systems. Cooking time and temperature control are the key processing conditions influencing the reduction of AR in foods.

Pretreatment Methods for the Determination of Antibiotics Residues in Food Samples and Detected by Liquid Chromatography Coupled with Mass Spectrometry Detectors: A Review

With the increasing use of antibiotics worldwide, antibiotic monitoring has become a topic of concern. After metabolizing of antibiotics in animals, the metabolites enter the environment through excreta or ingested by the human body via food chain that may exacerbate the emergence of antibiotic resistance and then threaten human's life. This article summarized several analytical methods used for the determination of antibiotics in recent 10 years. Due to the complex matrices and low concentration level of antibiotics in the food samples, a reliable analysis method is required to maximize the recovery rate. Several techniques like solid phase extraction (SPE), dispersive liquid-liquid microextraction (DLLME) and QuEChERS have been frequently used in the pretreatment process for analytes extraction and concentration. After the pretreatment, ultra-high performance liquid chromatography combined with mass spectrometry has been a reliable method for quantitative analysis and is able to determine multiple antibiotics simultaneously. This review also gives an overview about analytical conditions for antibiotics residues in different food samples and their method validation parameters.

Quantum dot-based fluorescence immunosorbent assay for the rapid detection of bacitracin zinc in feed samples

Bacitracin zinc (BAC), a polypeptide antibiotic, is utilized as a feed additive due to its ability to promote growth in animals. However, the abuse of BAC can lead to a great threat to food safety. Therefore, there is an urgent need to develop a rapid and sensitive detection method. In this study, a monoclonal antibody (mAb) against BAC with excellent sensitivity and specificity was obtained. For the first time, quantum dots (QDs) were conjugated with the prepared mAb against BAC and rabbit anti-mouse antibody to fabricate a direct and an indirect competitive fluorescence-linked immunosorbent assay (dc-FLISA and ic-FLISA) to detect BAC. The IC₅₀ of dc-FLISA and ic-FLISA were 0.28 ng/ml and 0.17 ng/ml, respectively. The limits of detection were 0.0016 ng/ml and 0.001 ng/ml, respectively, and the detection ranges were 0.0016-46.50 ng/ml and 0.001-35.65 ng/ml, respectively. In addition, the recovery rate of the two methods ranged from 93.5% to 112.0%, and the coefficient of variation (CV) was less than 10%. Therefore, the methods developed in this work have the merits of low cost, simple operation, and high sensitivity, which provide an effective analytical tool for BAC residue detection in feed samples.

Direct determination of nosiheptide residue in animal tissues by liquid chromatography-tandem mass spectrometry

Because only very weak signals of fragment ions of nosiheptide can be obtained, nosiheptide is usually detected by liquid chromatography-tandem mass spectrometry (LC-MS/MS) via the determination of its hydrolyzed degradation product named HMIA in previous studies. The indirect method suffers from several problems, such as complicated samplepreparation, unavailable commercial HMIA, and the risk of the false-positive result by HMIA. However, we found that nosiheptide could produce several significant fragment ions under high collision energy (CE). Therefore, we developed a method for the direct determination of nosiheptide by LC-MS/MS in animal tissues. The sample was extracted with ACN, then degreased with n-hexane, and purified by an HLB solid-phase extraction (SPE) cartridge. After being filtered through the PTFE filter, it was analyzed by LC-MS/MS in selected reaction monitoring (SRM) mode. The influencing factors, such as mobile phase, SPE cartridge, filter material, and matrix effect, were investigated. Nosiheptide showed a good linear relationship (R2 ≥ 0.999) within the concentration range from 0.3 μg/L to 20 μg/L under optimized conditions. The limit of detection (LOD) was 0.3 μg/kg, while the limit of quantification (LOQ) was 1.0 μg/kg in chicken, bovine muscle, swine muscle, and swine liver. The average recoveries at spiked levels of 1.0, 2.0, and 10 μg/kg ranged from 83% to 101%, with the relative standard deviations (RSDs) <12%. Compared with the methods previously reported, our newly developed method was more simple, convenient, and sensitive. Moreover, it was successfully applied for the determination of nosiheptide residue in medicated chicken samples.

Development of a liquid chromatography-tandem mass spectrometry method to determine colistin, bacitracin and virginiamycin M1 at cross-contamination levels in animal feed

Cross-contamination of animal feed with antibiotics may occur during manufacturing in feed mills, because shared production lines can be used for medicated and non-medicated feed, but may also occur during transport, storage and at the farm level. This is a major issue in the current context where antimicrobial usage must be controlled in order to maintain their effectiveness. A LC-MS/MS method was developed for the determination of colistin, bacitracin A and virginiamycin M1 in feed for pigs, poultry and rabbits at concentrations similar to those encountered in cross-contamination. After investigating various issues related to colistin behaviour and matrix effects, we successfully validated this method according to the requirements of European regulations in terms of linearity, trueness, precision, limit of quantification and limit of decision. Trueness ranged 88.6-107.8% and precision ranged 12.6-21.2%. We then applied this method to the analysis of medicated pig feed to check the performance of the method on "real" samples of medicated feed. We subsequently analysed non-medicated pig, and rabbit feed samples, collected directly on farms, to check the rate of cross-contamination. No samples were contaminated by colistin, bacitracin, or virginiamycin.

Resistance Detection and Transmission Risk Analysis of Pig-Derived Pathogenic Escherichia coli in East China

Objective: Antibiotics play an essential role in the treatment and prevention of diseases in pig farms. However, the irrational use of antibiotics leads to the emergence of multi-drug resistance of bacteria, which poses a critical threat to the efficacy of antibiotic treatments. Therefore, the study is designed to analyze the drug resistance of pathogenic Escherichia coli isolated from large-scale pig farms in East China, which provides a theoretical basis for precisely targeted clinical drugs in swine farms. Method: The pathogenic E. coli were isolated and identified from clinical samples of swine farms, and the drug resistance of pathogenic E. coli was detected by antimicrobial susceptibility test (AST) and minimum inhibitory concentration test (MIC). Moreover, the prevalence of plasmid-mediated β-lactam resistance genes was analyzed by PCR. Results: A total of 67 pathogenic E. coli were isolated from 152 samples collected from 20 large-scale pig farms in East China. All isolated pathogenic E. coli are associated with severe drug resistance. Moreover, 70% of isolated pathogenic E. coli is resistant to more than four antibiotics. Besides, there were 19 serotypes including O2, O4, O5, O6, O14, O26, O38, O42, O49, O57, O92, O93, O95, O101, O121, O131, O143, O158, and O161, of which the O4 and O92 serotype were the main serotypes in swine farms. The main extended-spectrum beta-lactamases (ESBLs)-encoding genes in East China were bla _CTX-M, bla _TEM, and bla _OXA by the detection of the ESBLs encoding genes of porcine pathogenic E. coli. The conjugation assays showed that a total of 30 transconjugants were obtained by conjugation, which indicated that drug resistance genes could be transmitted horizontally through conjugative plasmids. Conclusion: The isolated pathogenic E. coli were all multi-drug resistant, and especially O4 and O92 were the main serotypes. The β-lactam resistance genes were prevalent in large-scale pig farms in East China, which provided a theoretical basis for the prevention and control of pig-derived pathogenic E. coli in the future.

Determination of Colistin in Contents Derived from Gastrointestinal Tract of Feeding Treated Piglet and Broiler

Colistin is considered as the last-resort treatment for multiantibiotic-resistant Gram-negative bacterial infections in humans. However, the oral administration of colistin to livestock and poultry results in the introduction of large amounts of colistin to the surrounding environment via urine and feces, potentially inducing the prevalence of colistin-resistant bacteria and the impact on the ecological environment. We established a quantitative mass spectrometry (MS) based method to measure colistin in contents recovered from the gastrointestinal segments of piglets and broilers, as well as colistin in feces from the animals. The mean recoveries of colistin from different matrices were between 73.2% and 103.9%. The quantitation limit values for different matrices ranged from 0.37 to 1.85 ng/g. In colistin-treated swine samples, the highest concentration of colistin was detected in feces samples at a level of 1248.3 ng/g. However, the highest concentration of colistin in broiler samples was around 4882.9 ng/g, which was found in the contents derived from broilers' ceca. The employment of the proposed method to assess colistin in animals' gastrointestinal tracts might help to understand the colistin absorption in animals' guts and the potential impact of colistin on the emergence of resistant bacteria in animals' gut flora and the ecological environment.

A rapid multiclass method for antibiotic residues in goat dairy products by UPLC-quadrupole/electrostatic field orbitrap high-resolution mass spectrometry

Background

Sulfanilamides, quinolones, nitroimidazoles, tetracyclines, cephalosporins, macrolides, and β-lactam are common tools in agriculture and can be found in animal-based foods such as goat milk and goat dried milk. To evaluate the risk of these species, reliable analytical methods are needed for accurate concentration determination, especially in goat milk and goat dried milk.

Method

We describe a method based on PRiME extraction coupled with UPLC-quadrupole/electrostatic field orbitrap high-resolution mass spectrometry to accomplish this task.

Result

Under optimal conditions, the limit of quantification for all antibiotics was 0.5–100 μg/L in goat milk and goat dried milk samples. The recoveries were 60.6–110.0% for goat milk and 60.1–109.6% for goat dried milk with a coefficient of variation less than 15%. The detection limits were 0.5–1.0 μg/kg. The limits of quantification for the analytes were 5.0–10.0 μg/kg. Finally, the method was used to screen veterinary antibiotics in 50 local goat milk and goat dried milk samples; metronidazole and enrofloxacin were detected in goat milk.

Conclusion

This method offers good reliability and the capacity for simultaneous detection can be used to detect residual contents and evaluate health risks in goat milk and goat dried milk.

Detection of a novel glycodelin biomarker using electrochemical immunosensor for endometriosis

Endometriosis is one of the important issues in women worldwide, which decreases the quality of women's lives in their reproductive age. The diagnosis of endometriosis is carried out by the invasive procedure, which is expensive and painful. In the last few decades, researchers have given more attention to constructing a suitable biomarker-based biosensor for semi/non-invasive diagnosis of endometriosis. As a result, glycodelin (GLY) was found as a promising biomarker because of its selectivity and sensitivity. To the best of our knowledge, it was the first study that reported the detection of GLY biomarker using an electrochemical immunosensor. Briefly, a label-free electrochemical immunosensing platform was constructed through in-situ surface modification of cysteamine layer and immobilisation of antibody (anti-GLY) with help of glutaraldehyde. The interaction between antigen and antibody was measured using square wave voltammetry (SWV). The SWV signal could decrease proportionally with the increasing GLY concentration ranging from 1 to 1000 ng mL^-1 (R² = 0.9981) and a detection limit (LOD) of 0.43 ng mL^-1. Moreover, an immunosensor could exhibit high sensitivity, selectivity, long-term stability, reproducibility and regeneration. Accuracy of the immunosensor was compared with enzyme-linked immunosorbent assay (ELISA), and satisfying results were obtained. The detection of GLY biomarker may be a new possibility for endometriosis diagnosis.

Understanding of Colistin Usage in Food Animals and Available Detection Techniques: A Review

Progress in the medical profession is determined by the achievements and effectiveness of new antibiotics in the treatment of microbial infections. However, the development of multiple-drug resistance in numerous bacteria, especially Gram-negative bacteria, has limited the treatment options. Due to this resistance, the resurgence of cyclic polypeptide drugs like colistin remains the only option. The drug, colistin, is a well-known growth inhibitor of Gram-negative bacteria like Acinetobacter baumanni, Enterobacter cloacae, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Technological advancements have uncovered the role of the mcr-1(mobilized colistin resistance) gene, which is responsible for the development of resistance in Gram-negative bacteria, which make them distinct from other bacteria without this gene. Additionally, food animals have been determined to be the reservoir for colistin resistance microbes, from which they spread to other hosts. Due to the adverse effects of colistin, many developed countries have prohibited its usage in animal foods, but developing countries are still using colistin in animal food production, thereby imposing a major risk to the public health. Therefore, there is a need for implementation of sustainable measures in livestock farms to prevent microbial infection. This review highlights the negative effects (increased resistance) of colistin consumption and emphasizes the different approaches used for detecting colistin in animal-based foods as well as the challenges associated with its detection.

Evaluation of three ELISA kits for the screening of colistin residue in porcine and poultry muscle according to the European guideline for the validation of screening methods

Colistin is a polypeptide antibiotic mainly used in porcine and poultry to treat gastrointestinal infections. It has been included by the World Health Organisation (WHO) in the list of critically important human antibiotics of high priority for antimicrobial resistance since 2017. Therefore, it is necessary to develop specific and sensitive screening methods for this molecule. Screening for colistin with immunoassays is an interesting alternative to LC-MS/MS screening methods. The performance of three commercially available ELISA kits was evaluated in poultry and porcine muscles for the detection of colistin in regards to its European maximum residue limit (MRL) (150 µg/kg). The applicability of the three ELISA kits to the detection of colistin at or below the MRL in porcine and poultry muscles was demonstrated. The detection capabilities (CCβ) of two kits were or lower than or equal to the MRL (150 µg/kg). The lowest detection capability (30 µg/kg) was achieved with the third ELISA kit. The specificity of the three kits was very satisfactory (false positive rates 0%). The three kits are very specific for the detection of colistin (colistin A and B) and polymyxin B.

Analysis of peptide antibiotic residues in milk using liquid chromatography-high resolution mass spectrometry (LC-HRMS)

A liquid chromatography-high resolution mass spectrometry (LC-HRMS) method was developed and validated for the determination of residual peptide antibiotics (bacitracin A, colistin A and B, enramycin A and B, virginiamycin M1 and S1) in bovine milk. LC-HRMS accurate mass data provided the necessary selectivity and sensitivity to quantitate and identify these important antibiotics in milk at residue levels without extensive sample preparation. Milk samples were extracted using 0.3% formic acid in acetonitrile with 0.06% trifluoroacetic acid added to improve peptide recoveries. Sample clean-up was minimal with an aliquot of the extract evaporated and reconstituted in a formic acid/water-acetonitrile mixture and then filtered. LC separation was performed with 0.3% formic acid in the gradient to improve the peak shape and reproducibility of the peptide analytes. A Quadruple-Orbitrap HRMS instrument with full-scan MS1 data collection followed by all-ion-fragmentation was used to obtain the exact mass of the precursor and confirmatory product ions. One advantage of LC-HRMS is that a combination of multiple precursor ions, including different charge states or adducts, can be used for quantification. The method was validated at four concentration levels ranging from 12.5 to 200 ng/g in three types of bovine milk. For bacitracin A, colistins and enramycins, the average recoveries compared to solvent standards ranged between 70% and 120%. Average recoveries for virginiamycin residues in milk extracts were unacceptably high (up to 138%) using solvent standards, but recoveries using matrix-matched calibration were determined to be 90-115%. Matrix effects were found to be less than 25% for the other analytes when internal standard correction was used for the colistins. Intra-day relative standard deviations were generally below 15%. The method detection limits for the peptide antibiotic residues in milk (0.5 to 5.5 ng/g) were well below regulatory levels of concern.

Determination of Polypeptide Antibiotic Residues in Food of Animal Origin by Ultra-High-Performance Liquid Chromatography-Tandem Mass Spectrometry

A novel UHPLC-MS/MS method for the determination of polypeptide antibiotic residues in animal muscle, milk, and eggs was developed and validated. Bacitracin A, colistin A, colistin B, polymyxin B1, and polymyxin B2 were extracted from the samples with a mixture of acetonitrile/water/ammonia solution 25%, 80/10/10 (v/v/v), and put through further evaporation, reconstitution, and filtration steps. The chromatographic separation was performed on a C18 column in gradient elution mode. Mass spectral acquisitions were performed in selective multiple reaction monitoring mode by a triple quadrupole mass spectrometer. The method was validated according to the criteria of Commission Decision 2002/657/EC. The method quantifies polypeptides in a linear range from 10 to 1000 μg kg⁻¹, where the lowest concentration on the calibration curve refers to the limit of quantification (LOQ). The recoveries ranged from 70 to 99%, the repeatability was below 13%, and within-laboratory reproducibility was lower than 15%. The decision limit (CCα) and detection capability (CCβ) values were calculated, and ruggedness and stability studies were performed, to fulfill the criteria for confirmatory methods. Moreover, the developed method may also be used for screening purposes by its labor efficiency.

Colloidal gold-based immunochromatographic strip assay for the rapid detection of bacitracin zinc in milk

In this study, a murine monoclonal antibody (mAb) of 6D2-G10 against bacitracin zinc (BAC) was produced and applied to an immunochromatographic strip (ICS) for the initial detection of BAC in milk. The ICS with a cut-off value of 25 ng/mL could be perceived by the naked eye within 10 min. With the assist of the strip reader, the limit of detection (LOD) was measured as 0.82 ng/mL, the half-maximal inhibitory concentration (IC₅₀) was recorded as 3.16 ng/mL, and the linear detection range was from 0.97 to 10.30 ng/mL. The recoveries ranged from 87.7% to 96.0% with the highest coefficient of variation (CV) of 9.1% in the intra-assay and from 84.3% to 90.2% with the highest CV of 10.7% in the inter-assay. In short, the established ICS provided a serviceable analytical tool for qualitatively and quantitatively monitoring BAC in milk.

Synthesis of Molecularly Imprinted Polymers for the Selective Extraction of Polymyxins from Environmental Water Samples

The emergence of colistin resistance gen has aroused public concern. It is significant to assess the concentrations of polymyxins residues in aquatic environment since resistant bacteria carrying colistin resistance gen are frequently isolated from wastewater; surface water and ground water. However; no literature on the determination of polymyxins in water is available; probably due to the absence of an efficient extraction method. Accordingly; molecularly imprinted polymers were synthesized by precipitation polymerization with colistin as the template. The polymers were successfully used as sorbents for the determination of polymyxins from water based on molecularly imprinted solid-phase extraction and high-performance liquid chromatography-ultraviolet detection. The molecularly imprinted cartridge showed excellent affinity and cross-reactivity to analytes in aqueous media. Recoveries obtained from water samples were between 65.9% and 90.1%, with relative standard deviations lower than 10.2%. Limits of detection were between 1.0 and 2.0 μg L^-1 concentration levels. Compared with C₁₈ cartridge; the molecularly imprinted cartridge could remove more interference from co-extracted matrices. This method is practical for the routine monitoring of polymyxin residues in environmental water; which will benefit studies on drug-resistance and occurrence of polymyxins in the environment.

Antibiotic residues in milk: Past, present, and future

Now-a-days, various types of antibiotics are being used worldwide in veterinary sector indiscriminately for promotion of growth and treatment of the livestock. Significant portions of antibiotics are released through milk of dairy animals unaltered and exert serious harmful effects on human health. This review evaluates and compare researches on antibiotic residues in milk in published literatures from Pubmed, CrossRef, CAB direct, DOAJ, JournalTOCs, AGRICOLA, ScientificGate, Electronic Journals Library, CAB abstracts, Global Health Databases, Global Impact Factor, Google Scholar, Park Directory of Open Access Journals, BanglaJOL and ISC E-Journals. Antibiotics residue in milk was first detected in 60s and then with an increasing trend with highest after 2,000 (188). The highest no. of works, 49 (21.87%) were accomplished in China, followed by Spain, 30 (13.39%); Germany, 11 (4.91%); and USA, 10 (4.46%). Continent-wise highest researches are published from Europe, 105 (46.88%), followed by Asia, 77 (34.38%); South America, 18 (8.04%); North America, 16 (7.14%); and Africa, 8 (3.57%). For detection, Bovine milk sample is mostly used, 193 (86.16%), followed by ovine, 19 (8.48%); and caprine, 14 (6.25%). Acetonitrile was used in maximum cases (77) for processing the samples. Chromatographic technique was the highest, 115 (51.34%) for detection. Residue of β-lactam group have been detected mostly 133 (36.54%), followed by tetracyclines, 51 (14.01%); fluoroquinolones, 49 (13.46%); sulfonamides, 46 (12.64%); and aminoglycosides, 38 (10.44%). This review observe that antibiotics residues are more common in milk samples that are being manifested in increasing researches on antibiotic detection and measures should adopt to cease this residue.

Freeze-thaw approach: A practical sample preparation strategy for residue analysis of multi-class veterinary drugs in chicken muscle

Seven drugs from different classes, namely, fluoroquinolones (enrofloxacin, ciprofloxacin, sarafloxacin), sulfonamides (sulfadimidine, sulfamonomethoxine), and macrolides (tilmicosin, tylosin), were used as test compounds in chickens by oral administration, a simple extraction step after cryogenic freezing might allow the effective extraction of multi-class veterinary drug residues from minced chicken muscles by mix vortexing. On basis of the optimized freeze-thaw approach, a convenient, selective, and reproducible liquid chromatography with tandem mass spectrometry method was developed. At three spiking levels in blank chicken and medicated chicken muscles, average recoveries of the analytes were in the range of 71-106 and 63-119%, respectively. All the relative standard deviations were <20%. The limits of quantification of analytes were 0.2-5.0 ng/g. Regardless of the chicken levels, there were no significant differences (P > 0.05) in the average contents of almost any of the analytes in medicated chickens between this method and specific methods in the literature for the determination of specific analytes. Finally, the developed method was successfully extended to the monitoring of residues of 55 common veterinary drugs in food animal muscles.

Analysis of Major Components of Bacitracin, Colistin and Virginiamycin in Feed Using Matrix Solid-phase Dispersion Extraction by Liquid Chromatography-electrospray Ionization Tandem Mass Spectrometry

A quantitative LC-MS/MS method has been developed for simultaneous determination of bacitracin A, bacitracin B, colistin A, colistin B and virginiamycin M1 in feed. This rapid simple and effective extraction method was based on matrix solid-phase dispersion. Qualitative and quantitative analyses were performed by LC-ESI-MS/MS. CCβ of polypeptide antibiotics upon the method ranged from 9.6 to 15.8 μg kg-1 and 19.4 to 27.5 μg kg-1, respectively. The limit of quantification of polypeptide antibiotics was 25 μg kg-1 in feed samples. The recoveries of polypeptide antibiotics spiked in feed samples at a concentration range of 25-100 μg kg-1 were found above 75.9-87.9% with relative standard deviations within days less than 15.7% and between days less than 20.6%. This rapid and reliable method can be used to efficiently separate, characterize and quantify the residues of polypeptide antibiotics in feed with advantages of simple pretreatment and environmental friendly.

Simultaneous determination of eight cyclopolypeptide antibiotics in feed by high performance liquid chromatography coupled with evaporation light scattering detection

A high throughput, reliable and reproducible analysis strategy based on high performance liquid chromatography combined to evaporative light scattering detector (HPLC-ELSD) was developed for simultaneous determination of eight cyclopolypeptide antibiotics including vancomycin, polymyxin B (polymyxin B1 and polymyxin B2), polymyxin E (colistin A and colistin B), teicoplanin, bacitracin A, daptomycin and virginiamycin M1 in animal Feed. Feed samples were extracted with methanol-2% formic acid aqueous solution, followed by a solid-phase extraction step using a HLB cartridge. Under the optimum chromatographic conditions and ELSD parameters, target compounds were separated well on a short column filled with biphenyl stationary phase. The method was developed in accordance with pig complete feed and then extended to detect polypeptide antibiotics in piglet premix, pig feed additive, poultry complete feed and fattening pig premix. The results showed that logarithmic calibration curves of eight analytes were linear (r² > 0.99) within the concentration range of 5-200 mg mL^-1. The developed method provided good accuracy and precision for quantification of eight polypeptides in five kinds of feeds with recoveries ranging from 72.0% to 105.4% with relative standard deviations <9.5%. The limits of detection ranged from 2 to 5 mg kg^-1. Finally, the method was successfully applied to analyze polypeptide antibiotics in commercial feed.

Fast gradient HPLC/MS separation of phenolics in green tea to monitor their degradation

The degradation of catechins and other phenolics in green tea infusions were monitored using fast HPLC/MS separation. The final separation was performed within 2.5min using Ascentis Express C18 column (50mm×2.1mm i.d.) packed with 2μm porous shell particles. Degradation was studied in relation to the temperature of water (70, 80, 90°C) and the standing time of the infusion (up to 6h). Along with chromatographic separation, the antioxidant properties of the infusions were monitored using two spectrophotometric methods. During staying of green tea infusion, the degradation of some catechins probably to gallic acid was observed. Finally, the influence of tea bag storage on antioxidant properties of green tea was evaluated. Rapid degradation of antioxidants after 3weeks was observed. The principal component analysis, factor analysis and discriminant analysis were used for the statistical evaluation of obtained experimental data.

Development and validation of rapid multiresidue and multi-class analysis for antibiotics and anthelmintics in feed by ultra-high-performance liquid chromatography coupled to tandem mass spectrometry

A new multi-residue method for the analysis of veterinary drugs, namely amoxicillin, chlortetracycline, colistins A and B, doxycycline, fenbendazole, flubendazole, ivermectin, lincomycin, oxytetracycline, sulfadiazine, tiamulin, tilmicosin and trimethoprim, was developed and validated for feed. After acidic extraction, the samples were centrifuged, purified by SPE and analysed by ultra-high-performance liquid chromatography coupled to tandem mass spectrometry. Quantitative validation was done in accordance with the guidelines laid down in European Commission Decision 2002/657/CE. Matrix-matched calibration with internal standards was used to reduce matrix effects. The target level was set at the authorised carryover level (1%) and validation levels were set at 0.5%, 1% and 1.5%. Method performances were evaluated by the following parameters: linearity (0.986 < R(2) < 0.999), precision (repeatability < 12.4% and reproducibility < 14.0%), accuracy (89% < recovery < 107%), sensitivity, decision limit (CCα), detection capability (CCβ), selectivity and expanded measurement uncertainty (k = 2).This method has been used successfully for three years for routine monitoring of antibiotic residues in feeds during which period 20% of samples were found to exceed the 1% authorised carryover limit and were deemed non-compliant.

Core-Shell Columns in High-Performance Liquid Chromatography: Food Analysis Applications

The increased separation efficiency provided by the new technology of column packed with core-shell particles in high-performance liquid chromatography (HPLC) has resulted in their widespread diffusion in several analytical fields: from pharmaceutical, biological, environmental, and toxicological. The present paper presents their most recent applications in food analysis. Their use has proved to be particularly advantageous for the determination of compounds at trace levels or when a large amount of samples must be analyzed fast using reliable and solvent-saving apparatus. The literature hereby described shows how the outstanding performances provided by core-shell particles column on a traditional HPLC instruments are comparable to those obtained with a costly UHPLC instrumentation, making this novel column a promising key tool in food analysis.

Signal suppression can bias selected reaction monitoring ratios. Implications for the confirmation of positive findings in residue testing

RATIONALE

Selected reaction monitoring (SRM) ratios based on two or more transitions are commonly used to confirm the identity of a suspected finding in residue testing. International norms like the EU directive commission decision 2002/657/EC (CD) require the use of such ratios to prove the unequivocal identification of a particular compound detected at trace level (confirmation of a suspected residue).

METHODS

In this study, the relative abundances of different precursor ions (e.g. protonated molecule, solvent adducts, characteristic fragment ions or multiply charged ions) derived from the same analyte molecule were found to be differently (asymmetrically) affected by matrix-related signal suppression effects. This observation was made when analyzing veterinary drug residues (colistin and amoxicillin) in animal tissue extracts.

RESULTS

The term 'asymmetric signal suppression' was coined since different ionic species produced from the same analyte molecule are differently (asymmetrically) suppressed by co-eluting matrix compounds. In the case of the colistin assay, the extent of asymmetric signal suppression is such that the measured SRM ratios lie beyond the defined (CD) tolerances. Hence, the compound present in a sample cannot be confirmed.

CONCLUSIONS

The [M+H](+) ion may be the most commonly used precursor ion in liquid chromatography coupled to electrospray operated in the positive ionization mode. However, the absence of a sufficiently intensive confirmation transition frequently leads to the selection of another precursor ion to be utilized for the confirmation transition. The SRM ratio derived from such transitions should not be compared to the SRM ratio derived from pure standard solutions but spiked blank matrix extracts.