Food safety evaluation: Detection and confirmation of chloramphenicol in milk by high performance liquid chromatography-tandem mass spectrometry

A new semiconductor heterojunction SERS substrate for ultra-sensitive detection of antibiotic residues in egg

Antibiotic residues in animal-derived food (egg) are threatening human health. Semiconductor heterojunction surface-enhanced Raman scattering (SERS) substrates can be used for ultra-sensitive detection of antibiotic residues in egg. Here, a TiO2/ZnO heterojunction was developed as a new SERS substrate based on an interface engineering strategy. Due to strong interfacial coupling and efficient carrier separating in heterostructure, utilization rate of photo-induced electrons in substrate was improved greatly, which realized the efficient charge transfer in substrate-molecule system, resulting in a prominent SERS enhancement. Taking the detection of enrofloxacin residue in egg as an example, the limit of detection (LOD) is only 13.1 μg/kg, which is far below the European Union standard, and lower than LODs of other conventional analytical methods and existing noble metal-based SERS methods. More importantly, benefiting from high sensitivity and selectivity of heterojunction and fingerprint characteristics of SERS, multiple antibiotic residues in egg can be identified simultaneously.

Recent Advances in and Applications of Electrochemical Sensors Based on Covalent Organic Frameworks for Food Safety Analysis

The international community has been paying close attention to the issue of food safety as a matter of public health. The presence of a wide range of contaminants in food poses a significant threat to human health, making it vital to develop detection methods for monitoring these chemical contaminants. Electrochemical sensors using emerging materials have been widely employed to detect food-derived contaminants. Covalent organic frameworks (COFs) have the potential for extensive applications due to their unique structure, high surface area, and tunable pore sizes. The review summarizes and explores recent advances in electrochemical sensors modified with COFs for detecting pesticides, antibiotics, heavy metal ions, and other food contaminants. Furthermore, future challenges and possible solutions will be discussed regarding food safety analysis using COFs.

A Visible Light Driven Photoelectrochemical Chloramphenicol Aptasensor Based on a Gold Nanoparticle-Functionalized 3D Flower-like MoS2/TiO2 Heterostructure

Developing a photoactive material by combining the characteristics of a wide light response range and effective separation of photogenerated electron-hole pairs remains a huge challenge for the construction of a photoelectrochemical (PEC) sensing platform. Herein, a gold nanoparticle (AuNP)/MoS₂/TiO₂ composite was prepared through the facile hydrothermal method coupled with an in situ photoreduction technology. Benefiting from both the compositional and structure merits, the composite not only extends the absorption range to visible light but also enhances the photoelectric conversion efficiency by transferring photogenerated electrons into the conduction band of semiconductors from the plasmonic AuNP. Meanwhile, the thiolated aptamers were attached to the surface of AuNP/MoS₂/TiO₂ composites through the Au-S bonding to construct a visible light driven PEC aptasensor for ultrasensitive detection chloramphenicol (CAP). In the presence of CAP, the aptamers anchored on the surface of the photoactive materials could specifically recognize CAP and interact with it to form a bioaffinity complex with a steric hindrance effect, resulting in the rapid decrease of photocurrent responses. Based on this photocurrent suppression strategy, the constructed PEC aptasensing platform exhibited a high sensitivity with a wide linear range from 5 pM to 100 nM and a low detection limit of 0.5 pM.

Determination of chloramphenicol in meat samples using liquid chromatography-tandem mass spectrometry

Chloramphenicol (CAP), a bacteriostatic antibiotic, is used for the treatment of bacterial infections in human and animals. Continual exposure of CAP residues into animal tissues may lead to antibiotic resistance. For the protection of humans and animals from this problem, a fast and highly sensitive analytical method based on ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) was developed and validated in this study for the quantitative determination of CAP in poultry meat and beef samples. Quick, easy, cheap, effective, rugged, and safe (QuEChERS) method was used for the extraction of CAP residues. The developed method was validated in terms of linearity, accuracy, precision, and specificity. Poultry meat and beef samples were extracted with 20 ml water-acetonitrile (1:1, v/v) and cleaned up by MgSO4, primary secondary amine, and C18 powder. The method was found to be linear in a wide concentration range, with correlation coefficient of higher than 0.999. The repeatability and reproducibility of this method were satisfactory. The achieved limit of detection and limit of quantification were 0.16 and 0.50 ng/g, respectively. Recoveries were estimated at 5 and 10 ng/g spiking levels in the range of 99%-111% with the coefficient of variation 0.48%-12.48% for spiked samples, and the matrix enhancement effects were mild in the range of 80%-85%. In this study, the levels of CAP residue in tested real samples were found below the detection limit. The method proved to be suitable for CAP determination in all kinds of samples tested and also efficient for the application of routine analysis.

A single method to analyse residues from five different classes of prohibited pharmacologically active substances in milk

In the European Union, the use of veterinary drugs belonging to the A6 group is prohibited in food-producing animals according to Commission Regulation (EU) No. 2010/37. The aim of this study was to improve the analytical control strategy by developing a single method to analyse residues of prohibited pharmacologically active substances in milk. For this, a single method was developed to analyse 16 prohibited pharmacologically active substances belonging to five different substance classes at required or recommended levels: nitroimidazoles at 3 μg kg^-1, nitrofurans at 0.5 μg kg^-1, chloramphenicol at 0.1 μg kg^-1, dapsone at 5 μg kg^-1 and chlorpromazine at 1 μg kg^-1. Milk sample preparation started with an acid hydrolysis combined with a derivatisation. These steps were followed by a clean-up consisting of a dispersive solid-phase extraction and a liquid-liquid extraction. Finally, the sample extracts were analysed by liquid chromatography combined with tandem mass spectrometry, operating alternately in the positive and negative mode. The method was fully validated according to Commission Decision 2002/657/EC for bovine milk and additionally validated for caprine milk. The validation proved that the method is highly effective to detect and confirm all 16 substances in bovine and caprine milk and, additionally to quantify 15 of these substances in bovine milk and 13 of these substances in caprine milk. This study resulted in a new multi-class method to detect, quantify and confirm the identity of 16 prohibited pharmacologically active substances belonging to five different substance classes in two types of milk.

Health Risk Assessment of Banned Veterinary Drugs and Quinolone Residues in Shrimp through Liquid Chromatography–Tandem Mass Spectrometry

The presence of antibiotic residues in seafood and their effect on public health constitute a matter of concern for consumers worldwide. Antibiotic residues can have adverse effects on both humans and animals, especially residues of banned veterinary drugs. In this study, we applied a validated method to analyze veterinary drug residues in shrimp, including the levels of banned chloramphenicol, malachite green, leucomalachite green, and four nitrofuran metabolites as well as thiamphenicol, florfenicol, and five quinolones, which have no recommended maximum residual levels in shrimp tissues in Taiwan. We collected 53 samples of whiteleg, grass, or giant river shrimp from Taiwanese aquafarms and production areas from July 2016 to December 2017. We found 0.31 ng/g of a chloramphenicol in one grass shrimp, 5.62 ng/g of enrofloxacin in one whiteleg shrimp, 1.52 ng/g of flumequine in one whiteleg shrimp, and 1.01 ng/g of flumequine in one giant river shrimp, indicating that 7.55% of the samples contained veterinary drug residues. We evaluated the health risk by deriving the estimated daily intake (EDI). The quinolone residue EDI was below 1.0% of the acceptable daily intake recommended by the United Nations Food and Agriculture Organization and World Health Organization. The risk was thus discovered to be negligible, indicating no immediate health risk associated with shrimp consumption. The present findings can serve as a reference regarding food safety and in monitoring of the veterinary drug residues present in aquatic organisms. Continual monitoring of residues in shrimp is critical for further assessment of possible effects on human health.

Diagnosis of penicillin allergy: a MOFs-based composite hydrogel for detecting β-lactamase in serum

A MOFs-based composite hydrogel 1@SA is presented for the diagnosis of penicillin anaphylaxis. This composite hydrogel reflects the enzymatic hydrolysis profiles of penicillin via β-lactamase. The determination of β-lactamase by this hydrogel was achieved through an “ON–OFF–OFF–ON” fluorescence trigger pattern. The potency of 1@SA was further demonstrated for its selectivity, sensitivity and convenient visual detection.

Degradation of Chloramphenicol in Synthetic and Aquaculture Wastewater Using Electrooxidation

Chloramphenicol (CAP) is a broad-spectrum antibiotic widely used in animal farming and aquaculture industries. Despite its ban in many countries around the world, it is still used in several developing countries, with harmful effects on the surrounding aquatic environment. In this study, an electrooxidation process using a Ti/PbO anode was used to investigate the degradation of CAP in both synthetic solution and real aquaculture wastewater. A central composite design was used to determine the optimum conditions for CAP removal. Current intensity and treatment time had the most impact on the CAP removal. These two factors accounted for ∼90% of CAP removal. The optimum conditions found in this study were current intensity of 0.65 A, treatment time of 34 min, and CAP initial concentration of 0.5 mg L. Under these conditions, 98.7% of CAP removal was achieved with an energy consumption of 4.65 kW h m. The antibiotic was not present in the aquaculture wastewater, which received 0.5 mg L of CAP and was treated (by electrooxidation) under the optimum conditions. A complete removal of CAP was obtained after 34 min of treatment. According to these results, electrooxidation presents an option for the removal of antibiotics, secondary compounds, and other organic and inorganic compounds from solution.

Detection of β-Lactams and Chloramphenicol Residues in Raw Milk-Development and Application of an HPLC-DAD Method in Comparison with Microbial Inhibition Assays

The present study was carried out to assess the detection sensitivity of four microbial inhibition assays (MIAs) in comparison with the results obtained by the High Performance Liquid Chromatography with Diode-Array Detection (HPLC-DAD) method for antibiotics of the β-lactam group and chloramphenicol in fortified raw milk samples. MIAs presented fairly good results when detecting β-lactams, whereas none were able to detect chloramphenicol at or above the permissible limits. HPLC analysis revealed high recoveries of examined compounds, whereas all detection limits observed were lower than their respective maximum residue limits (MRL) values. The extraction and clean-up procedure of antibiotics was performed by a modified matrix solid phase dispersion procedure using a mixture of Plexa by Agilent and QuEChERS as a sorbent. The HPLC method developed was validated, determining the accuracy, precision, linearity, decision limit, and detection capability. Both methods were used to monitor raw milk samples of several cows and sheep, obtained from producers in different regions of Greece, for the presence of examined antibiotic residues. Results obtained showed that MIAs could be used effectively and routinely to detect antibiotic residues in several milk types. However, in some cases, spoilage of milk samples revealed that the kits’ sensitivity could be strongly affected, whereas this fact does not affect the effectiveness of HPLC-DAD analysis.

Development of in-house ELISA for detection of chloramphenicol in bovine milk with subsequent confirmatory analysis by LC-MS/MS

This study was undertaken to develop and validate direct competitive ELISA for the determination of chloramphenicol residues in bovine milk. Antisera and an enzyme-tracer for chloramphenicol were prepared and used to develop an ELISA with inhibition concentrations, IC₂₀ and IC₅₀, of 0.09 and 0.44 ng mL^-1, respectively. Milk samples were spiked with standards equivalent to 0, 0.2, 0.3, 0.5, 1.0 & 1.5 ng mL^-1 and extracted in methanol. The mean recoveries were found to be 73-100% with coefficient of variance 7-11%. The decision limit (CCα) and detection capability (CCβ) were calculated as 0.10 and 0.12 ng mL^-1, respectively. The results were found comparable with the commercial ELISA, having recoveries of 87 to 100%, CCα 0.09 ng mL^-1 and CCβ 0.12 ng mL^-1. As per Commission Decision 2002/657/EC, in-house ELISA was further validated by using LC-MS/MS. Mass spectral acquisition was done by using electrospray ionization in the negative ion mode applying single reaction monitoring of the diagnostic transition reaction for CAP (m/z 152, 194 and 257). The calibration curve showed good linearity in concentrations from 0.025 to 1.6 ng mL^-1 with correction coefficient 0.9902. The mean recoveries were found to be 88 to 100%. The CCα was calculated as 0.057 ng mL^-1 and CCβ 0.10 ng mL^-1. Since CCα and CCβ are less than half of the MRPL (0.15 ng mL^-1), the test was found suitable for screening and quantification of CAP residues in bovine milk samples. Results of surveillance studies indicated that out of 31 analyzed milk samples, 12.9% samples were found with CAP residues but only 3.2% samples were declared positive with maximum concentration 0.31 ng mL^-1, slightly above the MRPL.

Analytical Strategy for Determination of Chloramphenicol in Different Biological Matrices by Liquid Chromatography - Mass Spectrometry

Introduction

The main problem in determination of chloramphenicol in food of animal origin is a large number of matrices. The main target of this study was to create a method for determination and confirmation of chloramphenicol in products and food of animal origin.

Material and Methods

Each 5 g matrix sample was mixed with 5 mL of water and 10 mL of acetonitrile/ethyl acetate, homogenised, and centrifuged. The organic layer was evaporated and redissolved in 6 mL of 4% NaCl. The extract was cleaned up by SPE technique. Chloramphenicol was analysed by LC-MS/MS in electrospray mode.

Results

The procedure was validated according to the Commission Decision No. 2002/657/EC. The apparent recoveries were in the range of 92.1% to 107.1% with a repeatability less than 11.0% (4.4%-11.0%) and within-laboratory reproducibility below 13.6% (4.7%-13.6%).

Conclusion

The method was successfully validated and proved to be efficient, precise, and useful for quantification of chloramphenicol in more than 20 different matrices.

Determination of Aflatoxin M1 and Chloramphenicol in Milk Based on Background Fluorescence Quenching Immunochromatographic Assay

Harsh demanding has been exposed on the concentration of aflatoxin M1 (AFM1) and chloramphenicol (CAP) in milk. In this study, we developed a new method based on background fluorescence quenching immunochromatographic assay (bFQICA) to detect AFM1 and CAP in milk. The detection limit for AFM1 was 0.0009 ng/mL, while that for the CAP was 0.0008 ng/mL. The assay variability was determined with 3 AFM1 standards (i.e., 0.25 ng/mL, 0.5 ng/mL, and 1.0 ng/mL), and the actual detection value was 0.2497, 0.5329, and 1.0941, respectively. For the assay variability of 3 CAP standards (i.e., 0.10 ng/mL, 0.30 ng/mL, and 0.50 ng/mL), the actual detection value was 0.0996, 0.3096, and 0.4905, respectively. The recovery rate of AFM1 was 99.7%-101.7%, while that for CAP was 95.3%-97.6%. For the test stability, AFM1 and CAP showed satisfactory test stability even at month 5. Compared with the sensitivity of liquid chromatography-mass spectrometry (LC-MS) method, no statistical difference was noticed in results of the bFQICA. Our method is convenient for the detection of AFM1 and CAP in milk with a test duration of about 8 minutes. Additionally, an internal WiFi facility is provided in the system allowing for quick connection and storage in the intelligent cell phone.

A label-free and universal platform for antibiotics detection based on microchip electrophoresis using aptamer probes

A novel label-free, universal, and high throughput aptasensor was developed based on a microchip electrophoresis (MCE) platform for automatic detection of antibiotic residues in food. Firstly, chloramphenicol (CAP) was employed as a model to be captured by its aptamer probe (Apt). Then, the partial complementary oligonucleotide of CAP's aptamer (C-DNA) was introduced into the reaction system. Because the Apt-CAP complex can't further hybrid with free C-DNA, the amount of hybrid Apt-C-DNA double strand DNA (dsDNA) was less than that without adding the target. Finally, the above mixture was introduced into the microchip electrophoresis (MCE) platform for detection, both dsDNA and Apt-CAP can be separated and produce different fluorescence signals in the MCE. In a certain concentration range, the ratio of signal between dsDNA and Apt-CAP (I_dsDNA/I _Apt-CAP) was proportional to the concentration of targets. Under the optimum conditions, the ratio showed a satisfactory linearity range from 0.008 to 1ng/mL of CAP with a detection limit of 0.003ng/mL. Thus, a universal MCE-based assay was developed for quantifying CAP automatically. The method was also successfully applied in the different food samples for CAP detection, which showed a good recovery (Milk: 91.1-108%, Fish: 86.1-114%) and the results were consistent with that of ELISA. This method owned many merits as follows: firstly, MCE was a high throughput screening platform and the detection time is limited to 3min for each sample. Secondly, the aptamer probes can be directly used for detection without labeling any signal tag which can facilitate the preparation procedures of probes. Thirdly, the operation was easy just by the following steps: firstly, the mixture of aptamer probes were incubated followed adding C-DNA; then measurement was performed. Moreover, the assay with MCE platform can be used to detect other targets just by changing the corresponding aptamer probe; it can even realize simultaneous detection when the targets have aptamers with different number of base pairs. Above all, it's a high- throughput and prospective method which can be applied in high throughput screening of antibiotics in food safety.

Matrix molecularly imprinted mesoporous sol-gel sorbent for efficient solid-phase extraction of chloramphenicol from milk

Highly selective and efficient chloramphenicol imprinted sol-gel silica based inorganic polymeric sorbent (sol-gel MIP) was synthesized via matrix imprinting approach for the extraction of chloramphenicol in milk. Chloramphenicol was used as the template molecule, 3-aminopropyltriethoxysilane (3-APTES) and triethoxyphenylsilane (TEPS) as the functional precursors, tetramethyl orthosilicate (TMOS) as the cross-linker, isopropanol as the solvent/porogen, and HCl as the sol-gel catalyst. Non-imprinted sol-gel polymer (sol-gel NIP) was synthesized under identical conditions in absence of template molecules for comparison purpose. Both synthesized materials were characterized by Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FT-IR) and nitrogen adsorption porosimetry, which unambiguously confirmed their significant structural and morphological differences. The synthesized MIP and NIP materials were evaluated as sorbents for molecularly imprinted solid phase extraction (MISPE) of chloramphenicol in milk. The effect of critical extraction parameters (flow rate, elution solvent, sample and eluent volume, selectivity coefficient, retention capacity) was studied in terms of retention and desorption of chloramphenicol. Competition and cross reactivity tests have proved that sol-gel MIP sorbent possesses significantly higher specific retention and enrichment capacity for chloramphenicol compared to its non-imprinted analogue. The maximum imprinting factor (IF) was found as 9.7, whereas the highest adsorption capacity of chloramphenicol by sol-gel MIP was 23 mg/g. The sol-gel MIP was found to be adequately selective towards chloramphenicol to provide the necessary minimum required performance limit (MRPL) of 0.3 μg/kg set forth by European Commission after analysis by LC-MS even without requiring time consuming solvent evaporation and sample reconstitution step, often considered as an integral part in solid phase extraction work-flow. Intra and inter-assay RSD values were less than 13% and accuracy expressed as relative recovery ranged from 85 to 106%.

Development of a subcritical water extraction approach for trace analysis of chloramphenicol, thiamphenicol, florfenicol, and florfenicol amine in poultry tissues

Subcritical water extraction was investigated as a novel and alternative technology for the separation of trace amounts of chloramphenicol, thiamphenicol, florfenicol and its major metabolite florfenicol amine from poultry tissues and its results were compared with those of conventional shaking extraction, ultrasonic extraction, and pressurized liquid extraction. Decreasing the polarity of water by successively increasing the extraction temperature from 50°C to 200°C at the moderate pressure enabled selective, highly effective extractions to be performed. Rapid quantification of the target compounds was carried out by ultra-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS). The critical parameters of subcritical water extraction such as solvent modifier, temperature, pressure, extraction time, and static cycles were varied with control. The optimized extraction procedures using subcritical water as extraction solvent, were carried out on a pressurized liquid extractor operated at 150°C and 100bar, applying two static cycles for 3min. Average recoveries of the four analytes from fortified samples ranged between 86.8% and 101.5%, with relative standard deviations (RSDs) lower than 7.7%. The limits of detection (LODs) and quantification (LOQs) for the target compounds were in the ranges of 0.03-0.5μgkg(-1) and 0.1-2.0μgkg(-1), respectively. The proposed method is fast, sensitive, water-based thus more environmental acceptable, making it a suitable replacement for conventional organic solvent extraction in veterinary drug residue analysis.

Rapid preparation of molecularly imprinted polymers by microwave-assisted emulsion polymerization for the extraction of florfenicol in milk

In this study, we proposed a rapid and simple method for the preparation of molecularly imprinted polymers (MIPs) by emulsion polymerization. The polymerization process was accelerated by microwave heating, and the reaction time was greatly shortened. The obtained MIPs were spherical in shape and exhibited a uniform morphology. The MIPs with selectivity and high affinity to florfenicol were successfully applied as solid-phase extraction materials to extract and clean up the florfenicol in milk, followed by liquid chromatography-tandem mass spectrometry (LC-MS) analysis. The parameters affecting the performance of extraction and LC-MS analysis were evaluated. The detection limit of the method was 4.1ngmL(-1). The relative standard deviations of intra- and inter-day were in the range of 3.5-4.7% and 3.9-7.5%, respectively.

Rapid detection of chloramphenicol residues in aquatic products using colloidal gold immunochromatographic assay

A colloidal gold immunochromatographic assay (GICA) was developed for rapid detection of chloramphenicol (CAP) residues in aquatic products. A nitrocellulose (NC) membrane was used as the carrier, and the polyclonal CAP antibody was used as the marker protein. The average diameter of as-prepared colloidal gold nanoparticles (AuNPs) was about 20 nm. The optimal pH value of colloidal gold solutions and the amount of the antibody of CAP were 8.0 and 7.2 μg/mL, respectively. The CAP antibody was immobilized onto the conjugate pad after purification. The CAP conjugate and goat anti-rabbit IgG (secondary antibody) were coated onto the NC membrane. Next, the non-specific sites were blocked with 1% bovine serum albumin. The minimum detectable concentration of CAP in standard solution is 0.5 ng/mL, with good reproducibility. For the real samples from crucian carps injected with a single-dose of CAP in the dorsal muscles, the minimum detectable concentration of CAP residues was 0.5 μg/kg. The chromatographic analysis time was less than 10 min, and the strip had a long storage lifetime of more than 90 days at different temperatures. The strips provide a means for rapid detection of CAP residues in aquatic products.

Development of a homogeneous immunoassay based on the AlphaLISA method for the detection of chloramphenicol in milk, honey and eggs

BACKGROUND

A homogenous light-induced chemiluminescence immunoassay was developed using AlphaLISA technology for the detection of chloramphenicol (CAP). This technology is based on two different kinds of bead, namely light-sensitive donor beads and beads containing chemiluminescers, also called acceptor beads. A competitive CAP AlphaLISA method was established using artificial antigen-coated acceptor beads, polyclonal antibodies, biotinylated goat anti-rabbit IgG and streptavidin-coated donor beads.

RESULTS

The sensitivity of detection was 0.0086 ng mL⁻¹ and the working range was from 0.0096 to 25 ng mL⁻¹. The intra- and inter-assay coefficients of variation were both below 10%. The average recovery rates at spiked levels of 0.05-10 ng mL⁻¹ were 103.2, 108.4 and 91.6% for milk, honey and eggs respectively. The data obtained from the samples showed good correlation with ELISA results.

CONCLUSION

The CAP AlphaLISA method is highly sensitive, specific and rapid and is suitable for screening large quantities of samples.

Multiresidue determination of veterinary drugs in aquaculture fish samples by ultra high performance liquid chromatography coupled to tandem mass spectrometry

A simple, selective and fast multiresidue method was developed for the determination of 32 veterinary drug residues belonging to several families, in gilthead sea bream (Sparus aurata) by ultra high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). The extraction was based on modified QuEChERS (quick, easy, cheap, effective, rugged and safe) procedure, using as extraction solution a mixture of acetonitrile and methanol (75:25, v/v), and it reduces sample handling, increasing sample throughput in relation to current methodologies. The developed method was validated and mean recovery ranged from 69% to 125% (at 10, 25, 50 and 100 μg/kg). Intra and interday precision, estimated as the same levels and expressed as relative standard deviation, RSD, were lower than 20% and 30%, respectively. Limits of detection (LODs) and quantification (LOQs) were lower than 7.5 and 25 μg/kg, respectively, except for danofloxacin, oxytetracycline and tetracycline (LOD and LOQ of 15.0 and 50 μg/kg, respectively). Decision limit (CC(α)) and detection capability (CC(β)) were also calculated and ranged from 16.7 μg/kg (levamisole) to 605.0 (flumequine) μg/kg and from 23.5 μg/kg (levamisole) to 611.5 μg/kg (flumequine), respectively. The expanded uncertainty, U, was also evaluated ant it was below 25% at 100 μg/kg level, except for tetracycline (28%). Finally, the method was applied to ten samples obtained from local supermarkets in Almería (Spain) and traces of some compounds were detected.

Simultaneous determination of chloramphenicol and florfenicol in liquid milk, milk powder and bovine muscle by LC-MS/MS

A validated method based on European and Brazilian legislation is reported. It is applicable to the simultaneous determination of chloramphenicol (CAP) and florfenicol (FF) by LC-MS/MS in liquid milk, milk powder and bovine muscle. The chromatographic analysis is completed in 6 min and the extraction procedure is very simple, involving only one step liquid-extraction with ethyl acetate. Where it proved necessary to include clean-up, an efficient and rapid step using C18-dispersive solid was added. Initially, a complete validation was performed with liquid milk matrix; later the scope was extended to the other matrices through extending the inter-day precision (within laboratory reproducibility) RSD values. An internal standard (d(5)-CAP) was employed for quantitative purposes. The method was shown to have good accuracy and precision for determining CAP residues at the level of 0.3-0.6 g kg(-1) and FF residues at the level of 5-15 µg kg(-1).

Simultaneous determination of chloramphenicol and aflatoxin M1 residues in milk by triple quadrupole liquid chromatography-tandem mass spectrometry

A reliable, rapid, and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for simultaneous determination of chloramphenicol and aflatoxin M(1) in milk has been developed. This method includes simple extraction of sample with acetonitrile, separation on a MGIII-C(18) column using 5 mM ammonium acetate aqueous solution/methanol (60:40, v/v) as mobile phase, and MS/MS detection using multiple reaction monitoring mode. The method was validated according to Commission Decision 2002/657/EC. The limits of detection (LODs) were 0.05 μg/kg for chloramphenicol and 0.005 μg/kg for aflatoxin M(1.) The limits of quantification (LOQs) were 0.2 μg/kg for chloramphenicol and 0.02 μg/kg for aflatoxin M(1). The recovery values ranged from 88.8% to 100.6%, with relative standard deviation lower than 15% in all cases, when samples were fortified at three different concentrations. The decision limits (CCα) and detection capability (CCβ) of the method were also reported. This method has been successfully applied for simultaneous analysis of chloramphenicol and aflatoxin M(1) residues in milk from local supermarkets in China.

Determination of chloramphenicol, enrofloxacin and 29 pesticides residues in bovine milk by liquid chromatography-tandem mass spectrometry

A sensitive method for determination of chloramphenicol, enrofloxacin and 29 pesticides residues in bovine milk by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was developed. Residues of the targets were extracted from milk with acetonitrile, cleaned up by C(18)-SPE cartridge, and then determined by HPLC-MS/MS. The MS detection was operated in positive or negative ionization mode, depending on the compounds. For confirmation of each target compound, two precursor ion>product ion transitions were selected by multi-reaction monitoring mode (MRM). The method showed good linearity for all the tested compounds over the studied concentration range with correlation coefficient higher than 0.9910. Recoveries for the studied compounds at three spiked levels (0.05, 0.10, 0.19mgkg(-1)) in bovine milk were in the range of 71-107% with RSDs not larger than 13.7%, except that recoveries of trifluralin ranged between 62% and 70% at the spiked levels. Limits of quantitation for the analytes were estimated to range between 0.03×10(-3) and 14.5×10(-3)mgkg(-1). The proposed method was applied for the determination of the analytes residues in real samples. The found levels of the analytes in milk samples were lower than maximum residues levels (MRL).

Multiresidue analysis of antibiotics in food of animal origin using liquid chromatography-mass spectrometry

Antibiotics are the most important drugs administered in veterinary medicine. Their use in food-producing animals may result in antibiotic residues in edible tissues, which are monitored to protect human and animal health, support the enforcement of regulations, provide toxicological assessment data, and resolve international trade issues. This chapter provides basic characterization of the most important classes of antibiotics used in food-producing animals (aminoglycosides, amphenicols, β-lactams, macrolides and lincosamides, nitrofurans, quinolones, sulfonamides, and tetracyclines), along with examples of practical liquid chromatographic-(tandem) mass spectrometric methods for analysis of their residues in food matrices of animal origin. The focus is on multiresidue methods that are favored by regulatory and other food testing laboratories for their ability to analyze residues of multiple compounds in a time- and cost-effective way.

Pre-electrospray ionisation manifold methylation and post-electrospray ionisation manifold cleavage/ion cluster formation observed during electrospray ionisation of chloramphenicol in solutions of methanol and acetonitrile for liquid chromatography-mass spectrometry employing a commercial quadrupole ion trap mass analyser

We have observed unusual mass spectra of chloramphenicol (CAP) in solutions of methanol or acetonitrile showing intense ions at m/z 297, m/z 311, m/z 325 and m/z 339. The observed ions were different from those which are traditionally observed in the full scan ESI mass spectra of CAP with ions of m/z 321, m/z 323 and m/z 325. We have evidence to show that this process starts with offline methylation of CAP in solutions of methanol or acetonitrile to give m/z 339. Investigations using nuclear magnetic resonance (NMR) spectroscopy showed that there is a methylene group somewhere within the CAP molecule but not attached to any of the carbon atoms when the CAP is dissolved in methanol or acetonitrile before infusion into the mass spectrometer. The possible locations of attachment were speculated to be the electronegative atoms apart from the chlorine atoms due to valence considerations. The methylene group is attached to the nitrogen atom and forms a bond as observed in the MS/MS spectra of m/z 297, m/z 311, m/z 325 and m/z 339 which give m/z 183 as the base peak in all cases. Further experiments showed that there is cleavage of the methylated CAP molecule followed by cluster ion formation involving addition of methylene groups to the CAP fragment with m/z 183 to produce ions of m/z including m/z 297, m/z 311, m/z 325 and m/z 339. This process occurs in the mass spectrometer in the region housing the tube lens and is triggered when the ions are accelerated through this region by application of a negative tube lens offset voltage. This region affords collision of the charged droplets with a collision gas in this case nitrogen to strip the droplets of their solvent molecules. Experiments to follow the intensities of m/z 183, m/z 311, m/z 321, m/z 323, m/z 325 and m/z 339 as the tube lens offset voltage was varied were done in which the intensities of m/z 311, m/z 325 and m/z 339 were observed to be at their peak when the tube lens offset voltage was set at -40 V. When the tube lens offset voltage is swung to +40 V, thus decelerating the ions through the capillary skimmer region via the tube lens, the traditionally observed spectra with m/z 321, m/z 323 and m/z 325 were observed.