Use of liquid chromatography-mass spectrometry in the analysis of residues of antibiotics in meat and milk

Stability-indicating method development for quantification of bromopride, its impurities, and degradation products by ultra-high performance liquid chromatography applying Analytical Quality by Design principles

A comprehensive forced degradation study for bromopride was carried out in accordance with International Conference on Harmonization (ICH) recommendations followed by the identification and prospecting of the major degradation products. The analytical quality by design (AQbD) concepts were used to develop a stability-indicating method for bromopride and five organic impurities quantitation by ultra-high performance liquid chromatography with UV detection (UHPLC-UV). Two screenings and one optimization design were performed, including a Monte Carlo simulation to assess the Method Operable Design Region (MODR). The AQbD approach provided a high degree of method understanding in a very short period of time, less than two weeks, and the validated MODR provided information on robust analytical conditions contributing to the assignment of suitable control strategies.

Employing molecularly imprinted polymers in the development of electroanalytical methodologies for antibiotic determination

Antibiotics, although being amazing compounds, need to be monitored in the environment and foodstuff. This is primarily to prevent the development of antibiotic resistance that may make them ineffective. Unsurprisingly, advances in analyticalsciences that can improve their determination are appreciated. Electrochemical techniques are known for their simplicity, sensitivity, portability and low-cost; however, they are often not selective enough without recurring to a discriminating element like an antibody. Molecular imprinting technology aims to create artificial tissues mimicking antibodies named molecularly imprinted polymers (MIPs), these retain the advantages of selectivity but without the typical disadvantages of biological material, like limited shelf-life and high cost. This manuscript aims to review all analytical methodologies for antibiotics, using MIPs, where the detection technique is electrochemical, like differential pulse voltammetry (DPV), square-wave voltammetry (SWV) or electrochemical impedance spectroscopy (EIS). MIPs developed by electropolymerization (e-MIPs) were applied in about 60 publications and patents found in the bibliographic search, while MIPs developed by other polymerization techniques, like temperature assisted ("bulk") or photopolymerization, were limited to around 40. Published works covered the electroanalysis of a wide range of different antibiotics (β-lactams, tetracyclines, quinolones, macrolides, aminoglycosides, among other), in a wide range of matrices (food, environmental and biological).

A kanamycin sensor based on an electrosynthesized molecularly imprinted poly-o-phenylenediamine film on a single-walled carbon nanohorn modified glassy carbon electrode

A single-walled carbon nanohorn (SWCNH) has been used to construct a molecularly imprinted electrochemical sensor for the first time. Kanamycin, a widely used aminoglycoside antibiotic, is used as a representative analyte to test the detection strategy. The kanamycin sensor was constructed by the electropolymerization of a molecularly imprinted poly-o-phenylenediamine film on a SWCNH modified glassy carbon electrode. The sensor was investigated in the presence or absence of kanamycin by cyclic voltammetry to verify the changes in the redox peak currents of K₃Fe(CN)₆. The sensor exhibits a linear range of 0.1-50 μM with a detection limit of 0.1 μM. It also shows high recognition ability, indicating that the SWCNH-based molecularly imprinted sensor is promising.

Long-term monitoring of sulfonamide leaching from manure amended soil into groundwater

Veterinary antibiotics such as sulfonamides are frequently applied in livestock farming worldwide. Due to poor absorption in the animal gut and/or reversible metabolization sulfonamides are excreted in considerable amounts and can subsequently be detected in liquid manure. As manure is utilized for soil fertilization, sulfonamides can enter the environment via this pathway. Water samples taken below an agriculture field in Lower Saxony revealed the permanent entrance of sulfamethazine into groundwater and concentrations up to 100 ng L^-1 were determined. During a long-term lysimeter study, nine sulfonamides were applied to two different soil types by using fortified liquid manure. Divert mobilities were found with sulfamethazine und sulfamethoxazole showing the highest detection frequency in water samples taken below both bedrock and sandy soil. Four years after the last application of fortified manure, sulfonamides were still detectable in the leachate. Based on analyses of manure and fermentation residue samples, a permanent input of sulfonamides to the soil can be excluded. Thus, the positive findings must be caused by the antibiotics once applied. Soils fertilized with manure contaminated with sulfonamides can consequently be a long-time source for the transfer of antibiotics into groundwater.

Transformation of Sulfonamides and Tetracyclines during Anaerobic Fermentation of Liquid Manure

Liquid manure is frequently used as soil fertilizer due to its high nutrient content. It can also contain residues of pharmaceuticals, such as antibiotics, if farm animals are medicated. The anaerobic fermentation process in biogas plants is discussed as one way to reduce the input of antibiotics into the environment. Therefore, 10 worldwide-applied sulfonamides (sulfachloropyridazine, sulfadiazine, sulfadimethoxine, sulfaguanidine, sulfamerazine, sulfamethazine, sulfamethoxazole, sulfamethoxypyridazine, sulfapyridine, and sulfathiazole) and four frequently used tetracyclines (chlortetracycline, doxycycline, oxytetracycline, and tetracycline) were investigated concerning their elimination pattern during anaerobic fermentation. Batch fermenters with autoclaved and non-autoclaved inoculum were utilized to distinguish between biotic and abiotic elimination pathways. Overall, sulfadimethoxine, sulfamethoxypyridazine, and sulfamethoxazole showed the highest elimination, which was considerably reduced by autoclaving before inoculation. Structure elucidation via nuclear magnetic resonance and different mass spectrometry techniques revealed only minor structural modifications such as O-demethylation and hydrogenation, which did not result in a considerably reduced antimicrobial activity. These results show that, especially, sulfonamides are more persistent than expected. Future studies should deal with the elucidation of relevant process parameters for an enhanced compound degradation.

Multi-residue determination of 115 veterinary drugs and pharmaceutical residues in milk powder, butter, fish tissue and eggs using liquid chromatography-tandem mass spectrometry

A simple and sensitive multi-residue method for the determination of 115 veterinary drugs and pharmaceuticals, belonging in more than 20 different classes, in butter, milk powder, egg and fish tissue has been developed. The method involves a simple generic solid-liquid extraction step (solvent extraction, SE) with 0.1% formic acid in aqueous solution of EDTA 0.1% (w/v)-acetonitrile (ACN)-methanol (MeOH) (1:1:1, v/v) with additional ultrasonic-assisted extraction. Precipitation of lipids and proteins was promoted by subjecting the extracts at very low temperature (-23°C) for 12h. Further cleanup with hexane ensures fat removal from the matrix. Analysis was performed by liquid chromatography coupled with electrospray ionization and tandem mass spectrometry (LC-ESI-MS/MS). Two separate runs were performed for positive and negative ionization in multiple reaction monitoring mode (MRM). Particular attention was devoted to extraction optimization: different sample-to-extracting volume ratios, different concentrations of formic acid in the extraction solvent and different ultrasonic extraction temperatures were tested in butter, egg and milk powder samples. The method was also applied in fish tissue samples. It was validated, on the basis of international guidelines, for all four matrices. Quantitative analysis was performed by means of standard addition calibration. For over 80% of the analytes, the recoveries were between 50% and 120% in all matrices studied, with RSD values in the range of 1-18%. Limits of detection (LODs) and quantification (LOQs) ranged from 0.008 μg kg(-1) (oxfendazole in butter) to 3.15 μg kg(-1) (hydrochlorthiazide in egg). The evaluated method provides reliable screening, quantification, and identification of 115 veterinary drug and pharmaceutical residues in foods of animal origin and has been successfully applied in real samples.

Development of a liquid chromatographic method for the quantification of paromomycin. Application to in vitro release and ex vivo permeation studies

We have developed a reversed phase high performance liquid chromatography pulsed amperometric detection (RPHPLC-PAD) method for the determination of paromomycin. It is sensitive, repeatable, and selective without the pretreatment step. Trifluoroacetic acid-water was utilized as the eluent and detected by PAD under NaOH alkaline conditions. The paromomycin detection limit (S/N=3.3) was 2μgmL(-1) and the quantification limit (S/N=10) was 6μgmL(-1). Coefficients of linear regression were higher than 0.99 for concentrations between 6.25 and 200μgmL(-1). The intra and inter-day precision (RSD) was less than 6.5%. The average recoveries were 97.53-102.01%. The proposed HPLC-PAD method presented advantageous performance characteristics and it can be considered suitable for the evaluation of paromomycin loaded nanogel formulation in ex vivo permeation and in vitro release studies.

Daily ingestion of tetracycline residue present in pasteurized milk: a public health problem

The objective of this study was to evaluate (qualitatively and quantitatively) the occurrence of antibiotic residue in pasteurized milk in Brazil. Pasteurized milk samples (n = 252) were collected monthly from Nov. 2010-Oct. 2011 from 21 commercial establishments (brands). A screening test (Delvotest® SP-NT) was applied to those samples. In positive (n = 19) and/or suspect samples (n = 24), we quantified oxytetracycline (OTC) and tetracycline (TC) by high-performance liquid chromatography with diode array detector (HPLC-DAD). OTCs were detected in all positive samples and TCs in six. In the 24suspected samples, OTCs were detected in 23 and TCs were not found in 8. Of the milk brands evaluated (n = 21), the presence of antibiotic residue was not detected in 4; in the other brands, both positive and suspect samples were verified. Results indicate the presence of antibiotic residue above legal limits. According to actual milk consumption in Brazil (441 mL/kg BW/day), in only 9 of the 17 brands of milk with antibiotic residue, the estimated daily intake was at or less than the maximum recommended by the European Union. The screening test used was effective to identify the presence of antibiotic residue (OTC and TC), confirmed by HPLC-DAD. The OTC is the predominant antimicrobial used by dairy farmers. Ingestion of contaminated milk by OTC and TC can increase the resistance of microorganisms to antibiotics.

Application of different modes of thin-layer chromatography and mass spectrometry for the separation and detection of large and small biomolecules

Biomolecules are widespread throughout the world. A biomolecule is any organic molecule produced by a living organism, including large polymeric molecules such as proteins, polysaccharides and nucleic acids. Many sample preparation techniques are used in biomolecule analysis; the method selected depends on the complexity of the sample, the nature of the matrix and the analytes, and the analytical technique available. This review covers the current state of knowledge on thin-layer chromatography and mass spectrometry for qualitative analysis of biomolecules. In the first part of the paper the reader will gain useful information to avoid some problems about performing various modes of thin-layer chromatography combined with mass spectrometry experiments and in the second part he will find useful information for application of these techniques for separation, detection, and qualitative investigation of structures and quantitative determination of biomolecules such as proteins, peptides, oligonucleotides, amino acids, DNA, RNA, and lipids.

Metabolites from fungal laccase-catalysed transformation of sulfonamides

Soil metabolism of sulfonamides is largely unknown. Hence the sulfonamides sulfanilamide (SAA), sulfadimethoxine (SDT) and sulfapyridine (SPY) were reacted in model experiments with a fungal laccase from Trametes versicolor. Enzymatic transformation after a reaction time of 15 d ranged from 10.0% for SAA up to 95.6% for SPY and the difference was attributed to the different molecular substituents. Metabolites were first tentatively assigned after LC-ESI(+)-MS full-scan analysis. Secondly, the proposed metabolites were further confirmed employing either multiple reaction monitoring in comparison with standard substances or precursor ion scan LC-ESI(+)-MS/MS experiments striving for the precursor and two to three product ions. Aniline was confirmed as a breakdown product of SPY and further metabolites of SPY and of SDT were identified as rearranged SO(2) extrusion products. Thirdly, some of the metabolites matched those that were previously reported for sulfonamide photodegradation and degradation in soil. It was concluded that enzymatic metabolism as investigated here also occurs in soil.

Discrimination of eight chloramphenicol isomers by liquid chromatography tandem mass spectrometry in order to investigate the natural occurrence of chloramphenicol

This paper describes the discrimination of eight different isomers of chloramphenicol (CAP), an antibiotic banned for use in food producing animals, by reversed phase and chiral liquid chromatography in combination with tandem mass spectrometric detection. Previously, by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) the presence of CAP was confirmed in some grass and herb samples collected on Mongolian pastures up to concentrations of 450 μg kg(-1). It was not possible to establish the cause of CAP residues which has initiated research on the natural occurrence of this drug. CAP occurs in the para-configuration and in the meta-configuration and contains two chiral centers thus eight different isomeric configurations exist, namely four (RR, SS, RS, SR) meta-stereoisomers and four para-stereoisomers. It is known that only RR-p-CAP has antimicrobial properties. To find out if the CAP detected in the plant material samples is the active configuration, a high resolution reversed phase LC-MS/MS system was tested for its ability to separate the different isomers. This system proved to be able to discriminate between some isomers, but not between RR-p-CAP and SS-p-CAP, also called dextramycin. Despite a detailed elucidation of the product ions and the fragmentation patterns of all isomers, MS/MS did not add sufficient specificity for full discrimination of the isomers. Therefore a chiral liquid chromatographic separation with MS/MS detection that is able to distinguish all isomers was developed and finally the isomeric ratio of non-compliant plant material samples and some CAP formulations was determined using this system. This showed that Mongolian grass and herb samples only contain the biological active isomer of CAP as do the obtained formulations. Therefore the CAP present in the plant material might origin from the production by soil organisms or from a manufactured source.

Evidence of natural occurrence of the banned antibiotic chloramphenicol in herbs and grass

Chloramphenicol (CAP), a broad-spectrum antibiotic, was detected in several herb and grass samples from different geographic origins. Due to its suspected carcinogenicity and linkages with the development of aplastic anemia in humans, CAP is banned for use in food-producing animals in the European Union (EU) and many other countries. However, products of animal origin originating from Asian countries entering the European market are still found noncompliant (containing CAP) on a regular basis, even when there is no history of chloramphenicol use in these countries. A possible explanation for the continued detection of these residues is the natural occurrence of CAP in plant material which is used as animal feed, with the consequent transfer of the substance to the animal tissues. Approximately 110 samples were analyzed using liquid chromatography coupled with mass spectrometric detection. In 26 samples, the presence of CAP was confirmed using the criteria for banned substances defined by the EU. Among other plant materials, samples of the Artemisia family retrieved from Mongolia and from Utah, USA, and a therapeutic herb mixture obtained from local stores in the Netherlands proved to contain CAP at levels ranging from 0.1 to 450 µg/kg. These findings may have a major impact in relation to international trade and safety to the consumer. The results of this study demonstrate that noncompliant findings in animal-derived food products may in part be due to the natural occurrence of chloramphenicol in plant material. This has implications for the application of current EU, USA, and other legislation and the interpretation of analytical results with respect to the consideration of CAP as a xenobiotic veterinary drug residue and the regulatory actions taken upon its detection in food.

Determination of penicillins in milk using LC-UV, LC-MS and LC-MS/MS

The aim of this work is to establish a method for the simultaneous determination of eight penicillins in milk samples by LC-UV, LC-MS and LC-MS/MS. The procedure involves a step for clean-up and to preconcentrate the analytes by SPE and a subsequent chromatographic analysis. LC-UV, LC-MS and LC-MS/MS have been used for the simultaneous quantification of penicillins in milk. The proposed methods have been validated according to the EU guideline and present LOQ below the maximum limits of residues (MRLs) established by the European Union for penicillins in milk. The developed methods were applied to different milk samples obtained from cows medicated with penicillins.