Quantitative analysis of oxytetracycline and its 4-epimer in calf tissues by high-performance liquid chromatography combined with positive electrospray ionization mass spectrometry

Accurate determination of four tetracycline residues in chicken meat by isotope dilution-liquid chromatography/tandem mass spectrometry

An analytical method based on isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC‒MS/MS) was developed to accurately determine four representative tetracyclines (tetracycline, chlortetracycline, doxycycline, and oxytetracycline) in chicken meat. Tetracyclines are known to have a great tendency for epimerization and keto-enol tautomerism, which often provoke major challenges in their determination. Since this isomerization was found to be unavoidable during the whole chain of the current analysis, the total content (µg kg^‒1) of individual tetracycline was quantified as a sum of each parent compound and its respective isomeric forms. Using this approach in combination with IDMS analysis, more consistent, accurate, and reproducible measurement results for the four tetracyclines in chicken meat were acquired. LC-MS/MS conditions and sample preparation processes were comprehensively optimized to minimize the chelating effect of tetracyclines and possible co-extracted interferences. Details of the sample preparation scheme, LC‒MS/MS detection, calculation equation, and method validation are described in this article. The method provided very good accuracy (97.7-102.6%) for all analytes across the concentration range of 10-200 µg kg^‒1, with relative standard deviations for intra-day and inter-day precision of less than 4%. The limits of quantification were below 0.2 µg kg^‒1, demonstrating the high sensitivity of the method. Furthermore, the measurement uncertainty was generally below 5.5%. Hence, the established method exhibits high-order metrological quality with superior performance over various existing methodologies. Moreover, this method can provide references for general food testing laboratories close to and far below the established maximum residue limits (100 µg kg^‒1) for animal muscle tissues.

Bridging of a Liquid Chromatography-Tandem Mass Spectrometry Method for Oxytetracycline, Chlortetracycline, and Tetracycline in Bovine Kidney with the Official Microbial Growth Inhibition Assay

BACKGROUND

Oxytetracycline (OTC), chlortetracycline (CTC), and tetracycline (TC) are approved antibiotics used to treat bacterial infections in cattle. To ensure human food safety, a tolerance has been established for the sum of these three TC residues as 12 parts per million in bovine kidney in the United States The current official regulatory method for quantifying these antibiotics in the target organ is a labor-intensive microbiological assay.

OBJECTIVE

Our laboratory developed and validated a fast, selective, and less laborious method utilizing LC-tandem mass spectrometry for the determination and confirmation of the three tetracyclines (TET) in bovine kidney.

METHODS

Briefly, homogenized kidney tissue was spiked with an internal standard (ISTD), and then was extracted with 1% phosphate buffer. The crude extract was cleaned up using solid-phase extraction cartridges before instrumental analysis.

RESULTS

Accuracies for quantifying these three drugs in fortified kidney homogenate were between 99.9 and 110% at multiple concentrations, with respective CVs all below 9.5%. Quantitative correlation between the two methods (bridging) was evaluated with incurred bovine kidney samples for each of the three tetracyclines separately. The results were statistically evaluated using a measurement model called Functional Relationship Estimation by Maximum Likelihood.

CONCLUSION

A linear quantitative relationship was demonstrated between the two methods within the concentration range of regulatory relevance.

HIGHLIGHTS

This instrumental method is in addition to the established microbial assay for the detection of tetracyclines residue in beef kidney to ensure the food safety of cattle products.

Synthesis, Characterization, and Antibacterial Evaluation of Heteroleptic Oxytetracycline-Salicylaldehyde Complexes

A new series of mixed ligand complexes of Cd(II) and Mo(V) were successfully synthesized by refluxing the mixture solution of oxytetracycline hydrochloride (OTC.HCl) with an aqueous and alcoholic solution of metal (M = Cd(II) and Mo(V)) salts and an alcoholic solution of salicylaldehyde (Sal). The complexes were characterized by modern analytical and spectral methods such as elemental microanalysis, pH, conductivity, surface tension, viscosity, melting point, and spectral methods such as FT-IR, NMR, electronic absorption, SEM, and mass spectrometry. Conductivity measurements of the complexes revealed their electrolytic nature. The kinetic and thermal stabilities were investigated using thermogravimetric and differential thermal analysis techniques. Thermodynamic and kinetic parameters such as E∗, ΔH∗, ΔS∗, and ΔG∗ were calculated from TG curves using the Coats–Redfern method. Geometry optimization of the proposed structure of the complexes was achieved by running MM2 calculations in a Gaussian-supported CS ChemOffice 3D Pro.12.0 version software. The final optimized geometrical energies for respective Cd-OTC/Sal and Mo-OTC/Sal complexes were found to be 923.1740 and 899.3184 kcal/mol. The electronic absorption spectral study revealed a tetrahedral geometry for the Cd-OTC/Sal complex and octahedral geometry for the Mo-OTC/Sal complex. The antibacterial sensitivity of the complexes was evaluated against three bacterial pathogens such as S. aureus, E. coli, and P. mirabilis using the modified Kirby–Bauer paper disc diffusion method. The antibacterial study revealed significant growth inhibitory action of the complexes.

A Critical Review of Properties and Analytical Methods for the Determination of Oxytetracyline in Biological and Pharmaceutical Matrices

Antibiotics have an unquestionable importance in the treatment of many infections. Oxytetracycline is an antibiotic belonging to the class of tetracyclines, available for use in human and veterinary medicine. Development of analytical methods that prove the quality and efficacy of these drugs is fundamentally important to the pharmaceutical industry. In this context, the research presents an overview of the analytical profile of oxytetracycline, describing its chemical and pharmacological properties, and analytical methods for quantification of this drug in biological samples and pharmaceutical products. Oxytetracycline can be analyzed in these matrices by many types of methodologies. However, high-performance liquid chromatography is the most widely used, being recommended by official compendia. This kind of study can be useful to support the development of new efficient and sustainable analytical methods that may be utilized in the quality control routine of oxytetracycline in pharmaceutical products and pharmacokinetic monitoring in biological samples.

6-Iso-chlortetracycline or keto form of chlortetracycline? Need for clarification for relevant monitoring of chlortetracycline residues in food

Chlortetracycline (CTC) is a broad-spectrum antibiotic used in veterinary medicine for pulmonary or digestive infections and having a regulatory maximum residue limit (MRL) necessitating an official analytical control method. The purpose of this study was to clarify the identification of different forms of CTC observed in standard solution, in spiked muscle samples and in naturally incurred muscle samples of pigs analysed by LC-MS/MS and to demonstrate the in vivo formation of 6-iso-chlortetracycline and 4-epi-6-iso-CTC as a metabolite of CTC and 4-epi-CTC in muscle. The six following forms were identified, all being isobaric with a protonated molecule at m/z 479 (precursor ion): the keto-enol forms of CTC and the keto-enol forms of 4-epi-chlortetracycline (4-epi-CTC), 6-iso-chlortetracycline (6-iso-CTC) and 4-epi-6-iso-chlortetracycline (4-epi-6-iso-CTC). The 6-iso-CTC and 4-epi-6-iso-CTC were observed only in incurred pig samples so were identified for the first time as metabolites of CTC and 4-epi-CTC. Identification of the different forms was obtained by comparing incurred muscle samples with standard solutions and with spiked samples. Then the differences between the features of the chromatograms obtained by LC-TQ-MS and the fragmentation study of the different forms of CTC obtained by LC-Q-TOF-MS helped us to support this identification. The extraction steps and the LC-MS/MS conditions developed to analyse muscle tissue samples are described. This clarification concerning the rigorous identification of chromatographic peaks allowed us to evaluate the relevance of our monitoring method with regard to the regulations in place in the European Union and could be of help to laboratories involved in official control of antibiotic residues in food of animal origin. Additional results are also presented highlighting the transformation of the CTC when prepared in a mixture with other antibiotics.

Production of a monoclonal antibody against oxytetracycline and its application for oxytetracycline residue detection in shrimp

A novel monoclonal antibody (MAb) against oxytetracycline (OTC) was generated and characterized. The MAb was used in the development of an enzyme-linked immunosorbant assay (ELISA)-based detection system. An OTC-bovine serum albumin (BSA) conjugate was prepared and used in the immunization of mice. A conventional somatic cell fusion technique was used to generate MAb-secreting hybridomas denoted 2-4F, 7-3G, and 11-11A. An indirect competitive ELISA (icELISA) was applied to measure the sensitivity and specificity of each MAb in terms of its 50% inhibitory concentration (IC50) and percentage of cross-reactivity, respectively. MAb 2-4F exhibited the highest sensitivity, with an IC50 of 7.01 ng/ml. This MAb showed strong cross-reactivity to rolitetracycline, but no cross-reactivity to other unrelated antibiotics. When MAb 2-4F was used to detect OTC from shrimp samples, the recoveries were in the range of 82%-118% for an intra-assay and 96%-113% for an inter-assay. The coefficients of variation of the assays were 3.9%-13.9% and 5.5%-14.9%, respectively.

Bioanalysis of drug in tissue: current status and challenges

Distribution of drugs into tissues is an important determinant of the overall PK and PD profile. Thus, bioanalysis of drugs and their metabolites in tissues can play an important role in understanding the pharmacological and toxicological properties of new drug candidates. Unlike liquid matrices, bioanalysis in tissues offers unique challenges such as proper tissue sampling, appropriate tissue sample preparation, efficient extraction of the analytes from the tissue homogenates, and demonstration of stability and recovery of analytes in intact tissues. This article provides a systematic review of tissue sample analysis for small molecules using LC–MS/MS. The authors provide rationale for tissue sample analysis, and discuss strategies for method development, method qualification or validation, and sample analysis. Unique aspects of method development and qualification/validation are highlighted based on authors’ direct experiences and literature summary. Analysis using intact tissue samples such as MALDI imaging is also briefly discussed.

Delivering oxytetracycline to first-feeding zebrafish, Danio rerio (Hamilton), and goby, Asterropteryx semipunctata Rüppell, larvae using lipid spray beads

Lipid spray beads (LSB) were evaluated for delivery of the low-molecular weight, water-soluble antibiotic, oxytetracycline.HCl (OTC) to fish larvae. Various OTC core-to-lipid ratios and OTC core concentrations were evaluated to maximize OTC delivery efficiency by LSB. Acceptability and digestion of LSB containing OTC and riboflavin by larval zebrafish, Danio rerio (Hamilton), and larval gobies, Asterropteryx semipunctata Rüppell, were also evaluated. Increasing LSB core-to-lipid ratios from 1:3 to 1:1 v/v resulted in an increase in encapsulation efficiency (EE) from 2.33 to 3.68% w/w. Increasing OTC concentrations of core solutions from 0.1 to 0.5 g OTC mL(-1) increased EE from 3.95 to 18.77% w/w, respectively. Although retention efficiency (RE) was unaffected by this increase, delivery efficiency was increased to 7.9 +/- 0.7% w/w, after correcting for leakage losses because of the suspension of beads in water for 60 min. Consumption of LSB containing OTC by first-feeding zebrafish and goby larvae was confirmed by analysis of feeding incidence and gut fullness. Visual observations of larvae fed on LSB containing riboflavin indicated that larvae of both species digested LSB. Zebrafish larvae fed on OTC LSB contained 39.3 +/- 2.5 ng OTC after purging LSB from their guts. Use of LSB provides an effective means of delivering therapeutics to fish larvae and could greatly reduce required doses compared with current methods of immersing larvae in solutions of therapeutic agents.

Recent studies of the electrospray ionisation behaviour of selected drugs and their application in capillary electrophoresis–mass spectrometry and liquid chromatography–mass spectrometry

This review is concerned with recent studies of electrospray ionisation-mass spectrometry (ESI-MS) of selected small molecular mass drugs and their application in qualitative and quantitative analytical methods using the techniques liquid chromatography mass spectrometry (LC-ESI-MS) and capillary electrophoresis mass spectrometry (CE-ESI-MS). The publications reviewed are taken from the Web of Knowledge database for the year 2006. The drugs have molecular mass less than 1000 Da and are chosen according to selected drug classifications in which they give ESI signals primarily as [M+H]+ ions. The drug classifications are antibiotics/antibacterials, steroids, anti-tumour drugs, erectile dysfunction agents, anti-epileptic drugs, antiasthmatic drugs, psychoactive drugs and miscellaneous drugs. Details are given on the fragmentations, where available, that these ionic species exhibit in-source and in ion trap, triple quadrupole and time-of-flight mass spectrometers. Analytical methods for the detection and determination of these small molecular mass drug molecules are also discussed, where appropriate, under the particular drug classifications. Analytical information on, for example, sample concentration techniques, separation conditions, recoveries from biological media and limits of detection/quantitation (LODs and LOQs) are provided.

Accurate determination of an immunosuppressant in stented swine tissues with LC–MS/MS

During stent development, accurate monitoring of the drug concentration in animal tissues can provide critical information on how the drug is released into the circulation and the surrounding tissues. To establish the relationship between the drug concentration and the distance from the stent to the target tissue, a comprehensive strategy was developed for sample collection, sample homogenization and sample storage as well as sample analysis. This strategy was developed with the analytical chemists and animal surgical specialists working together as a team. The optimized sampling process was designed to yield a representative sample, appropriately located and of an appropriate size. The sampling process was also designed to eliminate the potential for carryover and cross-contamination. During sample processing, the analyte solution was spiked into blank tissues using a sharp needle and a gas-tight syringe to prepare tissue quality control samples. These tissue quality controls were then used to evaluate the stability of the drug in solid tissue and homogenate, the homogenization carryover, the cross-contamination and the recovery of the drug during method validation and to monitor the overall process of drug analysis of the swine tissues. This thorough strategy has been applied to the accurate determination of zotarolimus in swine tissues for regulated toxicology studies. The entire process was controlled, including precise tissue sampling, compound-based tissue homogenization, method validation, and the application of the method to regulated toxicokinetics studies. The results demonstrate that analytical chemistry concepts can be successfully integrated into toxicokinetics studies in order to collect precise samples and obtain meaningful results. The strategy can be applied to similar toxicokinetics studies of locally administrated drugs in tissues.

Determination of tetracycline antibiotics in cow's milk by liquid chromatography/tandem mass spectrometry

A liquid chromatographic/tandem mass spectrometric (LC/MS/MS) multiresidue method for the simultaneous quantitative determination of oxytetracycline, 4-epi-oxytetracycline, tetracycline, 4-epi-tetracycline, chlortetracycline, 4-epi-chlortetracycline and doxycycline in milk has been developed. An extraction procedure consisting of a liquid extraction of the milk samples with trichloroacetic acid was performed. The extract was centrifuged and the supernatant was filtered. Solid-phase extraction (SPE) with an OASIS HLB SPE column was used to clean up the sample extracts. The samples were analysed by LC/MS/MS. The LC separation was performed on a reversed-phase C18 column using gradient elution with a mobile phase consisting of water and a mixture of methanol/acetonitrile. The tetracycline analytes were detected with a quadrupole mass spectrometer using positive ion electrospray ionisation. The confirmatory method has acceptable detection limits and the different tetracyclines can be detected at a residue concentration between 5 and 20 microg/L. The method is validated according to the European requirements for veterinary drug residues and all determined parameters were found to conform to the criteria. The recovery values ranged from 90.4 to 101.2% with relative standard deviations (RSDs) no larger than 9.7%. The overall or between-day precision of the analytical assay determined as repeatability at several residue concentrations and expressed as RSD ranged from 3.3 to 10%. This analytical assay is a useful tool within the Belgian monitoring programme for confirmation of samples which have been positively screened for residues of tetracyclines in raw farm cow's milk.

Screening of tetracycline residues in fish muscles by CCD camera-based solid-surface fluorescence

A methodology for the screening of tetracyclines (TCs), including tetracycline (TC), oxytetracycline (OTC), and chlorotetracycline (CTC), in different fish muscle matrices has been proposed. This method was based on in situ fluorescent derivation of TCs, transferring weakly fluorescing TCs to highly fluorescent species, on alkaline-activated solid silica gel G plates (SGGPs). By coupling solid-surface fluorescence (SSF) with charge-coupled device (CCD) camera imaging, a CCD camera-based SSF (CCD-SSF) methodology has been developed. Calibration curve, repeatability, selectivity, limit of detection (LOD), and limit of quantification (LOQ) have been explored for evaluating the performance of the method itself. Linear calibration curves were obtained over a range of 0.20-1.0 ng/spot for all three TCs. The LODs, defined as 3sigma, for TC, OTC, and CTC were 0.14, 0.15, and 0.16 ng/spot, respectively. The trueness of method was validated by HPLC, and no significant difference between CCD-SSF and HPLC was found, on a basis of 95% confidence level. By spiked recovery studies, a linear calibration curve ranging from 20 to 300 microg/kg of TC in fish muscle samples with a correlation coefficient (R 2) equal to 0.994 was obtained. The total average recovery for TC in fish muscle samples from six different fish matrices, fortified with TC at 50, 100, and 200 microg/kg levels, was 75.7% with average relative standard deviations (RSDs) ranging from 2.0 to 7.7%. RSDs ranged from 2.5 to 5.8% and from 5.2 to 7.6% for in-day and interday repeatability, respectively. The detection and quantification limits in fish muscle matrices were 16 and 53 microg/kg of TCs, respectively. The newly developed CCD-SSF method has been applied to the screening of the TC residues in fish muscle samples. The method has been demonstrated to bear some advantages, such as its simplicity, high throughput, low cost, use of fewer pollutants, and reasonable sensitivity.

Development and validation of an HPLC confirmatory method for the determination of tetracycline antibiotics residues in bovine muscle according to the European Union regulation 2002/657/EC

A high-performance liquid chromatographic method with diode-array detection, at 351 nm, was developed and validated for the determination of five tetracyclines (TCs): minocycline, tetracycline, oxytetracycline, chlortetracycline, and doxycycline in bovine muscle. Samples were macerated with a buffer solution, centrifuged, and purified using Abselut Nexus SPE cartridges. The separation of the examined TCs was achieved on an Inertsil ODS-3 5 microm, 250 x 4 mm analytical column, at ambient temperature. A multistep gradient elution was followed using 0.05 M oxalic acid and CH3CN, at a flow rate of 1.65 mL/min. The procedure was validated according to the European Union regulation 2002/657/EC determining selectivity, stability, decision limit, detection capability, accuracy, and precision. The results of the validation process demonstrate that the method can be readily applied to European Union statutory veterinary drug residue surveillance programmes. Mean recoveries of TCs from bovine muscle samples spiked at three concentrations (100, 250, and 400 ng/g) were in the range of 98.7-103.3%. Method's LOQ values achieved were 40 microg/kg for MNC, CTC, and DC and 25 microg/kg for OTC and TC. The decision limits (CCalpha) were in the range of 104.7-109.8 microg/kg, while the detection capability (CCbeta) was in the range of 108.4-116.7 microg/kg for all compounds.

Method development and validation for zotarolimus concentration determination in stented swine arteries by liquid chromatography/tandem mass spectrometry detection

Drug-eluting stents have attracted significant attention in the medical community and pharmaceutical industry due to their proven success in significantly reducing restenosis. Abbott Laboratories is developing a drug-eluting stent coated with zotarolimus and swine was recently used as an animal model for the pre-clinical study of stent implantation. In this article, we present a detailed experimental design and results for the validation and sample analysis of zotarolimus drug concentration in stented swine artery samples. Introduction of tissue quality control (QC) samples allows evaluation of the entire analytical process as well as the stability of the drug in both original tissue and homogenized tissue samples. In addition, a novel approach using 100% swine blood as the homogenization solution was developed for the consistency of the liquid-liquid extraction recovery and stability of the zotarolimus in tissue homogenates. Standards were prepared by spiking zotarolimus working solution in swine blood and tissue QC samples were used along with the artery samples during the sample analysis. The linear dynamic range of blood standard samples is from 0.61 to 333.20 ng/mL to accommodate the predicted artery homogenate concentrations. Overall tissue QC %CV during the method validation was from 4.4% to 8.6%. The overall %bias of tissue QC samples during the method validation was from -7.3% to 16.6%. The method was successfully applied for the analysis of swine artery samples. A similar approach for method validation and sample analysis has been successfully applied for the analysis of swine myocardium, kidney and liver tissue samples.

Quantitative determination of chlortetracycline content in animal plasma at controlled keto-enol tautomerism by liquid chromatography–electrospray ionization-tandem mass spectrometry

Chlortetracycline (CTC) is a member of the group of the tetracycline antibiotics used in human and veterinary medicine. Its reliable measurement in plasma - necessary to study its pharmacokinetics - is hampered by the fact that CTC is subjected to keto-enol tautomerism resulting in its keto- and enol-form. Also, it undergoes epimerization to form its 4-epimer. In this paper, we present an LC-ESI-MS/MS method to analyze the CTC content in animal plasma, with the originality that it apports a solution to overcome the possible interference of the keto-enol tautomerism equilibrium, which is influenced by several factors. Therefore, the plasma samples were incubated at 56 degrees C, forcing the equilibrium completely in favour of the CTC keto-form. The CTC keto-tautomer was stable after deproteinization of the samples with concentrated trifluoroacetic acid, and was quantified by LC-ESI-MS/MS, as a measure of the total CTC content. The method could be validated for pig and chicken plasma by a series of parameters - linearity, trueness, precision, limit of quantification, specificity, stability - in accordance with the European guidelines, and was used for pharmacokinetic studies on pigs and chickens medicated with CTC via the feed.

Analytical procedure for the determination of chlortetracycline and 4-epi-chlortetracycline in pig kidneys

A liquid chromatography-diode array detection (LC-DAD) procedure has been developed for assaying chlortetracycline (CTC) and its 4-epimer (4-epi-CTC) residues in pig kidneys. The procedure involved extraction with 0.1 M oxalic buffer followed by protein precipitation with trichloroacetic acid. Further solid-phase extraction (SPE) clean-up on a Strata X polymeric cartridge was allowed to obtain an extract suitable for LC analysis. Chromatographic separation was carried out on a C8 analytical column, using isocratic elution with methanol-acetonitrile-0.01 M oxalic acid (15:15:70, v/v/v) at ambient temperature. The flow-rate was 1.2 ml/min and the eluate was analysed at 365 nm. The whole procedure was evaluated according to the requirements of the European Union regulation 2002/657/EC determining specificity, decision limit (CCalpha), detection capacity (CCbeta), trueness, precision and robustness during validation process. The decision limit (CCalpha) was 674.8 microg/kg for CTC and 683.6 microg/kg for 4-epi-CTC. The detection capacity (CCbeta) was 683.6 and 696.3 microg/kg for CTC and 4-epi-CTC, respectively. The recoveries of CTC and 4-epi-CTC from spiked samples at the levels of 300, 600 and 900 microg/kg (0.5 x MRL, 1 x MRL and 1.5 x MRL) were higher than 70%. This method has higher throughput than reported previously extraction method with oxalic acid and acetonitrile used for dechelation and deproteinization.

Determination of tetracyclines residues in honey using high-performance liquid chromatography with potassium permanganate–sodium sulfite–β-cyclodextrin chemiluminescence detection

A novel method was developed for the simultaneous determination of tetracycline antibiotic (TCA) residues such as oxytetracycline (OTC), tetracycline (TC), and metacycline (MTC) by high-performance liquid chromatography (HPLC) coupled with chemiluminescence (CL) detection. The procedure was based on the chemiluminescent enhancement by TCAs of the potassium permanganate-sodium sulfite-beta-cyclodextrin system in a phosphoric acid medium. The separation was carried out with an isocratic elution using a mixture of acetonitrile and 0.001 M phosphoric acid. For the three TCAs, the detection limits at a signal-to-noise of 3 ranged from 0.9 to 5.0 ng/ml. The relative standard deviations for the determination of TCAs ranged from 3.1 to 7.4% within a day (n=11) and ranged from 2.2 to 8.6% in 3 days (n=9), respectively. The method was successfully applied to the determination of TCA residues in honey samples. The possible mechanism of the CL reaction was also discussed.

Complexities in tetracycline analysis—chemistry, matrix extraction, cleanup, and liquid chromatography

The extraction and cleanup of commonly used tetracyclines (oxytetracycline, tetracycline, chlortetracycline, and doxycycline) from sample matrix, and their subsequent determination via liquid chromatography can be problematic. Many manuscripts report on various challenges encountered when developing a method for tetracycline antibiotics determination. These complexities often result in less than perfect recoveries or chromatograms and are based on the underlying chemistry associated with tetracyclines. This review compiles, compares, and discusses the results and observations found in published methods, while focusing on chemical principles in order to increase the practicing chemist's understanding of TCs to aid him/her in developing useful analyses.

Analytical strategies for residue analysis of veterinary drugs and growth-promoting agents in food-producing animals—a review

After a brief introduction into the field of veterinary drugs and growth-promoting agents, the most important EU regulations and directives for the inspection of food-producing animals and animal products regarding the residue control of these substances are presented and discussed. Main attention in the review is on the methods of analysis in use today for the most important classes of veterinary drugs and growth-promoting agents viz. anthelmintics, antibiotics, coccidiostats, hormones, beta-agonists and tranquillizers. Emphasis is given to the potential, and limitations, of state-of-the-art analytical procedures and their performance characteristics. The most obvious conclusion is that, today (reversed-phase) liquid chromatography combined with tandem mass spectrometric detection--either triple-quadrupole or ion-trap multi-stage--is the preferred technique in a large majority of all cases. In the field of sample treatment, the combined use of liquid extraction--i.e., liquid partitioning or liquid-liquid extraction--and liquid-solid extraction--primary on- or off-line solid-phase extraction--is most popular. Finally, while the analytical tools required to meet the demands typically formulated by governments and international organizations today, generally speaking are available, several problems still do exist. To quote three examples, problems are encountered in the area of simultaneously extracting and pre-treating groups of analytes with mutually widely different polarities, with regard to identification-point--based confirmation of analyte identity, and regarding quantification errors caused by ion-suppression effects. Improving the speed of analysis is another aspect that should, and will, receive dedicated interest in the near future.

Analysis of tetracyclines in honey by high-performance liquid chromatography/tandem mass spectrometry

A confirmatory method coupling liquid chromatography to tandem mass spectrometry (LC/MS/MS) is described for the determination of tetracycline, oxytetracycline, doxycycline and chlortetracycline in honey. Demeclocycline, another tetracycline molecule not reported for its usage in honey, was used as internal standard to quantify the four analytes. The sample preparation entails a clean-up on an Oasis HLB solid-phase extraction cartridge and analyses were realised by LC/MS/MS in selected reaction monitoring mode. The stability of tetracyclines was checked under various storage conditions at -20, +4 and +20 degrees C (both under dark and light exposures). Indeed, tetracyclines are not stable molecules and the epimerisation phenomenon was evaluated in this work. Appropriate correction factors of the MS/MS responses of each epimer were studied for each of the four tetracyclines to accurately quantify them. Moreover, the matrix effects encountered during the LC/MS/MS analyses were also studied in spiked experiments from blank honey samples of various geographical origins and different flower types.

Electrocatalytic Tetracycline Oxidation at a Mixed-Valent Ruthenium Oxide−Ruthenium Cyanide-Modified Glassy Carbon Electrode and Determination of Tetracyclines by Liquid Chromatography with Electrochemical Detection

Mixed-valent films of ruthenium oxide-ruthenium cyanide were electrodeposited onto glassy carbon and characterized for the electrocatalytic oxidation of tetracycline. The currents produced by tetracycline were higher than from previously reported electrode modifications or pretreatments. In H(2)SO(4) pH 1.0 + 0.5 M K(2)SO(4), the second-order rate constant for the reaction between tetracycline and the Ru(III/IV) couple of ruthenium oxide was 3 x 10(5) +/- 1 x 10(5) mol(-1) cm(3) s(-1), and the rate of charge diffusion through the films was 4.5 x 10(-7) +/- 3.5 x 10(-7) cm(2) s(-1). Reaction was localized at the film-solution interface. When used as detectors in liquid chromatography (in H(3)PO(4) pH 2.5 + 0.1 M KH(2)PO(4) + 20% CH(3)CN, E = 1.10 V vs SCE), the electrodes gave limits of detection (>3 S/N) of 0.1 ppm for tetracycline and oxytetracycline and 0.5 ppm for doxycycline and chlorotetracycline. These limits were suitable for FDA and Codex Alimentarius guidelines for tetracyclines in food. Recoveries of the four tetracyclines from sea and freshwater shrimp were in the range 73-111%, which was higher or similar to the previously reported recoveries from shrimp.

Method development for the quantitation of ABT-578 in rabbit artery tissue by 96-well liquid-liquid extraction and liquid chromatography/tandem mass spectrometric detection

Quantitative determination of drug concentrations in tissue samples can provide critical information for drug metabolism, kinetics, and toxicity evaluations. For analysis of tissue samples using liquid chromatography/tandem mass spectrometric (LC/MS/MS) detection, homogenization is a critical step in achieving good assay performance. Assay performance can be closely evaluated by spiking the drug directly into tissue samples prior to homogenization. It is especially important to include this assay evaluation for the analysis of artery tissue samples because artery tissue is very elastic, making it quite a challenge to develop an effective procedure for homogenization. An LC/MS/MS assay in 96-well format using liquid-liquid extraction was developed for analyzing ABT-578 in rabbit artery samples. Tissue quality control samples were prepared by spiking ABT-578 stock solutions directly into the tissue before homogenization. The usage of the tissue control samples gives a thorough evaluation of the sample preparation process that includes both homogenization and sample extraction. A 20% blood in saline solution was used as a homogenization solution. Calibration standards were made by spiking ABT-578 into rabbit whole blood. Blood quality control samples were also prepared by spiking ABT-578 into rabbit whole blood. These blood QC samples were used to confirm the validity of the calibration curve. A lower limit of quantitation of 0.050 ng/mL was achieved. The linear dynamic range of blood standards was from 0.050-30.3 ng/mL with the correlation coefficient (r) ranging from 0.9969-0.9996. Overall %CV was between 1.3 and 7.0%, and analytical recovery was between 98.2 and 105.8% for blood QC samples. The %CVs for tissue QC samples were between 6.7 and 13.0%, and analytical recovery after correction was between 93.5 and 114.3%.