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

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.

Efficacy and safety testing of mycotoxin-detoxifying agents in broilers following the European Food Safety Authority guidelines

Contamination of feeds with mycotoxins is a worldwide problem and mycotoxin-detoxifying agents are used to decrease their negative effect. The European Food Safety Authority recently stated guidelines and end-points for the efficacy testing of detoxifiers. Our study revealed that plasma concentrations of deoxynivalenol and deepoxy-deoxynivalenol were too low to assess efficacy of 2 commercially available mycotoxin-detoxifying agents against deoxynivalenol after 3 wk of continuous feeding of this mycotoxin at concentrations of 2.44±0.70 mg/kg of feed and 7.54±2.20 mg/kg of feed in broilers. This correlates with the poor absorption of deoxynivalenol in poultry. A safety study with 2 commercially available detoxifying agents and veterinary drugs showed innovative results with regard to the pharmacokinetics of 2 antibiotics after oral dosing in the drinking water. The plasma and kidney tissue concentrations of oxytetracycline were significantly higher in broilers receiving a biotransforming agent in the feed compared with control birds. For amoxicillin, the plasma concentrations were significantly higher for broilers receiving an adsorbing agent in comparison to birds receiving the biotransforming agent, but not to the control group. Mycotoxin-detoxifying agents can thus interact with the oral bioavailability of antibiotics depending on the antibiotic and detoxifying agent, with possible adverse effects on the health of animals and humans.

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.

Stability of frozen stock solutions of beta-lactam antibiotics, cephalosporins, tetracyclines and quinolones used in antibiotic residue screening and antibiotic susceptibility testing

The stability of frozen stock solutions of antibiotics belonging to three different families was evaluated using an agar diffusion test, with Bacillus subtilis as a test strain. Diameters of inhibition zones were measured at monthly intervals during 6 months, and the decline in active substance was calculated. Penicillin and amoxicillin lost nearly half of their potency, the cephalosporins ceftiofur and cefapirin one quarter, but ampicillin was more stable. The quinolones flumequine, enrofloxacin and marbofloxacin were relatively stable; the loss of activity was less than 10% after 6 months of preservation at -20 degrees C. This was also the case for doxycycline and chlortetracycline, while oxytetracycline and tetracycline lost about 25% of their potency. When used in microbiology, i.e. for residue testing or for determination of minimum inhibitory concentrations, a diminution of activity less than 25% will not be noticed. For these applications, the four tetracyclines and three quinolones tested can be kept for 6 months at -20 degrees C, while the beta-lactam antibiotics should be discarded after 3 months. Standard stock solutions of beta-lactam antibiotics and cephalosporins should preferably be used the same day when they are intended for quantitative residue analysis.

Role of zwitterionic structures in the solid-phase extraction based method development for clean up of tetracycline and oxytetracycline from honey

Solid-phase extraction (SPE) based sample clean up of tetracycline (TC) and oxytetracycline (OTC) from honey samples was evaluated using a neutral polymeric sorbent (strata-X), a weak cation exchange polymeric sorbent (strata-X-CW) and a combination of neutral and strong cation exchange sorbents (strata-X plus Strata-Screen-C or strata-X-C). Both TC and OTC are recovered in low yields from the strong cation exchange sorbents strata-X-C and Strata-Screen-C under basic (pH >9) or acidic (pH >or=2) elution conditions. The cleanest extracts along with quantitative recoveries were obtained with strata-X-CW under either acidic or basic elution conditions, as demonstrated by analysis of eluates by both LC/UV and LC/MS-MS. On the other hand, the neutral sorbent (strata-X) was less efficient in eliminating the honey matrix constituents, since it could not retain the tetracyclines with the strong organic wash needed to remove other compounds. The differences in the elution behavior of the strong and weak cation exchange sorbents is rationalized on the basis of divergent deprotonation mechanisms of the tetracyclines, which exist in the zwitterionic structures under the SPE conditions.

Control of the keto-enol tautomerism of chlortetracycline for its straightforward quantitation in pig tissues 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 edible tissues 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-electrospray ionization (ESI)-MS/MS method to analyze the CTC content in pig tissues, with the originality that it apports a solution to overcome the possible interference on the measurement of the keto-enol tautomerism equilibrium, which is influenced by several factors. Therefore, the minced tissue samples were incubated at 56 degrees C, forcing the equilibrium in favour of the CTC keto-form. The CTC keto-tautomer, as a measure of the total CTC content, was then quantified by LC-ESI-MS/MS, after further extraction of the tissue samples, consisting of a liquid extraction with sodium succinate solution (pH 4.0), followed by protein removal with trichloroacetic acid and paper filtration, and finally solid-phase clean-up on an hydrophilic-lipophilic balance (HLB) polymeric reversed-phase column. The method could be validated for pig muscle, liver and kidney tissues--for which maximum residue limits (MRLs) have been fixed by the European Union--with respect to linearity, trueness and precision, in accordance with the European guidelines.

Optimizing the integrated pulsed amperometric multicycle step waveform for the determination of tetracyclines

A method of modified integrated pulsed amperometric detection with multicycle step waveform (Multi-IPAD) following high-performance liquid chromatography (HPLC) was applied for the determination of tetracyclines (TCs) including dimethyltetracycline (DMTC), oxytetracycline (OTC) and tetracycline (TC). The key advantages of the Multi-IPAD are the abilities to enhance sensitivity and reproducibility and the ability to keep working electrode clean through the use of a high-frequent waveform alteration in integration step and the use of a cleaning potential, which is quite different from conventional three-step potential waveform. The analyses were carried out using the mobile phase of acetonitrile-water mixture solution (10:90, v/v) containing 1% perchloric acid on a C(18) column at a flow rate of 0.21 mL/min. The IPAD waveform parameters were optimized to maximize the signal-to-noise ratio (S/N) and successfully applied for the sensitive detection of TCs. The detection limits (S/N=3, 20 microL injected) were 0.07 mg/L for DMTC, 0.08 mg/L for OTC and 0.05 mg/L for TC. The peak height relative standard deviations (RSDs) of every compound for replicate injection (n=15) determined were below 4.6%.

Biotransformation of the triketone herbicide mesotrione by a Bacillus strain. Metabolite profiling using liquid chromatography/electrospray ionization quadrupole time-of-flight mass spectrometry

The metabolic pathway involved in the biotransformation of the herbicide mesotrione by the bacterial strain Bacillus sp. 3B6 was investigated by a reliable liquid chromatography/electrospray ionization quadrupole time-of-flight mass spectrometry (LC/ESI-QTOF-MS) method. The LC/ESI-MS method, both in positive and negative mode, with the assistance of MS(2) fragments and isotopic pattern analyses, allowed us to identify five metabolites. This work constitutes the first complete monitoring of mesotrione degradation kinetics. Among the transformation products found by both techniques, one was formed by intramolecular cyclization between a hydroxylamine and a keto function, which is quite a rare biological reactivity process. For each identified metabolite, a fragmentation pathway is proposed for negative and positive mode.