Extraction, clean-up and gas chromatography-mass spectrometry characterization of zilpaterol as feed additive in fattening cattle

Determination of zilpaterol in a residue depletion study using LC-MS/MS in cattle plasma, muscle, liver and kidney

Zilpaterol is a β-agonist compound which promotes fat loss and muscle gain in cattle, providing economic benefits. However, zilpaterol residues in the animal might introduce a significant risk to humans after consumption. In the present manuscript, a highly specific, sensitive method using Selected Reaction Monitoring (SRM) in positive electrospray ionization (ESI +) mode by liquid chromatography coupled to triple quadrupole mass spectrometry (LC-MS/MS) for plasma, muscle, liver and kidney is presented. For method development, composition of the aqueous mobile phase, precipitation agent, and solid phase extraction (SPE) conditions were optimized. The method was fully validated showing a good linearity and recovery average greater than or equal to 97 % for all matrices. The method was applied to residue depletion studies in cattle after withdrawal of zilpaterol supplementation at 3, 4, 5 and 6 days showing that tissues can be consumed by humans after 4th day of zilpaterol withdrawal.

Detection and Confirmation of Zilpaterol in Equine Hair Using Liquid Chromatography - Mass Spectrometry

Zilpaterol is a β₂ -adrenergic agonist and a repartitioning agent that has a high potential for abuse in equine performance athletes. Analysis of zilpaterol in hair is an alternative sampling matrix that extends detection time periods beyond those found in urine or blood samples. Our laboratory has been screening for zilpaterol in hair for many years and recently detected and confirmed its presence in official samples. Accordingly, a liquid chromatography - mass spectrometry method was developed and validated to detect and confirm zilpaterol in equine hair. Briefly, equine hair was decontaminated, cut, and pulverized prior to disruption and liquid-liquid extraction in basic conditions. Following extraction, the sample was introduced to an Agilent 1260 HPLC and zilpaterol was separated using a reverse phase gradient with a total run time of 12.5 minutes. Following chromatographic separation, zilpaterol and its corresponding stable isotope labeled internal standard were introduced via positive mode electrospray ionization to a Thermo Q-Exactive Plus mass spectrometer and spectra collected using parallel reaction monitoring. The methodology was validated using in-house criteria including characterization of accuracy, precision, recovery, linear range, matrix effects, limit of detection and limit of quantitation and the method was found to be fit-for-purpose to confirm the presence of zilpaterol in equine hair. This methodology has been used to detect and confirm the presence of zilpaterol from out-of-competition hair samples submitted by regional racing authorities.

[Determination of Zilpaterol in Livestock Products by LC-MS/MS]

An analytical method for the determination of zilpaterol in livestock products was developed. The sample was stirred with n-hexane and n-hexane saturated acetonitrile, and zilpaterol in the sample was extracted with acetonitrile. The extract was cleaned up on a ODS cartridge column (1 g) and SCX cartridge column (500 mg). The LC separation was carried out using an Inertsil ODS-4 column and linear gradient elution with 0.1%formic acid and acetonitrile containing 0.1% formic acid as mobile phase. Detection of MS was carried out positive ion electrospray ionization mode. Average recoveries (n=5) of zilpaterol from 6 kinds of livestock products fortified at the MRLs (0.01 mg/kg) were 87.0-99.4%, and the relative standard deviations were 2.4-6.3%. The limits of quantitation were 0.01 mg/kg.

Simultaneous analysis of spectinomycin, halquinol, zilpaterol, and melamine in feedingstuffs by ion-pair liquid chromatography-tandem mass spectrometry

A method for the simultaneous analysis of veterinary drug residues (spectinomycin, halquinol, and zilpaterol) and contaminants (melamine) in feedingstuffs by liquid chromatography-tandem mass spectrometry was developed. Method performance for all analytes was evaluated by reversed-phase liquid chromatography, reversed-phase with altered chemical equilibrium, and hydrophilic interaction (HILIC) as chromatographic modes. Validation was in accordance to Commission Decision 657/2002/CE, by considering the best chromatographic approach. Ion-pair liquid chromatography with C₁₈ as stationary phase led to the lowest random uncertainties, effective analyte separation and shorter time of analysis. Low precision deviations and good recovery rates were obtained and thus method reliability and sensitivity could be consolidated. Method applicability was evaluated by the analysis of samples of feedingstuffs, such as cattle, pig, and poultry feeds, feed ingredients of both animal and vegetable origins, and mineral feeds. Some samples showed quantifiable concentrations of halquinol and zilpaterol, reinforcing the importance of this new analytical control method.

Simultaneous determination of β-agonists and monitoring in bovine tissues by liquid chromatography-tandem mass spectrometry

The misuse of β-agonists leads to a potential risk to public health and is forbidden in many countries. We developed a rapid, sensitive and reliable multi-residue detection method for zilpaterol, ractopamine, and clenbuterol in bovine tissues by liquid chromatography–tandem mass spectrometry. Residues were extracted in ethyl acetate after protein precipitation, and then analyzed by the developed method. Good linearities (R2 > 0.99) were observed, and the recoveries of zilpaterol, ractopamine, and clenbuterol were 99%, 74%, and 102%, respectively. The limits of quantitation for zilpaterol, ractopamine, and clenbuterol were 1.3, 5.0, and 1.7 ng/g, respectively. The method is also applied successfully to bovine tissues within the Korean National Residue Programme. None of the 3 β-agonists were detected from 50 domestic samples. However, zilpaterol (6.3 ng/g) was quantified in one out of the 50 imported samples. The application of this method will be helpful in quality control analysis of β-agonists residues in bovine tissues.

Determination of multiresidue analysis of β-agonists in muscle and viscera using liquid chromatograph/tandem mass spectrometry with Quick, Easy, Cheap, Effective, Rugged, and Safe methodologies

The official analytical method of the Taiwan Food and Drug Administration, Ministry of Health and Welfare for testing for veterinary drug residues in foods is the multiresidue analysis of β-agonists. Samples are pretreated through liquid–liquid extraction and solid-phase extraction. This method is time consuming and requires the intensive use of solvents. To improve analytical efficiency and reduce costs, our study incorporated QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) techniques to establish a new method of multiresidue analysis of β-agonists in animal muscle and viscera. The pretreatment time was shortened and solvent usage was minimized. The modified analysis was conducted using liquid chromatography/tandem mass spectrometry (LC–MS/MS) and quantification was performed using multiple reaction monitoring. The results demonstrated that the correlation coefficients of the tissue calibration curve were higher than 0.99 and the limit of quantification (LOQ) was 1 ppb. The average recoveries in spiked samples varied from 70% to 120%, and the relative difference between duplicated analysis results was lower than 10%. On the basis of the results, the proposed method was concluded to be an appropriate procedure for determining the presence of β-agonists, and demonstrated the advantages of high recovery rates in spiked samples, high precision, reduced analysis time and solvent usage, and lower costs.

Rapid screening of toxic salbutamol, ractopamine, and clenbuterol in pork sample by high-performance liquid chromatography—UV method

A rapid and simple high-performance liquid chromatography–UV method was developed for the separation and quantification of salbutamol, ractopamine, and clenbuterol in pork. A mixture of acetonitrile–formic acid–ammonium acetate was used as the mobile phase to separate three β-agonists on a C18 column with gradient. The effects of the addition of formic acid and ammonium acetate to mobile phases on the separation of β-agonists were investigated. These additives can greatly improve the resolution and sensitivity. Under the optimized chromatographic condition, this separation does not need extra sample preparation. Complete baseline separation of three β-agonists was achieved in < 20 minutes; the linear range is 0.2–50 μg/L with a correlation coefficient R² value of > 0.99. Excellent method reproducibility was found by intra- and interday precisions with a relative standard deviation of < 3%. The detection limit (S/N = 3) was found to be <0.05 μg/L; this method can be used for routine screening of the β-agonist residues in foods of animal origin before being identified by confirmatory methods.

Tissue residues and urinary excretion of zilpaterol in sheep treated for 10 days with dietary zilpaterol

Zilpaterol is a beta-adrenergic growth promoter approved in Mexico and South Africa for use in cattle. Understanding the rates of zilpaterol depletion from tissues and urine is of interest for the development of strategies to detect the off-label use of zilpaterol. Eight sheep were fed 0.15 mg/kg/day dietary zilpaterol hydrochloride (Zilmax) for 10 consecutive days; two sheep each were slaughtered 0, 2, 5, and 9 days after discontinuation of exposure to the zilpaterol-containing diet. Tissue zilpaterol levels rapidly decreased during the withdrawal period. On the basis of LC-MS/MS-ES (external standard) measurements, liver zilpaterol residues in sheep were 29.3, 1.5, 0.13, and 0.10 ng/g after 0, 2, 5, and 9 day withdrawal periods, respectively; kidney residues were 29.6, 1.10, and 0.09 ng/g and below the detection limit; and muscle residues were 13.3, 0.86, 0.12, and 0.08 ng/g at the same respective withdrawal periods. Between-animal variation in urinary zilpaterol concentrations during the feeding period was considerable, although zilpaterol concentrations converged somewhat as steady state was reached. During the first 3 days of the withdrawal period, zilpaterol elimination followed a first-order excretion pattern, having an average elimination half-life of 15.3 +/- 1.8 h. Urinary zilpaterol concentrations during the withdrawal period were determined using ELISA, HPLC-fluorescence, LC-MS/MS-ES (external standard), and LC-MS/MS-IS (internal standard). Comparison of these methods showed a high correlation with each other. With the exception of LC-MS/MS-IS, the regression coefficients of the linear equations with a zero intercept were between 0.90 and 1.25, indicating the near equivalence of the methods. Because of its simplicity, ELISA is a convenient assay for determining zilpaterol levels in urine giving similar results to HPLC-fluorescence and LC-MS/MS-ES without requiring the extensive cleanup of the latter methods.

Inhibitory effects of the beta-adrenergic receptor agonist zilpaterol on the LPS-induced production of TNF-alpha in vitro and in vivo

In this study the anti-inflammatory properties of zilpaterol, a beta2-adrenergic receptor (AR) agonist specifically developed as a growth promoter in cattle were investigated. Although zilpaterol has a different structure compared with the beta2-AR agonists known to date, it was noted that it was able to bind to both the beta2-AR (Ki = 1.1 x 10(-6)) and the beta1-AR (Ki = 1.0 x 10(-5)). Using lipopolysaccharide (LPS)-exposed U937 macrophages, the production of cyclic adenosine-3',5'-cyclic monophosphate (cAMP) and tumor necrosis factor alpha (TNF-alpha) were investigated. Zilpaterol inhibited TNF-alpha release and induced intracellular cAMP levels in a dose-dependent manner. The inhibition of TNF-alpha release and induction of cAMP production was mainly mediated via the beta2-AR, as indicated by addition of beta1- and beta2-specific antagonists. The effects of zilpaterol were investigated in LPS-treated male Wistar rats after pretreatment with zilpaterol. Zilpaterol dosed at 500 microg/kg body weight reduced the TNF-alpha plasma levels. In conclusion, zilpaterol is a beta2-adrenergic agonist and an inhibitor of TNF-alpha production induced by LPS both in vivo and in vitro.

Development of a monoclonal antibody-based enzyme-linked immuosorbent assay for the beta-adrenergic agonist zilpaterol

Zilpaterol is a beta-adrenergic agonist approved for use as a growth promoter in cattle in South Africa and Mexico but not in the European Union, United States, or Asia. Here, we report the development of a monoclonal antibody-based enzyme-linked immunosorbent assay (ELISA) for zilpaterol. Mice immunized with zilpaterol-butyrate-keyhole limpet hemocyanin were utilized for monoclonal antibody generation whereas zilpaterol-butyrate-bovine serum albumin was used as a coating antigen for ELISA. Thirteen clones were isolated, and after the initial sensitivity and isotyping experiments, three clones were selected for further ELISA optimization. Studies indicated that the optimum pH was near 7.4. Clone 3H5 had the highest sensitivity to zilpaterol and some interaction with clenbuterol and terbutaline at high concentrations but not other N-alkyl [bamethane, (-)-isoproterenol, (+)-isoproterenol, metaproterenol, or salbutamol] or N-arylalkyl (fenoterol, isoxsuprine, ractopamine, or salmeterol) beta-agonists tested. However, clone 3H5 was not functional at high salt concentrations, which precluded further development for urine analysis. Clone 2E10 showed increased sensitivity as salt concentrations were increased and did not cross-react with any of the structural analogues tested. However, its sensitivity to salt and urine concentration changes could cause high variability. Clone 7A8 showed good sensitivity and only a modest change with the salt concentration changes. Clone 7A8 also demonstrated smaller changes in IC(50) and B(0) with increasing sheep urine or cattle urine concentrations as compared to clones 2E10 or 3H5 and, thus, was selected for further development. The IC(50) for all of the antibodies showed exponential increases with increasing organic solvents concentrations, making it desirable to minimize solvent levels. In conclusion, a sensitive, specific zilpaterol monoclonal antibody-based ELISA has been developed that can serve as a rapid screening assay.

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.

Enzyme-linked immunosorbent assay development for the beta-adrenergic agonist zilpaterol

Zilpaterol is an beta-adrenergic agonist approved for use in cattle in South Africa and Mexico as a growth promoter. It is not currently approved for use in the EU, USA, or Asia. Here, we report the development of an ELISA for zilpaterol. Zilpaterol was reacted with ethyl 4-bromobutyrate followed by refluxing in 0.1 M potassium hydroxide. The resulting hapten was reacted with two carrier proteins, bovine serum albumin (BSA) or keyhole limpet hemocyanin (KLH), using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) as an activating agent. Immunization of goats with the zilpaterol-butyrate-KLH resulted in an antibody useful for an ELISA. We utilized zilpaterol-butyrate-BSA as a coating antigen for ELISA development. The average IC(50) derived from the developed zilpaterol immunoassay was 3.94 +/- 0.48 ng/mL (n = 25). The antibody did not cross react with N-alkyl [bamethane, clenbuterol, (-)-isoproterenol, (+)-isoproterenol, metaproterenol, or salbutamol] or N-arylalkyl (dobutamine, fenoterol, isoxsuprine, ractopamine, or salmeterol) beta-agonists. The assay was tolerant of up to 10% (v/v) of acetone, ethanol, or methanol, and 15% (v/v) of acetonitrile or DMSO. Salt concentrations ranging from 0.05 to 1.0 M minimally affected B(0) or IC(50) values. When buffer pH was <7 or >8.8, the IC(50) values increased in comparison to those measured at pH 7.4. In conclusion, a sensitive, specific zilpaterol ELISA has been developed that can serve as a rapid screening assay.