Analysis of thyreostatic drugs in thyroid samples by liquid chromatography tandem mass spectrometry: Comparison of two sample treatment strategies

Thiouracil: Comprehensive profile

Thiouracil, 2-sulfanylidene-1H-pyrimidin-4-one, has been used as anti-thyroid, coronary vasodilator, and in congestive heart failure. It was found to cause agranulocytosis and it is suspected to be teratogenic and carcinogenic. Owing to its high frequency of adverse reactions, especially agranulocytosis, its use was abandoned in favor of other, less toxic drugs, such as propylthiouracil and methimazole. Thiouracil refers both to a specific molecule consisting of a sulfated uracil and a family of molecules based upon the structure. An important member of this family is propylthiouracil, which is a thiourea antithyroid drug that acts by blocking the production of thyroid hormones; it also inhibits the peripheral deiodination of thyroxine to tri-iodothyronine. This profile is prepared to discuss and explain physical and chemical properties, proprietary and nonproprietary names of thiouracil and propylthiouracil. It also includes uses and applications, methods of preparation, thermal and spectral behavior and methods of analysis. In addition, metabolism, excretion and pharmacology of propylthiouracil are also discussed.

Subcritical water extraction of thyreostats from bovine muscle followed by liquid chromatography-tandem mass spectrometry

Thyreostats can be used fraudulently to promote a rapid increase in weight of breeding animals at low cost. Their severe toxicological effects impose the development of reliable analytical methods to be used in monitoring plans. This work describes an alternative approach to isolate residues of thiouracil, methyl-thiouracil, propyl-thiouracil, phenyl-thiouracil, tapazole and mercaptobenzimidazole from bovine muscle tissue. The developed procedure is based on the following three steps: i) matrix solid-phase dispersion with C₁₈ for the preliminary sample preparation; ii) subcritical water extraction (SWE) at 160°C and 100 bar; iii) clean-up on an Oasis HLB cartridge. The quantitative determination was performed by LC-MS/MS in dual polarity ionization by using internal standardization. The SWE-LC-MS/MS method was validated according to the identification criteria of the Commission decision 2002/657/EC. The relative recoveries ranged from 72 to 97%; within-lab reproducibility was less than 18%. The decision limit and the detection capability of all analytes were below the recommended concentration, set at 10 µg kg^-1, but the validation results demonstrated that this method could only be applied for screening of thiouracil and methyl-thiouracil. Besides the analytical advantages related to the use of water as solvent extraction, the procedure allowed significant removal of lipids, whose detrimental effects on instrumentation and MS sensitivity are well-known.

A method for the determination of total and reduced methimazole in various biological samples

A simple, rapid, reproducible and sensitive method based on HPLC with ultraviolet detection was developed for the determination of methimazole (MMI) in animal tissues and plasma samples. Under the optimum experimental conditions, the calibration curves for MMI were linear in the tested range 0.5-20 mg kg(-1) tissue sample (mg l(-1) plasma) with correlation coefficients better than 0.99. The performance of the proposed method was tested for the determination of MMI levels in brain, liver, thyroid gland and plasma of MMI-treated hens, as well as in their eggs and embryos. The proposed method reduces time and simplifies the sample preparation procedure.

Use of gel permeation chromatography for clean-up in the analysis of coccidiostats in eggs by liquid chromatography-tandem mass spectrometry

An analytical method for determination and confirmation of nine coccidiostatics in eggs is reported. Ethyl acetate is used as extraction solvent, with satisfactory results, and simple automated clean-up is based on gel-permeation chromatography (GPC) . The target compounds are then analysed by liquid chromatography-electrospray ionization-tandem mass spectrometry. The method was validated in-house in accordance with Commission Decision 2002/657/EC. Trueness and precision were determined at four concentrations, and the mean errors obtained were <10 %, with relative standard deviations ranging from 3 to 18 %. For three non-authorized coccidiostatics (clopidol, ethopabate, and ronizadole), decision limit and detection capability were in the ranges 0.12-0.16 and 0.18-0.23 μg kg(-1), respectively. The results obtained prove the suitability of this new analytical method for routine monitoring of these substances in eggs.

Comparison of different sample pre-treatments for multi-residue analysis of organochlorine and pyrethroid pesticides in chrysanthemum by gas chromatography with electron capture detection

The widespread use of insecticides in Chinese herbal medicines has created a compelling need for the development of a multiresidue analytical method to help assure herbs safety. The operating variables affecting the performance of the multiresidue analysis of 34 organochlorine and 12 pyrethroid pesticides in chrysanthemum, a widely used kind of Chinese herbal medicines, were evaluated. Three different extraction solvents including n-hexane and its mixtures with acetone and petroleum ether were compared, and n-hexane was found to be an appropriate option. A combination of gel permeation chromatography and SPE was selected as the optimum cleanup, in comparison with dispersive SPE, or the two former methods alone. The determination of the 46 pesticide residues in the spiked chrysanthemum samples was performed by GC with electron capture detection. The average recoveries ranged from 71.3 to 102.6% with RSDs of 1.4-15.7% for all of the pesticides. The LOQs were in the range of 0.0015-0.2 mg/kg, while the LODs were between 0.0005 and 0.1 mg/kg. The satisfactory accuracy, and precision, in combination with a good separation and few interferences, have demonstrated the strong potential of this technique for its application in chrysanthemum analysis.

Analysis of antithyroid drug residues in food animals

In the late 1970s, concerns were raised regarding why antithyroid drugs were being administered to food animals to promote growth despite the fact that they had been implicated as being carcinogenic and teratogenic; the growth promotion process produced an inferior quality meat with increased water retention in the animal's gastrointestinal tract. An increased incidence of aplasia cutis (a characteristic scalp defect) in consumers in Spain was linked to an increased consumption of antithyroid-contaminated meat. Therefore, to protect human health, the EU banned the use of antithyroid drugs in food animal production in 1981. This article reviews the impact of this regulatory decision on the regulatory analysis of these compounds in foods of animal origin. It discusses the physiology of the thyroid gland, the chemistry of antithyroid drugs and critically evaluates the suitability of the analytical methods that have been developed and validated to support enforcement of the regulation.

Optimization of ion-pair based hollow fiber liquid phase microextraction combined with HPLC-UV for the determination of methimazole in biological samples and animal feed

Ion-pair based hollow fiber liquid phase microextraction (IP-HFLPME) coupled with high performance liquid chromatography-ultraviolet detection was applied for the preconcentration and determination of methimazole in biological samples and animal feed. Optimization of the conditions for the high extraction efficiency was studied simultaneously using the experimental design. For the first step, the Plackett-Burman design was applied to screen the significant factors on the extraction efficiency. Central composite design (CCD) was then used for the optimization of important factors and the response surface equations were obtained. The optimum experimental conditions were donor phase pH, 12.2; extraction temperature, 45°C; extraction time, 50 min; sodium perchlorate concentration, 1.5 M; cetyltrimethylammonium bromide concentration, 0.65 mM, and without salt addition in donor phase. The limit of detection and the dynamic linear range were in the range of 0.1-0.7 μg L(-1) and 0.5-1000 μg L(-1), respectively. Preconcentration factors were obtained in the range of 93-155 in different matrices. Finally, the performance of the proposed method was tested for the determination of trace amounts of methimazole in plasma, urine, bovine milk, and animal feed samples, and satisfactory results were obtained (RSDs < 7.1%).