Determination of fipronil and its metabolites in chicken egg,muscle and cake by a modified QuEChERS method coupled with LC-MS/MS

An easy-to-use method for determining the levels of fipronil and its metabolites (fipronil-desulfinyl, fipronil-sulfone and fipronil-sulfide) in chicken egg, muscle and cake was developed and validated using a modified quick, easy, cheap, effective, rugged and safe (QuEChERS) approach coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. The samples were extracted using acetonitrile, salted out with sodium chloride at ?20°C, and then purified by combined PSA and C18 phases and anhydrous magnesium sulphate. The recoveries were 80.4–119% with relative standard deviations (RSDs) < 10% for the different matrixes. The validated method was used to analyse the target compounds in 214 real samples collected in Beijing. The metabolite fipronil-sulfone was detected in most of the samples and was identified as the main residue in the egg and cake. The method was validated using a proficiency test for fipronil in products of animal origin published by Wageningen University &; Research in 2017.     

Determination of Baclofen Residue in Muscle,Liver, Kidney and Fat of Swine by Liquid Chromatography-Tandem Mass Spectrometry

Baclofen was illegally used in veterinary clinical medicine as a growth-promoting agent. To date, few methods have been developed for the monitoring of baclofen in animal tissues. In this study, a sensitive and efficient liquid chromatography-tandem mass spectrometry (LC-MS/MS) method to identify and quantify baclofen in the muscle, liver, kidney, and fat of swine was developed and validated. Baclofen was extracted from tissues with ammonium acetate buffer (pH 5.2) and isolated with isopropyl-ethyl acetate (4:6, v/v). Then, a solid phase extraction using MCX cartridge was used to clean up the extracts. The elution was evaporated to dryness and reconstituted with water/methanol (90:10 v/v). All samples were determined by LC-MS/MS system through positive ionization in a multiple reaction monitoring (MRM) mode. The proposed method was validated by evaluation of specificity, linearity, recovery, accuracy, precision, LOD, and LOQ values according to Commission Decision 2002/657/EC. Estimated limit of quantification for baclofen in the muscle, liver, kidney, and fat of this method was 1.00 μg/kg, respectively. The mean intra- and inter-day assay accuracies fell within a range 88.5–93.9% and 86.2–93.2%, respectively. The mean intra- and inter-day precisions were 1.78 and 4.95% (RSD < 15%), respectively. The proposed method has proved to be suitable for accurate quantitative determination of baclofen for residue analysis.     

Simultaneous determination of veterinary drugs in livestock foods and seafoods using liquid chromatography/tandem mass spectrometry

A simultaneous determination of veterinary drugs in livestock food and seafood using liquid chromatography with tandem mass spectrometry (LC/MS/MS) was developed. Veterinary drugs were extracted with 95% acetonitrile. The solution was passed through a Florisil column, and the solvent was replaced with phosphate buffer. The extract was charged on a Sep-Pak Plus C(18) mini-column and divided into 40% methanol eluate fraction and 70% acetonitrile eluate fraction. Test solutions were analyzed by LC/MS/MS with gradient elution. By using this method, 37 kinds of veterinary drugs were obtained with over 60% recovery, and quantitation was possible in cattle muscle, egg and fish. This method was inapplicable to 28 kinds of veterinary drugs. Although quantitation was not achieved, 42 other kinds of veterinary drugs can be screened. Since the limit of quantitation for this method is less than the provisional limit in general, it is useful as a screening method in residual analysis of veterinary drugs.     

Multi-residue method for the confirmation of four avermectin residues in food products of animal origin by ultra-performance liquid chromatography–tandem mass spectrometry

A confirmatory method was developed for the rapid determination of abamectin, ivermectin, doramectin and eprinomectin residues in various food products of animal origin, such as pork muscle, pork liver, fish and milk. Samples were homogenized, extracted and de-proteinized by acetonitrile, cleaned via two-step cleaning procedure using Bond Elut C₁₈ SPE columns and then alumina-N cartridges. All the four avermectin residues in different animal-food products were simultaneously separated and determined by ultra-performance liquid chromatography–electrospray ionization tandem mass spectrometry (UPLC–ESI–MS/MS) within 3.5?min. Data acquisition under positive ESI–MS/MS was performed by applying multiple reaction monitoring (MRM) for both identification and quantification, and mass spectrometric conditions were optimized to increase selectivity and sensitivity. The matrix-matched calibration curves for different matrices, such as pork muscle, pork liver, fish and milk, were constructed and the interference effect of different sample matrices on the ionization was effectively eliminated. The UPLC–MS/MS method was validated with satisfactory linearity, recovery, precision and stability. Matrix-matched calibration curves of abamectin, ivermectin, doramectin and eprinomectin in four different matrices were linear (r^{2 ?}≥?0.990, goodness-of-fit coefficients ≤12.8%) in the range 2.5–200?µg?kg^?1. The limits of detection and quantification for the four avermectins were in the range 0.05–0.68 and 0.17–2.27?µg?kg^?1, respectively. Recoveries were 62.4–104.5% with good intra- and inter-day precision. The method was rapid, sensitive and reliable, and can be applied to the quantitative analysis of avermectin residues in different animal-food products.     

Development of a Liquid Chromatography Tandem Mass Spectrometric Method for Simultaneous Determination of 15 Aminoglycoside Residues in Porcine Tissues

A quantitative and confirmatory method has been developed for simultaneous determination of 15 aminoglycoside (AG) residues in porcine tissues (muscle, liver and kidney) by liquid chromatography tandem mass spectrometry (LC-MS/MS). The analytes were extracted from different matrices with aqueous trichloroacetic acid solution (5 %, w/v) followed by solid phase extraction (SPE) clean-up under optimised conditions. Due to the different pK _a values of the compounds, two consecutive SPE steps using Oasis HLB cartridges were used to purify all 15 AGs from sample extracts, with 9 AGs quantitatively retained on Oasis HLB cartridges at pH?<1 and the other 6 AGs retained at pH 8.5. The analytes were separated on a reversed-phase C18 column and eluted with water and acetonitrile containing the ion-pair reagent heptafluorobutyric acid (HFBA). The LC-MS/MS method was validated according to Decision 2002/657/EC. The optimised procedure was successfully applied to analyse 100 real porcine tissue samples (60 muscles, 20 livers and 20 kidneys) collected from local markets in southern China, demonstrating that the method is robust and useful for determination of residues of the 15 target AGs in porcine tissue samples.     

Selenium speciation analysis of Misgurnus anguillicaudatus selenoprotein by HPLC–ICP–MS and HPLC–ESI–MS/MS

Analytical methods for selenium (Se) speciation were developed using high-performance liquid chromatography (HPLC) coupled to either inductively coupled plasma mass spectrometry (ICP?CMS) or electrospray ionization tandem mass spectrometry (ESI?CMS/MS). Separations of selenomethionine (Se-Met) and selenocysteine (Se-(Cys)₂) with favorable peak shape and resolution were obtained by both HPLC-ICP-MS and HPLC?CESI?CMS/MS. Both methods achieved low limits of detection, high sensitivity and favorable stability. With HPLC?CESI?CMS/MS, signal suppression was observed when complex matrix was co-eluted, but excellent structural characterization was still achieved. Thus, HPLC-ICP-MS is better for the detection of Se species, and HPLC?CESI?CMS/MS is essential for molecular identification and confirmation. A water-soluble selenoprotein from purified M. anguillicaudatus muscle tissue was analyzed by the two complementary systems (HPLC-ICP-MS and HPLC?CESI?CMS/MS) with high sensitivity and accuracy. The results demonstrated that Se-Met was the predominant selenoamino acid in the purified selenoprotein from M. anguillicaudatus muscle tissue, and the concentration of Se-Met in the selenoprotein was 6.280?mg/kg (dry mass). In addition, in HPLC-ICP-MS, an unknown Se-containing compound with similar polarity to Se-(Cys)₂ was discovered. Using complementary data from HPLC?CESI?CMS/MS, it was determined that this unknown Se-containing compound was not Se(Cys)_2.     

Optimisation and validation of a quantitative and confirmatory LC-MS method for multi-residue analyses of β-lactam and tetracycline antibiotics in bovine muscle

A multi-residue method for the determination of the β-lactam antibiotics ampicillin, cefazolin, cloxacillin, dicloxacillin, nafcillin, oxacillin, penicillin G, penicillin V and the tetracyclines chlotetracycline, tetracycline and oxytetracycline was optimised and validated in bovine muscle. The method is based on the extraction of the residues from muscle using water/acetonitrile (2/8, v/v) with subsequent use of dispersive solid-phase C18 and hexane for purification. Extracts were analysed using ultra-performance liquid chromatography (UPLC-MS/MS) coupled with the mass spectrometer in positive electrospray ionisation mode (ESI+) for all analytes. The method was validated according to the requirements of European Commission Decision 2002/657/EC. The validation results were obtained within the MRL range of 0-1.5 of the MRL, with recoveries varying from 90% to 110% and CV < 20% (n = 54), except for cloxacillin, dicloxacillin and nafcillin. However, matrix interference was observed. The decision limit (CCα) ranged from 10% to 15% of the MRL. The uncertainty measurement was estimated based on both bottom-up and top-down strategies and the uncertainty values were found to be lower than 20% of the MRL. The method has a simple extraction procedure whereby analytes are separated with reasonable resolutions in a single 11-min chromatographic run. According to the validation results, this method is suitable for monitoring β-lactams and tetracyclines according to National Program for Residue and Contaminant Control - Brazil (NPRC-Brazil) in bovine muscle.     

Confirmatory method for the determination of various acetylgestagens in animal kidney fat using liquid chromatography–tandem mass spectrometry

A confirmatory method has been developed and validated that allows for the simultaneous detection of medroxyprogesterone acetate (MPA), megestrol acetate (MGA), melengestrol acetate (MLA), chlormadinone acetate (CMA) and delmadinone acetate (DMA) in animal kidney fat using liquid chromatography–tandem mass spectrometry (LC–MS/MS). The compounds were extracted from kidney fat using acetonitrile, defatted using a hexane wash and subsequent saponification. Extracts were then purified on Isolute? CN solid-phase extraction cartridges and analysed by LC–MS/MS. The method was validated in animal kidney fat in accordance with the criteria defined in Commission Decision 2002/657/EC. The decision limit (CCα) was calculated to be 0.12, 0.48, 0.40, 0.63 and 0.54 µg kg^–1, respectively, for MPA, MGA, MLA, DMA and CMA, with respective detection capability (CCβ) values of 0.20, 0.81, 0.68, 1.07 and 0.92 µg kg^–1. The measurement uncertainty of the method was estimated at 16, 16, 19, 27 and 26% for MPA, MGA, MLA, DMA and CMA, respectively. Fortifying kidney fat samples (n = 18) in three separate assays showed the accuracy of the method to be between 98 and 100%. The precision of the method, expressed as % RSD, for within-laboratory reproducibility at three levels of fortification (1, 1.5 and 2 µg kg^–1 for MPA, 5, 7.5 and 10 µg kg^–1 for MGA, MLA, DMA and CMA) was less than 5% for all analytes.     

Analysis of Ascorbic Acid and Isoascorbic Acid in Orange and Guava Fruit Juices Distributed in Thailand by LC-IT-MS/MS

This work describes the determination of ascorbic acid (AA) and isoascorbic acid (IAA) in fruit juices by liquid chromatography coupled with ion trap tandem mass spectrometry (LC-IT-MS/MS), with a reversed phase column (C₁₈) and simple isocratic conditions of 0.1 % formic acid. The negative ion mode of electrospray ionization (ESI) and the MS/MS transition of m/z 175 were used for the quantitation of AA- and IAA-generated product ions with m/z 115. The method was validated in terms of linearity, limit of detection (LOD), limit of quantitation (LOQ), precision, and accuracy. Good linearity was achieved with 0.6 and 1.8 μg/mL for the LOD and LOQ, respectively. The intraday and intermediate precisions were approximately 4 and 7 %, respectively. Recovery percentages ranged from 88 to 108 %. All validation parameters were found to be within the acceptable range for both AA and IAA. Hence, the proposed method is suitable for simultaneously determining AA and IAA. Fourteen fruit juice samples were analyzed including fruit juices from supermarkets, local markets, and laboratory preparations. Ten fruit juice samples (100 %) from different brands in the supermarkets were investigated for AA and IAA content. AA could be detected in all the samples, ranging from 5.2?±?2 to 44.4?±?1.3 μg/mL, and the values of vitamin C in 4 guava samples were less than the values specified by the manufacturer. IAA was observed in 4 of 10 samples ranging from 3.4?±?0.9 to 78.3?±?3.9 μg/mL, and the highest value of IAA was approximately two fold higher than the highest value of AA. For freshly prepared fruit juices, AA was detected in both local market- and laboratory-prepared juices. The value ranged from 13.2?±?0.9 to 105.1?±?1.3 μg/mL. In addition, the AA stability after opening the package was evaluated. The results showed that after 4 days of storage in the refrigerator, approximately 30 and 15 % losses of AA were observed for the orange and guava juices, respectively. Fresh fruit juices were thus demonstrated to be good sources of AA, with the highest value observed for guava juice prepared in the laboratory.     

Analysis of isothiazolinone biocides in paper for food packaging by ultra-high-performance liquid chromatography–tandem mass spectrometry

A novel and simple method to detect isothiazolinone-type biocides (2-methyl-3-isothiazolinone (MI), 5-chloro-2-methyl-3-isothiazolinone (CMI), 1,2-benzisothiazolinone (BIT) and 2-octyl-3-isothiazolinone (OIT)) in paper used for food packaging by ultrasonic extraction coupled with UPLC-MS/MS was developed. Parameters affecting process efficiency such as extraction solvents, UPLC mobile phase, gradient elution procedure and MS/MS conditions were studied to optimise the operating conditions. Using the optimised gradient elution procedure, the retention time was less than 6?min. The limits of detection (LODs) were found to be between 0.001 and 0.010?mg?kg^?1, which was validated using actual concentrations. After diluting the standard solution with a blank matrix, the linear calibration curve ranges were 0.002–1.000?mg?kg^?1 for BIT and OIT, 0.005–1.000?mg?kg^?1 for MI, and 0.020–1.000?mg?kg^?1 for CMI, with correlation coefficients higher than 0.9985 (n?=?6). A good level of precision with a mean recovery greater than 81.3% and a relative standard deviation (RSD) less than 6.2% were also obtained. A methodology has been proposed for the analysis of isothiazolinones in paper.     

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.     

Characterization of Longissimus thoracis, Semitendinosus and Masseter muscles and relationships with technological quality in pigs. 2. Composition of muscles

The composition of three porcine muscles (Longissimus thoracis: LT, Semitendinosus: ST, Masseter: MS) was characterized and its link with muscle quality was evaluated. The LT muscle had a higher content of tyrosine, tryptophan, and carbohydrates and a lower content of vitamin E and haem iron than the MS muscle, while the ST had similar composition to MS but a lower content of haem iron. Large differences between muscles were observed in relative amounts of most of the major fatty acids. The LT muscle had higher saturated fatty acids (SFA) and n− 6:n− 3 fatty acid ratio, and lower polyunsaturated fatty acids (PUFA), PUFA:SFA ratio, unsaturation index and average fatty acid chain length than the ST and MS muscles. Muscle pH, redness and chroma were positively correlated with vitamin E and unsaturated lipids and negatively correlated with tyrosine, tryptophan, carbohydrates and saturated lipids, whereas muscle lightness and expressible juice showed similar correlations but an opposite sign with these variables.     

Single-Step Multiresidue Determination of β-Lactam Antibiotics and β-Agonists in Porcine Muscle by Liquid Chromatography-Tandem Mass Spectrometry

A multiresidue method has been optimized and validated for the rapid determination of 12 veterinary drugs belonging to β-agonists and β-lactam antibiotics in porcine muscle. It has been based on liquid chromatography-tandem mass spectrometry and a simple extraction procedure using acetonitrile/H₂O. The extract was centrifuged, and the supernatant was directly analyzed by LC-MS/MS in positive ion mode with multiple reaction monitoring (MRM). The linearity of each analyte was almost the coefficient of determination (r) > 0.99. Mean recoveries for all analytes ranged from 74.6 to 115.3% with intra-day RSD ≤ 17.2% and inter-day RSD ≤18.1%. Limits of detection (LODs) and limits of quantification (LOQs) ranged from 0.4 to 2.0 and 1.0 to 8.0 ng/g, respectively. Finally, the validated method was successfully applied to the quantitative analysis of real samples, and clorprenaline was detected in one out of 15 pork samples.     

Liquid Chromatography-Tandem Mass Spectrometry Determination and Depletion Profile of Chlortetracycline,Doxycycline, and Oxytetracycline in Broiler Chicken Muscle After Oral Administration

A simple and fast method based on liquid chromatography–electrospray ionization-tandem mass spectrometry (LC–ESI-MS/MS) was developed and validated for determination of tetracyclines in broiler chicken muscle. Sample preparation was performed using extraction with acetonitrile, followed by low-temperature purification (at ??20 °C) and further concentration. The chromatographic analysis was carried out using a Zorbax SB-C18 column with gradient elution using water and methanol both acidified with 0.025 M of formic acid. Mass spectrometry with electrospray ionization was operated in positive polarity using selected reaction monitoring (SRM) analysis mode, achieving the requirements of four identification points for each compound. Demeclocycline was used as internal standard. The method validation was done according to the criteria of Commission Decision 2002/657/EC. Parameters such as recovery, matrix effects, selectivity/specificity, linearity, precision (intra- and inter-day precision), accuracy, limits of detection (LOD) and quantification (LOQ), decision limit (CCα), detection capability (CCβ), and robustness were determined. Intra-day precision values were within the range 2.2–5.8% and inter-day precision was less than 10% for all analytes. Accuracy ranged from 98.2 to 103.2%. The method was successfully applied for depletion studies of chlortetracycline, doxycycline, and oxytetracycline in broiler chicken tissues after multiple oral administrations. After the depletion studies, the present study support more prudent use of CTC, DOX, and OTC for treatment of chickens and suggest a dose of 60 mg kg^?1 body weight for CTC and OTC and 20 mg kg^?1 body weight for DOX, orally administrated for five consecutive days.     

Simultaneous detection of 15 antibiotic growth promoters in bovine muscle,blood and urine by UPLC-MS/MS

ABSTRACT

An analytical method was established for the rapid detection of antibiotic growth promoters (AGPs) in bovine muscle, and bovine blood and bovine urine, using ultra high performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS). After the addition of an aqueous solution of EDTA-Na₂, the pH of bovine urine samples was directly adjusted to 5.2 by acetic acid-ammonium acetate and purified by HLB solid-phase extraction cartridge; bovine muscle and bovine blood samples processing were extracted with acetonitrile (ACN) and ACNwater (90:10; v/v) without any purification step. The samples were then centrifuged, concentrated and analysed by UPLC-MS/MS on an ACQUITY UPLC® BEH C18 column using gradient elution. The developed method was validated and mean recovery percentages at three spiked levels were 74–119%, 76–115% and 76–119%, respectively, in bovine muscle, bovine blood, and bovine urine. The relative standard deviation (RSD) ranged from 1.0% to 14.7% in spiked bovine muscle, bovine blood and bovine urine. The limits of detection (LOD) of all analytes were in the ranges 0.11–3.82 µg kg^?1, 0.10–2.49 µg kg^?1 and 0.06–4.53 µg kg^?1 in bovine muscle, bovine blood, and bovine urine, respectively. The method was sensitive, accurate and was applied to monitor real samples. To the best of our knowledge, this is first method available for simultaneous determination of several classes of APGs in bovine muscle, and bovine blood and bovine urine.     

Pilot survey of commercial pasteurized milk consumed in the metropolitan area of Rio de Janeiro,Brazil, for tetracyclines residues,including the 4-epimers of oxytetracycline,tetracycline and chlortetracycline

This pilot survey aimed to assess the occurrence of tetracyclines and the 4-epimers of oxytetracycline, tetracycline and chlortetracycline in commercial pasteurized milks sold in the metropolitan area of Rio de Janeiro, Brazil, between October 2009 and March 2010. A liquid chromatography–tandem mass spectrometry (LC–MS/MS) method, developed and validated in our laboratory, was used. All 100 analyzed samples were compliant, but 14 contained oxytetracycline in concentrations ranging from the method limit of detection (3.7?µg?l^–1) to the method limit of quantification (12.2?µg?l^–1). One sample contained oxytetracycline and tetracycline simultaneously (at a concentration slightly higher than method limit of quantification, 7.0?µg?l^–1). The presence of 4-epioxytetracycline and 4-epitetracycline in contaminated samples with the parent drugs could not be confirmed as traces were detected only in the quantification MRM transition. No other tetracyclines were detected.     

Development of enzyme-linked immunosorbent assay (ELISA) for the detection of neomycin residues in pig muscle,chicken muscle,egg, fish,milk and kidney

A colorimetric competitive direct enzyme-linked immunosorbent assay (ELISA) method was developed using polyclonal antibody to determine neomycin residues in food of animal origin. No cross-reactivity of the antibody was observed with other aminoglycosides. The limit of detection of the method was 0.1 μg/kg. A simple and efficient sample extraction method was established with recoveries of neomycin ranged from 75% to 105%. The detection limits were 5 μg/kg(l) in pig muscle, chicken muscle, fish and milk, 10 μg/kg in kidney and 20 μg/kg in egg, respectively. Chemiluminescence assay was developed for detecting neomycin residues in pig muscle and chicken muscle. The limit of detection of the method was 0.015 μg/kg, and the detection limits were 1.5 μg/kg in pig muscle and 6 μg/kg in chicken muscle. The ELISA tests were validated by HPLC, and the results showed a good correlation (r²) which was greater than 0.9.     

Development of a Quantitative Multi-Mycotoxin Method in Rice, Maize, Wheat and Peanut Using UPLC-MS/MS

Mycotoxins are secondary metabolites produced by fungi, such as Fusarium, Penicillium, and Aspergillus, which are toxic to humans with high risk factors and pose a significant threat to human health. This study was focused mostly on well-known mycotoxins, such as aflatoxins (AFB₁, AFB₂, AFG₁ and AFG₂), fumonisin (FB₁, FB₂), deoxynivalenol (DON), zearalenone (ZON), ochratoxin A, T-2 and HT-2, in grains. The multi-mycotoxin methods developed in this study utilise an analysis of mycotoxin through liquid chromatography tandem mass spectrometry (LC-MS/MS), which can significantly improve sample analysis efficiency. The Myco6in1? immunoaffinity column was used for purification to reduce interference from the substrate. Gradient separation to obtain the best peak shift was conducted using solvent with 0.1 % formic acid in deionised water and methanol, and gradient separation was performed on an ACQUITY BEH C18 column chromatograph. The recovery rate test for each toxin using substrates such as rice, peanut, wheat and maize mostly indicated good average recovery rates between 70 % and 120 % and the coefficient of variation mostly under 15 %. The limits of quantification (LOQ) identified by this method are less than 5 ng/g in most toxins, except for 20 ng/g in FB₁and FB₂. This method can rapidly and simultaneously analyse 11 mycotoxins in 9 min. It can be applied for the practical examination of mycotoxins in food to protect public health.     

Quantitative analysis of veterinary drugs in bovine muscle and milk by liquid chromatography quadrupole time-of-flight mass spectrometry

ABSTRACT

A simple and reliable multiresidue method for quantitative determination of veterinary drugs in bovine muscle and milk using liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) was developed. Critical MS parameters such as capillary voltage, cone voltage, collision energy, desolvation gas temperature and extraction mass window were carefully optimised to obtain the best possible sensitivity. Analytical samples were prepared using extraction with acetonitrile and hexane in the presence of anhydrous sodium sulphate and acetic acid, followed by ODS cartridge clean-up. The developed method was validated for 82 veterinary drugs in bovine muscle and milk at spike levels of 0.01 and 0.1 mg kg^–1. With the exception of cefoperazone and phenoxymethylpenicillin, all these compounds exhibited sufficient signal intensity at 0.01 μg ml^–1 (equivalent to 0.01 mg kg^–1), indicating the high sensitivity of the developed method. For most targets, the determined accuracies were within 70–120%, with repeatability and reproducibility being below 20% at both levels. Except for sulfathiazole in bovine muscle, no interfering peaks at target compound retention times were detected in the blank extract, indicating that the developed method is highly selective. The absence of sulfathiazole in bovine muscle was confirmed by simultaneous acquisition at low and high collision energies to afford exact masses of molecular adduct and fragment ions. Satisfactory linearity was observed for all compounds, with matrix effects being negligible for most targets in bovine muscle and milk at both spike levels. Overall, the results suggest that the developed LC-QTOF-MS method is suitable for routine regulatory-purpose analysis of veterinary drugs in bovine muscle and milk.     

Determination of tadalafil and N-desmethylsibutramine in health and dietary supplements using ultra-performance liquid chromatography (UPLC) coupled with quadrupole-time-of-flight mass spectrometry (Q-TOF MS)

The adulteration of dietary supplements with drugs is potentially dangerous for human health. In this study, a method was used to test simultaneously for the presence of three synthetic PDE-5 inhibitors (sildenafil, vardenafil and tadalafil), and sibutramine and its two major metabolites (N-desmethylsibutramine and N-didesmethylsibutramine) using ultra-performance liquid chromatography (UPLC) coupled with quadrupole-time-of-flight mass spectrometry (Q-TOF MS) in dietary supplements. This approach with UPLC/Q-TOF MS uses the high accurate mass of six compounds for identification and has a short run time. The recovery was from 87% to 113%; precision was less than 12.8%. The limit of detection and limit of quantification were from 0.4 to 2.0?µg?kg^?1 and from 1.3 to 6.0?µg?kg^?1, respectively. This method allows easy and fast analysis and detection of diverse adulterants.