The challenges of developing a generic extraction procedure to analyze multi-class veterinary drug residues in milk and honey using ultra-high pressure liquid chromatography quadrupole time-of-flight mass spectrometry

Occurence of antimicrobial residues in milk and labneh consumed in Lebanon

Antimicrobials are administered in livestock for different uses leading to milk contamination and several undesirable effects. Because there is a lack of surveillance of antimicrobial residues (AMRs) in milk and dairy products in Lebanon, this study aims to determine the occurrence of AMRs in 90 Lebanese samples of milk and labneh (concentrated yoghurt). Multi-residue screening methods with suitable sample preparations were applied to detect 71 AMRs in milk and labneh, respectively, using LC-MS/MS. Of the total number of samples, 71% was contaminated with AMRs and (fluoro)quinolones and macrolides were the most detected families. Additional confirmation tests proved that 6.7% of the milk samples were non-compliant for the macrolides tilmicosin, tulathromycin and spiramycin. Moreover, some labneh prepared from contaminated milk samples was analysed to determine the fate of AMRs during the manufacturing process. The results showed that some AMRs could be concentrated, eliminated or degraded, based on their physicochemical characteristics.

Multiresidues Multiclass Analytical Methods for Determination of Antibiotics in Animal Origin Food: A Critical Analysis

Veterinary drugs are widely used to prevent and treat diseases. The European Union has forbidden the use of antibiotics as growth promoters since 2006. Its abusive use leads to the presence of antibiotic residues (AR) in foods of animal origin which is associated with antibiotic resistance. The monitoring of AR in food intended for human consumption is of utmost importance to assure Food Safety. A systematic bibliographic review was carried out on the analytical methodologies, published in 2013, for the determination of AR in foods of animal origin. The food processing effect in the AR detected in animal products is also addressed. However, there is a preference for multiresidues multiclass methods, i.e., methodologies that allow determining simultaneously different classes of antibiotics, which is still a challenge for researchers. The wide diversity of physico-chemical properties of these drugs is an obstacle to achieving excellent analytical performance for a vast number of molecules analyzed concurrently. New techniques in sample preparation continue to be developed in order to obtain a compromise between good recoveries and extracts without interferences (clean extracts). The most widely used analytical methodology for the determination of AR is liquid chromatography coupled with mass spectrometry. However, the current trend is focused on the use of powerful high-resolution MS detectors such as Time of Flight and Orbitrap with modern chromatographic systems. Cooking time and temperature control are the key processing conditions influencing the reduction of AR in foods.

Screening and Analysis of Multiclass Veterinary Drug Residues in Animal Source Foods using UPLC-Q-Exactive Orbitrap/MS

A rapid, simple, and sensitive method of detecting veterinary drug residues in animal food sources, including poultry and pork, was developed and validated. The method was optimized for over 155 veterinary drugs of 21 different classes. Sample pretreatment included a simple solid-liquid extraction step with 0.2% formic acid-acetonitrile-water and a purification step with a PRiME HLB (hydrophile-lipophile balance) solid-phase extraction cartridge. Data were collected using ultra-high-performance liquid chromatography coupled to Quadrupole-Exactive Orbitrap mass spectrometry. The limits of detection of 155 veterinary drugs ranged from 0.1 µg/kg to 10 µg/kg. The recovery rates were between 79.2 and 118.5 % in all matrices studied, with relative standard deviation values less than 15% (n = 6). The evaluated method allows the reliable screening, quantification, and identification of 155 veterinary drug residues in animal source food and has been successfully applied in authentic samples.

Comparison of four different multiclass, multiresidue sample preparation methods in the analysis of veterinary drugs in fish and other food matrices

In 2018, AOAC International issued Standard Method Performance Requirements (SPMR) 2018.010 - Screening and Identification Method for Regulated Veterinary Drug Residues in Food. In response, we compared 4 different multiresidue methods of sample preparation using the same analytical method entailing ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). Tilapia was chosen for testing, and the analytes and monitoring levels were from SPMR 2018.010. The methods consist of efficient procedures with published validation results from the US Department of Agriculture (USDA), Food and Drug Administration (FDA), and Canadian Food Inspection Agency (CFIA), and an enhanced-matrix removal (EMR)-Lipid protocol from China. Each method was used to prepare 102 final extracts of tilapia spiked or not at different levels with the 78 targeted analytes plus metabolites. The same FDA/USDA rules of mass spectral identification were employed in all analyses to assess rates of false positives and negatives. Quantitative accuracy of the methods was also compared in terms of recoveries and reproducibility of spiked tilapia, incurred catfish, and spiked and certified reference material of bovine muscle. Each method yielded generally acceptable results for the targeted veterinary drugs, but the USDA "extract & inject" method was the fastest, simplest, and cheapest to achieve equally or more acceptable results for the widest scope of analytes for the tested food matrices.

Validation of two UHPLC-MS/MS methods for fast and reliable determination of quinolone residues in honey

Antibiotic usage for beekeeping, including quinolones, can lead to residues in honey and these residues usually result from the drugs used in the treatment of American or European foulbrood diseases. Residues in honey may cause allergic reactions as well as increased antibiotic resistance. Within this study, rapid and breakthrough analysis methods were developed using UHPLC-ESI-MS/MS and sample preparation processes were minimised. Practical, low cost, time-effective analysis was provided utilising 'dilute & shoot' methodology and a QuEChERS-based procedure has been developed alternatively for improved sensitivity. Recovery values were 85%-112% for the 'dilute & shoot' method, and 82%-117% for the modified QuEChERS method. For accuracy studies, RSD% values were between 0.7% and 13.4% for both methods in intra-day and inter-day precision studies. CCα (1.1 μg/kg and 0.6 μg/kg) and CCβ (1.2 μg/kg and 0.6 μg/kg) mean values were calculated for the 'dilute & shoot' and QuEChERS method, respectively. These novel methods achieved simultaneous quantification of 21 quinolones in 7 min with high specificity and were used to analyse 50 honey samples. Quinolone residues were found in samples, and enrofloxacin, danofloxacin, pipemidic acid, lomefloxacin, cinoxacin, and ciprofloxacin were quantified.

Hydrophilic interaction liquid chromatography coupled to quadrupole time-of-flight mass spectrometry as a potential combination for the determination of sulfonamide residues in complex infant formula matrices

An accurate, sensitive and selective analytical method is proposed for sulfonamide residues analysis in infant formulas based on hydrophilic interaction liquid chromatography (HILIC) and quadrupole time-of-flight mass spectrometry in full scan mode. The sample preparation approach involves low-temperature lipid precipitation followed by dispersive solid-phase extraction with PSA and C₁₈ sorbents, which was successfully optimized using Plackett-Burman design. In order to achieve high analytical sensitivity, the influence of HILIC conditions on sulfonamide ionization was investigated, such as the mobile phase composition, buffer concentration, and sample diluent for injection. The method performance characteristics, including linearity (range 5-120 µg kg^-1), reliable limits of quantification (between 5 and 20 µg kg^-1), recovery (72.9-109.2%) and precision (coefficient of variation values ≤ 19.8%) under repeatability and within-laboratory reproducibility conditions, were in accordance with the Codex Alimentarius Commission CAC/GL 71-2009 for quantitative analytical methods for veterinary drug residues in foods. Moreover, adequate identification of the compounds was provided with accurate mass measurement of both precursor and fragment ions in one single run. Finally, the developed method was applied to thirty-five powdered milk-based infant formula samples available in the Brazilian market.

The use of ultra-high-pressure-liquid-chromatography tandem time-of-flight mass spectrometry as a confirmatory method in drug residue analysis: Application to the determination of antibiotics in piglet liver

Consumption of food containing antibiotic residues can cause direct toxic effects, such as allergic reactions, or indirect effects, like the possibility to contribute to the development of antimicrobial resistance. It is essential for consumer food safety, as well as for public health, to monitor antibiotics in foods of animal origin intended for human consumption, particularly in piglets, a highly consumed meat in Portugal. Concerning the lack of regulations regarding the validation criteria for the ToF-MS (time-of-flight mass spectrometry) drug residues determination, this study presents an approach for the use of UHPLC (ultra-high-pressure-liquid-chromatography)-ToF-MS not only for screening but also for confirmatory purposes of 45 antibiotics from 7 different classes. Thus, a method was optimized and validated in accordance with Decision 2002/657/EC by evaluating CCα, CCβ, specificity, selectivity, recovery, ruggedness, repeatability and reproducibility. For antibiotics with no MRL set, the lowest values achieved for CCα and CCβ were, respectively, of 0.1 μg kg^-1 and 0.2 μg kg^-1 for cinoxacin. Regarding precision, the CV values obtained ranged from 5% to 21% for repeatability and from 6% to 22% for reproducibility. Recoveries were calculated falling between 82% and 120%. After validation, the method was used to analyse piglet liver samples. Antibiotic residues were determined in 47% of the 21 analysed samples. Nevertheless, all the antibiotics were detected at concentrations below the MRLs.

Comparison of Sample Preparation and Determination of 60 Veterinary Drug Residues in Flatfish Using Liquid Chromatography-Tandem Mass Spectrometry

This study was performed to optimize the analytical method for multi-residues of 60 compounds in flatfish samples. Three sample preparation methods were tested to identify the optimal recovery conditions for target analytes. As a result, 10 mL of water/acetonitrile (1:4, v/v) was used to extract analytes from fish samples. For purification, C₁₈ and 10 mL of acetonitrile saturated hexane were used to treat the samples. After evaporation and reconstitution, the fish samples were analyzed by ultra-performance liquid chromatography-tandem mass spectrometry. The proposed method was validated according to the CODEX guidelines (CAC/GL-71). Our results showed the recoveries of 73.2%-115% and coefficients of variation of 1.6%-22.1%. The limit of quantification was 0.0005-0.005 mg/kg in the fishery products. In analysis of real samples, no samples exceeded the limit of quantification. This analytical method can be used for multi-residue screening and confirmation of the residues of veterinary drugs in fishery products.

Multiclass and multiresidue screening of veterinary drugs and pesticides in infant formula using Quadrupole-Orbitrap MS with PRM scan mode

A multiclass and multiresidue method for screening veterinary drugs and pesticides in infant formula was developed and validated using ultrahigh-performance liquid chromatography coupled to Quadrupole-Orbitrap high-resolution mass spectrometry (UHPLC-HRMS). A total of 49 veterinary drugs and pesticides investigated belong to 11 classes including antivirals, anticoccidials, macrolides, pyrethroids, insecticides, sulfonamides, beta-agonists, sedatives, thyreostats, nonsteroidal anti-inflammatory drugs, and other pharmacologically active substances. A generic sample preparation and highly selective acquisition mode of parallel reaction monitoring (PRM) were deliberately incorporated to perform efficient screening analysis. As a result, the screening target concentrations of the analytes varied from 1 to 500 μg/kg with ≤5% of false compliant rate as specified in Decision 2002/657/EC for screening analysis. The average recoveries ranged from 40.7 to 124.9% as well as the relative standard deviations from 4.2 to 26.6%, respectively. The matrix effects and interferences were effectively controlled by integrated application of dispersive solid phase extraction, PRM scan mode, and matrix-matched standard calibration. The proposed method will be helpful to provide applicable strategy for screening residues in infant formula with surveillance purpose.

Comparison of three different lipid removal cleanup techniques prior to the analysis of sulfonamide drug residues in porcine tissues

A number of 17 sulfonamides (SNs) determination in porcine tissues using two new materials including Enhanced Matrix Removal for Lipid (EMR-L) and Oasis PRiME hydrophilic-lipophilic balance (HLB), and the conventional liquid-liquid extraction with n-hexane (LLE) sample preparation methods were evaluated and compared. Samples were extracted uniformly with acidified acetonitrile and cleaned up by the three sample preparation methods, and then, analytes were further separated by ultrahigh-performance liquid chromatography (UHPLC) and detected by a triple quadrupole mass spectrometry (MS/MS) or a quadrupole-time-of-flight tandem mass spectrometry (Q-TOF/MS). The results showed that the matrix effects from the EMR-L and HLB were significantly lower than that from LLE, suggesting that these two new materials are superior to n-hexane in the precipitation of proteins and the adsorption of lipids. Moreover, the recoveries of 17 SNs were quantified by the matrix-matched calibration curve at spiked level of 5, 10, and 20 μg/kg, and 97.0% of the results satisfied method validation requirements. The samples cleaned up by EMR-L and HLB achieved the highest average recovery in liver and kidney with high moisture content, and muscle which is high in fat, respectively. In addition, Q-TOF/MS could play a good role in aided verification based on the result of repeated validation test. In summary, either combination of approaches could be used to achieve monitoring purposes; it is still worthwhile to adopt a specific sample preparation method and MS detector for the quantification in a specific matrix.

Transfer of a Multiclass Method for over 60 Antibiotics in Food from High Resolution to Low Resolution Mass Spectrometry

A multiclass method has been developed to screen and confirm a wide range of anti-microbial residues in muscle and milk, and validated using liquid-chromatography coupled to (low-resolution, LR) tandem mass spectrometry (LC-QqQ). Over sixty antibiotics, belonging to ten distinct families, were included in the method scope. The development process was rapidly concluded as a result of two previously implemented methods. This consisted of identical sample treatments, followed by liquid chromatography, and coupled with high-resolution (HR) mass spectrometry (LC-Q-Orbitrap). The validation study was performed in the range between 10-1500 μg·kg^-1 for muscles and 2-333 μg·kg^-1 for milk. The main performance characteristics were estimated and, then, compared to those previously obtained with HR technique. The validity of the method transfer was ascertained also through inter-laboratory studies.

Hydrophilic-interaction planar chromatography in ultra-sensitive determination of α-aminocephalosporin antibiotics. Application to analysis of cefalexin in goat milk samples using modified QuEChERS extraction technique

A highly sensitive, selective and precise HPTLC method coupled with fluorescence detection was developed and validated for the determination of α-aminocephalosporin antibiotics; namely cefalexin, cefadroxil and cefradine in their standard solutions. The applicability of the developed methodology was demonstrated via analysis of cefalexin in goat milk samples. Full optimization of the fluorescence derivatization reaction was carried out with regard to the standard solutions of the studied compounds or after extraction of milk samples. The separation of the studied compounds was performed on HPTLC precoated silica gel plates 60 F₂₅₄ using acetonitrile: water in a ratio 85:15 (v/v) as a mobile phase. The retention behavior of the formed derivatives was discussed in detail. It was found that hydrophilic interaction mode is the main interaction mechanism governing the retention of the formed derivatives. In addition, an experimental design approach was conducted for optimization of the chromatographic conditions. Modified QuEChERS was applied as an efficient extraction technique of cefalexin from both spiked and real goat milk samples. Optimization of QuEChERS extraction technique to achieve the highest extraction recovery was performed and the results indicate that this method provides a good extraction recovery (83-116%) for cefalexin from goat milk samples. Limit of detection (LOD) of the developed method was found to be 0.023, 0.005, and 0.023 ng band^-1 for cefalexin, cefadroxil and cefradine, respectively in their standard solutions and 0.165 ng band^-1 for cefalexin in goat milk samples. According to the achieved LOD values, the method sensitivity was quasi-equivalent to other methods based on expensive techniques such as HPLC-UV and HPLC-MS and it is sufficient to determine cefalexin below its MRL in milk samples. Moreover, the method was successfully applied to a pharmacokinetic study of cefalexin in goat milk after single intramuscular injection of 10 mg of cefalexin kg^-1 per body weight.

A Simple, Sensitive, and Reliable Method for the Simultaneous Determination of Multiple Antibiotics in Vegetables through SPE-HPLC-MS/MS

Antibiotics, widely used in livestock breeding, enter the environment through animal manure because of incomplete absorption in animals, especially the farmland ecosystem. Therefore, antibiotics may be adsorbed by plants and even become hazardous to human health through the food chain. In this study, a simple, sensitive, and reliable method was developed for the simultaneous determination of eleven antibiotics, including four sulfonamides, two tetracyclines, three fluoroquinolones, tylosin, and chloramphenicol in different vegetable samples using SPE-HPLC-MS/MS. Vegetable samples were extracted by acetonitrile added with hydrochloric acid (125:4, v/v). The extracts were enriched by circumrotating evaporation, and then cleaned through SPE on a hydrophilic-lipophilic balance (HLB) cartridge. All compounds were determined on a C₁₈ reverse phase column through HPLC-MS/MS. The mean recoveries of 11 antibiotics from spiked samples of vegetables ranged from 71.4% to 104.0%. The limits of detection and quantification were 0.06⁻1.88 μg/kg and 0.20⁻6.25 μg/kg, respectively. The applicability of this technique demonstrated its good selectivity, high efficiency, and convenience by the analysis of 35 vegetable samples available from a vegetable greenhouse. Antibiotic residues in vegetables have aroused wide concern from the public. Therefore, standards should be established for antibiotic residues in vegetables to ensure food safety and human health.

Targeted Multiresidue Analysis of Veterinary Drugs in Milk-Based Powders Using Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

An analytical method was developed and validated for the determination of 40 veterinary drugs in various milk-based powders. The method involves acetonitrile/water extraction, solid-phase filtration for lipid removal in fat-containing matrices, and analysis using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The limits of quantitation (LOQ) ranged from 0.02 to 82 ng/g. Acceptable recoveries (70-120%, RSD < 20%) were reached for 40 of 52 target compounds at three fortification levels in nonfat milk powder. Similar results were obtained for whole milk powder, milk protein concentrate, whey protein concentrate, and whey protein isolate. This new method will allow for better monitoring of a wide range of veterinary drugs in milk-based powders.

Veterinary drugs residues: a review of the latest analytical research on sample preparation and LC-MS based methods

The world population is increasing and there is a growing demand for food, leading to intensification of farming methods and a requirement for more coadjuvants. Potential high profits sometimes lead to fraudulent use of drugs and pesticides. Veterinary drugs in particular can pose a real risk to human health if their residues are allowed to enter the food chain. Parent drugs and their metabolites can occur in foodstuffs individually or as multicomponent mixtures with enhanced adverse effects. In order to protect consumer safety, the European Union has established lists of forbidden substances, maximum residue limits for authorised drugs and precise criteria for confirmation analyses and interpretation of the results. Due to their nature and potential danger, the 'best available technique' should always be applied. Following this principle, this review examines the procedures and techniques applied to monitoring pharmaceutical products of major concern (e.g. anthelmintics, NSAIDs, corticosteroids, coccidiostats) in foods of animal origin, discussing advances over the past five years and future trends in the field of food safety. Our goal was both to focus attention on this important topic and to provide a selection of the most relevant recent papers on drug residues in foodstuffs.

Multiclass method for the determination of 62 antibiotics in milk

A multiclass method for screening and confirmatory analysis of antimicrobial residues in milk has been developed and validated. Sixty-two antibiotics belonging to ten different drug families (amphenicols, cephalosporins, lincosamides, macrolides, penicillin, pleuromutilins, quinolones, rifamycins, sulfonamides and tetracyclines) have been included. After the addition of an aqueous solution of EDTA, the milk samples were extracted twice with acetonitrile, evaporated and dissolved in ammonium acetate. After centrifugation, 10 µl were analysed using LC-Q-Orbitrap operating in positive electrospray ionization mode. The method was validated in bovine milk in the range 2-150 µg kg(-1) for all antibiotics; for four compounds with maximum residue limits higher than 100 µg kg(-1) , the validation interval has been extended until 333 µg kg(-1) . The estimated performance characteristics were satisfactory complying with the requirements of Commission Decision 2002/657/EC. Good accuracies were obtained also taking advantage from the versatility of the hybrid mass analyser. Identification criteria were achieved verifying the mass accuracy and ion ratio of two ions, including the pseudomolecular one, where possible. Finally, the developed procedure was applied to 13 real cases of suspect milk samples (microbiological assay) confirming the presence of one or more antibiotics, although frequently, the maximum residue limits were not exceeded. The availability of rapid multiclass confirmatory methods can avoid wastes of suspect, but compliant, raw milk samples. Copyright © 2016 John Wiley & Sons, Ltd.

Simultaneous determination of 200 pesticide residues in honey using gas chromatography-tandem mass spectrometry in conjunction with streamlined quantification approach

A sensitive, accurate and reliable multi-class GC-MS/MS assay protocol for quantification and confirmation of 200 common agricultural pesticides in honey was developed and validated according to EU guidelines. A modified extraction procedure, based on QuEChERS method (quick, easy, cheap, effective, rugged and safe) was employed. Mass spectrophotometric conditions were individually optimized for each analyte to achieve maximum sensitivity and selectivity in MRM mode. The use of at least two reactions for each compound allowed simultaneous identification and quantification in a single run. The pesticides under investigation were separated in less than 31 min using the ultra-inert capillary column (DB-35MS). For all analytes, neat standard calibration curves in conjunction with correction for matrix effect were successfully employed. The detection limits of the assay ranged from 1.00 to 3.00 ng mL(-1) for the studied pesticides. The developed assay was linear over concentration range of 10.00-500.00 ng mL(-1), with correlation coefficient of more than 0.996. At the LOQ, 81% of the studied pesticides were efficiently recovered in the range of 70.00-120.00%, with CV% less than 15.00% while 99.3% compounds had mean percentage recovery of 60.00-140.00%, with CV% less than 21.00% (N=18, over three different days). The proposed assay was successfully applied for the analysis of the studied pesticide residues in one PT sample and 64 commercial honey samples collected over 1 year from different districts around Egypt. Results revealed that only one honey sample out of the 64 analyzed samples was contaminated with tau-Fluvalinate (10.00 μg kg(-1)). This wide scope assay protocol is applicable for monitoring pesticide residues in honey by national regulatory authorities and accredited labs; that should help ensure safety of such widely used product.

Development and Validation of a Multiclass Method for Analysis of Veterinary Drug Residues in Milk Using Ultrahigh Performance Liquid Chromatography Electrospray Ionization Quadrupole Orbitrap Mass Spectrometry

This paper presents the development and validation of a multiclass method for the analysis of veterinary drug residues in milk using ultrahigh performance liquid chromatography electrospray ionization quadrupole Orbitrap mass spectrometry (UHPLC/ESI Q-Orbitrap). The 12 classes of veterinary drugs (a total of 125) included in this study were endectocides, fluoroquinolones, ionophores, macrolides, nitroimidazole, NSAIDs, β-lactams, penicillins, phenicols, sulfonamides, tetracyclines, and aminoglycosides. Veterinary drug residues in milk were extracted using a modified salting-out supported liquid extraction (SOSLE) method, which entailed the precipitation of milk proteins using an extraction buffer (oxalic acid and EDTA, pH 3) and acetonitrile, a salting-out acetonitrile/water phase separation using ammonium sulfate, and solid-phase extraction (SPE) using polymeric reversed-phase sorbent cartridges. The final extracts were concentrated and reconstituted into a buffer solution and analyzed using UHPLC/ESI Q-Orbitrap mass spectrometry. The developed method was validated using a nested experimental design to evaluate the method performance characteristics, such as overall recovery, intermediate precision, and measurement uncertainty. The method was able to quantify or screen up to 105 veterinary drugs from 11 different classes, except aminoglycosides. The limits of quantification were as low as 1.0 μg/kg, with an analytical range from 1.0 to 100.0 μg/kg in milk.

Challenges in implementing a screening method for veterinary drugs in milk using liquid chromatography quadrupole time-of-flight mass spectrometry

High resolution mass spectrometry (HRMS) is a valuable tool for the analysis of chemical contaminants in food. Our laboratory has successfully developed methods to screen for veterinary drug residues using liquid chromatography quadrupole time-of-flight (Q-TOF). There have been, however, significant challenges as methods are transferred from the development stage to routine regulatory analysis. Having experimental retention time and product ion information for analytes greatly facilitates the ability to determine if residues found by the HRMS searching software are false detects. These data were collected for over 200 veterinary drug residues using LC Q-TOF MS. The screening levels of detection for over 150 veterinary drug residues in milk were determined, and over half of those tested can be detected at concentrations of 10 ng/mL or less; 72% can be found in milk when present at 100 ng/mL. Tentative identification of the product ions from these analytes is also presented.

Liquid chromatography-mass spectrometry method for the quantitative determination of residues of selected veterinary hormones in powdered ingredients derived from bovine milk

A rugged, quantitative liquid chromatography-tandem mass spectrometry method with modified QuEChERS (quick, easy, cheap, effective, rugged, and safe) sample preparation for 17 selected veterinary hormones in six different powdered ingredients derived from bovine milk was developed and comprehensively validated. A universal post-extraction spiked matrix-matching approach based on whole milk powder has been successfully implemented. Three validation runs based on four levels of pre-extraction spiked quality control (QC) samples have been conducted. Overall accuracy (86-117%), overall precision (<20% RSD), selectivity, absolute extraction recovery (62-82%), matrix effect (<15% for most compounds), limits of detection (0.1-0.8 μg/kg, except for diethylstilbestrol at 3.8 μg/kg), limits of quantitation (0.2-2.0 μg/kg, except for diethylstilbestrol at 10.0 μg/kg), and extract stability (48 h) have been determined. The method is proposed for the routine analysis of hormones potentially present in powdered ingredients derived from bovine milk.