Determination of personal care products in sewage sludge by pressurized liquid extraction and ultra high performance liquid chromatography–tandem mass spectrometry

This paper describes a method for the determination of a group of personal care products including four UV filters, four preservatives and two antimicrobials in sewage sludge. The method combines pressurized liquid extraction and ultra high performance liquid chromatography–tandem mass spectrometry. Most of the parameters that affect the extraction step such as temperature, pressure, static extraction time, number of cycles, purge time and flush volume were optimized using a fractional experimental design. In the chromatographic step, the compounds were detected by using tandem mass spectrometry with a triple quadrupole analyzer with electrospray ionization in positive and negative modes. The use of small diameter particles (1.8 μm) in the chromatographic column allowed the compounds to be eluted in 9 min. The entire process took a total of 39 min. All recoveries were higher than 72% except for 2,4-dihydroxybenzophenone (a UV filter), whose recovery was 30%. The repeatability and reproducibility between days expressed as RSD (%) (n = 3) were less than 8% and 13%, respectively. The LODs and LOQs were lower than 8 μg/kg and 12.5 μg/kg of dry weight (d.w.), respectively. When the method was applied to determine the compounds in sewage sludge from a domestic sewage treatment plant, triclosan (an antimicrobial) and octocrylene (a UV filter) showed the highest levels, 1490 μg/kg (d.w.) and 1842 μg/kg (d.w.), respectively. This paper describes for the first time the determination of parabens and two UV filters (octyldimethyl-p-aminobenzoic acid and benzophenone-3) in sewage sludge.     

Determination of biocides in different environmental matrices by use of ultra-high-performance liquid chromatography–tandem mass spectrometry

A sensitive and robust method using solid-phase extraction and ultrasonic extraction for preconcentration followed by ultra-high-performance liquid chromatography–tandem mass spectrometry (UHPLC–MS–MS) has been developed for determination of 19 biocides: eight azole fungicides (climbazole, clotrimazole, ketoconazole, miconazole, fluconazole, itraconazole, thiabendazole, and carbendazim), two insect repellents (N,N-diethyl-3-methylbenzamide (DEET), and icaridin (also known as picaridin)), three isothiazolinone antifouling agents (1,2-benzisothiazolinone (BIT), 2-n-octyl-4-isothiazolinone (OIT), and 4,5-dichloro-2-n-octyl-isothiazolinone (DCOIT)), four paraben preservatives (methylparaben, ethylparaben, propylparaben, and butylparaben), and two disinfectants (triclosan and triclocarban) in surface water, wastewater, sediment, sludge, and soil. Recovery of the target compounds from surface water, influent, effluent, sediment, sludge, and soil was mostly in the range 70–120?%, with corresponding method quantification limits ranging from 0.01 to 0.31?ng?L^?1, 0.07 to 7.48?ng?L^?1, 0.01 to 3.90?ng?L^?1, 0.01 to 0.45?ng?g^?1, 0.01 to 6.37?ng?g^?1, and 0.01 to 0.73?ng?g^?1, respectively. Carbendazim, climbazole, clotrimazole, methylparaben, miconazole, triclocarban, and triclosan were detected at low ng?L^?1 (or ng?g^?1) levels in surface water, sediment, and sludge-amended soil. Fifteen target compounds were found in influent samples, at concentrations ranging between 0.4 (thiabendazole) and 372?ng?L^?1 (methylparaben). Fifteen target compounds were found in effluent samples, at concentrations ranging between 0.4 (thiabendazole) and 114?ng?L^?1 (carbendazim). Ten target compounds were found in dewatered sludge samples, at concentrations ranging between 1.1 (DEET) and 887?ng?g^?1 (triclocarban).     

Determination of commonly used azole antifungals in various waters and sewage sludge using ultra-high performance liquid chromatography–tandem mass spectrometry

Sensitive and reliable methods have been developed and validated for determination of commonly consumed azole antifungal pharmaceuticals (clotrimazole, econazole, ketoconazole, and miconazole) and biocides (propiconazole and tebuconazole) in various waters and sewage sludge. Solid phase extraction (SPE) combined with ultra-high performance liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS) was used to determine the azole antifungals in waters. Azole antifungals in sewage sludge were extracted with ultrasonic-assisted extraction, followed by SPE cleanup and UHPLC–MS/MS detection. Quantification was performed by internal standard calibration in multiple reaction monitoring mode. Recoveries were mostly in the range of 52–110% with relative standard deviations generally within 20%. Method quantification limits were 0.5–6 ng L⁻¹ in waters and 3–9 ng g⁻¹ dry weight (dw) in sewage sludge, respectively. The methods were applied to determine the azole antifungals in wastewater, river water, sediment, and sewage sludge sampled from the Pearl River Delta, China. Clotrimazole, ketoconazole, and miconazole were widely detected at low ng L⁻¹ in waters, low ng g⁻¹ dw in river sediment, and low μg g⁻¹ dw in sewage sludge. The methods can provide valuable tools for investigating occurrence and fate of the azole antifungals in the environment.     

Determination of evodiamine and rutecarpine in human serum by liquid chromatography–tandem mass spectrometry

Evodiamine and rutecarpine are two kinds of indole alkaloids contained in the fruit of Evodiae fructus, which have been shown to exhibit various bioactivities in humans. A liquid chromatography–tandem mass spectrometric method (LC–MS/MS) was developed for the determination of evodiamine and rutecarpine in human serum. The serum was extracted by solid-phase extraction (SPE) and analyzed using a C18 column and a mobile phase consisting of methanol–water (85:15) solution containing 5 mmol/L ammonium formate at a flow rate of 0.5 mL/min. The mass spectrometer was operated in positive mode, employing the extracted ion chromatogram (EIC) for detection and quantitation of evodiamine (m/z 288) and rutecarpine (m/z 304). Good linear relationships between the peak area and the concentration were obtained in the ranges of 5.2–1040 ng/mL and 10.2–1020 ng/mL, with correlation coefficients (r) of 0.999 and 0.998, for evodiamine and rutecarpine, respectively. The repeatabilities (RSD, n=6) of quantitation for evodiamine and rutecarpine were 2.18–4.00% and 2.99–5.67%, respectively, and the recovery ranged from 90.5% to 98.1%. A comparative study of the different ionization and quantitation modes, including ESI–MS, ESI–MS/MS, APCI–MS and APCI–MS/MS, was also accomplished. The MS/MS fragmentation mechanism of the base peak ([M+H]⁺, m/z 304) of evodiamine was investigated in order to identify the analytes in more complicated body fluid samples.      

Determination of cyclopiazonic acid in food and feeds by liquid chromatography–tandem mass spectrometry

A new, fast and efficient multiple reaction monitoring (MRM) high-performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS) method for the determination of cyclopiazonic acid (CPA) in mixed feed, wheat, peanuts and rice is presented. The analytical methodology involves sample extraction with an alkaline methanol–water mixture, defatting with hexane and quantification using HPLC–MS/MS without further treatment of sample extracts. Reversed-phase liquid chromatography using a C18 stationary phase coupled to negative mode electrospray triple quadrupole tandem mass spectrometry was applied. The limit of detection was 5 μg/kg while the limit of quantification was 20 μg/kg in the matrices investigated. The detector response was found to be linear over the range 25–250 μg/kg in feed and 25–500 μg/kg in wheat, peanuts and rice. The mean overall recoveries (n = 18) of CPA varied from 79% to 114% in the range of concentrations studied over a period of 4 months. Mean recoveries (n = 3 or 6) of CPA in wheat, peanuts and rice varied from 70% to 111%, 77% to 116% and 69% to 92%, respectively. The method was successfully applied to the analysis of feed and rice samples artificially infected with the fungal strain Penicillium commune, where the toxin was found at different levels.     

Determination of pharmaceuticals from different therapeutic classes in wastewaters by liquid chromatography–electrospray ionization–tandem mass spectrometry

A sensitive analytical method has been developed and validated for simultaneous determination of pharmaceuticals from different therapeutic classes, i.e. five sulfonamide (SA) and trimethoprim antimicrobials and the anti-inflammatory drug diclofenac, in effluent wastewaters at trace levels. Effluent samples from treatment of wastewater were enriched by solid-phase extraction (SPE) using the Waters Oasis HLB cartridge. The analytes were identified and quantified by reversed-phase liquid chromatography-tandem mass spectrometry operated in the selected reaction monitoring (SRM) mode, using positive electrospray ionization. The pharmaceuticals were, consequently, quantified both by use of isotopically labelled internal standards and by standard addition methods to address the issue of matrix effects related to signal suppression by co-eluting compounds. Average recoveries from fortified samples were usually >70%, with relative standard deviations below 20%. Method detection limits in wastewater matrices were between 7.0 and 10 ng L(-1). Identification points (IPs) were used for unequivocal identification of target analytes in real samples. Diclofenac, trimethoprim, and sulfamethoxazole were mainly detected, in the concentration range 10 to 400 ng L(-1), in effluent samples collected from four different sewage-treatment plants in Greece.     

Ultra-high-performance liquid chromatography–tandem mass spectrometry for determining the presence of eleven personal care products in surface and wastewaters

Personal care products (PCPs) are widely used emerging contaminants which can cause adverse environmental effects. This paper reports the development and validation of a method based on solid-phase extraction (SPE) and ultra-high-performance liquid chromatography–electrospray ionisation–tandem mass spectrometry (UHPLC–(ESI)MS–MS) for simultaneously determining eleven PCPs: 4 preservatives (methylparaben; ethylparaben; benzylparaben; propylparaben); 2 antimicrobial agents (triclocarban and triclosan) and 5 UV filters (2,4-dihydroxybenzophenone; 2,2-dihydroxy-4-methoxybenzophenone; benzophenone-3; octocrylene and octyldimethyl-p-aminobenzoic acid) in environmental waters in only 9 run minutes of chromatographic separation. The SPE was carried out with two polymeric cartridges (Oasis HLB and Bond Elut Plexa). The recoveries obtained with Bond Elut Plexa were between 69% and 101% for 500 mL of river waters, with the exception of octyldimethyl-p-aminobenzoic acid (46%). Limits of detection for 500 mL of river water were in the range of 1–5 ng/L. Oasis HLB was chosen for wastewater samples with recoveries between 38% and 92% (250 mL of effluents) and 36–89% (100 mL of influents). In both wastewater samples, octyldimethyl-p-aminobenzoic acid and methylparaben showed the lowest recoveries (20% and 27%). The method revealed benzophenone-3 as having the highest concentration levels (7 ng/L) in river waters. Most of PCPs determined were found in influent waters being methylparaben and propylparaben the ones found at highest concentration with values of 5613 and 1945 ng/L, respectively. In effluent waters, significant lower levels of some PCPs were found, being benzophenone-3 the one found at the highest concentration (100 ng/L).     

Determination of meloxicam in human plasma by ultra-high-performance liquid chromatography–tandem mass spectrometry and its application in a pharmacokinetic study

A rapid, selective and sensitive ultra-high-performance liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS) method was developed to detect meloxicam in human plasma. A triple quadrupole tandem mass spectrometer equipped with an electrospray ionization source was used in positive ion mode. Protein precipitation with acetonitrile was used for sample preparation. Meloxicam and ¹³C₆-meloxicam internal standard were analyzed on an Acquity CSH C₁₈ column with a mobile phase of acetonitrile and water in 0.1% formic acid using a gradient program for separation. The retention time of meloxicam was 1.1 min and the total run time was only 2.0 min. Detection was performed in multiple reaction monitoring mode using an electrospray ionization source with optimized mass spectrometry parameters. The calibration curves were linear in the range 10.0–3.00 × 10³ ng/ml (r ≥ 0.99). The within-run and between-run RSDs were ≤14.8%. The within-run and between-run REs ranged from −4.6 to 10.7%. There was no significant matrix effect, and the recovery rate was high. This method was fully validated, including reinjection reproducibility in human plasma. The method was applied to the pharmacokinetic study. All of the incurred sample reanalysis methods met the criteria.     

Enantiomeric determination of azole antifungals in wastewater and sludge by liquid chromatography–tandem mass spectrometry

A sensitive and reliable liquid chromatographic-tandem mass spectrometric method for enantiomeric determination of five chiral azole antifungals (econazole, ketoconazole, miconazole, tebuconazole, and propiconazole) in wastewater and sludge has been established and validated. An isotope-labeled internal standard was used for quantification. Recovery of the individual enantiomers was usually in the range of 77-102 % for wastewater and 71-95 % for sludge, with relative standard deviations within 20 %. No significant difference (p>0.05) was observed between recovery of pairs of enantiomers of the chiral azole antifungals except for those of tebuconazole. Method quantification limits for individual enantiomers were 0.3-10 ng L(-1) and 3-29 ng g(-1) dry weight for wastewater and sludge, respectively. The method was used to investigate the enantiomeric composition of the azole pharmaceuticals in wastewater and sludge samples from a sewage treatment plant in China. Enantiomers of miconazole, ketoconazole, and econazole were widely detected. The results showed that the azole antifungals in wastewater and sludge were generally racemic or marginally non-racemic. The method is a useful tool for investigation of the enantiomeric occurrence, behavior, and fate of the chiral azole antifungals in the environment.     

Multi-residue analytical method for human pharmaceuticals and synthetic hormones in river water and sewage effluents by solid-phase extraction and liquid chromatography–tandem mass spectrometry

Pollutants such as human pharmaceuticals and synthetic hormones that are not covered by environmental legislation have increasingly become important emerging aquatic contaminants. This paper reports the development of a sensitive and selective multi-residue method for simultaneous determination and quantification of 23 pharmaceuticals and synthetic hormones from different therapeutic classes in water samples. Target pharmaceuticals include anti-diabetic, antihypertensive, hypolipidemic agents, β2-adrenergic receptor agonist, antihistamine, analgesic and sex hormones. The developed method is based on solid phase extraction (SPE) followed by instrumental analysis using liquid chromatography-electrospray ionization-tandem mass spectrometry (LC–ESI-MS/MS) with 30 min total run time. River water samples (150 mL) and (sewage treatment plant) STP effluents (100 mL) adjusted to pH 2, were loaded into MCX (3 cm³, 60 mg) cartridge and eluted with four different reagents for maximum recovery. Quantification was achieved by using eight isotopically labeled internal standards (I.S.) that effectively correct for losses during sample preparation and matrix effects during LC–ESI-MS/MS analysis. Good recoveries higher than 70% were obtained for most of target analytes in all matrices. Method detection limit (MDL) ranged from 0.2 to 281 ng/L. The developed method was applied to determine the levels of target analytes in various samples, including river water and STP effluents. Among the tested emerging pollutants, chlorothiazide was found at the highest level, with concentrations reaching up to 865 ng/L in STP effluent, and 182 ng/L in river water.     

Determination of amitraz and its transformation products in pears by ethyl acetate extraction and liquid chromatography–tandem mass spectrometry

A method has been developed for identification and quantification of the acaricide amitraz and its transformation products, 2,4-dimethylaniline (DMA), 2,4-dimethylformamidine (DMF) and N-2,4-dimethylphenyl-N-methylformamidine (DMPF) in pears. The analytes were extracted using ethyl acetate and anhydrous sodium sulphate. Analysis was performed by liquid chromatography–electrospray tandem mass spectrometry (LC–ESI-MS/MS) in the positive ion mode using a triple quadrupole (QqQ) instrument. Two precursor-product ion transitions were monitored for each compound in the selected reaction monitoring (SRM) mode. The method was validated with pears taken from the orchard before the amitraz treatment and spiked at the limit of quantification (LOQ), 10 times the LOQ and the maximum residue limit (MRL). Recoveries were between 70 and 106% and relative standard deviations were below 19% (n = 5 at each spiked level). Excellent sensitivity resulted in limits of detection (LODs) for all the compounds below 10 μg kg⁻¹. Quantification was carried out using matrix-matched standards calibration, response was a linear function of the concentration from the LOQs to, at least, three orders of magnitude. Recoveries and standard deviations were comparable to those obtained after hydrolysis of amitraz and its metabolites to DMA. Occurrence of amitraz and its metabolites in field-treated pears showed that, seven days after the treatment, DMPF and DMF are the main degradation products. This work reports for the first time the use of a conventional pesticide multiresidue method and LC–ESI-MS/MS for determining amitraz and its metabolites in pears.     

Determination of multi-class pharmaceuticals in wastewater by liquid chromatography–tandem mass spectrometry (LC–MS–MS)

An analytical method for multi-class pharmaceuticals determination in wastewater has been developed and validated. Target compounds were: sulfonamides (sulfadiazine, sulfaguanidine, sulfamethazine, sulfamethoxazole), fluoroquinolones (ciprofloxacin, enrofloxacin, norfloxacin), diaminopyrimidine (trimethoprim), anaesthetic (procaine), anthelmintic (praziquantel and febantel), and macrolide (roxithromycin). The method involves pre-concentration and clean-up by solid-phase extraction (SPE) using Strata-X extraction cartridges at pH 4.0. Target analytes were identified and quantitatively determined by liquid chromatography–tandem mass spectrometry using multiple reaction monitoring (MRM). Recoveries were higher than 50% with relative standard deviation (RSD) below 18.3% for three concentrations. Only for sulfaguanidine was low recovery obtained. Matrix effect was evaluated using matrix-matched standards. The method detection limit (MDL) was between 0.5 and 5 ng L⁻¹ in spiked water samples. The precision of the method, calculated as relative standard deviation, ranged from 0.5 to 2.0% and from 1.4 to 8.3 for intra-day and inter-day analysis, respectively. The described analytical method was used for determination of pharmaceuticals in effluent wastewaters from the pharmaceutical industry.     

Determination of steryl sulphates in invertebrate tissue by liquid chromatography–tandem mass spectrometry

A method for the identification and quantification of underivatised steryl sulphates in invertebrates by liquid chromatography (LC) coupled with tandem mass spectrometry (MS) involving a single cleanup step has been developed. Negative electrospray ionisation and positive and negative atmospheric-pressure chemical ionisation (APCI) spectra of steryl sulphate showed pseudomolecular ions ([M+H–H₂SO₄]⁺or [M–H]⁻). Collision-induced dissociation (CID) was efficient only in positive APCI. LC-MS in negative APCI was least susceptible to interference and possible differences in response factors. The detection limits (signal-to-noise ratio of 3) based on cholest-5-enyl-3-sulphate in positive and negative APCI modes are 3.66 and 0.73 pmol μL⁻¹, respectively. Calibration plots and response factors for cholest-5-enyl-3-sulphate relative to the internal standard, cholecalciferyl-3-sulphate, in both positive and negative polarities, were linear in the concentration range from 1.22 to 16.4 pmol μL⁻¹ with good coefficients of determination (R ²>0.98). It is suggested that the structure elucidation of steryl sulphates is best achieved in CID positive APCI mode, whereas their quantification should be carried out using negative APCI.     

Determination of endocrine-disrupting chemicals in the liquid and solid phases of activated sludge by solid phase extraction and gas chromatography–mass spectrometry

The highly complex matrix of activated sludge in sewage treatment plants (STPs) makes it difficult to detect endocrine-disrupting chemicals (EDCs) which are usually present at low concentration levels. To date, no literature has reported the concentrations of steroid estrogens in activated sludge in China and very limited data are available worldwide. In this work, a highly selective and sensitive analytical method was developed for simultaneous determination of two classes of EDCs, including estrone (E1), 17β-estradiol (E2), estriol (E3), 17α-ethynylestradiol (EE2), 4-nonylphenol (NP) and bisphenol A (BPA), in the liquid and solid phases of activated sludge. The procedures for sample preparation, extracts derivatization, and gas chromatography–mass spectrometry (GC–MS) quantification were all optimized to effectively determine target EDCs while minimizing matrix interference. The developed method showed good calibration linearity, recovery, precision, and a low limit of quantification (LOQ) for all selected EDCs in both liquid and solid phases of activated sludge. It was successfully applied to determine the concentrations of EDCs in activated sludge samples from two STPs located in Beijing and Shanghai of China, respectively.     

Determination of non-steroidal anti-inflammatory drugs in sewage sludge by direct hollow fiber supported liquid membrane extraction and liquid chromatography–mass spectrometry

In this study, a three-phase hollow fiber liquid-phase microextraction (HF-LPME) method combined with liquid chromatography–mass spectrometry was developed for direct determination of four non-steroidal anti-inflammatory drugs (ketoprofen, naproxen, diclofenac and ibuprofen) in sewage sludge. The drugs were extracted from non-spiked and spiked slurry samples with different amounts of sludge into an organic phase and then back-extracted into an aqueous phase held in the lumen of the hollow fiber. High enrichment factors ranging from 2761 to 3254 in pure water were achieved. In sludge samples, repeatability and inter-day precision were tested with relative standard deviation values between 10–18% and 7–15%, respectively. Average concentrations of 29 ± 9, 138 ± 2, 39 ± 5 and 122 ± 7 ng/g were determined in dried sludge from Källby sewage treatment plant (Sweden) for ketoprofen, naproxen, diclofenac and ibuprofen, respectively.     

Determination of anabolic steroids in muscle tissue by liquid chromatography–tandem mass spectrometry

A specific and sensitive multi-method based on liquid chromatography–tandem mass spectrometry using atmospheric pressure chemical ionization (LC–APCI–MS/MS) has been developed for the determination of 20 anabolic steroids in muscle tissue (diethylstilbestrol, β-estradiol, ethynylestradiol, α/β-boldenone, α/β-nortestosterone, methyltestosterone, β-trenbolone, triamcinolone acetonide, dexamethasone, flumethasone, α/β-zearalenol, α/β-zearalanol, zearalenone, melengestrol acetate, megestrol acetate and medroxyprogesterone acetate). The procedure involved hydrolysis, extraction with tert-butyl methyl ether, defattening and final clean-up with solid phase extraction (SPE) on Oasis HLB and Amino cartridges. The analytes were analyzed by reversed-phase LC–MS/MS, in positive and negative multiple reaction monitoring (MRM) mode, acquiring two diagnostic product ions from each of the chosen precursor ions for the unambiguous confirmation of the hormones. The method was validated at the validation level of 0.5 ng/g. The accuracy and precision of the method were satisfactory. The decision limits CCα ranged from 0.03 to 0.14 ng/g while the detection capabilities CCβ ranged from 0.05 to 0.24 ng/g. The developed method is sensitive and useful for detection, quantification and confirmation of these anabolic steroids in muscle tissue and can be used for residue control programs.     

Determination of tandospirone in human plasma by a liquid chromatography–tandem mass spectrometry method

A rapid, sensitive, and selective liquid chromatography–tandem mass spectrometry method for the detection of tandospirone in human plasma is described. It was employed in a pharmacokinetic study. The analyte and internal standard diphenhydramine were extracted from plasma using liquid–liquid extraction, then separated on a Zorbax XDB C₁₈ column using a mobile phase of methanol–water–formic acid (80:20:0.5, v/v/v). The detection was performed with a tandem mass spectrometer equipped with an electrospray ionization source. Linearity was established in the concentration range of 10.0-5,000 pg/ml. The lower limit of quantification was 10.0 pg/ml. The intraday and interday relative standard deviation across three validation runs over the entire concentration range was less than 13%. Accuracy determined at three concentrations (25.0, 200, and 4,000 pg/ml for tandospirone) ranged from 94.4 to 102.1%. Each plasma sample was chromatographed within 3.4 min. The method proved to be highly selective and suitable for bioequivalence evaluation of different formulations containing tandospirone and clinical pharmacokinetic investigation of tandospirone.     

Determination of non-steroidal anti-inflammatory drugs and their metabolites in milk by liquid chromatography–tandem mass spectrometry

Non-steroidal anti-inflammatory drugs are widely used for treatment of animals. According to Council Directive 96/23/EC, residues of these drugs must be monitored because of the potential risk they pose to the consumers' health. For this reason an LC-MS-MS method was developed for detection of wide range of NSAIDs, including both "acidic" NSAIDs (carprofen, diclofenac, flunixin, meloxicam, phenylbutazone, oxyphenbutazone, tolfenamic acid, mefenamic acid, naproxen, ketoprofen, ibuprofen, firocoxib, rofecoxib, and celecoxib) and "basic" NSAIDs (four metamizole metabolites). Analytes were extracted from milk samples with acetonitrile in the presence of ammonium acetate. One portion of the extract was directly analyzed for the presence of metamizole metabolites; a second portion was cleaned with an amino cartridge. All NSAIDs were separated on a Phenomenex Luna C8(2) column and analyzed by LC-MS-MS in negative (acidic NSAIDs) and positive (metamizole metabolites) ion modes. The method was validated in accordance with the requirements of Commission Decision 2002/657/EC. Within-laboratory reproducibility was in the range 7-28%, and accuracy was in the range 71-116%. The method enabled detection of all the analytes with the expected sensitivity, below the recommended concentrations. The method fulfills the criteria for confirmatory methods and, because of its efficiency, may also be used for screening purposes. The procedure was also successfully verified in the proficiency test organized by EU-RL in 2010. As far as the authors are aware, this is one of the first methods capable of detecting diclofenac residues below the MRL in milk (0.1 μg kg(-1)). An additional advantage is the possibility of simultaneous determination of "acidic" NSAIDs and metamizole metabolites.