Simultaneous extraction and clean-up of polybrominated diphenyl ethers and polychlorinated biphenyls from sheep liver tissue by selective pressurized liquid extraction and analysis by gas chromatography-mass spectrometry

We describe a selective pressurized liquid extraction (SPLE) method, followed by gas chromatography–mass spectrometry (GC–MS), for the simultaneous extraction and clean-up of polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) in sheep liver tissue samples. The on-line clean-up of liver tissue by SPLE was tested using differing amount of acid-modified silica (sulphuric acid:silica gel, 1:2, w/w), the most effective amount being 20 g. Different extraction solvents (iso-hexane and dichloromethane), either alone or in various combinations, were used to extract these target compounds from spiked liver samples. Variables affecting the SPLE extraction efficiency, including temperature, pressure, number of extraction cycles and static extraction time were studied; the optimum parameters were 80 °C, 10.3 MPa, 2 cycles and 5 min, respectively. The SPLE based method was compared with more traditional Soxhlet, off-line PLE, ultrasonic and heating extraction methods. Overall the mean percentage recoveries for all target chemicals using SPLE were 86–103% (n = 3, SD < 9%), and compared favourably with the Soxhlet (63–109%, n = 3, SD < 8%), off-line PLE (82–104%, n = 3, SD < 18%), ultrasonic (86–99%, n = 3, SD < 11%) and heating (72–102%, n = 3, SD < 21%) extraction methods. The limits of detection of the proposed method were 5–96 pg g⁻¹ and 2–29 pg g⁻¹ for the different PBDE and PCB chemicals studied, respectively. The outputs of the proposed method were linear over the range from 0.02 to 30 ng g⁻¹, for all PCB and PBDE congeners except for PBDE 100 and 153 (0.05–30 ng g⁻¹) and PBDE 183 (0.1–30 ng g⁻¹). The method was successfully applied to sheep liver samples for the determination of the target PBDE and PCB compounds.     

Suitability of selective pressurized liquid extraction combined with gas chromatography-ion-trap tandem mass spectrometry for the analysis of polybrominated diphenyl ethers

A one-step extraction and clean-up method using pressurized liquid extraction (PLE) (selective PLE) combined with gas chromatography-ion-trap tandem mass spectrometry (GC-ITMS-MS) was evaluated for the analysis of polybrominated diphenyl ethers (from tri- to hepta-PBDEs) at low concentrations in fish and shellfish samples. To this end, the performance of an on-line PLE extraction/clean-up method and of a classical Soxhlet extraction and clean-up method using a multi-layer modified silica column were compared. The two sample treatment methods provided similar results, although an important reduction in the sample treatment time (40 min per sample) was achieved using the selective PLE method. In addition, the suitability of the PLE combined with GC-ITMS-MS method was evaluated by comparing the results obtained in the analysis of fish samples with those obtained by gas chromatography-high resolution mass spectrometry (GC-HRMS). Good agreement between both techniques was obtained with differences between the mean values of less than 16%. The selective PLE method coupled to GC-ITMS-MS produced accurate results for PBDE determination with low limits of detection (1.0-16.8 pg g⁻¹ wet weight) and quantification (3.1-51 pg g⁻¹ wet weight) as well as good precision (RSD < 16%). This method has been applied to the analysis of PBDEs in fish and shellfish samples collected at fish markets in Catalonia (NE Spain).     

Feasibility of gas chromatography--ion trap tandem mass spectrometry for the determination of polychlorinated biphenyls in food

The different parameters affecting the ionisation and fragmentation of selected polychlorinated biphenyls (PCBs) in an IT detector working in the MS/MS mode, ITD(MS/MS), have been optimised for maximum selectivity and sensibility. The low LODs (in the range 0.03-0.3 microg/L), the satisfactory repeatability (RSDs in general below 11%) and reproducibility (RSDs below 17%) obtained when analysing standard solutions ensured proper determination of the PCBs studied at the concentrations typically found in food samples. Foodstuffs naturally contaminated with varying levels of PCBs have been analysed using the optimised GC-ITD(MS/MS) method. The results obtained compared favourably with those found using more conventional detectors, such as (micro-)electron capture detection (for ortho-PCBs) and high-resolution MS (for non-ortho-PCBs), as well as with the consensus PCB levels established for these particular samples via an international interlaboratory exercise. The relative merits of these three detectors have been discussed.     

Development and validation of a multiclass method for the analysis of antibiotic residues in eggs by liquid chromatography-tandem mass spectrometry

A multiclass method for the analysis of residues, in egg matrices, of 41 antimicrobial agents belonging to seven families (sulfonamides, diaminopyridine derivates, quinolones, tetracyclines, macrolides, penicillins and lincosamides) was developed and validated according to the requirements of European Commission Decision 2002/657. Compounds were extracted with a pressurized liquid extraction (PLE) technique using a 1:1 mixture of acetonitrile and a succinic acid buffer (pH 6.0) at 70 °C. As this resulted in clear extracts, no further clean-up was necessary. Analytes were determined by ultra-high-pressure liquid chromatography–tandem mass spectrometry (UHPL–MS/MS) in a chromatographic run of 13 min. Calibration was carried out with spiked blank samples subjected to the entire analytical procedure. Five compounds, two of them isotopically labelled, were used as internal standards. Most analytes were quantified with errors below 10%. Precision in terms of reproducibility standard deviation was between 10% and 20% in most cases. CCα values were in the range 0.5–3.8 μg kg⁻¹ for the non-authorized compounds. The proposed method would enable an experienced analyst to process about 25 samples per day.     

Ultra-performance liquid chromatography-tandem mass spectrometry: a novel challenge in multiresidue pesticide analysis in food

Potential of ultra-performance liquid chromatography (UPLC) separation strategy coupled with tandem (in space) mass spectrometric detection (MS/MS) in multiresidue pesticide analysis was critically assessed. Performance parameters such as number of theoretical plates, height of theoretical plate, peak symmetry and peak capacity were measured/calculated on the basis of data generated by analysis of apple extracts containing 17 (semi)polar pesticides representing various classes of active ingredients of widely used crop protective preparations. Ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) procedure provided improved chromatographic parameters resulting in significantly increased sample throughput including lower solvent consumption and lower limits of quantitation (LOQs) for most of target analytes compared to common method employing conventional high-performance liquid chromatography (HPLC) separation.     

Application of semi-permeable membrane dialysis/ion trap mass spectrometry technique to determine polybrominated diphenyl ethers and polychlorinated biphenyls in milk fat

Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are hazardous food contaminants, their maximum legally allowable levels in food and environment are in the low pg g⁻¹ range. Therefore some highly selective and sensitive analytical methods must be used to determine them. The 96/23/EC Directive implemented by EC Decision of 12 August 2002 requires recovery rate of an analyte at a concentration below 1 ng g⁻¹ within the 50–120% range at relative standard deviation (RSD) as low as possible.     

Ultrasound-assisted leaching-dispersive solid-phase extraction followed by liquid-liquid microextraction for the determination of polybrominated diphenyl ethers in sediment samples by gas chromatography-tandem mass spectrometry

Ultrasound-assisted leaching-dispersive solid-phase extraction followed by dispersive liquid-liquid microextraction (USAL-DSPE-DLLME) technique has been developed as a new analytical approach for extracting, cleaning up and preconcentrating polybrominated diphenyl ethers (PBDEs) from sediment samples prior gas chromatography-tandem mass spectrometry (GC-MS/MS) analysis. In the first place, PBDEs were leached from sediment samples by using acetone. This extract was cleaned-up by DSPE using activated silica gel as sorbent material. After clean-up, PBDEs were preconcentrated by using DLLME technique. Thus, 1 mL acetone extract (disperser solvent) and 60 μL carbon tetrachloride (extraction solvent) were added to 5 mL ultrapure water and a DLLME technique was applied. Several variables that govern the proposed technique were studied and optimized. Under optimum conditions, the method detection limits (MDLs) of PBDEs calculated as three times the signal-to-noise ratio (S/N) were within the range 0.02-0.06 ng g⁻¹. The relative standard deviations (RSDs) for five replicates were <9.8%. The calibration graphs were linear within the concentration range of 0.07-1000 ng g⁻¹ for BDE-47, 0.09-1000 ng g⁻¹ for BDE-100, 0.10-1000 ng g⁻¹ for BDE-99 and 0.19-1000 ng g⁻¹ for BDE-153 and the coefficients of estimation were ≥0.9991. Validation of the methodology was carried out by standard addition method at two concentration levels (0.25 and 1 ng g⁻¹) and by comparing with a reference Soxhlet technique. Recovery values were ≥80%, which showed a satisfactory robustness of the analytical methodology for determination of low PBDEs concentration in sediment samples.     

Novel pressurized solvent extraction vessels for the analysis of polychlorinated biphenyl congeners in avian whole blood

Persistent organic pollutants remain a serious threat to many food-chain systems. New pollutants continue to emerge. The present study has created novel extraction vessels which are compatible with readily available commercial instrumentation to validate the analysis of one class of persistent organic pollutants, polychlorinated biphenyls (PCBs), in avian blood. The volumes used can be reasonably sampled without sacrificing individuals, or comprising breeding or migratorial success. The procedure consists of the pressurized solvent extraction (PSE) of analytes in a novel PSE extraction vessel. The new extraction cell contains a 38-cm long, coiled, re-packable, in situ clean-up column. Lipid elimination, using Florisil, occurs within the coiled region of the extraction vessel, eliminating the requirement for post extraction clean-up. For development, 0.2 g samples of chicken whole blood have been used. Extract volumes are reduced from (30 to 10) cm³, compared to unmodified systems. The new PSE vessel with its integrated clean-up method showed satisfactory performance for the analysis of ten environmentally relevant PCB congeners in chicken whole blood samples with recoveries in the range of (70-130)%. Detection limits using gas chromatography coupled with large volume injection ion-trap mass spectrometry (GC-LVI-ITMS-MS) were in the range of (0.05-0.5) ng g⁻¹. The relative standard deviations for all congeners investigated were better than 5%. This is the first PSE validation to have been conducted on unaltered whole blood samples.     

Multi-residue method for trace level determination of pharmaceuticals in solid samples using pressurized liquid extraction followed by liquid chromatography/quadrupole-linear ion trap mass spectrometry

A simple and sensitive method for simultaneous analysis of 43 pharmaceutical compounds in sewage sludge and sediment samples was developed and validated. The target compounds were extracted using pressurized liquid extraction (PLE) and then purified and pre-concentrated by solid phase extraction (SPE) using a hydrophilic-lipophilic balanced polymer. PLE extraction was performed on temperature of 100 °C, with methanol/water mixture (1/2, v/v) as extraction solvent. The quantitative analysis was performed by liquid chromatography tandem mass spectrometry using a hybrid triple quadrupole-linear ion trap mass spectrometer (LC-QqLIT-MS). Data acquisition was carried out in selected reaction monitoring (SRM) mode, monitoring two SRM transitions to ensure an accurate identification of target compounds in the samples. Additional identification and confirmation of target compounds were performed using the Information Dependent Acquisition (IDA) function. The method was validated through the estimation of the linearity, sensitivity, repeatability, reproducibility and matrix effects. The internal standard approach was used for quantification because it efficiently corrected matrix effects. Despite the strong matrix interferences, the recoveries were generally higher of 50% in both matrixes and the detection and quantification limits were very low. Beside the very good sensitivity provided by LC-QqLIT-MS, an important characteristic of the method is that all the target compounds can be simultaneously extracted, treated and analysed. Hence, it can be used for routine analysis of pharmaceuticals providing large amount of data. The method was applied for the analysis of pharmaceuticals in river sediment and wastewater sludge from three treatment plants with different treatment properties (i.e. capacity, secondary treatment, quality of influent waters). The analysis showed a widespread occurrence of pharmaceuticals in the sludge matrices.     

Determination of tetracycline residues in soil by pressurized liquid extraction and liquid chromatography tandem mass spectrometry

An optimized extraction and cleanup method for the analysis of chlortetracycline (CTC), doxycycline (DC), oxytetracycline (OTC) and tetracycline (TC) in soil is presented. Soil extraction in a pressurized liquid extraction system, followed by extract clean up using solid-phase extraction (SPE) and tetracycline determination by liquid chromatography tandem mass spectrometry (LC-MS/MS) provided appropriate efficiency and reproducibility. Different dispersing agents and solvents for soil extraction and several SPE cartridges for cleanup were compared. The best extraction results were obtained using ethylenediamine tetraacetic acid-treated sand as dispersing agent, and water at 70 °C. The most effective cleanup was obtained using Strata-X^TM sorbent in combination with a strong anion exchange cartridge. Recoveries ranged from 71% to 96% and precision, as indicated by the relative standard deviations, was within the range of 8–15%. The limits of quantification (LOQs) by using LC-MS/MS, based on signal-to-noise ratio (S/N) of 10, ranged from 1 μg kg⁻¹ for TC to 5 μg kg⁻¹ for CTC. These results pointed out that this technique is appropriate to determine tetracyclines in soils. Analysis of 100 samples taken in the Valencian Community revealed that, in soil, up to 5 μg kg⁻¹ CTC, 15 μg kg⁻¹ OTC, 18 μg kg⁻¹ TC, and 12 μg kg⁻¹ DC could be detected. Detection of the analytes in several samples, which typify great part of the Spanish agricultural soils, should be outlined as most important result of this study. Electronic supplementary material  The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

Comparison of ultrasonic and pressurized liquid extraction for the analysis of polycyclic aromatic compounds in soil samples by gas chromatography coupled to tandem mass spectrometry

A pressurized liquid extraction (PLE) method has been optimized for the determination of polycyclic aromatic hydrocarbons (PAHs) in soil samples and it was compared with ultrasonic extraction. The extraction step was followed by gas chromatography-triple quadrupole mass spectrometry (GC-QqQ-MS/MS) analysis. Parameters such as type of solvent, extraction time, extraction temperature and number of extractions were optimized. There were no significant differences among the two extraction methods although better extraction efficiencies were obtained when PLE was used, minimizing extraction time and solvent consumption. PLE procedure was validated, obtaining limits of detection (LODs) ranging from 0.02 to 0.75 μg kg⁻¹ and limits of quantification (LOQs) ranging from 0.07 to 2.50 μg kg⁻¹ for the selected PAHs. Recoveries were in the range of 59-110%, except for naphthalene, which was the most volatile PAH. Finally, the method was applied to real soil samples from Southeast of Spain. PAHs concentrations were low, and phenanthrene, pyrene, fluorene, benzo[a]pyrene and chrysene were the most frequently detected analytes in the samples.     

固相萃取-液相色谱-串联质谱法同时测定水中14种短链和长链全氟化合物

建立了固相萃取-超高压液相色谱-三重四极杆质谱同时测定水中14种短链和长链全氟化合物（PFCs）的方法。水样经WAX混合型固相萃取小柱富集和净化后,采用BEH C18色谱柱、甲醇和5 mmol/L乙酸铵水溶液作为流动相进行梯度洗脱,质谱采用多反应监测模式,内标法定量分析。14种PFCs在0.1~50 μg/L范围内线性关系良好,相关系数大于0.99,方法检出限和定量限分别为0.09~1.15 ng/L和0.29~3.85 ng/L。在2、10和20 ng/L加标水平下,8种PFCs的平均回收率为85.0%、120.2%和117.4%,平均相对标准偏差为9.2%、9.0%和6.6%,6种PFCs的回收率相对较低,主要由于其在瓶/管壁上的吸附作用导致。应用本方法分析某淡水湖水样,检出4种短链和5种长链PFCs,质量浓度为41.29~49.05 ng/L和98.43~111.02 ng/L。结果表明该方法适用于对环境水体中短链和长链PFCs的同时分析测定。     

Determination of pharmaceuticals in soils and sediments by pressurized liquid extraction and liquid chromatography tandem mass spectrometry

The present work describes the development of a sensitive analytical method based on pressurized liquid extraction (PLE) and pre-concentration by solid-phase extraction (SPE), followed by liquid chromatography–electrospray tandem mass spectrometry (LC–ESI-MS/MS) for the determination of seventeen pharmaceuticals in soils and sediments. The method is based on sample homogenisation using Na₂–EDTA washed sand and extraction with water at 90 °C. Special emphasis was placed on the optimization of the extraction procedure to develop a green method that reduces, at a maximum, the use of organic solvents in order to eliminate matrix components during the clean-up. The proposed method was linear in a concentration range from 0.3 to 333 ng g⁻¹, with correlation coefficients higher than 0.993. Method detection (MDLs) and quantification (MQLs) limits ranged from 0.1 to 6.8 ng g⁻¹ and from 0.25 to 23 ng g⁻¹, respectively. Absolute recoveries were analyte dependent, varying between 50% and 105% at the MQL level, except for fenofibrate (40%) and diclofenac (34%). The intra-day and inter-day precision was given by RSD values from 0.7% to 7.9% and from 1.6% to 14.5%, respectively. Acetaminophen, carbamazepine, ciprofloxacin, clofibric acid, codeine, diazepam, fenofibrate, metropolol, ofloxacin and propanolol were detected at concentrations from MDL to 35.62 ng g⁻¹ in soils and sediments from marsh areas. Due to the low recoveries, results for fenofibrate and diclofenac can only be considered as semi-quantitative. The method was fully suitable for the other 15 pharmaceuticals.     

超声辅助萃取气相色谱-三重四极杆质谱法测定室内灰尘中的39种多氯联苯

建立了测定室内灰尘样品中39种多氯联苯(PCBs)的分析方法。样品经吸尘器采集、正己烷-二氯甲烷(1：1,v/v)超声萃取、浓缩后,利用气相色谱-三重四极杆质谱法(GC-MS/MS)在选择反应监测(SRM)模式下测定。结果表明,39种PCBs在30 min内得到了很好的分离,在0.1~100 μg/L范围内线性关系良好,相关系数为0.9910~0.9999,方法的加标回收率为57.2%~120.3%,日内测定的相对标准偏差(RSD)为0.3%~24.7%,日间测定的RSD为0.6%~29.9%,检出限(信噪比为3)为0.0003~0.2080 ng/g。本方法灵敏度高、准确度和精密度好,简便快速,溶剂消耗量少,适用于灰尘中多种多氯联苯的同时测定。     

Selective pressurized liquid extraction of estrogenic compounds in soil and analysis by gas chromatography-mass spectrometry

A selective pressurized liquid extraction (SPLE) method, followed by gas chromatography–mass spectrometry (GC–MS), for the simultaneous extraction and clean-up of estrone (E1), 17β-estradiol (E2), 17α-ethynylestradiol (EE2), estriol (E3) and bisphenol A (BPA) from soil samples is described. The on-line clean-up of soil by SPLE was achieved using different organic matter retainers, including silica, alumina and Florisil, the most effective being silica. Thus, different amounts of silica, in conjunction with different extraction solvents (acetone, ethyl acetate, isohexane and dichloromethane), either alone or in combination, were used to extract the target chemicals from spiked soil samples. It was shown that 3 g silica resulted in satisfactory rates of recovery of target compounds and acetone:dichloromethane (1:3, v/v) was efficient in extracting and eluting estrogenic compounds for SPLE. Variables affecting the SPLE efficiency, including temperature and pressure were studied; the optimum parameters were 60 °C and 1500 psi, respectively. The limits of detection (LODs) of the proposed method were 0.02–0.37 ng g⁻¹ for the different estrogenic chemicals studied. The outputs using the proposed method were linear over the range from 0.1 to 120 ng g⁻¹ for E1, E2, EE2, 0.2–120 ng g⁻¹ for E3, and 0.5–120 ng g⁻¹ for BPA. The optimized method was further verified by performing spiking experiments in natural soil matrices; good rates of recovery and reproducibility were achieved for all selected compounds and the method was successfully applied to soil samples from Northeast Scotland, for the determination of the target compounds.     

Determination of polychlorinated biphenyls in ambient air by gas chromatography coupled to triple quadrupole tandem mass spectrometry

A multiresidue method for determining 22 polychlorinated biphenyls (PCBs) in air has been developed and validated by gas chromatography (GC) coupled to tandem mass spectrometry (MS/MS) using a triple quadrupole analyzer (QqQ). The method was validated in terms of both steps of sampling and analysis. The sampling method, which is based on active sampling using polyurethane foam (PUF) as adsorbent, was validated by generating standard atmospheres. The retention capacity of this sampling sorbent allows up to 5 m³ of air to be sampled without any breakthrough for most compounds. Two solvent extraction methods were compared: sonication and Soxhlet extraction with a mixture of n-hexane:diethyl ether (95:5 v/v). Both extraction methods yielded similar results, but the first one required less solvent and time. The method exhibited good accuracy (80.3–99.8%), precision (2.2–15.2%) and lower limits that allowed quantification and confirmation at levels as low as 0.008 ng/m³. Finally, the method was applied to the analysis of PCBs in the air in areas near to a municipal solid-waste landfill and directly above the refuse in the landfill, where it indicatedd the presence of some of the target compounds. Figure General chemical structure of polychlorinated biphenyls     

Capillary electrophoresis-mass spectrometry of Spirulina platensis proteins obtained by pressurized liquid extraction

In this work, the usefulness of CE-MS to monitor and optimize the pressurized liquid extraction (PLE) of proteins from Spirulina platensis microalga is demonstrated. Crude and purified PLE extracts from microalga were analyzed by CE-MS. It was observed that the use of purification protocols of phycobiliproteins (namely, ultrafiltration or precipitation-dialysis-freeze drying) resulted in better CE resolution and MS signals, demonstrating that sample matrix plays an important role in CE-MS of proteins in real samples. Ultrafiltration was found less laborious and much faster than precipitation-dialysis-freeze drying (1 vs. 48 h). Direct analysis of crude extracts was demonstrated to be also possible by CE-MS, providing less-quality information but enough to characterize PLE extracts in a much faster way. Therefore, the latter protocol was selected to monitor and optimize the extraction process of phycobiliproteins from S. platensis. To do that, different extraction conditions were tested, including time, temperature and pressure of extraction, nature of pressurized liquid, distribution of microalga inside the extraction cell, type of packing, etc. It is demonstrated that the combined use of PLE and CE-MS allows the attainment of extracts rich in phycobiliproteins in short extraction times (namely, yields of 20% can be obtained in less than 2 h under the optimum PLE process in an automatic way). To our knowledge, this work shows for the first time the usefulness of CE-MS for monitoring and optimizing a PLE process.     

Selective pressurized liquid extraction of polybrominated diphenyl ethers in fish

A fast and simple method for the analysis of polybrominated diphenyl ethers (PBDEs) in fish samples was developed using a one-step extraction and clean-up by means of pressurized liquid extraction (PLE) combined with gas chromatography-ion trap tandem mass spectrometry (GC-ITMS-MS). The selective PLE method provided to obtain ready-to-analyse extracts without any additional clean-up step, using a sorbent as fat retainer inside the PLE cell. Several PLE operating conditions, such as solvent type, extraction temperature and time, number of cycles and type of fat retainer, were studied. Using Florisil as fat retainer, maximum recoveries of PBDEs (83-108%) with minimum presence of matrix-interfering compounds were obtained using a mixture of n-hexane:dichloromethane 90:10 (v/v) as solvent, an extraction temperature of 100 °C and a static extraction time of 5 min in combination with three static cycles. Quality parameters of the method were established using standards and fish samples. Limits of detection and quantification ranged from 10 to 34 pg g⁻¹ wet weight and between 34 and 68 pg g⁻¹ wet weight, respectively. In addition, good linearity (between 1 and 500 ng ml⁻¹) and high precision (RSD % < 15%) were achieved. The method was validated using the standard reference material SRM-1945 (whale blubber) and was then applied to the analysis of PBDEs in fish samples.     

Determination of pesticides in milk-based infant formulas by pressurized liquid extraction followed by gas chromatography tandem mass spectrometry

An efficient and selective automated analytical method for the determination and quantification of a selected group of 12 organochlorine and organophosphorous pesticides in milk-based infant formulas has been developed. The samples were extracted by pressurized liquid extraction (PLE) and analysed using GC-MS/MS. The use of alumina as the fat retainer in the PLE extraction cell, together with the application of an injector temperature program during the GC injection process, avoided typical matrix interferences without the application of additional cleanup steps. Mean recoveries of between 70 and 110% were achieved for most of the compounds, except for chlorpyrifos methyl (50%), vinclozoline (48%), fenitrothion (56%) and procymidone (53%), with relative standard deviations ranging from 9 to 17%. Low limits of quantification were obtained for the studied compounds, from 0.01 to 2.6 μg kg⁻¹, thus guaranteeing their accurate determination within the rigorous requirements established for baby food. The validated method was applied to a pilot monitoring study in Spain. Twenty five samples of different brands of powdered infant formulas were obtained from supermarkets. Positive findings of endosulfan I, endosulfan II, fenitrothion, chlorpyrifos ethyl and bifenthrin were detected at concentrations ranging from 0.03 to 5.03 μg kg⁻¹.