Microwave assisted extraction combined with dispersive liquid–liquid microextraction as a sensitive sample preparation method for the determination of haloanisoles and halophenols in cork stoppers and oak barrel sawdust

In this paper, a method based on microwave assisted extraction (MAE) in combination with dispersive liquid–liquid microextraction (DLLME) has been proposed as a new approach for the sensitive determination of cork taint responsible compounds in cork stoppers and oak barrel sawdust. For this purpose, haloanisoles and halophenols were extracted from the solid samples using a MAE method. Subsequently, a DLLME-derivatisation procedure was applied on the MAE extracts and the analytes were determined by gas chromatography–electron capture detection (GC–ECD). Parameters affecting the DLLME-derivatisation method were exhaustively investigated by means of experimental design methodology. Once optimised, the proposed method showed satisfactory linearity (correlation coefficients over 0.991), repeatability (below 10.4%) and inter-day precision (below 11.2%). Detection limits obtained were similar or even lower than previously reported. The results obtained proved the suitability of the combination of MAE with DLLME as a sensitive sample preparation methodology for the analysis of haloanisoles and halophenols in solid enological matrices.     

Determination of tetracyclines in multi-specie animal tissues by pressurized liquid extraction and liquid chromatography–tandem mass spectrometry

A specific, sensitive and robust pressurized liquid extraction (PLE) and liquid chromatography tandem mass spectrometry (LC–MS/MS) method for determining tetracycline, chlortetracycline, oxytetracycline and doxycycline in bovine, swine, poultry and lamb muscle tissues is presented. PLE was performed using an ASE^® 200 from Dionex and water as extractant, followed by solid-phase extraction (SPE) using an Oasis HLB cartridge. The method was validated for beef, chicken, pork and lamb meat in compliance with the requirements set by Commission Decision, 2002/657/EC [Commission Decision 2002/657/EC (2002). Implementing Council Directive 96/23/EC concerning the performance of analytical methods and interpretation of results. Official Journal of European Communities, L239, 66–98. (Available at: <http://europe.eu.int>)]. The average recoveries of the different meat samples, spiked with the four tetracyclines at three levels (1, 100 and 200 μg kg⁻¹ of each tetracycline), were always higher than 89% with intraday and interday precision lower than 15% and 17%, respectively. A good linearity was established for the four tetracyclines in the range from 5 to 10,000 μg kg⁻¹ with r > 0.995. The limits of quantification (LOQs) were between 0.5 and 1 μg kg⁻¹, which are well below the tolerance levels set by the European Union. The decision limit (CCα) and the decision capability (CCβ) were in the range 101–116 and 112–130 μg kg⁻¹, respectively. Compared with previous methods, sample preparation time required for the analysis and LOQs, are reduced. The method demonstrated its successful application for the analysis of 100 meat samples. Two samples of beef and one sample of chicken out of 25 of each type tested positive while none of 25 samples of either, lamb or pork, tested positive.     

Improved sample treatment and chromatographic method for the determination of isoflavones in supplemented foods

Isoflavones are a group of substances that belong to the family of phytoestrogens. These natural substances may offer several benefits to human health. One of the most important sources for human isoflavone intake is soy and soybean food derivatives. An improved sample treatment followed by a high performance liquid chromatographic method for the determination of isoflavones in supplemented milk and juices is proposed and compared to the AOAC official method. Detection limits found were between 0.2 and 0.3 mg L⁻¹ for daidzein and genistein respectively. Quantification limits found were between 0.7 mg L⁻¹ for daidzein to 1.0 mg L⁻¹ for genistin, while inter and intra-day variability was under 10% in all cases. Recoveries for spiked samples were over 90% and under 110%. The method was validated by comparison with the AOAC method and by recovery assay methodology.     

Selective determination of copper and iron in various food samples by the solid phase extraction

The solid phase extraction method developed using N-benzoyl-N-phenylhydroxylamine as a chelating reagent and Amberlite XAD-1180 as an adsorbent was used for the determination of Cu(II) and Fe(III) in various food samples by flame atomic absorption spectrometry. The samples were digested by using nitric acid and hydrogen peroxide. The Cu concentrations ranged from 1.01 to 5.81 μg g⁻¹ in cereals, from 0.40 to 9.67 μg g⁻¹ in vegetable and fruits and from 0.37 to 0.70 μg g⁻¹ in infusions while the Fe concentrations ranged from 7.48 to 34.3 μg g⁻¹ in cereals, from 5.74 to 260 μg g⁻¹ in vegetable and fruits, from 1.63 to 5.12 μg g⁻¹ in infusions and from 0.24 to 1.56 mg L⁻¹ in beverage samples. The Cu and Fe concentrations found were compared with the results obtained from the other food studies in the world.     

电驱动膜萃取法在蔬菜水果硒元素检测中的应用

提出一种新方法,将样品通过混合酸消化后应用电驱动膜萃取技术富集其中的硒元素,然后测定其含量。结果表明,该方法缩短了检测时间,减少了试剂消耗,实际样品检出限可达到0.005mg/kg,平均回收率为92.4%。通过国家标准物质验证,试验结果符合其不确定度要求。该方法适宜蔬菜水果中硒的检验。     

Determination of volatile N-nitrosamines in meat products by microwave-assisted extraction coupled with dispersive micro solid-phase extraction and gas chromatography – Chemical ionisation mass spectrometry

A sensitive procedure, microwave-assisted extraction (MAE) coupled dispersive micro solid-phase extraction (D-μ-SPE), was developed to extract N-nitrosodimethylamine (NDMA) and other six volatile N-nitrosamines (NAms) from meat products. Parameters affecting the efficiency of MAE and D-μ-SPE were systematically investigated. For MAE, 5-g of a homogenised meat sample was extracted with 30 mL of a sodium hydroxide (0.025 M) solution at 100 °C for 10 min. The optimum D-μ-SPE conditions were immersing 100 mg of Carboxen™ 1000 adsorbent in the MAE extract. After vigorously shaking for 30 min, the NAms were then desorbed by treatment with 200 μL of dichloromethane. A 10 μL aliquot was determined by gas chromatography with chemical ionisation mass spectrometry (GC–CI-MS) using the selected-ion-storage (SIS) mode. The limits of quantitation (LOQs) were 0.03–0.36 ng/g. Preliminary results revealed that NDMA was present in the highest concentration, ranging from 0.8 to 3.2 ng/g.     

Salting-out assisted liquid–liquid extraction with dansyl chloride for the determination of biogenic amines in food

Biogenic amines (BAs) are compounds present in foodstuff of animal origin that not only can be harmful to the consumer but can also serve as indicators of the product's edibility status. However, BAs’ analysis is rather complicated. Derivatisation methods have been employed to make their analysis less challenging. Salting-out assisted liquid–liquid extraction (SALLE) was herein applied to decrease time that the derivatising agent dansyl chloride (DNS-Cl) requires to be effective. DNS-Cl derivates were separated and analysed by high-performance liquid chromatography with UV and fluorescence detection (HPLC-UV/FD). It was by this way possible to analyse methylamine, dimethylamine, ethylamine, β-phenylethylamine, isopentylamine, putrescine, cadaverine, histamine, tyramine, spermidine and spermine in a straightforward manner in several fish-based and meat-based samples, obtaining results in the order of magnitude of about a few mg per kg. All calibrations curves had r² higher than 0.99, and limits of detection ranged from 0.0075 to 1.6 mg L⁻¹.     

Sample preparation method for the analysis of some organophosphorus pesticides residues in tomato by ultrasound-assisted solvent extraction followed by dispersive liquid–liquid microextraction

A very simple and economic method for organophosphorus pesticides (OPPs) residues analysis in tomato by means of gas chromatography–flame photometric detection (GC–FPD) has been developed. The method involves a rapid and small-scale extraction. The sample was homogenised and extraction of the OPPs with acetone was carried out assisted by sonication. No clean-up or evaporation were required after extraction. Pre-concentration of the OPPs from the acetone extract was done by using dispersive liquid–liquid microextraction (DLLME) technique. Chlorobenzene was added in micro-level volume as extraction solvent and triphenylphosphate as internal standard in DLLME procedure. The method showed good linearity over the range assayed (0.5–1000 μg kg⁻¹) and the detection limits for the pesticides studied varied from 0.1 to 0.5 μg kg⁻¹. Repeatability studies resulted a relative standard deviation lower than 10% in all cases. The proposed method was used to determine pesticides levels in tomatoes grown in open field.     

Determination of acrylamide in foods by pressurized fluid extraction and liquid chromatography-tandem mass spectrometry used for a survey of Spanish cereal-based foods

An automated and rapid method for the determination of acrylamide in different food products is presented. The method involves pressurized fluid extraction (PFE) of foods with acetonitrile and precipitation with Carrez reagents. The final extract is analysed by liquid chromatography coupled to electrospray ionization tandem mass spectrometry (ESI-MS-MS). The main parameters affecting the performance of ESI-MS-MS and PFE were optimized using a design of experiments approach. The limit of quantification of the method was 5 µg kg^-1, and recoveries from incurred samples ranged between 93 and 101%. The accuracy was evaluated using the reference test materials FAPAS T3002, T3005 and T3011. Using the optimized method, 62 food samples of potato chips, snacks, biscuits, breakfast cereals and crisp bread sampled from Valencia, Spain, supermarkets were surveyed for acrylamide levels. The levels were similar to those reported in the European Union and USA.     

加速溶剂萃取结合亲水液相色谱柱分离测定坚果中的8种生育酚异构体

目的建立加速溶剂萃取(ASE)结合亲水液相色谱(HILIC)柱分离测定坚果中8种生育酚异构体的方法。方法 2 g坚果样品经ASE提取富集后,用BEH Amide色谱柱(150 mm×3.0 mm,1.7μm)分离,以90%正己烷,10%叔丁基甲基醚-四氢呋喃-甲醇(20∶1∶0.1,V/V)作为流动相等度洗脱,荧光检测器激发波长294 nm,发射波长328 nm检测,外标法定量。结果 4种生育酚在0.5~80.0μg/ml、4种生育三烯酚在0.5~30.0μg/ml之间具有良好的线性(r~20.998),方法检出限在0.032~0.070 mg/kg之间,方法定量限范围0.096~0.210 mg/kg,三个水平加标回收率在87.5%~114.2%之间,6次重复测定相对标准偏差(RSD)均≤12%。结论本方法具有良好的灵敏度、回收率和重复性,适用于坚果中8种生育酚异构体的含量分布的测定。     

High throughput analysis of amnesic shellfish poisoning toxins in bivalve molluscs by dispersive solid-phase extraction and high-performance liquid chromatography using a monolithic column

Domoic acid and its isomers are algal neurotoxins responsible for the human intoxication syndrome known as amnesic shellfish poisoning. A rapid and simple HPLC–UV/DAD method based on the use of a monolithic silica column is proposed for the determination of ASP toxins in shellfish samples. To the best of our knowledge, a monolithic column is applied for the first time to the analysis of marine toxins.     

Validation of a size exclusion liquid chromatographic method for determination of methylcellulose and hydroxypropyl methylcellulose food gums as soluble dietary fiber in food and food product

A size exclusion liquid chromatographic method was developed for the determination of methylcellulose (MC) and hydroxypropyl methylcellulose (HPMC) as dietary fiber in food. These modified cellulose food gums are used in a wide variety of foods and physiologically behave as dietary fibers but are not determined using existing analytical dietary fiber methods. This article reports a single laboratory validation of a new method based on AOAC 991.43, and uses a liquid chromatograph with a refractive index detector. This new method was validated for foods containing 0.2–27% of MC and HPMC employing AOAC’s Single Laboratory Validation protocol. Ten food samples of meat, bread, milk powder, potato and orange juice drink mix were studied. Precision of the new method, measured as total standard deviation (St), varied from 0.01 to 2 for foods containing 0.2–27% MC; and from 0.05 to 0.2 for foods containing 0.5–3.8% HPMC. Recovery varied from 76% to 85% for MC, and from 75% to 113% for HPMC. Use of a blank matrix proved successful in correcting for indigenous food fibers. The method demonstrated excellent linearity down to 0.03%. This provides the sensitivity required for food nutrition labeling purposes. These results show the method is suitable for determination of MC and HPMC in food and support further validation through a collaborative study.     

Sensitive determination of domoic acid in shellfish by on-line coupling of weak anion exchange solid-phase extraction and liquid chromatography–diode array detection–tandem mass spectrometry

An automated method based on the use of on-line solid-phase extraction (SPE) coupled to liquid chromatography with diode array detection and tandem mass spectrometry (LC–DAD–MS/MS) has been developed for the determination of domoic acid in shellfish. The on-line coupling of SPE and liquid chromatography was accomplished by a column switching approach. A weak anion exchange (WAX) sorbent was selected for the SPE procedure, allowing a selective cleanup of shellfish extracts. High sensitivity was achieved by on-line pre-concentration of large volume injections (50–1000 μL). A simple protein precipitation cleanup with acetone was used to efficiently remove proteins from shellfish extracts, preventing possible column clogging during chromatographic separation.     

固相萃取–液相色谱–荧光检测法测定半夏中 苯并[a]芘残留量

目的建立半夏样品中苯并[a]芘残留量的固相萃取-液相色谱-荧光检测法。方法样品用水浸泡后,用正己烷萃取,硅胶固相萃取柱和ENV固相萃取柱净化,分析时采用SUPELCOSILTM LC-PAH(25 cm×4.6 mm,5μm)色谱柱分离,以乙腈-水(85:15=V:V)为流动相,荧光检测激发波长384 nm,发射波长406 nm,外标法定量。结果苯并[a]芘的检出限为0.1μg/kg,在1.0~50.0 ng/m L浓度范围内,苯并[a]芘的线性相关系数为0.9999,线性关系良好,方法回收率在78.0%~102.5%范围内,相对标准偏差低于9.6%。结论该方法准确、实用、简便、快速,在中药材的苯并[a]芘残留量检测方面有广泛应用前景。     

Multiresidue determination of pesticides in honey samples by gas chromatography–mass spectrometry and application in environmental contamination

A simple and fast multiresidue method has been developed to determine 48 pesticides within the major groups of pesticides (organohalogen, organophosphorous, pyrethroids and organonitrogen) in representative samples of locally produced honey, in Bauru (State of São Paulo, Brazil) during 2003–2004. The recovery results found ranged from 76% to 95% and the limits of detection were lower than 0.01 mg/kg for gas chromatography with electron impact mass spectrometric detection in the selected ion monitoring mode (GC–MS-SIM). The results indicated that most pesticides found in the samples belonged to the organohalogen and organophosphorous groups and lower levels of residues of some organonitrogen and pyretroids were also detected. Malathion residues were detected in all the samples, in a high concentration, owing to its applications to control dengue mosquitoes in the area studied.     

Cloud-point extraction and reversed-phase high-performance liquid chromatography for the determination of synthetic phenolic antioxidants in edible oils

A cloud-point extraction (CPE) method using Triton X-114 (TX-114) nonionic surfactant was developed for the extraction and preconcentration of propyl gallate (PG), tertiary butyl hydroquinone (TBHQ), butylated hydroxyanisole (BHA), and butylated hydroxytoluene (BHT) from edible oils. The optimum conditions of CPE were 2.5% (v/v) TX-114, 0.5% (w/v) NaCl and 40 min equilibration time at 50 °C. The surfactant-rich phase was then analyzed by reversed-phase high-performance liquid chromatography with ultraviolet detection at 280 nm, using a gradient mobile phase consisting of methanol and 1.5% (v/v) acetic acid. Under the studied conditions, 4 synthetic phenolic antioxidants (SPAs) were successfully separated within 24 min. The limits of detection (LOD) were 1.9 ng mL(-1) for PG, 11 ng mL(-1) for TBHQ, 2.3 ng mL(-1) for BHA, and 5.9 ng mL(-1) for BHT. Recoveries of the SPAs spiked into edible oil were in the range 81% to 88%. The CPE method was shown to be potentially useful for the preconcentration of the target analytes, with a preconcentration factor of 14. Moreover, the method is simple, has high sensitivity, consumes much less solvent than traditional methods, and is environment-friendly. Practical Application: The method established in this article uses less organic solvent to extract SPAs from edible oils; it is simple, highly sensitive and results in no pollution to the environment.     

Determination of malachite green residues in rainbow trout muscle with liquid chromatography and liquid chromatography coupled with tandem mass spectrometry

A method for the determination of malachite green and its major metabolite leucomalachite green in rainbow trout muscle is reported with limits of detection of 0.8 and 0.6 μg kg^-1, respectively. Residues were extracted with an acetonitrile-acetate buffer mixture and partitioned into methylene chloride. Clean-up of the extracts was performed on alumina and propylsulfonic acid solid-phase extraction columns using the automated solid-phase extraction system. The chromatographic separation of malachite green and leucomalachite green was achieved on a Chromspher 5B column using an acetonitrile-acetate buffer mobile phase. Leucomalachite green was converted to malachite green by post-column oxidation before spectrophotometric detection at 600 nm. The mean recoveries of malachite green and leucomalachite green from control rainbow trout muscle spiked at 2-50 μg kg^-1 were 65% (range 63.4-65.9%, relative standard deviation 3.9-16.1%) and 74% (range 58.3-82.6%, relative standard deviation 3.3-11.4%), respectively. Qualitative confirmation of the determined residues was performed with liquid chromatography coupled with tandem mass spectrometry detection with limits of detection of 2.5 and 1 μg kg^-1 for malachite green and leucomalachite green, respectively.     

Applications of sample preparation techniques in the analysis of pesticides and PCBs in food

Pesticides and polychlorinated biphenyls (PCBs) are found in various parts of the environment in quite small concentrations, but they accumulate and thus become a threat to human health and life. A review is focused on the application of some popular techniques for sample preparation in analysis of these compounds in food. Even with the emergence of advanced techniques of final analysis, complex matrices, such as food, require extensive sample extraction and purification. Traditional sample preparation techniques are time consuming and require large amount of solvents, which are expensive, generate considerable waste, contaminate the sample and can enrich it for analytes. There have been many sample preparation techniques proposed to meet the requirements connected with the multiplicity of food. Optimal sample preparation can reduce analysis time, sources of error, enhance sensitivity and enable unequivocal identification and quantification. Sample extraction and purification techniques are discussed and their most recent applications in food analysis are provided. This review pointed out that sample preparation is the critical step.     

Simultaneous determination of nine lignans using pressurized liquid extraction and HPLC-DAD in the fruits of Schisandra chinensis

The pressurized liquid extraction and HPLC-DAD was developed for extraction and determination of bioactive lignans in Schisandra chinensis. The efficient PLE conditions employed methanol as extraction solvent, 125 °C of extraction temperature, 5 min of static extraction time and only one cycle. A rapid HPLC-DAD method was described for simultaneous determination of nine lignans, including schisandrol A, gomisin J, schisandrol B, tigloylgomisin H, angeloylgomisin H, schisandrin A, γ-schisandrin, gomisin N and schisandrin C. The extraction efficiency of PLE was observed to be comparable with reflux and sonication. In addition, the contents of nine lignans in S. chinensis from different regions were analysed by PLE and HPLC-DAD method.