Comparison of five extraction methods for measuring PCBs,PBDEs, organochlorine pesticides,and lipid content in serum

An increasing number of studies use blood obtained noninvasively to monitor organohalogen contaminants; however, blood can be difficult to analyze because of its aqueous nature and high protein content. We compared five methods for extracting polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), organochlorine pesticides, and lipids from serum using National Institute of Standards and Technology Standard Reference Material 1589a PCBs, Pesticides, PBDEs, and Dioxins/Furans in Human Serum. Liquid:liquid (LLE), cavity-dispersed microwave-assisted (MAE), focused microwave-assisted (FME), solid-phase (SPE), and pressurized fluid (PFE) extraction techniques were compared. FME extraction yielded the optimal recovery of internal standards (IS). All methods resulted in similar contaminant concentrations that also agreed with the certified values for SRM 1589a, except for only a few compounds measured by methods other than FME. Based on these findings, the FME method was determined to be the best overall extraction method. One procedural factor was found to affect contaminant concentrations; use of IS carrier solvents that were immiscible with serum (or when the serum was not directly physically mixed with IS) resulted in a 30% underestimation of organohalogen concentrations. This study offers valid, novel extraction alternatives beyond traditional methods (e.g., LLE) for blood contaminant measurements. Figure       

An improved method for the analysis of volatile polyfluorinated alkyl substances in environmental air samples

This article describes the optimisation and validation of an analytical method for the determination of volatile polyfluorinated alkyl substances (PFAS) in environmental air samples. Airborne fluorinated telomer alcohols (FTOHs) as well as fluorinated sulfonamides and sulfonamidoethanols (FOSAs/FOSEs) were enriched on glass-fibre filters (GFFs), polyurethane foams (PUFs) and XAD-2 resin by means of high-volume air samplers. Sensitive and selective determination was performed using gas chromatography/chemical ionisation–mass spectrometry (GC/CI–MS). Five mass-labelled internal standard (IS) compounds were applied to ensure the accuracy of the analytical results. No major blank problems were encountered. Recovery experiments were performed, showing losses of the most volatile compounds during extraction and extract concentration as well as strong signal enhancement for FOSEs due to matrix effects. Breakthrough experiments revealed losses of the most volatile FTOHs during sampling, while FOSAs/FOSEs were quantitatively retained. Both analyte losses and matrix effects could be remediated by application of adequate mass-labelled IS. Method quantification limits (MQLs) of the optimised method ranged from 0.2 to 2.5 pg/m³ for individual target compounds. As part of the method validation, an interlaboratory comparison of instrumental quantification methods was conducted. The applicability of the method was demonstrated by means of environmental air samples from an urban and a rural location in Northern Germany. Figure High-volume air sampling of volatile polyfluorinated alkyl substances using glass fibre filters and PUF/XAD-2 cartridges at a background monitoring site (Waldhof, Germany)     

Evaluation of solid-phase microextraction conditions for the determination of polycyclic aromatic hydrocarbons in aquatic species using gas chromatography

This paper describes a headspace solid-phase microextraction (HS-SPME) procedure coupled to gas chromatography with mass spectrometric detection (GC–MS) for the determination of eight PAHs in aquatic species. The influence of various parameters on the PAH extraction efficiency was carefully examined. At 75 °C and for an extraction time of 60 min, a polydimethylsiloxane–divinylbenzene (PDMS/DVB) fiber coating was found to be most suitable. Under the optimized conditions, detection limits ranged from 8 to 450 pg g⁻¹, depending on the compound and the sample matrix. The repeatability varied between 7 and 15% (RSD). Accuracy was tested using the NIST SRM 1974b reference material. The method was successfully applied to different samples, and the studied PAHs were detected in several of the samples. Figure Headspace SPME sampling followed by GC–MS facilitates routine monitoring of PAHs in aquatic species     

Advantages of LC–MS–MS compared to LC–MS for the determination of nitrofuran residues in honey

In the framework of developing analyses for exogenous contaminants in food matrices such as honey, we have compared data obtained by high-performance liquid chromatography coupled with mass spectrometry (LC–MS) to those provided by high-performance liquid chromatography and tandem mass spectrometry (LC–MS–MS). Initial results obtained with LC–MS showed that the technique lacked selectivity, which is why the method was validated by LC–MS–MS. This method involves a solid-phase extraction (SPE) of nitrofuran metabolites and nitrofuran parent drugs, a derivatization by 2-nitrobenzaldehyde for 17 h, and finally a clean-up by SPE. The data obtained show that the limits of detection varied between 0.2 and 0.6 μg kg⁻¹ for the metabolites and between 1 and 2 μg kg⁻¹ for nitrofuran parent drugs. The method was applied to different flower honeys. The results showed that nitrofurans (used as antibiotics) are consistently present in this matrix, the predominant compound being furazolidone. Figure Working bees     

SPME in environmental analysis

Recent advances in the use of solid-phase microextraction (SPME) in environmental analysis, including fiber coatings, derivatization techniques, and in-tube SPME, are reviewed in this article. Several calibration methods for SPME, including traditional calibration methods, the equilibrium extraction method, the exhaustive extraction method, and several diffusion-based calibration methods, are presented. Recent developed SPME devices for on-site sampling and several applications of SPME in environmental analysis are also introduced.      

Mineral oil certified reference materials for the determination of polychlorinated biphenyls from the National Metrology Institute of Japan (NMIJ)

Four mineral oil certified reference materials (CRMs), NMIJ CRM 7902-a, CRM 7903-a, CRM 7904-a, and CRM 7905-a, have been issued by the National Metrology Institute of Japan, which is part of the National Institute of Advanced Industrial Science and Technology (NMIJ/AIST), for the determination of polychlorinated biphenyls (PCBs). The raw materials for the CRMs were an insulation oil (CRM 7902-a and CRM 7903-a) and a fuel oil (CRM7904-a and CRM 7905-a). A solution of PCB3, PCB8, and technical PCB products, comprising four types of Kaneclor, was added to the oil matrices. The total PCB concentrations in the PCB-fortified oils (CRM 7902-a and CRM 7904-a) are approximately 6 mg kg⁻¹. In addition, the mineral oils which were not fortified with PCBs were also distributed as CRMs (CRM 7903-a and CRM 7905-a). Characterization of these CRMs was conducted by the NMIJ/AIST, where the mineral oils and the PCB solution were analyzed using multiple analytical methods such as dimethylsulfoxide extraction, normal-phase liquid chromatography, gel permeation chromatography, reversed-phase liquid chromatography, and chromatography using sulfoxide-bonded silica; and/or various capillary columns for gas chromatography, and two ionization modes for mass spectrometry. The target compounds in the mineral oils and those in the PCB solution were determined by one of the primary methods of measurement, isotope dilution–mass spectrometry (ID-MS). Certified values have been provided for 11 PCB congeners (PCB3, 8, 28, 52, 101, 118, 138, 153, 180, 194, and 206) in the CRMs. These CRMs have information values for PCB homologue concentrations determined by using a Japanese official method for determination of PCBs in wastes and densities determined with an oscillational density meter. Because oil samples having arbitrary PCB concentrations between respective property values of the PCB-fortified and nonfortified CRMs can be prepared by gravimetric mixing of the CRM pairs, these CRMs can be used for validation of PCB analyses using various instruments which have different sensitivities. Figure Preparation and certification processes of the mineral oil CRMs (example shown is polychlorinated biphenyls in insulation oil, high/low concentrations) Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A poly-dopamine based metal-organic framework coating of the type PDA-MIL-53(Fe) for ultrasound-assisted solid-phase microextraction of polychlorinated biphenyls prior to their determination by GC-MS

The authors describe an ultrasonic-assisted headspace method for solid phase micro-extraction (UA-HS-SPME) of 7 polychlorinated biphenyls (PCBs) with codes PCB28, PCB52, PCB101, PCB118, PCB138, PCB153 and PCB180. The coating is based on a poly-dopamine metal-organic framework [PDA-MIL-53(Fe)] on a stainless steel wire. The coating can be prepared and evenly deposited on the stainless fiber by dipping the PDA fiber into a solution of MIL-53(Fe). The assay is also environmentally friendly because water is used as the solvent. The effects of extraction time, addition of salts, pH value and power of ultrasonic power were optimized. The coating is found to possess a high selectivity and adsorption capacity for PCBs compared to commercial SPME fibers such as the divinylbenzene/carboxen/polydimethylsiloxane fibers. Following desorption, the PCBs were quantified by GC-MS. The detection limits are between 50 and 90 pg?g^?1 of PCBs in soil. The fibers can be easily prepared, and the batch-to-batch reproducibility (RDS) is <10% (for n = 6). The fibers are inexpensive, re-usable and can be easily manipulated, and particularly well suited for screening polychlorinated biphenyls in soil.

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Graphical abstract Schematic of the preparation of an extraction fiber using stainless steel wire as substrate, PDA as adhesive, and MIL-53(Fe) as the adsorbent. It was applied to the extraction of PCBs from soil. The fiber is durable and inexpensive.

     

Profiling of 3,4-methylenedioxymethamphetamine by means of high-performance liquid chromatography

An impurity-profiling method for 3,4-methylenedioxymethamphetamine (MDMA) is presented. The impurities of interest were extracted by solid-phase extraction (SPE) on Bakerbond C₁₈ spe columns from a weakly alkaline solution (pH 8.5). Development of the extraction conditions covered selection of the buffer for dissolution of the sample and the volume of the eluent used to elute the impurities. An important part of the studies was to optimise the separation conditions, and the simplex method was used for this purpose. Cluster analysis was applied for comparison of samples and its grouping. The developed method was based on the areas of 33 selected peaks corresponding to MDMA impurities. All examined samples were correctly classified into clusters corresponding to the synthetic route.      

SPE-HPLC purification of endocrine-disrupting compounds from human serum for assessment of xenoestrogenic activity

Assessment of xenoestrogenic activity in human serum samples requires the removal of endogenous sex hormones to assure that the activity measured originates from xenobiotic compounds only. Serum samples representing high, medium and lower accumulation of persistent organic pollutants (POPs) were extracted using solid-phase extraction (SPE) followed by normal-phase high-performance liquid chromatography (NP-HPLC) for separation of POPs from endogenous hormones. The recovery of polychlorinated biphenyl (PCB) congeners in spiked serum samples was up to 86 %, making the extraction method suitable for the study. MVLN cells, stably transfected with an estrogen receptor (ER) luciferase reporter vector (estrogen response element chemically activated luciferase expression, ERE-CALUX), were exposed to the reconstituted SPE-HPLC extracts for determination of the integrated estrogenic activity. The effects of PCBs were analyzed by direct in vitro exposure of PCBs (nos. 138, 153, 180) and by ex vivo analysis of SPE-HPLC extracts from serum spiked with the PCBs. Similar effects on ER transactivation were observed for the direct in vitro and the ex vivo analysis experiments. The ER transactivation responses determined for actual serum samples were in the linear range of the dose-response curve. 17β-Estradiol titrations showed that the xenoestrogenic effects were mediated via ER. Moreover, our SPE-HPLC-ERE-CALUX assay was demonstrated to elicit high interlaboratory correlation. In the present study the combination of SPE-HPLC purification and the ex vivo estrogenic responses measured by ERE-CALUX was validated and considered to be a valuable tool to assess the combined ER effect of lipophilic serum POPs where additive/synergistic and agonistic/antagonistic effects are integrated giving an overall estimate of exposure and bioactivity.      

Improved online coupling of planar chromatography with electrospray mass spectrometry: extraction of zones from glass plates

A plunger-based extraction device for HPTLC/MS coupling, which was originally designed for extraction on TLC aluminum foils, was enhanced. The threefold modifications enabled extraction of analytes from glass-backed HPTLC/TLC plates after separation. A buffering of the plunger reduced the occurrence of leakage. The involvement of a torque screwdriver for the fixation resulted in a reproducible contact pressure and avoided breaking the glass plates. The employment of this device was also extended to plates with a layer thickness of 100 μm by reducing the height of the plunger’s cutting edge. Repeatability of the extraction from glass-backed plates, linearity of the signal obtained, and detection capability were shown to be comparable to the original device, which was only usable with aluminum foils. The influence of the elution solvent on the intensity of the MS signal was demonstrated to be a compromise between high elution power of the solvent and good solubility of the analyte in the elution solvent. The extraction device was employed for plates from different lots and for plates with different stationary phases thereby proving its general applicability in planar chromatography.      

Dispersive liquid–liquid microextraction using an in situ metathesis reaction to form an ionic liquid extraction phase for the preconcentration of aromatic compounds from water

A novel microextraction method is introduced based on dispersive liquid–liquid microextraction (DLLME) in which an in situ metathesis reaction forms a water-immiscible ionic liquid (IL) that preconcentrates aromatic compounds from water followed by separation using high-performance liquid chromatography. The simultaneous extraction and metathesis reaction forming the IL-based extraction phase greatly decreases the extraction time as well as provides higher enrichment factors compared to traditional IL DLLME and direct immersion single-drop microextraction methods. The effects of various experimental parameters including type of extraction solvent, extraction and centrifugation times, volume of the sample solution, extraction IL and exchanging reagent, and addition of organic solvent and salt were investigated and optimized for the extraction of 13 aromatic compounds. The limits of detection for seven polycyclic aromatic hydrocarbons varied from 0.02 to 0.3 μg L⁻¹. The method reproducibility produced relative standard deviation values ranging from 3.7% to 6.9%. Four real water samples including tap water, well water, creek water, and river water were analyzed and yielded recoveries ranging from 84% to 115%.      

Determination of trapidil in human serum and urine by derivative UV spectrophotometry after selective solid-phase extraction

A novel analytical technique able to determine the anti-ischemic drug trapidil in human serum and urine is proposed. In order to achieve satisfactory sensitivity and selectivity, an extraction procedure was required to isolate the drug from complex matrixes such as serum and urine. A solid-phase extraction procedure was investigated to both increase the analyte concentration and eliminate the interfering molecules present in large amounts in both matrixes. Optimization of the extraction step was realized by selecting a new polymeric sorbent based on a surface-modified styrene–divinylbenzene polymer which provided fast and efficient drug extraction. Drug quantification was performed by using the third-order derivative spectra of the SPE eluates. Absorbance specific signals at ³D_335,316 and ³D₃₁₆ nm for urine and serum, respectively, were demonstrated to be directly proportional to drug concentration and barely affected by residual matrix interferences. Under the optimized experimental conditions the calibration plots were linear over the concentration range 0.2–50 μg mL⁻¹. The method was validated by analysis of a series of spiked samples. Accuracy (recovery of 95 and 94% for serum and urine, respectively) and precision (RSD below 4%) were good. Figure Assay of Trapidil in biological fluids by SPE and derivative spectrophotometry     

Headspace solid-phase microextraction gas chromatography tandem mass spectrometry for the determination of brominated flame retardants in environmental solid samples

A headspace solid-phase microextraction gas chromatography coupled with tandem mass spectrometry (HSSPME-GC-MS-MS) methodology for determination of brominated flame retardants in sediment and soil samples is presented. To the best of our knowledge, this is the first time that SPME has been applied to analyze polybrominated biphenyls (PBBs) and polybrominated diphenyl ethers (PBDEs) in environmental solid samples. Analyses were performed using 0.5-g solid samples moisturized with 2 mL water, employing a polydimethylsiloxane (PDMS) fiber coating, exposed to the headspace at 100 °C for 60 min. Several types of environmental solid samples were included in this study and the extraction efficiency was related to the organic matter content of the sample. Calibration was performed using real samples, and the method showed good linearity over a wide concentration range, precision, and afforded quantitative recoveries. The obtained detection limits were in the sub-ng g⁻¹ for all the target analytes in both samples. The proposed procedure was applied to several marine and river sediments and soils, some of which were found to contain PBDEs at concentrations in the ng g⁻¹ level; BDE-47, BDE-100, and BDE-99 were the major congeners detected. The proposed method constitutes a rapid and low-cost alternative for the analysis of the target brominated flame retardants in environmental solid samples, since the clean-up steps, fractionation, and preconcentration of extracts inherent to the classical multi-step solvent extraction procedures are avoided.      

Comparison of two solid-phase microextraction methods for the quantitative analysis of VOCs in indoor air

Competitive adsorption on adsorptive solid-phase microextraction (SPME) fibres implies careful determination of operating conditions for reliable quantitative analysis of VOCs in indoor air. With this objective, two analytical approaches, involving non-equilibrium and equilibrium extraction, were compared. The average detection limit obtained for GC-MS analysis of nine VOCs by the equilibrium method is 0.2 μg m⁻³, compared with 1.9 μg m⁻³ with the non-equilibrium method. The effect of the relative humidity of the air on the calibration plots was studied, and shown to affect acetone adsorption only. Hence, the concentrations that can be accurately determined are up to 9 μmol m⁻³. The methods were then applied to indoor air containing different concentrations of VOCs. The non-equilibrium method, involving short extraction time, can be used for detection of pollution peaks whereas equilibrium extraction is preferable for measurement of sub-μg m⁻³ ground concentration levels.      

Nuclear magnetic resonance of mass-limited samples using small RF coils

Figure Schematic diagram of a typical arrangement used for hyphenating chemical microseparations (e.g. capillary HPLC, CE, or CEC) with microcoil NMR detection     

Modelling of toluene solid-phase microextraction for indoor air sampling

Solid-phase microextraction (SPME) is a convenient and efficient sampling technique recently applied to indoor air analysis. We propose here a theoretical model of the adsorption kinetics of toluene on SPME fibre under static extraction conditions. We discuss the effects of sampling volume and initial concentration of analyte on the adsorption kinetics. This model is used to estimate the limits of detection taking into account operating conditions and to calculate theoretical calibration curves. Results of comparison with experimental data are encouraging: only 11% difference for calibration curves and 30% for the estimation of the limit of detection. On the basis of this kinetics model, the solid concentration gradient in the Carboxen coating was modelled with Fick’s second law of diffusion in unsteady-state mass-transfer mode. Mass diffusion from the gas sample to the SPME fibre was also investigated. It was shown that diffusion is the limiting step of the mass-transfer process in the static mode. Thus, the model developed, allows a better understanding of adsorption on Carboxen fibre and in the future could be a useful tool for cheap and time-saving development of SPME methods and the estimation of sampling performance. Figure PDMS/Carboxen SPME fibre (scanning electron microscopy – magnification x 220)     

Optimization of a sensitive method for the determination of nitro musk fragrances in waters by solid-phase microextraction and gas chromatography with micro electron capture detection using factorial experimental design

A solid-phase microextraction method (SPME) followed by gas chromatography with micro electron capture detection for determining trace levels of nitro musk fragrances in residual waters was optimized. Four nitro musks, musk xylene, musk moskene, musk tibetene and musk ketone, were selected for the optimization of the method. Factors affecting the extraction process were studied using a multivariate approach. Two extraction modes (direct SPME and headspace SPME) were tried at different extraction temperatures using two fiber coatings [Carboxen–polydimethylsiloxane (CAR/PDMS) and polydimethylsiloxane–divinylbenzene (PDMS/DVB)] selected among five commercial tested fibers. Sample agitation and the salting-out effect were also factors studied. The main effects and interactions between the factors were studied for all the target compounds. An extraction temperature of 100 °C and sampling the headspace over the sample, using either CAR/PDMS or PDMS/DVB as fiber coatings, were found to be the experimental conditions that led to a more effective extraction. High sensitivity, with detection limits in the low nanogram per liter range, and good linearity and repeatability were achieved for all nitro musks. Since the method proposed performed well for real samples, it was applied to different water samples, including wastewater and sewage, in which some of the target compounds (musk xylene and musk ketone) were detected and quantified. Figure Stardardized Pareto charts for the main effects and interactions     

A liquid chromatography/tandem mass spectrometric multi-mycotoxin method for the quantification of 87 analytes and its application to semi-quantitative screening of moldy food samples

This paper describes the extension of a previously published method based on liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC/ESI-MS/MS) from 39 to currently 87 analytes. Besides the mycotoxins for which regulated concentrations exist, the method now comprises not only almost all mycotoxins for which standards are commercially available, but also a number of other important metabolites produced by fungi involved in food spoilage. The method is based on a single extraction step using an acidified acetonitrile/water mixture followed by analysis of the diluted crude extract. Method performance characteristics were determined after spiking breadcrumbs as model matrix at multiple concentration levels. With very few exceptions, coefficients of variation of the whole procedure of <5% and repeatabilities at the highest spiking level of <7% were obtained. Limits of detection ranged between 0.02 and 225 μg kg⁻¹. The quantitative determination of ergopeptides was disturbed by epimerization due to the acidic conditions. From the remaining 77 analytes, the apparent recoveries of nine substances deviated significantly from the CEN target range of 70–110% due to incomplete extraction and/or matrix effects. In principle, the latter can be compensated for by the application of matrix-matched calibration. The developed method was applied to 18 moldy samples (including bread, fruits, vegetables, jam, cheese, chestnuts and red wine) from private households. This study revealed the great value of the described method: 37 different fungal metabolites were identified at concentrations of up to 33 mg kg⁻¹, and some of these have never been reported before in the context of moldy food products. Figure ESI (+) MS/MS chromatogram (total ion current of all MRMs) of a sample of moldy dark bread     

Comparative performance study of different sample introduction techniques for rapid and precise selenium isotope ratio determination using multi-collector inductively coupled plasma mass spectrometry (MC-ICP/MS)

The analytical performance of five sample introduction systems, a cross flow nebulizer spray chamber, two different solvent desolvation systems, a multi-mode sample introduction system (MSIS), and a hydride generation (LI2) system were compared for the determination of Se isotope ratio measurements using multi-collector inductively coupled plasma mass spectrometry (MC-ICP/MS). The optimal operating parameters for obtaining the highest Se signal-to-noise (S/N) ratios and isotope ratio precision for each sample introduction were determined. The hydride generation (LI2) system was identified as the most suitable sample introduction method yielding maximum sensitivity and precision for Se isotope ratio measurement. It provided five times higher S/N ratios for all Se isotopes compared to the MSIS, 20 times the S/N ratios of both desolvation units, and 100 times the S/N ratios produced by the conventional spray chamber sample introduction method. The internal precision achieved for the ⁷⁸Se/⁸²Se ratio at 100 ng mL⁻¹ Se with the spray chamber, two desolvation, MSIS, and the LI2 systems coupled to MC-ICP/MS was 150, 125, 114, 13, and 7 ppm, respectively. Instrument mass bias factors (K) were calculated using an exponential law correction function. Among the five studied sample introduction systems the LI2 showed the lowest mass bias of −0.0265 and the desolvation system showed the largest bias with −0.0321. Figure Illustration of the multi-mode sample introduction system for Se isotope ratiomeasurements     

Analysis of glycans in glycoproteins by diffusion-ordered nuclear magnetic resonance spectroscopy

Enzymatically cleaved glycans from sub-milligram quantities of erythropoietin (EPO) and ovalbumin have been analyzed, without further purification, by two-dimensional diffusion-ordered nuclear magnetic resonance spectroscopy. At NMR sample concentrations below 50 μmol L⁻¹ the major components of the oligosaccharide fractions could be distinguished by their anomeric proton chemical shift and their size-dependent diffusion coefficients. Figure ¹H NMR diffusion decay curves of anomeric protons in the EPO glycan fraction