Determination of some phthalate acid esters in artificial saliva by gas chromatography–mass spectrometry after activated carbon enrichment

Preparation of Carbon-Based Solid Acid Catalyst from High-Sulfur Petroleum Coke with Nitric Acid and Ball Milling, and a Computational Evaluation of Inherent Sulfur Conversion Pathways

A series of petroleum coke (petcoke)-derived solid acid catalysts were prepared via nitric acid treatment with or without ball milling pretreatment. The inherent sulfur in petcoke was converted to sulfonic groups, which were active sites for the esterification of octanoic acid and methanol at 60 °C, with ester yields of 14-43%. More specifically, samples without ball milling treated at 120 °C for 3 h had a total acidity of 4.67 mmol/g, which was 1.6 times that of the samples treated at 80 °C, despite their -SO3H acidities being similar (~0.08 mmol/g). The samples treated for 24 h had higher -SO3H (0.10 mmol/g) and total acidity (5.25 mmol/g) but not increased catalytic activity. Ball milling increased the defects and exposed aromatic hydrogen groups on petcoke, which facilitated further acid oxidation (0.12 mmol -SO3H/g for both materials and total acidity of 5.18 mmol/g and 5.01 mmol/g for BP-N-3/120 and BP-N-8/90, respectively) and an increased ester yield. DFT calculations were used to analyze the pathways of sulfonic acid group formation, and the reaction pathway with NO2• was the most thermodynamically and kinetically favourable. The activities of the prepared catalysts were related to the number of -SO3H acid sites, the total acidity, and the oxygen content, with the latter two factors having a negative impact.

Development and Validation of an Ultrasensitive LC-MS/MS Method for the Quantification of Melatonin in Human Saliva

A growing body of literature describes the potential effects of circadian disruption on human health. Indeed, psychiatric diseases, metabolic syndrome, and cancers may be linked to disturbance of the circadian rhythm. Currently, the best practice to assess circadian rhythm is the measurement of melatonin levels. Our goal was thus to develop and validate a highly sensitive LC-MS/MS method to follow salivary melatonin levels throughout the day and night. Our method reached a lower limit of the measuring interval (LLMI) of 0.8 pg/mL. To our knowledge, it is the most sensitive method allowing quantitation of melatonin in saliva. Saliva, obtained from passive drooling or salivette, was extracted by an efficient and quick liquid-liquid extraction with no further cleanup needed. The method was validated according to the European Medicines Agency (EMA) guidelines and provided excellent results regarding accuracy, precision, linearity, selectivity, and specificity. Comparison between radioimmunoassay and our method was performed and showed differences at low levels, most likely due to cross-reactivity with other indols. To assess daytime melatonin levels in humans, salivary melatonin levels of ten volunteers were monitored throughout the day and showed lower daytime levels than reported in previous studies.

Nanofiber-based sorbents: Current status and applications in extraction methods

Advanced sorbents gradually become a research hotspot on account of the increasing attention paid to environmental problems. Due to the prominent physicochemical features of nanofibers (NFs), such as high porosity, large surface area, favorable interconnectivity, high adsorption capacity, wettability, and the possibility of surface modification using functional groups, these nanostructures are regarded as excellent candidates for extraction applications. Therefore, the research in the field of NFs and their nanocomposites has been increasing in recent years. In the present review, we summarize the most recent studies on NFs-based sorbents focusing on strategies for preparation, characterization, and their unique capabilities as porous sorbents in various sorbent-based extraction methods. Moreover, we further described the performance and selectivity of sorbents to achieve improved extraction efficiency. Finally, some perspectives on the challenges and outlook are provided to aid future investigations related to this topic.

Polyvinyl Chloride Microplastics Leach Phthalates into the Aquatic Environment over Decades

Phthalic acid esters (phthalates) have been detected everywhere in the environment, but data on leaching kinetics and the governing mass transfer process into aqueous systems remain largely unknown. In this study, we experimentally determined time-dependent leaching curves for three phthalates di(2-ethylhexyl) phthalate, di(2-ethylhexyl) terephthalate, and diisononyl phthalate from polyvinyl chloride (PVC) microplastics and thereby enabled a better understanding of their leaching kinetics. This is essential for exposure assessment and to predict microplastic-bound environmental concentrations of phthalates. Leaching curves were analyzed using models for intraparticle diffusion (IPD) and aqueous boundary layer diffusion (ABLD). We show that ABLD is the governing diffusion process for the continuous leaching of phthalates because phthalates are very hydrophobic (partitioning coefficients between PVC and water log K_PVC/W were higher than 8.6), slowing down the diffusion through the ABL. Also, the diffusion coefficient in the polymer D_PVC is relatively high (∼8 × 10^-14 m² s^-1) and thus enhances IPD. Desorption half-lives of the studied PVC microplastics are greater than 500 years but can be strongly influenced by environmental factors. By combining leaching experiments and modeling, our results reveal that PVC microplastics are a long-term source of phthalates in the environment.

Migration of hazardous contaminants from WEEE contaminated polymeric toy material by mouthing

This study evaluated the migration of brominated flame retardants (BFRs), phosphate flame retardants (PFRs), bisphenols (BPA, BPF), and phthalate ester-based plasticizers from recycled polymeric toy material, containing waste electrical and electronic equipment (WEEE), in artificial saliva simulating 1 h of mouthing. In total 12 parts of 9 different toys were tested in triplicate after confirming WEEE specific contamination. Up to 11 contaminants were detected in saliva from one toy sample. The highest migration rate up to 128 ng/(cm² x h) was found for BPA followed by bis(2-ethylhexyl) phthalate (DEHP) and diisobutyl phthalate (DIBP) with migration rates up to 25.5 and 8.27 ng/(cm² x h), respectively. In addition to DecaBDE, which was detected in 3 saliva samples at migration rates between 0.09 and 0.31 ng/(cm² x h), the decaBDE replacements 2,4,6-tris(2,4,6-tribromophenoxy)-1,3,5-triazine (TTBP-TAZ), decabromodiphenyl ethane (DBDPE), resorcinol bis(diphenyl phosphate) (RDP), and hexabromocyclododecane (HBCDD) were detected as well with comparable migration rates. 2,4,6-tribromphenol (246-TBP) reached migration rates up to 1.15 ng/(cm² x h) in correspondence to the presence of TTBP-TAZ. Tetrabromobisphenol A (TBBPA), BPA, 246-TBP, DEHP, DIBP and triphenyl phosphate (TPHP) were predominantly observed in saliva with a detection frequency between 50 and 75%. Daily intake (DI) values were calculated for relevant analytes and compared to tolerable daily intake (TDI) values. The highest DI values of 72.4, 14.3, 5.74, 2.28 and 2.09 ng/(kg BW x day), were obtained for BPA, DEHP, DIBP, TBBPA, and TPHP, respectively. None of them exceed the TDI value or respective reference dose (RfD).

STRATEGIES AND CHALLENGES IN METHOD DEVELOPMENT AND VALIDATION FOR THE ABSOLUTE QUANTIFICATION OF ENDOGENOUS BIOMARKER METABOLITES USING LIQUID CHROMATOGRAPHY-TANDEM MASS SPECTROMETRY

Metabolomics is a dynamically evolving field, with a major application in identifying biomarkers for drug development and personalized medicine. Numerous metabolomic studies have identified endogenous metabolites that, in principle, are eligible for translation to clinical practice. However, few metabolomic-derived biomarker candidates have been qualified by regulatory bodies for clinical applications. Such interruption in the biomarker qualification process can be largely attributed to various reasons including inappropriate study design and inadequate data to support the clinical utility of the biomarkers. In addition, the lack of robust assays for the routine quantification of candidate biomarkers has been suggested as a potential bottleneck in the biomarker qualification process. In fact, the nature of the endogenous metabolites precludes the application of the current validation guidelines for bioanalytical methods. As a result, there have been individual efforts in modifying existing guidelines and/or developing alternative approaches to facilitate method validation. In this review, three main challenges for method development and validation for endogenous metabolites are discussed, namely matrix effects evaluation, alternative analyte-free matrices, and the choice of internal standards (ISs). Some studies have modified the equations described by the European Medicines Agency for the evaluation of matrix effects. However, alternative strategies were also described; for instance, calibration curves can be generated in solvents and in biological samples and the slopes can be compared through ratios, relative standard deviation, or a modified Stufour suggested approaches while quantifying mainly endogenous metabolitesdent t-test. ISs, on the contrary, are diverse; in which seven different possible types, used in metabolomics-based studies, were identified in the literature. Each type has its advantages and limitations; however, isotope-labeled ISs and ISs created through isotope derivatization show superior performance. Finally, alternative matrices have been described and tested during method development and validation for the quantification of endogenous entities. These alternatives are discussed in detail, highlighting their advantages and shortcomings. The goal of this review is to compare, apprise, and debate current knowledge and practices in order to aid researchers and clinical scientists in developing robust assays needed during the qualification process of candidate metabolite biomarkers. © 2019 John Wiley & Sons Ltd. Mass Spec Rev.

Novel strategy for disposable pipette extraction (DPX): Low-cost Parallel-DPX for determination of phthalate migration from common plastic materials to saliva simulant with GC-MS

In widespread use in commercial products as plasticizers, phthalic acid esters (phthalates) have worried researchers and society in general, given the negative impacts on living organisms, especially human health. Since they are not chemically linked to the polymeric matrix, their migration is evident for samples that come into contact with plastics that contain them, such as water, food and saliva. In this work, a new strategy is described, named parallel-disposable pipette extraction (Pa-DPX), in a fast, efficient and robust analytical method using five simultaneous extractions for the determination of migration of 6 phthalates from common plastic materials (children's toys, school supplies, dog toys and oral contact items) to saliva simulant, using gas chromatography-mass spectrometry (GC-MS). The optimized conditions were 5 extraction cycles with 1600 μL of saliva simulant and desorption with 200 μL of ethyl acetate using 5 cycles with the same aliquot. The calibration curves resulted in determination coefficients higher than 0.9915, limits of detection at 1.5 μg L^-1, and the quantification limits were 5.0 μg L^-1. Excellent results were obtained for repeatability (relative standard deviation ranging from 8.7% to 20.1% for 5 μg L^-1) and intermediate precision, varying the day of analyses (7.9%-16.2%). The analyte recovery ranged from 75% to 114% for two different samples, in four different levels of concentration. The Pa-DPX-GC-MS method was successfully applied to determine the migration of PAE from 21 samples. At least one PAE was detected in 81% of samples, and di-n-octyl phthalate was found in higher concentration, achieving the migration of almost 30 μg per g of sample.

Methods for the Determination of Endocrine-Disrupting Phthalate Esters

Phthalates are endocrine disruptors frequently occurring in the general and industrial environment and in many industrial products. Moreover, they are also suspected of being carcinogenic, teratogenic, and mutagenic, and they show diverse toxicity profiles depending on their structures. The European Union and the United States Environmental Protection Agency (US EPA) have included many phthalates in the list of priority substances with potential endocrine-disrupting action. They are: dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), butylbenzyl phthalate (BBP), diethylhexyl phthalate (DEHP), di-iso-nonyl phthalate (DINP), di-iso-decyl phthalate (DIDP), di-n-decyl phthalate (DnDP), and dioctyl phthalate (DOP). There is an ever-increasing demand for new analytical methods suitable for monitoring different phthalates in various environmental, biological, and other matrices. Separation and spectrometric methods are most frequently used. However, modern electroanalytical methods can also play a useful role in this field because of their high sensitivity, reasonable selectivity, easy automation, and miniaturization, and especially low investment and running costs, which makes them suitable for large-scale monitoring. Therefore, this review outlines possibilities and limitations of various analytical methods for determination of endocrine-disruptor phthalate esters in various matrices, including somewhat neglected electroanalytical methods.

Diethyl phthalate removal from aqueous phase using poly(EGDMA-MATrp) beads: kinetic, isothermal and thermodynamic studies

In this study, poly(ethylene glycol dimethacrylate-N-methacryloyl-L-tryptophan methyl ester) [poly(EGDMA-MATrp)] beads (average diameter=106-300 µm), which were synthesized by co-polymerizing of N-methacryloyl-L-tryptophan methyl ester (MATrp) with ethylene glycol dimethacrylate (EGDMA), were used for diethyl phthalate (DEP) adsorption. The various factors affecting the adsorption of DEP from aqueous solutions such as pH, initial concentration, contact time and temperature were analysed. Adsorption behaviour of DEP on the poly(EGDMA-MATrp) beads was investigated by varying pH values of solution, contact time, initial concentration and temperature. An optimum adsorption capacity of 590.7 mg/g for DEP was obtained at 25 °C. The present adsorption process obeyed a pseudo-second-order kinetic model. All the isotherm data can be fitted with the Langmuir, Freundlich and Dubinin-Radushkevich isotherm models. Thermodynamic parameters ΔH=7.745 kJ/mol, ΔS=81.92 J/K/mol and ΔG=-16.69 kJ/mol to -18.31 kJ/mol with the rise in temperature from 25 °C to 45 °C indicated that the adsorption process was endothermic and spontaneous.

Graphene-dispersive solid-phase extraction of phthalate acid esters from environmental water

Graphene is a novel carbon nanomaterial with an ultra-high specific surface area. In this paper, we explored graphene as adsorbent for efficient enrichment of 15 phthalate acid esters (PAEs) under different water matrixes (ultrapure water, river and sea). A simple and inexpensive method of dispersive solid-phase extraction (DSPE) combined with gas chromatography-mass spectrometry (GC-MS) was used and acceptable results were provided for most PAEs with overall average recoveries between 71 and 117%. The extraction conditions such as the amount of graphene, the desorption solvent, adsorption time, desorption time and the solution pH were optimized. Finally, the method was applied for the determination of PAEs in environmental water samples including 9 rivers and 2 seas from 7 areas in China.

Removal of diethyl phthalate from aqueous phase using magnetic poly(EGDMA-VP) beads

The barium hexaferrite (BaFe(12)O(19)) containing magnetic poly(ethylene glycol dimethacrylate-vinyl pyridine), (mag-poly(EGDMA-VP)) beads (average diameter=53-212 μm) were synthesized and characterized. Their use as an adsorbent in the removal of diethyl phthalate (DEP) from an aqueous solution was investigated. The mag-poly(EGDMA-VP) beads were prepared by copolymerizing of 4-vinyl pyridine (VP) with ethylene glycol dimethacrylate (EGDMA). The mag-poly(EGDMA-VP) beads were characterized by N(2) adsorption/desorption isotherms (BET), vibrating sample magnetometer (VSM), X-ray powder diffraction (XRD), elemental analysis, scanning electron microscope (SEM) and swelling studies. At a fixed solid/solution ratio, the various factors affecting the adsorption of DEP from aqueous solutions such as pH, initial concentration, contact time and temperature were analyzed. The maximum DEP adsorption capacity of the mag-poly(EGDMA-VP) beads was determined as 98.9 mg/g at pH 3.0, 25°C. All the isotherm data can be fitted with both the Langmuir and the Dubinin-Radushkevich isotherm models. The pseudo first-order, pseudo-second-order, Ritch-second-order and intraparticle diffusion models were used to describe the adsorption kinetics. The thermodynamic parameters obtained indicated the exothermic nature of the adsorption. The DEP adsorption capacity did not change after 10 batch successive reactions, demonstrating the usefulness of the magnetic beads in applications.