Recent advances in mass spectrometry analysis of phenolic endocrine disruptors and related compounds

An ultrasensitive electrochemical biosensor for bisphenol A based on aptamer-modified MrGO@AuNPs and ssDNA-functionalized AuNP@MBs synergistic amplification

Bisphenol A (BPA) is a harmful endocrine disruptor, sensitive and rapid quantification of BPA is highly desirable. In this work, a novel synergistic signal-amplifying electrochemical biosensor was developed for BPA detection by using a recognition probe (RP) constructed by BPA aptamer modified gold nanoparticles-loaded magnetic reduced graphene oxide (Aptamer-MrGO@AuNPs), and a signal probe (SP) constructed by BPA aptamer-complementary single-stranded DNA (ssDNA) functionalized methylene blue (MB)-loaded gold nanoparticle (ssDNA-AuNP@MBs). The RP and SP can self-assemble to form a stable RP-SP complex through complementary base pairing. The current intensity of the biosensor correlates with the number of RP-SP complexes. In the presence of BPA, the BPA aptamer can capture BPA with high selectivity and affinity, form an RP-BPA complex and dissociate the RP-SP complex to release SP, resulting in a decrease in the current signal intensity of the biosensor. A single AuNP could be loaded with multiple BPA aptamers and MBs, which improves the recognition efficiency and enhances the signal intensity. Due to the magnetic properties of MrGO@AuNPs, the magnetic separation and adsorption of RP or RP-SP complex is very convenient, enabling all reaction processes to be carried out in solution, which not only improves the mass transfer efficiency, but also simplifies the operation. Under optimal conditions, the developed biosensor had a detection limit as low as 0.141 pg/mL and had been successfully applied to the detection of real environmental water samples. Therefore, the synergistic signal amplification strategy of RP and SP has potential value in the detection of trace pollutants in the water environment.

Multiresidue method for the determination of high production volume plastic additives in river waters

The aim of this study was to develop a high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS)-based method for the multiresidue analysis of 21 plastic additives in river water. Analysed compounds included phthalates, benzophenone, bisphenol A and long- and short-chain alkylphenols (APs), which are of relevance because most of them are high production volume chemicals largely used in the plastic industry. These compounds can reach river waters due to direct discharge from wastewater treatment plants and leaching from plastic materials and microplastics present in rivers. In a first step, ionisation and acquisition parameters were optimised to obtain high sensitivity and structural information. Then, different solid-phase extraction cartridges and elution conditions were tested using Milli-Q and river water. With the optimised conditions, quality control parameters (recoveries, limits of detection, intra- and inter-day variability and blank contribution) proved that the method was accurate and selective for the trace monitoring of these compounds in river water. For nonylphenol, octylphenol and bis(2-ethylhexyl)phthalate, included in the Water Framework Directive, limits of detection were below environmental quality standard concentrations considering blank contributions. All other compounds were efficiently detected at trace levels, and focus was given to o- and p-substituted and di- and tri-substituted APs, which are first reported in the present study. A pilot survey was finally carried out to determine the occurrence of plastic additives in river waters surrounding the city of Barcelona.

Metal organic framework/chitosan foams functionalized with polyethylene oxide as a sorbent for enrichment and analysis of bisphenols in beverages and water

MIL-53(Al)/CS/PEO foam as a sorbent for the vortex assisted solid phase extraction of a trace amount of five bisphenols in beverages and water.

Electrochemical Enzyme Biosensor Bearing Biochar Nanoparticle as Signal Enhancer for Bisphenol A Detection in Water

An electrochemical tyrosinase enzyme (Tyr) biosensor using a highly conductive sugarcane derived biochar nanoparticle (BCNP) as a transducer and signal enhancer (BCNPs/Tyr/Nafion/GCE) was developed for the sensitive detection of bisphenol A (BPA). The BCNPs/Tyr/Nafion/GCE biosensor exhibited improved amperometric current responses such as higher sensing signal, decreased impedance and lowered reduction potential compared with the Tyr/Nafion/GCE due to high conductivity property of the biochar nanoparticle. Under the optimized conditions, it could detect BPA in good sensitivity with linear range from 0.02 to 10 μM, and a lowest detection limit of 3.18 nM. Moreover, it showed a low K_m value, high reproducibility and good selectivity over other reagents, and the BCNPs/Tyr complex solution also showed good stability with 86.9% of sensing signal maintained after one month storage. The biosensor was also successfully utilized for real water detection with high accuracy as validated by high performance liquid chromatography. Therefore, the biochar nanoparticle based enzyme biosensor proved to be a potential and reliable method for high performance detection of pollutants in the environment.

Spherical covalent organic frameworks as advanced adsorbents for preconcentration and separation of phenolic endocrine disruptors, followed by high performance liquid chromatography

As a promising generation of porous micro-materials, covalent organic frameworks (COFs) have great potentials for applications in separation and adsorption. In the present study, an advanced food-safety inspection method involving COFs as the adsorbents of solid phase extraction (SPE) is proposed for sensitive and accurate determination of target hazardous substances. Typical spherical TpBD COFs with large surface area and superior chemical stability were utilized as adsorbents for the preconcentration of phenolic endocrine disruptors (PEDs), followed by high performance liquid chromatography (HPLC) analysis. The well-prepared TpBD COFs were encapsulated in SPE cartridges and applied in food research, namely, for the separation and enrichment of four target endocrine disruptors in food samples. The possible factors influencing the SPE performance including the composition of the sample solvent, sample solution pH, sample flow rate, composition of the eluent, and the volume of the eluent were investigated and optimized. Due to the porous architecture and superior surface area of spherical TpBD, the enrichment of analytes via a COF-filled SPE column gave extremely low detection limits of 0.056–0.123 μg L⁻¹ along with a wide linear range of 0.5–100 μg L⁻¹ for all the analytes. Nine parallel determinations of the mixed standard with a concentration of 10 μg L⁻¹ produced the relative standard deviations of 2.23–3.08%, indicating the excellent repeatability of the COF-SPE assay. This study can open up a new route for the employment of COFs as efficient SPE adsorbents for the enrichment and quantification of trace/ultra-trace hazardous materials in complex food samples.

Spherical COFs as efficient adsorbents for preconcentration and separation of phenolic endocrine disruptors, followed by high performance liquid chromatography.

A high-throughput screening method of bisphenols, bisphenols digycidyl ethers and their derivatives in dairy products by ultra-high performance liquid chromatography-tandem mass spectrometry

A simple and universal analytical method based on ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) for high throughput screening of 21 bisphenols, bisphenols digycidyl ethers and their derivatives in dairy products was developed. Response Surface Methodology (RSM) was used to optimize sample preparation conditions based on a quick, easy, cheap, effective, rugged and safe (QuEChERS) method. The analytes were extracted by using 15 mL acetonitrile with 1% acetic acid, and the extracts were further purified by using 190 mg of C18 and 390 mg of PSA. The extracts were analyzed by UHPLC-MS/MS with electrospray ionization (ESI) source. Linearity was assessed by using matrix-matched standard calibration and good correlation coefficients (r² > 0.99) were obtained. The limits of quantitation (LOQs) for the analytes ranged from 0.02 to 5 μg kg^-1. The extraction recoveries were in a range of 88.2%-108.2%. Good method reproducibility in terms of intra- and inter-day precision was observed, yielding relative standard deviations (RSDs) less than 8.9% and 9.9%, respectively. The validation method results revealed that the proposed method was sensitive and reliable. Finally, this method was successfully applied to dairy product analysis.

Aptamer-based electrochemical biosensor by using Au-Pt nanoparticles, carbon nanotubes and acriflavine platform

Herein, an ultrasensitive electrochemical aptasensor for quantitative detection of bisphenol A (BPA) was fabricated based on a novel signal amplification strategy. This aptasensor was developed by electrodeposition of gold-platinum nanoparticles (Au-PtNPs) on glassy carbon (GC) electrode modified with acid-oxidized carbon nanotubes (CNTs-COOH). In this protocol, acriflavine (ACF) was covalently immobilized at the surface of glassy carbon electrode modified with Au-PtNPs/CNTs-COOH nanocomposite. Attachment of BPA-aptamer at the surface of modified electrode was performed through the formation of phosphoramidate bonds between the amino group of ACF and phosphate group of the aptamer at 5'end. By interaction of BPA with the aptamer, the conformational of aptamer was changed which lead to retarding the interfacial electron transfer of ACF as a probe. Sensitive quantitative detection of BPA was carried out by monitoring the decrease of differential pulse voltammetric (DPV) responses of ACF peak current with increasing the BPA concentration. The resultant aptasensor exhibited good specificity, stability and reproducibility, indicating that the present strategy was promising for broad potential application.

Elucidation of the fragmentation pathways of a complex 3,7-O-glycosyl flavonol by CID, HCD, and PQD on an LTQ-Orbitrap Velos Pro hybrid mass spectrometer

The present study was designed to systematically investigate the ESI-MS(n) behavior of a complex 3, 7-O-glycosyl flavonol, kaempferol 3-O-α-L-[2,3-di-O-β-D-(6-E-p-coumaroyl)glucopyranosyl]-rhamnopyranosyl-7-O-α-L-rhamnopyranoside (KO) isolated from Epimedium wushanense, and to address the elimination priority among different glycosylation sites and different sugars/substituents. The direct-infusion ESI-MS(n) experiment of KO was performed on a hybrid LTQ-Orbitrap Velos Pro mass spectrometer in both negative and positive ion modes by three different fragmentation mechanisms (CID, HCD, and PQD). The CID, HCD, and PQD analyses of KO exhibited remarkable discrimination in respect of the scan range, richness, and distribution of product ions through the entire spectra. KO experienced different fragmentation pathways between two ionization modes: the negative mode CID of KO eliminated the glycosyl portions (priority: 7-sugar > 3-substituent and terminal substituents > inner sugar) and produced aglycone product ions at m/z 284.03/285.04; however, abundant sodium-adduct B(3)2 together with subsequent (i,j)X(3)0 cleavages were found characteristic for the positive mode CID-MS(n). The fragmentation pathways by CID for KO were proposed by analyzing the high accuracy ESI-MS(n) data. Complementary structural information of KO regarding the aglycone and glycosyl portions was obtained by analyzing the ESI-MS(n) data in both ionization modes. In conclusion, the LTQ-Orbitrap method facilitates highly reliable qualitative analysis of bioactive flavonoids with three alternative fragmentation modes.

A study of the influence on diabetes of free and conjugated bisphenol A concentrations in urine: Development of a simple microextraction procedure using gas chromatography-mass spectrometry

The association between bisphenol A (BPA) exposure and adult health status is examined by measuring the urinary BPA concentration using a miniaturized technique based on dispersive liquid-liquid microextraction (DLLME) in combination with gas chromatography-mass spectrometry (GC-MS). Both the free bioactive and the glucuronide conjugated forms of BPA were measured, the glucuronide form usually being predominant. The main analogs of BPA, including bisphenol Z (BPZ), bisphenol F (BPF) and biphenol (BP) were also determined. Several parameters affecting enzymatic hydrolysis, derivatization by in-situ acetylation and the DLLME stages were carefully optimized by means of multivariate designs. DLLME parameters were 2mL urine, 1mL acetone and 100μL chloroform, and hydrolysis was performed using β-glucuronidase and sulfatase at pH 5. No matrix effect was observed and quantification was carried out by aqueous calibration with a surrogate standard. Detection limits were in the range 0.01-0.04ngmL(-1). The intraday and interday precisions were lower than 11% in terms of relative standard deviation. Satisfactory values for all compounds were obtained in recovery studies (92-117%) at two concentration levels. Other bisphenols (BPF, BPZ and BP) were not detected in the urine samples, while BPA was the only bisphenol detected in the free form (creatinine adjusted) at concentration levels ranging from the detection limit to 15.9ngg(-1), and total BPA was detected at concentrations ranging from 0.46 to 24.5ngg(-1) levels. A comparison of the BPA content for both groups of patients revealed that slightly higher mean values were obtained for both free BPA and total BPA for diabetic patients, than for non-diabetic patients. However, a statistical comparison of the contents of BPA revealed that there were no significant differences. The procedure was validated using a certified reference material.

Steroids and endocrine disruptors--History, recent state of art and open questions

This introductory chapter provides an overview of the levels and sites at which endocrine disruptors (EDs) affect steroid actions. In contrast to the special issue of Journal of Steroid Biochemistry and Molecular Biology published three years ago and devoted to EDs as such, this paper focuses on steroids. We tried to point to more recent findings and opened questions. EDs interfere with steroid biosynthesis and metabolism either as inhibitors of relevant enzymes, or at the level of their expression. Particular attention was paid to enzymes metabolizing steroid hormones to biologically active products in target cells, such as aromatase, 5α-reductase and 3β-, 11β- and 17β-hydroxysteroid dehydrogenases. An important target for EDs is also steroid acute regulatory protein (StAR), responsible for steroid precursor trafficking to mitochondria. EDs influence receptor-mediated steroid actions at both genomic and non-genomic levels. The remarkable differences in response to various steroid-receptor ligands led to a more detailed investigation of events following steroid/disruptor binding to the receptors and to the mapping of the signaling cascades and nuclear factors involved. A virtual screening of a large array of EDs with steroid receptors, known as in silico methods (≡computer simulation), is another promising approach for studying quantitative structure activity relationships and docking. New data may be expected on the effect of EDs on steroid hormone binding to selective plasma transport proteins, namely transcortin and sex hormone-binding globulin. Little information is available so far on the effects of EDs on the major hypothalamo-pituitary-adrenal/gonadal axes, of which the kisspeptin/GPR54 system is of particular importance. Kisspeptins act as stimulators for hormone-induced gonadotropin secretion and their expression is regulated by sex steroids via a feed-back mechanism. Kisspeptin is now believed to be one of the key factors triggering puberty in mammals, and various EDs affect its expression and function. Finally, advances in analytics of EDs, especially those persisting in the environment, in various body fluids (plasma, urine, seminal fluid, and follicular fluid) are mentioned. Surprisingly, relatively scarce information is available on the simultaneous determination of EDs and steroids in the same biological material. This article is part of a Special Issue entitled 'Endocrine disruptors & steroids'.

Development and validation of a liquid chromatography isotope dilution mass spectrometry method for the reliable quantification of alkylphenols in environmental water samples by isotope pattern deconvolution

We present here a new measurement method for the rapid extraction and accurate quantification of technical nonylphenol (NP) and 4-t-octylphenol (OP) in complex matrix water samples by UHPLC-ESI-MS/MS. The extraction of both compounds is achieved in 30min by means of hollow fiber liquid phase microextraction (HF-LPME) using 1-octanol as acceptor phase, which provides an enrichment (preconcentration) factor of 800. On the other hand we have developed a quantification method based on isotope dilution mass spectrometry (IDMS) and singly (13)C1-labeled compounds. To this end the minimal labeled (13)C1-4-(3,6-dimethyl-3-heptyl)-phenol and (13)C1-t-octylphenol isomers were synthesized, which coelute with the natural compounds and allows the compensation of the matrix effect. The quantification was carried out by using isotope pattern deconvolution (IPD), which permits to obtain the concentration of both compounds without the need to build any calibration graph, reducing the total analysis time. The combination of both extraction and determination techniques have allowed to validate for the first time a HF-LPME methodology at the required levels by legislation achieving limits of quantification of 0.1ngmL(-1) and recoveries within 97-109%. Due to the low cost of HF-LPME and total time consumption, this methodology is ready for implementation in routine analytical laboratories.

Ultra-high performance liquid chromatography/tandem mass spectrometry determination of feminizing chemicals in river water, sediment and tissue pretreated using disk-type solid-phase extraction and matrix solid-phase dispersion

This study developed and validated a method of measuring the feminizing chemicals 4-tert-octylphenol, 4-nonylphenol, nonylphenol monoethoxycarboxylate (NP(1)EC), nonylphenol monoethoxylate (NP(1)EO), nonylphenol diethoxylate (NP(2)EO), estrone, 17β-estradiol, estriol, 17α-ethinyl estradiol and bisphenol A in river water, sediment, and tissue using ultra-high performance liquid chromatography/tandem mass spectrometry (UHPLC/MS/MS) and isotope-dilution techniques. Water samples were pretreated using disk-type automated solid-phase extraction (SPE). Solid samples of sediment, fish, and clams were treated with matrix solid-phase dispersion (MSPD) using C(8) adsorbent. Eluents were directly passed following alumina cartridges for cleanup. The signal intensity of analytes on electrospray ionization (ESI) was compared with that of atmospheric pressure photoionization (APPI). The analytes were separated on a UHPLC C(18) column with aqueous 10-mM ammonium acetate for NPEOs and aqueous 10-mM N-methylmorpholine for the other compounds. On-line cleanup was evaluated using two-dimensional liquid chromatography (2-D LC). ESI could provide satisfactory response for all of the analytes. Though APPI did not offer suitable response for NP(1)EO, NP(2)EO and NP(1)EC, it provided better signal intensities for the steroid estrogens (1.0-2.4 times) and the phenols (3.2-4.4 times) than ESI. UHPLC shortened chromatographic time to less than 10 min. Disk-type automated SPE and MSPD dramatically increased the throughput of sample preparation. The extraction efficiency on surface water samples ranged from 10% to 91%. The extraction efficiency of MSPD on sediment, fish, and clams was 51-101%, 36-109%, and 30-111%, respectively. Acidic alumina cleanup was essential for the analysis of the tissue sample, and reduced matrix effects better than 2-D LC on-line cleanup. The limits of detection (LODs) in water ranged from 0.81 ng/L to 89.9 ng/L. The LODs in sediment and tissue ranged from tens of pg/g wet weight to only a few ng/g wet weight. This method proved to be accurate and reproducible, as both quantitative biases and relative deviations remained smaller than 20% at three spiked levels.

Photo-SRM: laser-induced dissociation improves detection selectivity of Selected Reaction Monitoring mode

Selected Reaction Monitoring (SRM) carried out on triple-quadrupole mass spectrometers coupled to liquid chromatography has been a reference method to develop quantitative analysis of small molecules in biological or environmental matrices for years and is currently emerging as a promising tool in clinical proteomic. However, sensitive assays in complex matrices are often hampered by the presence of co-eluted compounds that share redundant transitions with the target species. On-the-fly better selection of the precursor ion by high-field asymmetric waveform ion mobility spectrometry (FAIMS) or increased quadrupole resolution is one way to escape from interferences. In the present work we document the potential interest of substituting classical gas-collision activation mode by laser-induced dissociation in the visible wavelength range to improve the specificity of the fragmentation step. Optimization of the laser beam pathway across the different quadrupoles to ensure high photo-dissociation yield in Q2 without detectable fragmentation in Q1 was assessed with sucrose tagged with a push-pull chromophore. Next, the proof of concept that photo-SRM ensures more specific detection than does conventional collision-induced dissociation (CID)-based SRM was carried out with oxytocin peptide. Oxytocin was derivatized by the thiol-reactive QSY® 7 C(5)-maleimide quencher on cysteine residues to shift its absorption property into the visible range. Photo-SRM chromatograms of tagged oxytocin spiked in whole human plasma digest showed better detection specificity and sensitivity than CID, that resulted in extended calibration curve linearity. We anticipate that photo-SRM might significantly improve the limit of quantification of classical SRM-based assays targeting cysteine-containing peptides.

Development of a fast liquid chromatography-tandem mass spectrometry method for the determination of endocrine-disrupting compounds in waters

A fast liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS-MS) method was developed to study five endocrine-disrupting compounds (4-n-nonylphenol, bisphenol A, estrone, 17β-estradiol and 17α-ethinylestradiol) in water. Different columns were tested; the chromatographic separation of the analytes was optimized on a Pinnacle DB biphenylic column with a water-acetonitrile gradient elution, which allowed the separation of the selected endocrine-disrupting compounds (EDCs) in less than 6 min. Quantitative analysis was performed in selected reaction monitoring (SRM) mode; two transitions were chosen for each compound, using the most abundant for quantitation. Calibration curves using bisphenol A-d (16) as internal standard were drawn, showing good correlation coefficients (0.9993-0.9998). All figures of merit of the method were satisfactory; limits of detection were in the low pg range for all analytes. The method was then applied to the determination of the analytes in real water samples: to this aim, polar organic chemical integrative samplers (POCIS) were deployed in the influent and in the effluent of a drinking water treatment plant in Liguria (Italy). The EDC level was rather low in the influent and negligible in the outlet, reflecting the expected function of the treatment plant.