Electrode In Aqueous Solution Research Articles

Chemical Potency of Cobalt Doped Modified Graphite Electrode Prepared by Electrochemical Method and its Application in Degrading Solution of Rhodamine-B dye

Primary goal of the present study is to progress a methodological framework for Rhodamine-B dye degradation using cobalt doped graphite modified electrode in aqueous solution by electrochemical method. This is environmentally friendly method. Rate study for Rh-B dye degradation under various parameters like concentration, applied current and temperature were studied and compared between Graphite electrode and Cobalt graphite electrode. Ultra Violet-Visible spectral data and Chemical oxygen demand values are evident for the complete degradation of Rhodamine-B in aqueous solution during anodic oxidation using the modified Co/graphite electrode. The dye degradation efficiency for Cobalt graphite modified electrode (Co/GME) increases by 77% compared to graphite electrode. The COD values decreases to ~98% than the initial COD after degradation with Co/GME. Increase in applied current, temperature increases the rate of degradation and follows first order kinetics up to 60% of the reaction. Hydroxyl (.OH) free radicals are produced by advanced oxidation processes (AOPs), which are attack the dye molecules and cause them to degrade. SEM/EDAX is used to observe the formation of cobalt layer in the rod of graphite. Under various laboratory settings ICE values were computed, it shows that Cobalt doped graphite modified electrode acts as a good anode to degrade Rh-B dye and it converted into CO2, H2O, and other basic inorganic salts. This procedure is straightforward, inexpensive, and can be used to treat wastewater that contains organics.

Measurement of Electric Double Layer Charging Dynamics on Platinum Electrodes in Aqueous Solutions of Alkali Sulfates and Nitrates

Measurement of Electric Double Layer Charging Dynamics on Platinum Electrodes in Aqueous Solutions of Alkali Sulfates and Nitrates

Electrocatalytic reduction of nitrate to ammonia by Pd/In modified Nickel foam electrode in aqueous solution

Nitrate pollution in surface water and ground water has drawn wide attention, which has brought challenges to human health and natural ecology. Electroreduction of nitrate to NH3 in waste water was a way to turn waste into wealth, which has attracted interest of many researchers. Using Nickel foam as substrate, we prepared Pd/In bimetallic electrode (NF–Pd/In) according to a two-step electrodeposition method. There are many irregularly shaped particles in the size range of 10 nm–100 nm accumulated on the surface of prepared NF–Pd/In electrode, which could supply high specific area and more active sites for nitrate electroreduction. FESEM-EDS, XRD and XPS analysis confirmed the uniform distribution of Pd and In on the surface of prepared NF–Pd/In electrode, with a mass ratio of 4.5/1. Above 96% of 100 mg/L NO3−-N was removed and 95% of NH3 selectivity was reached after 5 h of reaction under −1.6 V vs. Ag/AgCl sat. KCl when using 0.05 mol/L of Na2SO4 as electrolyte. High concentration of NaCl (0.05 mol/L) in the test solution dramatically decreased the NH3 selectivity because the produced NH3 could be further oxidized to N2 by the formed HClO from Cl−. EIS tests indicated that the prepared NF–Pd/In electrode showed much lower electrode resistance than NF due to the adsorptive property and electrocatalytic ability for nitrate removal. Density functional theory (DFT) calculations indicated that the presence of In could promote the conversion of NO3− to *NO3 during the process of nitrate electroreduction to NH3. Circulating tests demonstrated the stability of prepared NF–Pd/In electrode.

Еlectrochemical behavior of cadmium by alternating current polarization in hydrocloric acid solution

This paper presents the results of a study of the electrochemical behavior of a cadmium electrode in aqueous solutions of hydrochloric acid under polarization by stationary and non-stationary currents and shows the possibility of synthesis of its chloride. The purpose is to develop the electrochemical behavior of cadmium under alternating current polarization in a solution of perchloric acid. Methods. During the study, it was found that when two cadmium electrodes are polarized with an alternating current of 50 Hz, their dissolution does not occur, however, when one electrode is replaced with a titanium one, cadmium is intensively dissolved. Results and discussion. The influence of the main parameters, such as the duration of electrolysis, current density, concentration and nature of the electrolyte on the electrochemical process has been studied. A schematic diagram of an installation for dissolving cadmium by polarization with a non-stationary current is proposed. It is shown that on the titanium electrode in the range of 20-80 kA/m2, the current yield of the dissolution of the cadmium electrode gradually increases, and with a current density equal to 80 kA/m2, the current yield reaches 135%. Conclusion. It is shown that with alternating current polarization, the rate of chemical dissolution of cadmium, increases with the release of hydrogen. During the experiment, with the polarization of the cadmium electrode by alternating current, the possibility of obtaining cadmium chloride was shown. Based on chemical and X-ray phase analyses, it was proved that cadmium forms compounds CdCl2∙H2O.

Study of the Graphene Oxide Nanosheets Synthesized from Pencil Electrode Using Electrochemical Method and Solar Energy as a Source of Power

Graphene Oxide nanosheets were synthesized using electrochemical exfoliation of pencil electrodes in aqueous solution containing 2% of magnesium sulfate salt. A solar panel of 20V was used as a power supply to turn the synthesis into a green method. Several measurements were carried out to investigate the product, namely: Raman scattering, X-ray diffraction, photoluminescence, UV-VIS-NIR spectroscopy, and FTIR spectroscopy. Raman scattering showed the existence of both D-band and G-band, which are an indication of graphene oxide existence. The D-to-G band ratio was 1.5. The results of X-ray showed a diffraction peak at 2θ = 20.7° corresponding to the space distance between graphene oxide nanosheets and a diffraction peak at 2θ = 26.25° corresponding to the short range interplanar spacing. Photoluminescence showed two peaks of emission (at wavelengths 355nm & 701nm) regarding to the π-π* transition. UV-VIS-NIR spectroscopy exhibited a 4.2eV photon energy absorption peak corresponding to the aromatic C=C bonds and 5.4eV photon energy absorption peak corresponding to the carbonyl groups. FTIR showed peaks related to hydroxyl groups, hydrogen-bonded OH groups of COOH, and functional groups such as C-OH (1375 cm-1), and C-O (1039 cm-1). FTIR results approved that graphene oxide nanosheets are functionalized. TEM images show that the synthesized graphene oxide is single-, double-, and multi-layer stacks with an amount of impurities.

Voltammetric Detection of Explosive Nitroaromatic Compounds Using Boron-Doped Carbon Nanowall Electrodes

Nitroaromatic highly energetic explosive compounds were widely used during the I and II World Wars. Some of them, like 2,4,6-trinitrotoluene (TNT), are still used in military munitions or in industrial applications i.e., underwater blasting, mining, deep well or dye production. The worldwide use of nitroaromatic compounds led to widespread pollution of the environment causing a danger to living organisms due to their high toxicity and possible carcinogenicity. The most commonly used techniques for the detection of explosive nitroaromatics are high-performance liquid chromatography or high-resolution gas chromatography coupled with different detectors like mass spectrometers. Both methods require: expensive instrumentation, complex sample preparation which is crucial to analysis, and well-trained staff to perform the experiments. Therefore it is difficult to implement chromatography in the field. Electrochemical sensing is emerging as a fast, sensitive and relatively simple technique for detecting explosive materials. To date, various materials have been used as working electrodes for this purpose, however, carbon materials are particularly promising [1-2]. Among carbonaceous materials, boron-doped carbon nanowall (B:CNW) electrodes are particularly attractive for the sensitive and rapid detection of nitro-based compounds [3] due to the high content of sp2 phase, wide electrochemical working potential window (from -1.6 V to 1.2 V in 0.5 M KCl) and high values of heterogeneous electron transfer rate constant.In this work, we present electrochemical detection of chosen nitroaromatic explosive compounds like TNT on boron-doped carbon nanowall electrodes in aqueous solutions using voltammetric electrochemical techniques (differential pulse voltammetry, square-wave voltammetry, cyclic voltammetry). B:CNW electrodes were obtained using microwave plasma-assisted chemical vapour deposition in a one-step growth process. B:CNW electrode show enhanced electrocatalytic activity towards nitro moieties attached to aromatic rings, resulting in improved sensitivity toward detecting these groups. Hence, it is an attractive nanocarbon surface for nitroaromatic compound determination.

Electrochemical Behavior of a Gold Electrode in the Aqueous Potassium Salt of Bridging 1,2,4,5-Tetraoxane

The behavior of a smooth gold electrode in aqueous solutions of the potassium salt of bridging 1,2,4,5-tetraoxane containing a biperoxide cyclic fragment was studied by cyclic voltammetry. The cathode process was analyzed in detail. It was shown that the process involves four electrons. The products of electrolysis of the potassium salt were studied, and a reaction mechanism was proposed.

Indirect Determination of Amitriptyline Hydrochloride by Square Wave Voltammetry of SnCl2.2H2O

A simple, fast and sensitive electroanalytical method consist studying the square wave of SnCl2.2H2O at hanging mercury dropping electrode in aqueous solution for the indirect determination of (AMI) drug. SnCl2.2H2O has revealed a major reduction potential at (-0.450) Volt against the reference electrode (Ag/AgCl/Sat.KCl). The calibration curve in the Phosphate buffer as the supporting electrolyte at pH=2 was constracted. The range concentrations up to (0.99X10-5–9.91X10-5) M, the correlation coefficient (r= 0.9989) and then studied the decreased of peak current of the drug by the (HMDE) behavior in the presence of SnCl2.2H2O. Results were as follow: The calibration curves were (0.316 X10-6 -3.136 X10-6) M and thismethods was successfully applied to determination of AMI in apharmaceutical formulations.

OBTAINING OF A COMPOSITE COATING OF COPPER-MOLYBDENUM (VI) OXIDE WITH CATHODIC POLARIZATION

In this paper, considered the ways of obtaining a composite electrochemical coating by entering molybdenum (VI) oxide into the copper matrix in order to improve the physicochemical properties of the copper coating. The influence of electrochemical parameters (solution concentration, current density, concentration of molybdenum (VI) oxide) is investigated with cathodic polarization of a titanium electrode in aqueous solutions of copper sulfate. In the course of studies of the influence of the concentration of a dispersed particle that is part of a copper-molybdenum oxide (VI) composite, it was found that at high concentrations of dispersed particles in solution, the cathode surface is passivated and the optimal concentration of the dispersed component is determined. It was noted that with increasing current density, the amount of molybdenum (VI) oxide penetrating into the copper matrix increases slightly, these data were explained by the charge difference of the particles, as well as adsorption properties. As a result of the study, a compact composite coating on the cathode in a dispersed suspension of the composite in a solution of copper (II) sulfate was obtained. The results of the physico-chemical analysis of the resulting composite coating showed that 1.2% dispersed molybdenum (VI) oxide entered the copper matrix. As a result of tests of a composite coating made of copper-molybdenum oxide for chemical corrosion, it was found that this coating has high corrosion resistance from a copper coating obtained without molybdenum (VI) oxide. The surface roughness of the coating obtained on the cathode surface was observed in microphotographs. This was explained by the fact that molybdenum (VI) oxide penetrates into the copper matrix in the form of dispersed granules and forms a composite electrochemical shell with a copper coating.

Anchoring H-Bond Donating/Accepting Pyrrolic Derivatives on Preorganized Scaffolds: Conformationally Switchable Bipedal/Tripodal and Locked Molecular Cage Ionophores for Potentiometric Sensing of Phosphate and Fluoride.

The ionophore properties of a myriad of conformationally switchable bipedal/tripodal receptors and locked molecular cages were evaluated here for the first time to fabricate potentiometric sensors for the determination of environmentally important phosphate and fluoride. Owing to the competent ionophore properties such as high binding selectivity and affinity, the developed ion-selective electrodes displayed response preference for phosphate and fluoride with a selectivity pattern that differs distinctly from traditional Hofmeister series. Binding constants of the ionophore-anion complexes are determined to underscore how modifications in the preorganization and H-bond donating/accepting ability of a given series of ionophores can be exploited to improve the performance for potentiometric sensing. While conformationally switchable bipedal/tripodal ionophores prefer tetrahedral oxyanions, locked molecular cages shift their preference to spherical halides gradually. Nernstian potential responses with good reversibility to target anions can be observed when shifting the optimized membrane electrodes in aqueous solutions within the concentration range of 10-6.5-10-2.0 M. Moreover, potentiometric determination of phosphate and fluoride in mineral water, soil, and tap water samples was achieved in a low μM concentration range with high accuracy, confirming their promising utility in real world applications.

CO2 Electroreduction in Organic Aprotic Solvents: A Mini Review

An annual increase of CO2 concentrations in the atmosphere causes global environmental problems, addressed by systematic research to develop effective technologies for capturing and utilizing carbon dioxide. Electrochemical catalytic reduction is one of the effective directions of CO2 conversion into valuable chemicals and fuels. The electrochemical conversion of CO2 at catalytically active electrodes in aqueous solutions is the most studied. However, the problems of low selectivity for target products and hydrogen evolution are unresolved. Literature sources on CO2 reduction at catalytically active cathodes in nonaqueous mediums, particularly in organic aprotic solvents, are analyzed in this article. Two directions of cathodic reduction of CO2 are considered—nonaqueous organic aprotic solvents and organic aprotic solvents containing water. The current interpretation of the cathodic conversion mechanism of carbon (IV) oxide into CO and organic products and the main factors influencing the rate of CO2 reduction, Faradaic efficiency of conversion products, and the ratio of direct cathodic reduction of CO2 are given. The influence of the nature of organic aprotic solvent is analyzed, including the topography of the catalytically active cathode, values of cathode potential, and temperature. Emphasis is placed on the role of water impurities in reducing CO2 electroreduction overpotentials and the formation of new CO2 conversion products, including formate and H2.

CdSe ve CdSe/ZnO Filmlerin Elektrokimyasal Sentezi: Morfolojik, Yapısal ve Elektronik Özellikler

CdSe films were electrochemically prepared on ITO electrode in aqueous solution applying a constant potential. Structural, morphological and optical features of CdSe thin films were examined with FE-SEM, XRD and UV-visible spectrophotometry techniques. XRD results revealed CdSe films were deposited, in the form of cubic crystals from aqueous solution of Cd2+ and Se4+, in presence of Na2SO4 supporting electrolyte. Band gap values of CdSe films were found between 1.88 and 2.0 eV. Wide band gap ZnO was electrochemically deposited on narrow band gap CdSe to improve its optoelectronic properties. Band gap value of CdSe/ZnO nanonorods was determined as 2.7 eV. Mott-Schottky equation was utilized to calculate flat band potential (EFB), as well as charge carrier density (ND) of materials. ND values were found as 1.623×1020 and 9.186×1020 cm-3 for CdSe and CdSe/ZnO, respectively. ZnO offers higher stability and lower band gap is promising material to be utilized in solar cell applications.

Deep Investigation Into the Electrodeposition Model of Mg Battery Anode.

Analysis of nucleation/growth dynamics is important to understand the molecular mechanism on the electrode surface. The electrocrystallization mechanism of Mg anode in aqueous electrolyte was comprehensively investigated which can help us understand the surface discharge mechanism of Mg anode and provide a new theoretical idea for the development of high performance magnesium ion battery. The influence of applied potential signals on normal growth constant and active site numbers was studied using i-t transient curves. The dimensionless processed transient curves confirmed that the initial nucleation/growth process of Mg electrode in aqueous solution followed the diffusion-controlled three-dimensional instantaneous nucleation model.

Electrodeposition: An efficient method to fabricate self-supported electrodes for electrochemical energy conversion systems.

The development of electrocatalysts for energy conversion systems is essential for alleviating environmental problems and producing useful energy sources as alternatives to fossil fuels. Improving the catalytic performance and stability of electrocatalysts is a major challenge in the development of energy conversion systems. Moreover, understanding their electrode structure is important for enhancing the energy efficiency. Recently, binder-free self-supported electrodes have been investigated because the seamless contact between the electrocatalyst and substrate minimizes the contact resistance as well as facilitates fast charge transfer at the catalyst/substrate interface and high catalyst utilization. Electrodeposition is an effective and facile method for fabricating self-supported electrodes in aqueous solutions under mild conditions. Facile fabrication without a polymer binder and controlability of the compositional and morphological properties of the electrocatalyst make electrodeposition methods suitable for enhancing the performance of energy conversion systems. Herein, we summarize recent research on self-supported electrodes fabricated by electrodeposition for energy conversion reactions, particularly focusing on cathodic reactions of electrolyzer system such as hydrogen evolution, electrochemical CO2 reduction, and electrochemical N2 reduction reactions. The deposition conditions, morphological and compositional properties, and catalytic performance of the electrocatalyst are reviewed. Finally, the prospective directions of electrocatalyst development for energy conversion systems are discussed.

Charge Storage Behaviour of α‐MoO3 in Aqueous Electrolytes – Effect of Charge Density of Electrolyte Cations

AbstractIn this paper, we show that the electrochemical performance of α‐MoO3 electrode is significantly dependent on the charge density of three studied aqueous electrolyte cations, i. e. Na+, Mg2+ and Al3+. The charge storage capacity of the α‐MoO3 electrode increases with increasing cation charge density. On the other hand, the initial coulombic efficiency decreases, and the charge transport kinetics are slowed with increasing charge density. This study provides an insightful understanding of the relationship between the charge density of metal ions and their electrochemical behaviour towards α‐MoO3 electrode in aqueous solutions. It also highlights the importance of the appropriate selection of aqueous electrolytes for enhancing electrochemical performance.

Electrochemically activated carbon-halogen bond cleavage and C-C coupling monitored by in situ shell-isolated nanoparticle-enhanced Raman spectroscopy.

The electroreductive cleavage of carbon-halogen bonds has attracted increasing attention in both electrosynthesis and pollution remediation. Herein, by employing the in situ electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) technique, we have successfully investigated the electroreductive dehalogenation process of aryl halides with the thiol group on a smooth Au electrode in aqueous solution at different pH values. The obtained potential-dependent Raman spectra directly reveal a mixture of the reduction products 4,4'-biphenyldithiol (BPDT) and thiophenol (TP). The conversion ratios of the C-Cl and C-Br bonds at pH = 7 are 37% and 55%, respectively. Furthermore, quantitative analysis of the intensity variations of ν(C-Cl), ν(C-Br) and aromatic ν(CC) stretching modes suggests electroreductive dehalogenation via both direct electron transfer reduction and electrocatalytic hydrodehalogenation. Molecular evidence for the C-C cross coupling process through TP reaction with benzene free radical intermediates is found at negative potentials, which leads to the increasing selectivity of biphenyl products.

Potentiometer study of the process of complexation of silver (I) ions with thiourea

The process of complexation of silver(I) ions with thiourea (Tu) in the temperature range 287.16–318.16 K at an ionic strength of 0.11 M (I = 0.1 NaNO3 + 0.01 HNO3) was studied by the potentiometric method using a silver electrode in aqueous solution. The study was performed at a concentration of silver(I) ions CAg+ = 1 · 10–5 and CAg+ = 1 · 10–3 M. The values of the stability constants of AgTui + complexes (i = 1–2) were estimated at CAg+ = 1 · 10–5 M. The AgTu3+ complex constant was determined at CAg+ = 1 · 10–3 M and CTu ≥ 0.01 M. The stability constants of complexes were calculated using the Leden method. The values of the complex constants at 298.16 K are equal to: lgβ1 = 5.59 ± 0.10 (AgTu+), lgβ2 = 10.62 ± 0.03 (AgTu2+) and lgβ3 = 13.05±0.11 (AgTu3+). It is established that the temperature effect does not affect the number of formed particles in the solution; an increase in temperature leads to a decrease in the stability of complexes. The analysis of the values of the stability constants by degrees shows that the step constants AgTu3+ (AgTu2+ + Tu = AgTu3+ + lgβ3 = 2.4) are much smaller than the constants for mono- and bis-coordinated complexes. The complexes thermodynamic parameters (ΔH0, ΔG0, ΔS0) were calculated by the temperature coefficient method. In the system under study, all complexation reactions are exothermic. The largest increase in the value of enthalpy (ΔH0) is observed in the formation of a complex containing two molecules of thiourea. The change in entropy (ΔS0) at the stage of formation of bis- and tris-coordinated complexes is negative, which is most likely due to a decrease in the number of particles in the system under study. It is determined that enthalpy-entropy dependences show a monotonic character. The spontaneous course of complexation reactions is determined by the value of the free Gibbs energy (ΔG0). In degrees G0 decreases (ΔG0)1 < (ΔG0)2 < (ΔG0)3) and has a negative value, which indicates a decrease in the affinity of the complexing agent to the ligand.

NIOBIUM’S BEHAVIOR IN AQUEOUS HYDRO­FLUORIC ACID SOLUTION

Thanks to the unique combination of physicochemical properties, niobium and its compounds are widely used in various fields of science and technology. The main areas of niobium’s applications are the production of superconductors, nuclear energy, chemical engineering, metallurgy, manufacture of optically active materials, thin-film lithium batte­ries, fuel cells. The aim of this work is to study the processes that take place on the niobium electrode in aqueous solutions of hydrofluoric acid, as well as to establish the composition of niobium compounds that are formed. The paper presents the results of studies the behavior of the niobium electrode in aqueous solutions 0.25 N. hydrofluoric acid. The kinetic para­meters of the processes occurring at the phase boundary are determined. It was found that the anodic polarization of the niobium electrode is accompanied by the formation of a passive layer, the destruction of which is facilitated by increasing the polarization potential and fluorine anions, in the presence of which complex fluoroiobate anions [NbF7]2- and [NbOF5]2-are formed. Cathodic polarization of niobium is accompanied by the formation of hydrides on its surface, which causes an increase in the overvoltage of hydrogen evolution. The anodic polarization of the niobium electrode in a solution of hydrofluoric acid causes the formation on its surface of a passive layer, which is destroyed with increasing potential.
 In the Nbo–NbO2–0.25 –0.25 n HF system, [NbF7]2-anions are formed, as evidenced by bands in the region of 500 nm on the electron absorption spectra. The rate constants of [NbF7]2- and [NbOF5]2- formation are estimated at 3.78 • 10-3 s-1 and 5.18 • 10-3 s-1, respectively.
 The reduction of hydrogen at the niobium cathode from a solution of hydrofluoric acid is accompanied by the formation of hydrides, which causes an increase in the overvoltage of hydrogen evolution and high values of the angular coefficients of the Tafel dependence.

Teaching the Tenets and Applications of Hydrodynamic Voltammetry Using an Inexpensive, User-Friendly, Hands-on Setup with a Rotating Platinum Electrode in Aqueous Solution to Fortify Student Comprehension of Voltammetry

With an awareness of the considerable discomfort of graduate students in grasping the crux of key concepts of voltammetry and its variants, I present an inexpensive and user-friendly hands-on setup based on the fabrication of a rotating platinum electrode to facilitate teaching the tenets and applications of hydrodynamic voltammetry (HV). Readily available materials such as a bicycle hub, a pair of wooden pulleys, thread, a platinum microelectrode fused to a glass tube, and a small synchronous motor were used in the assembly of this hands-on setup, which provides a means for instructors to fortify the concepts of electro-analytical principles in HV such as electrochemical processes, redox reactions, the nature of voltammograms, diffusion limited current, and pertinent equations. This activity aims to engage students in strengthening comprehension of the tenets of HV and prompts design thinking in them to explore its applications. The activity is suitable for graduate STEM students with some chemistry background.

Electrochemical degradation of perfluorooctanoic acid in aqueous solution by boron-doped diamond electrodes under pulsed voltage conditions

• Degradation of persistent substance by pulsed electrochemical oxidation. • Pulsed degradation more efficient than direct current. • Pulse width affects the degradation rate. • Degradation of PFOA with Pt and graphite electrodes. The aim of this study was the electrochemical degradation with boron-doped diamond (BDD) electrodes using pulsed direct current (PDC). An electrochemical characterization of the BDD electrode in aqueous solution was performed to determine the optimal parameters for the PDC. By means of cyclic voltammetry a capacity of 81 µFcm −2 of the electrolytic double layer was determined and confirmed by impedance spectroscopy. Impedance spectroscopy showed an optimal frequency range of 1–5 Hz and thus an ON-time of the voltage pulse of 100-300 ms. An OFF-time of minimum 100 ms was determined by chronoamperometry. Perfluorooctanoic acid (PFOA) was selected as a model substance to investigate the influence of pulsed operation on electrochemical degradation. Based on the PDC experiments, an amplitude of 8 V was obtained for the pulsed electrochemical degradation of PFOA in aqueous solution. The variation of the ON-time showed an influence on the degradation rate of PFOA. The pulsed degradation with an ON-time and an OFF-time of 300 ms showed a degradation of PFOA of 56%. In contrast, only 42% degradation was achieved under direct current conditions. In addition, comparative experiments were carried out with platinum and graphite electrodes, showing the degradation of PFOA. Degradation and transformation products of PFOA were identified by liquid chromatography with high resolution mass spectrometry.