Determination of trace impurities in titanium dioxide by slurry sampling electrothermal atomic absorption spectrometry

A slurry sampling electrothermal atomic absorption spectrometry method for the determination of Al, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, Pb, Sr, Tl and Zn in powdered titanium dioxide is described. The behaviour of the titanium matrix in the atomizer and its interferences with the determination of Al, Fe, Co, Ni and Mn were studied. A tungsten carbide modified graphite tube was used to improve the signal shape and the repeatability for the determination of Fe. For all elements, except for Cd and Pb, quantification by a calibration curve established with aqueous standards was possible. No chemical modifier was used throughout in order to minimize contamination. For the contamination risk elements such as Ca, Fe, K, Mg, Na and Zn, the slurry sampling technique allows to achieve limits of detection (3σ of the blank) 5–20 times lower than the solution technique, resulting for these elements in values of 1, 3, 0.5, 0.5, 0.9 and 2 ng g⁻¹, respectively, and, generally being in the range of 0.2 ng g⁻¹ (Cd) to 10 ng g⁻¹ (Al and Tl). The results obtained by the slurry sampling technique are compared with those of other independent methods including four solution methods and neutron activation analysis.     

Study on the solid phase extraction and spectrophotometric determination of cobalt with 5-(2-benzothiazolylazo)-8-hydroxyquinolene

A highly sensitive, selective and rapid method for the determination of cobalt based on the rapid reaction of cobalt(II) with 5-(2-benzothiazolylazo)-8-hydroxyquinolene BTAHQ and the solid phase extraction of the Co(II)-BTAHQ complex with C18 membrane disks were developed. In the presence of pH = 6.4 buffer solution and cetylpyridenium chloride (CPC) medium, BTAHQ reacts with cobalt to form a deep violet complex with a molar ratio of 1:1 (cobalt to BTAHQ). This complex was enriched by the solid phase extraction with C18 membrane disks. An enrichment factor of 100 was obtained by elution of the complex from the disks with a minimal amount of isopentyl alcohol. In isopentyl alcohol medium, the molar absorptivity of the complex is 2.42 × 10⁵ L mol⁻¹ cm⁻¹ at 658 nm. Beer’s law is obeyed in the range of 0.01–0.38 μg mL⁻¹ in the measured solution. The relative standard deviation for 11 replicate samples of 0.20 μg mL⁻¹ level is 1.37%. The detection and quantification limits reach 3.1 and 9.7 ng mL⁻¹ in the original samples. This method was applied for the determination of cobalt in biological, water, soil and pharmaceutical preparation samples with good results.     

In situ atom trapping of Bi on W-coated slotted quartz tube flame atomic absorption spectrometry and interference studies

Analytical performances of metal coated slotted quartz tube flame atomic absorption spectrometry (SQT-FAAS) and slotted quartz tube in situ atom trapping flame atomic absorption spectrometry (SQT-AT-FAAS) systems were evaluated for determination of Bi. Non-volatile elements such as Mo, Zr, W and Ta were tried as coating materials. It was observed that W-coated SQT gave the best sensitivity for the determination of Bi for SQT-FAAS and SQT-AT-FAAS. The parameters for W-coated SQT-FAAS and W-coated SQT-AT-FAAS were optimized. Sensitivity of FAAS for Bi was improved as 4.0 fold by W-coated SQT-FAAS while 613 fold enhancement in sensitivity was achieved by W-coated SQT-AT-FAAS using 5.0 min trapping with respect to conventional FAAS. MIBK was selected as organic solvent for the re-atomization of Bi from the trapping surface. Limit of detection values for W-coated SQT-FAAS and W-coated SQT-AT-FAAS was obtained as 0.14 μg mL^− 1 and 0.51 ng mL^− 1, respectively. Linear calibration plot was obtained in the range of 2.5–25.0 ng mL^− 1 for W-coated SQT-AT-FAAS. Accuracy of the W-coated SQT-AT-FAAS system was checked by analyzing a standard reference material, NIST 1643e.     

Determination of Pt,Pd and Rh in Brassica Napus using solid sampling electrothermal vaporization inductively coupled plasma optical emission spectrometry

Conventional approaches for the analysis of platinum group elements (PGEs) in plant material suffer from sample digestion which results in sample dilution and therefore requires high sample intakes to maintain the sensitivity. The presented solid-sampling method avoids sample digestion while improving sensitivity when compared to digestion-based inductively coupled plasma optical emission spectrometry (ICP-OES) methods and allows the analysis of sample masses of 5 mg or less. Detection limits of 0.38 μg g^− 1, 0.14 μg g^− 1 and 0.13 μg g^− 1 were obtained for Pt, Pd and Rh, respectively using a sample intake of 5 mg. The reproducibility of the procedure ranged between 4.7% (Pd) relative standard deviation (RSD, n = 7) and 7.1% (Rh) RSD for 25 ng analytes. For quantification, aqueous standards were applied on paper filter strips and dried. Only the dried filters were introduced into the electrothermal vaporization unit. This approach successfully removed memory-effects observed during analysis of platinum which occurred only if liquid standards came into contact with the graphite material of the furnace. The presented method for overcoming the Pt-memory-effects may be of further interest for the analysis of other carbide-forming analytes as it does not require any technical modification of the graphite furnace (e.g., metal inlays, pyrolytic coating). Owing to lack of suitable certified reference materials, the proposed method was compared with conventional ICP-OES analysis of digested samples and a good agreement was obtained. As a result of the low sample consumption, it was possible to determine the spatial distribution of PGEs within a single plant. Significant differences in PGE concentrations were observed between the shoots (stem, leaves) and the roots. Pd was mainly found in the roots, whereas Pt and Rh were also found in higher concentrations in the shoots.     

Determination of atorvastatin in human serum by salting out assisted solvent extraction and reversed-phase high-performance liquid chromatography–UV detection

A simple and rapid technique based on salting out assisted solvent extraction was developed for extraction of atorvastatin from serum sample and high performance liquid chromatography–UV was used for its detection. In the present study, 1.0 mL serum was extracted by 0.5 mL of acetonitrile and some parameters that can affect extraction such as type and volume of extraction solvent, type of salt, and pH were optimized. Under optimized experimental conditions, the calibration curve was found to be linear in the range of 0.001–10 ng mL⁻¹ in human serum and the correlation coefficient (R²) and the limits of detection were >0.99 and 0.0005 ng mL⁻¹, respectively. The accuracy of the method in terms of average recovery of the compound in spiked serum and water samples was better than 90%.     

A novel approach for determining total titanium from titanium dioxide nanoparticles suspended in water and biosolids by digestion with ammonium persulfate

Titanium dioxide (i.e. TiO₂) in nano-form is a constituent of many nanomaterials that are used in sunscreens, cosmetics, industrial products and in biomedical applications. Quantification of TiO₂ nanoparticles in various matrixes is a topic of great interest for researchers studying the potential health and environmental impacts of nanoparticles. However, analysis of TiO₂ as Ti⁴⁺ is difficult because current digestion techniques require use of strong acids that may be a health and safety risk in the laboratory. To overcome this problem, we developed a new method to digest TiO₂ nanoparticles using ammonium persulfate as a fusing reagent. The digestion technique requires short times to completion and optimally requires only 1 g of fusing reagent. The fusion method showed >95% recovery of Ti⁴⁺ from 6 μg mL^?1 aqueous suspensions prepared from 10 μg mL^?1 suspension of different forms of TiO_2, including anatase, rutile and mixed nanosized crystals, and amorphous particles. These recoveries were greater than open hot-plate digestion with a tri-acid solution and comparable to microwave digestion with a tri-acid solution. Cations and anions commonly found in natural waters showed no significant interferences when added to samples in amounts of 10 ng to 110 mg, which is a much broader range of these ions than expected in environmental samples. Using ICP-MS for analysis, the method detection limit (MDL) was determined to be 0.06 ng mL^?1, and the limit of quantification (LOQ) was 0.20 ng mL^?1. Analysis of samples of untreated and treated wastewater and biosolids collected from wastewater treatment plants yielded concentrations of TiO₂ of 1.8 and 1.6 ng mL^?1 for the wastewater samples, respectively, and 317.4 ng mg^?1 dry weights for the biosolids. The reactions between persulfate ions and TiO₂ were evaluated using stoichiometric methods and FTIR and XRD analysis. A formula for the fusing reaction is proposed that involves the formation of sulfate radicals.     

Multiplex electrochemical immunoassay using gold nanoparticle probes and immunochromatographic strips

We describe a multiplex electrochemical immunoassay based on the use of gold nanoparticle (Au-NP) probes and immunochromatographic strips (ISs). The approach takes advantage of the speed and low cost of the conventional IS tests and the high sensitivities of the nanoparticle-based electrochemical immunoassays. Rabbit IgG (R-IgG) and human IgM (H-IgM) were used as model targets for the demonstration of the proof of concept. The Au-NPs based sandwich immunoreactions were performed on the IS, and the captured gold nanoparticle labels on the test zones were determined by highly sensitive stripping voltammetric measurement of the dissolved gold ions (III) with a carbon paste electrode. The detection limits are 1.0 and 1.5 ng ml⁻¹ with the linear range of 2.5–250 ng ml⁻¹ for quantitative detection of R-IgG and H-IgM, respectively. The total assay time is around 25 min. Such multiplex electrochemical immunoassay could be readily highly multiplexed to allow simultaneous parallel detection of numerous proteins and is expected to open new opportunities for protein diagnostics and biosecurity.     

Evaluation of microwave and ultrasound extraction procedures for arsenic speciation in bivalve mollusks by liquid chromatography–inductively coupled plasma-mass spectrometry

Liquid chromatography–inductively coupled plasma-mass spectrometry (LC–ICP-MS) was used for arsenic speciation analysis in tissues of bivalve mollusks (Anomalocardia brasiliana sp. and Macoma constricta sp.). Microwave and ultrasound radiation, combined with different extraction conditions (solvent, sample amount, time, and temperature), were evaluated for As-species extraction from the mollusks' tissues. Accuracy, extraction efficiency, and the stability of As species were evaluated by analyzing certified reference materials (DORM-2, dogfish muscle; BCR-627, tuna fish tissue; and SRM 1566b, oyster tissue) and analyte recovery tests. The best conditions were found to be microwave-assisted extraction using 200 mg of samples and water at 80 °C for 6 min. The agreement of As-species concentration in samples ranged from 97% to 102%. Arsenobetaine (AsB) was the main species present in bivalve mollusk tissues, while monomethylarsonic acid (MMA) and arsenate (As(V)) were below the limit of quantification (0.001 and 0.003 μg g^− 1, respectively). Two unidentified As species also were detected and quantified. The sum of the As-species concentration was in agreement (90 to 104%), with the total As content determined by ICP-MS after sample digestion.     

Study of the chemical composition of particulate matter from the Rio de Janeiro metropolitan region,Brazil, by inductively coupled plasma-mass spectrometry and optical emission spectrometry

Air quality in the metropolitan region of Rio de Janeiro was evaluated by analysis of particulate matter (PM) in industrial (Santa Cruz) and rural (Seropédica) areas. Total suspended particles (TSP) and fine particulate matter (PM_2.5) collected in filters over 24 h were quantified and their chemical composition determined. TSP exceeded Brazilian guidelines (80 μg m^− 3) in Santa Cruz, while PM_2.5 levels exceeded the World Health Organization guidelines (10 μg m^− 3) in both locations. Filters were extracted with water and/or HNO₃, and the concentrations of 20 elements, mostly metals, were determined by inductively coupled plasma mass spectrometry (ICP-MS) and optical emission spectrometry (ICP OES). Water soluble inorganic anions were determined by ion chromatography (IC). To estimate the proportion of these elements extracted, a certified reference material (NIST SRM 1648a, Urban Dust) was subjected to the same extraction process. Concordant results were obtained by ICP-MS and ICP OES for most elements. Some elements could not be quantified by both techniques; the most appropriate technique was chosen in each case. The urban dust was also analyzed by the United States Environmental Protection Agency (US EPA) method, which employs a combination of hydrochloric and nitric acids for the extraction, but higher extraction efficiency was obtained when only nitric acid was employed. The US EPA method gave better results only for Sb. In the PM samples, the elements found in the highest average concentrations by ICP were Zn and Al (3–6 μg m^− 3). The anions found in the highest average concentrations were SO₄^2 − in PM_2.5 (2–4 μg m^− 3) and Cl⁻ in TSP (2–6 μg m^− 3). Principal component analysis (PCA) in combination with enrichment factors (EF) indicated industrial sources in PM_2.5. Analysis of TSP suggested both anthropogenic and natural sources. In conclusion, this work contributes data on air quality, as well as a method for the analysis of PM samples by ICP-MS.     

Determination of zinc and copper in human hair by slurry sampling employing sequential multi-element flame atomic absorption spectrometry

The present work proposes a direct method based on slurry sampling for the determination of zinc and copper in human hair samples by multi-element sequential flame atomic absorption spectrometry. The slurries were prepared by cryogenic grinding and sonication of the samples. The optimization step was performed using univariate methodology and the factors studied were: nature and concentration of the acid solution, amount sample/slurry volume, sonication time, and particle size. The established experimental conditions are the use of a sample mass of 50 mg, 2 mol L^− 1 nitric acid solution, sonication time of 20 min and slurry volume of 10 mL. Adopting the optimized conditions, this method allows the determination of zinc and copper with detection limits of 88.3 and 53.3 ng g^− 1, respectively, and precision expressed as relative standard deviation (RSD) of 1.7% and 1.6% (both, n = 10) for contents of zinc and copper of 100.0 and 33.3 μg g^− 1, respectively. The accuracy was checked and confirmed by analysis of two certified reference materials of human hair. The procedure was applied for the determination of zinc and copper in two human hair samples. The zinc and copper contents varied from 100.0 to 175.6 and from 3.2 to 32.8 μg g^− 1, respectively. These samples were also analyzed after complete digestion in a closed system and determination by FAAS. The statistical comparison by t-test (95% confidence level) showed no significant difference between these results.     

Polyaniline-nylon-6 electrospun nanofibers for headspace adsorptive microextraction

A headspace adsorptive microextraction technique was developed using a novel polyaniline-nylon-6 (PANI-N6) nanofiber sheet, fabricated by electrospinning. The homogeneity and the porosity of the prepared PANI-N6 sheet were studied using the scanning electron microscopy (SEM) and nanofibers diameters were found to be around 200 nm. The novel nanofiber sheet was examined as an extracting medium to isolate some selected chlorobenzenes (CBs), as model compounds, from aquatic media. The extracted analytes were desorbed using μL-amounts of solvent and eventually an aliquot of extractant was injected into gas chromatography–mass spectrometry (GC–MS). Various parameters affecting the extraction and desorption processes were optimized. The developed method proved to be convenient and offers sufficient sensitivity and a good reproducibility. Limits of detection achieved for CBs with the developed analytical procedure ranged from 19 to 33 ng L^?1, while limits of quantification were from 50 to 60 ng L^?1. The relative standard deviations (RSD) at a concentration level of 0.1 ng mL^?1 and 1 ng mL^?1 were in the range of 8–14% and 5–11% (n = 3), respectively. The calibration curves of analytes were investigated in the range of 50–1000 ng L^?1 and R² between 0.9739 and 0.9932 were obtained. The developed method was successfully applied to the extraction of selected CBs from tap and river water samples. The relative recovery (RR) percentage obtained for the spiked real water samples at 0.1 ng mL^?1 and 1 ng mL^?1 level were 93–103% and 95–104%, respectively. The whole procedure showed to be conveniently applicable and quite easy to handle.     

Determination of heavy metals by inductively coupled plasma mass spectrometry after on-line separation and preconcentration

A method for the determination of Cu, As, Se, Cd, In, Hg, Tl, Pb and Bi in waters and in biological materials by inductively coupled plasma mass spectrometry, after an on-line separation, is described. The matrix separation and analyte preconcentration is accomplished by retention of the analytes complexed with the ammonium salt of O,O-diethyl dithiophosphoric acid in a HNO₃ solution on C₁₈ immobilized on silica in a minicolumn. Methanol, as eluent, is introduced in the conventional pneumatic nebulizer of the instrument. In order to use the best compromise conditions, concerning the ligand and acid concentrations, the analytes were determined in two separate groups. The enrichment factors were in the range from 5 to 61, depending on the analyte. The limits of detection varied from 0.43 ng L⁻¹ for Bi to 33 ng L⁻¹ for Cu. The sample consumption is only 2.3 mL for each group and the sampling frequency is 21 h⁻¹. The accuracy was tested by analysing five certified reference materials: water, riverine water, urine, bovine muscle and bovine liver. The agreement between obtained and certified concentrations was very good, except for As. The relatively small volume of methanol, used as eluent, minimizes the problems produced by the introduction of organic solvent into the plasma.     

Determination of triclosan,triclocarban and methyl-triclosan in aqueous samples by dispersive liquid–liquid microextraction combined with rapid liquid chromatography

In this study, dispersive liquid–liquid microextraction (DLLME) combined with ultra-high-pressure liquid chromatography (UHPLC)–tunable ultraviolet detection (TUV), has been developed for pre-concentration and determination of triclosan (TCS), triclocarban (TCC) and methyl-triclosan (M-TCS) in aqueous samples. The key factors, including the kind and volume of extraction solvent and dispersive solvent, extraction time, salt effect and pH, which probably affect the extraction efficiencies were examined and optimized. Under the optimum conditions, linearity of the method was observed in the range of 0.0500–100 μg L^?1 for TCS, 0.0250–50.0 μg L^?1 for TCC, and 0.500–100 μg L^?1 for M-TCS, respectively, with correlation coefficients (r²) > 0.9945. The limits of detection (LODs) ranged from 45.1 to 236 ng L^?1. TCS in domestic waters was detected with the concentration of 2.08 μg L^?1. The spiked recoveries of three target compounds in river water, irrigating water, reclaimed water and domestic water samples were achieved in the range of 96.4–121%, 64.3–84.9%, 77.2–115% and 75.5–106%, respectively. As a result, this method can be successfully applied for the rapid and convenient determination of TCS, TCC and M-TCS in real water samples.     

Cu determination in crude oil distillation products by atomic absorption and inductively coupled plasma mass spectrometry after analyte transfer to aqueous solution

Cu was determined in a wide range of petroleum products from crude oil distillation using flame atomic absorption spectrometry (FAAS), electrothermal atomic absorption spectrometry (ETAAS) and inductively coupled plasma mass spectrometry (ICP-MS). Different procedures of sample preparation were evaluated: (i) mineralization with sulfuric acid in an open system, (ii) mineralization in a closed microwave system, (iii) combustion in hydrogen–oxygen flame in the Wickbold's apparatus, (iv) matrix evaporation followed by acid dissolution, and (v) acidic extraction. All the above procedures led to the transfer of the analyte into an aqueous solution for the analytical measurement step. It was found that application of FAAS was limited to the analysis of the heaviest petroleum products of high Cu content. In ICP-MS, the use of internal reference method (with Rh or In as internal reference element) was required to eliminate the matrix effects in the analysis of extracts and the concentrated solutions of mineralized heavy petroleum products. The detection limits (in original samples) were equal to, respectively, 10, 86, 3.3, 0.9 and 0.4 ng g^− 1 in procedures i–v with ETAAS detection and 10, 78, 1.1 and 0.5 ng g^− 1 in procedures i–iii and v with ICP-MS detection. The procedures recommended here were validated by recovery experiments, certified reference materials analysis and comparison of results, obtained for a given sample, in different ways. The Cu content in the analyzed samples was: 50–110 ng g^− 1 in crude oil, < 0.4–6 ng g^− 1 in gasoline, < 0.5–2 ng g^− 1 in atmospheric oil, < 6–100 ng g^− 1 in heavy vacuum oil and 140–300 ng g^− 1 in distillation residue.     

A two-step atomizer system using a transversely heated furnace with Zeeman background correction: Design and first solid sampling applications

A two-step-atomizer consisting of a transversely heated graphite atomization tube and a movable vaporizer graphite cup is described. The atomizer is placed between the poles of an electromagnetic field providing longitudinal Zeeman-effect background correction capability. The tube and the cup are heated by independent power supplies enabling the performance of atomic absorption measurements at temporally and spatially isothermal conditions. The design of the vaporizer provides several advantageous features including direct introduction of solid and liquid samples with extremely low contamination risk and a sampling volume of up to 105 μl. The performance of this system was assessed by analysis of the bovine liver NIST SRM 1577b and of a well characterized titanium dioxide material. Calibration curves for quantification were recorded by using aqueous standards. In comparison of the results obtained by this method with the certified values and with the results of independent methods, excellent to reasonable agreement was achieved. For the elements Fe, K, Mg, Mn, Na and Zn in titanium dioxide, the achievable limits of detection were between 60 pg g^− 1 (Mg) and 0.7 ng g^− 1 (Fe).     

Insoluble metal hexacyanoferrates as supercapacitor electrodes

Nano-sized insoluble iron, cobalt and nickel hexacyanoferrates (Mhcf) were prepared by a simple co-precipitation method. The potential of using these materials for supercapacitor was examined by cyclic voltammogram and constant charge/discharge. Due to the different types of the second metal (M), the Mhcf electrodes showed different electrochemical capacitive performances. The specific discharge capacitances of Fehcf, Nihcf and Cohcf electrodes at the current density of 0.2 A g⁻¹ were 425 F g⁻¹, 574.7 F g⁻¹ and 261.56 F g⁻¹, respectively. Meanwhile, the Mhcf electrodes showed good cyclic performance.     

Treatment of wastewater having estrogen activity by ionizing radiation

Decomposition of endocrine disrupting chemicals (EDCs) in wastewater was investigated by use of ⁶⁰Co γ-ray. Estrogen activities of wastewaters were estimated by the yeast two-hybrid assay based on human or medaka estrogen receptors. The dose required for the elimination of estrogen activity of wastewater below 1 ng dm⁻³ was about 200 Gy (J kg⁻¹). The elimination dose of the estrogen activity depended on the amounts of total organic carbons in wastewater. The economic cost of the treatment process of EDCs using electron beam was estimated at 17 yen m⁻³.     

Pseudocapacitive effect and Li+ diffusion coefficient in three-dimensionally ordered macroporous vanadium oxide for energy storage

In order to act as extrinsic pseudocapacitor materials, nanoscale vanadium oxides are required to simultaneously exhibit a capacitance-based high power density and an intercalation-based high energy density. We have fabricated a three-dimensionally ordered macroporous (3DOM) structure with a wall thickness of 14 nm that fulfills the above requirements. The 3DOM vanadium oxide film exhibits high rate performance with 355 F g^− 1 at 0.5 A g^− 1 and 125 F g^− 1 at 15 A g^− 1. The enhanced pesudocapacitive effect and Li-ion diffusion coefficient based on the 3DOM nanostructure, also contributes to the high rate capability of vanadia, which can be confirmed by cyclic voltammetry and chronoamperometry.     

Electronic structure and Raman spectroscopy study of dibarium magnesium orthoborate,Ba2Mg(BO3)2

The samples of dibarium magnesium orthoborate Ba₂Mg(BO₃)₂ were synthesized by solid-state reaction. The X-ray diffraction (XRD) patterns and Raman spectra of the samples were collected. Electronic structure and vibrational spectroscopy of Ba₂Mg(BO₃)₂ were systematically investigated by first principle calculation. A direct band gap of 4.4 eV was obtained from the calculated electronic structure results. The top valence band is constructed from O 2p states and the low conduction band mainly consists of Ba 5d states. Raman spectra for Ba₂Mg(BO₃)₂ polycrystalline were obtained at ambient temperature. The factor group analysis results show the total lattice modes are 5E_u + 4A_2u + 5E_g + 4A_1g + 1A_2g + 1A_1u, of which 5E_g + 4A_1g are Raman-active. Furthermore, we obtained the Raman active vibrational modes as well as their eigenfrequencies using first-principle calculation. With the assistance of the first-principle calculation and factor group analysis results, Raman bands of Ba₂Mg(BO₃)₂ were assigned as E_g (42 cm⁻¹), A_1g (85 cm⁻¹), E_g (156 cm⁻¹), E_g (237 cm⁻¹), A_1g (286 cm⁻¹), E_g (564 cm⁻¹), A_1g (761 cm⁻¹), A_1g (909 cm⁻¹), E_g (1165 cm⁻¹). The strongest band at 928 cm⁻¹ in the experimental spectrum is assigned to totally symmetric stretching mode of the BO₃ units.     

VO2 nano-sheet negative electrodes for lithium-ion batteries

Vanadium dioxide (VO₂) nano-sheets were directly synthesized via a continuous hydrothermal process and were investigated as electrodes in a wide potential range of 0.05–3 V vs. Li/Li⁺. The nano-sheets showed excellent capacity retention, with a specific capacity of 350 mAh g^− 1 at an applied current of 0.1 A g^− 1 and 95 mAh g^− 1 at 10 A g^− 1. Further electrochemical testing suggested that a significant proportion of the charge storage in the cells was due to pseudocapacitive processes.