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This study presents a new method for the determination of mass-dependent Te isotope compositions. The process encompasses a new column chromatographic procedure which separates Te from chondritic and iron meteorites and diverse terrestrial rocks with high yield and purity, combined with a robust 125Te–128Te double spike and optimised multi collector ICP-MS protocols. This allows for precise (2SD = 0.07‰) determination of the mass-dependent 130Te/125Te isotope ratio using analyte solutions containing as little as 6 ng of natural Te. The efficacy of the method is demonstrated by repeat analyses of terrestrial rock reference materials and meteorites, which show overall good agreement with previous work. In addition, an inter-laboratory cross-calibration of three different Te standard solutions was performed. This inter-laboratory cross-calibration is highly advantageous, as a well-calibrated isotope reference material is not yet available for Te. Isotope mass balance and mixing equations performed in this study show that hypothetical mass-independent Te isotope effects of reasonable magnitude are unlikely to have a significant impact on the measured mass-dependent Te isotope compositions at the current level of analytical precision. Finally, this study presents the first precise mass-dependent Te isotope composition obtained for an iron meteorite, Canyon Diablo, and komatiite reference material KAL-1 using the double spike technique.

Material inherited from different nucleosynthesis sources imparts distinct isotopic signatures to meteorites and terrestrial planets. These nucleosynthetic isotope anomalies have been used to constrain the origins of material that formed Earth. However, anomalies have only been identified for elements with high condensation temperatures, leaving the origin of Earth’s volatile elements unconstrained. We determined the isotope composition of the moderately volatile element zinc in 18 bulk meteorites and identified nucleosynthetic zinc isotope anomalies. Using a mass-balance model, we find that carbonaceous bodies, which likely formed beyond the orbit of Jupiter, delivered about half of Earth’s zinc inventory. Combined with previous constraints obtained from studies of other elements, these results indicate that ~10% of Earth’s mass was provided by carbonaceous material.

Zinc and Cd isotope compositions are presented for a comprehensive suite of terrestrial rocks to constrain the extent of Zn and Cd isotope fractionation during igneous processes and better define the δ66Zn and δ114Cd values of the silicate Earth (the δ values denote per mille deviations of 66Zn/64Zn from JMC Lyon Zn and of 114Cd/110Cd from NIST SRM 3108 Cd). Analyses of spinel lherzolites provide a bulk silicate Earth (BSE) δ114CdBSE value of –0.06 ± 0.03 ‰ (2SD). For Zn, the peridotite data of the current and previous studies define a mean δ66ZnBSE = 0.20 ± 0.05 ‰ (2SD). Komatiite analyses of this and published investigations yield similar mean values, which suggests that the Zn and Cd isotope compositions of the mantle remained fairly constant since the Archean. Data for loess provide upper continental crust compositions of δ114Cd = 0.03 ± 0.10 ‰ and δ66Zn = 0.23 ± 0.07 ‰. The Zn isotope and abundance data for peridotites and oceanic basalts are in accord with the previous observation of a mantle array, with basalts having higher Zn concentrations and δ66Zn values than the peridotites. To a first order, this reflects slightly incompatible behaviour of Zn during mantle melting and melt differentiation with associated enrichment of heavy Zn isotopes in the melt phase. Cadmium is marginally more incompatible than Zn during igneous processes and the oceanic basalts also display a minor enrichment of heavy Cd isotopes relative to peridotites. However, secondary processes produce significant Cd isotope variability in both mantle melts and peridotites, obscuring the primary igneous array. The δ66ZnBSE estimates of this and previous studies resemble the Zn isotope compositions of CV and CO carbonaceous and some enstatite chondrites. In contrast, the BSE has a lower δ114CdBSE value than enstatite and carbonaceous chondrites. This implies that the Cd isotope composition of the BSE was either fractionated during accretion or that Earth's Cd inventory was not exclusively acquired from material related to carbonaceous and enstatite chondrites. Importantly, delivery of Zn and Cd to the BSE solely by CI and CM chondrites is not in accord with the meteorite and terrestrial stable isotope data of these elements., Geochimica et Cosmochimica Acta, 338, ISSN:0016-7037, ISSN:1872-9533

Funding: SL, AB and HP report financial support was provided by Natural Environment Research Council. Anthropogenic activities have significantly enhanced atmospheric metal inputs to the ocean, which has potentially important consequences for marine ecosystems. This study assesses the potential of Zn and Cu isotope compositions to distinguish between natural and anthropogenic atmospheric inputs of these metals to the surface ocean. To this end, the isotopic compositions of Zn and Cu in aerosols collected from the eastern tropical Atlantic Ocean on the GEOTRACES GA06 cruise are examined. Enrichment factors and fractional solubility measurements indicate the presence of a significant anthropogenic component in the aerosols collected furthest from the North African dust plume for both Zn and Cu. The mean δ65CuNIST SRM 976 for the fully digested aerosols is +0.07 ± 0.39 ‰ (n = 9, 2 SD), which is indistinguishable from the lithogenic value, and implies that Cu isotopes are not an effective tracer of aerosol sources in this region. The mean δ66ZnJMC-Lyon value for the aerosols that underwent a total digestion is +0.17 ± 0.22 ‰ (n = 11, 2 SD). The aerosols leached with ammonium acetate have similar Zn isotope compositions, with a mean of +0.15 ± 0.16 ‰ (n = 7, 2 SD). The aerosols were collected in a region with prevalent mineral dust but, despite this, exhibit isotopically lighter Zn than lithogenic Zn with δ66Zn ≈ +0.3 ‰. When coupled with the previously published Pb isotope data, the aerosols exhibit coupled Zn-Pb isotope systematics that are indicative of mixing between mineral dust (δ66Zn = +0.28 ‰ and 206Pb/207Pb = 1.205) and anthropogenic emissions (δ66Zn = −0.22 ‰ and 206Pb/207Pb = 1.129). This demonstrates the potential of Zn isotopes to trace atmospheric Zn inputs from anthropogenic sources to the surface ocean. Publisher PDF

We present the first high-precision vanadium (V) isotope data for lunar basalts. Terrestrial magmatic rock measurements can display significant V isotopic fractionation (particularly during (Fe, Ti)oxide crystallisation), but the Earth displays heavy V (i.e. higher 51V/50V) isotopic compositions compared to meteorites. This has been attributed to early irradiation of meteorite components or nucleosynthetic heterogeneity. The Moon is isotopically-indistinguishable from the silicate Earth for many refractory elements and is expected to be similar in its V isotopic composition. Vanadium isotope ratios and trace element concentrations were measured for 19 lunar basalt samples. Isotopic compositions are more variable (∼2.5‰) than has been found thus far for terrestrial igneous rocks and extend to lighter values. Magmatic processes do not appear to control the V isotopic composition, despite the large range in oxide proportions in the suite. Instead, the V isotopic compositions of the lunar samples are lighter with increasing exposure age ( t e ). Modelling nuclear cross-sections for V production and burnout demonstrates that cosmogenic production may affect V isotope ratios via a number of channels but strong correlations between V isotope ratios and t e ⁎ [Fe]/[V] implicate Fe as the primary target element of importance. Similar correlations are found in the latest data for chondrites, providing evidence that most V isotope variation in chondrites is due to recent cosmogenic production via Fe spallation. Contrary to previous suggestions, there is no evidence for resolvable differences between the primary V isotopic compositions of the Earth, Moon, chondrites and Mars.

The disruption of Zn homeostasis has been linked with breast cancer development and progression. To enhance our understanding of changes in Zn homeostasis both inside and around the tumour microenvironment, Zn concentrations and isotopic compositions (δ66Zn) were determined in benign (BT) and malignant (MT) tumours, healthy tissue from reduction mammoplasty (HT), and histologically normal tissue adjacent to benign (NAT(BT)) and malignant tumours (NAT(MT)). Mean Zn concentrations in NAT(BT) are 5.5 µg g−1 greater than in NAT(MT) (p = 0.00056) and 5.1 µg g−1 greater than in HT (p = 0.0026). Zinc concentrations in MT are 12.9 µg g−1 greater than in HT (p = 0.00012) and 13.3 µg g−1 greater than in NAT(MT) (p

The application of Pb isotopes to marine geochemistry is currently hindered by challenges associated with the analysis of Pb isotopes in seawater. The current study evaluates the performance of multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS) measurements of seawater Pb isotope compositions following Pb separation by either solid-phase extraction with Nobias Chelate PA-1 resin or coprecipitation with Mg(OH)2 and using either a Pb double spike or external normalization to Tl for mass bias correction. The four analytical combinations achieve results of similar quality when measuring 1-7 ng of seawater Pb, with reproducibilities (two standard deviations, 2SD) of 100-1200 ppm for 206Pb/207Pb and 208Pb/207Pb and 300-1700 ppm for ratios involving the minor 204Pb isotope. All four procedures enable significantly improved sample throughput compared to an established thermal ionization mass spectrometry (TIMS) double-spike method and produce unbiased seawater Pb isotope compositions with similar or improved precision. Nobias extraction is preferable to coprecipitation due to its greater analytical throughput and suitability for analyses of large seawater samples with high Si(OH)4 contents. The most accurate Pb isotope data are produced following Nobias extraction and double-spike correction as such analyses are least susceptible to matrix effects. However, Nobias extraction with Tl normalization constitutes an attractive alternative as, unlike the double-spike procedure, only a single mass spectrometric measurement is required, which improves analytical throughput and optimizes Pb consumption for analysis. Despite the advantages of solid-phase extraction, coprecipitation represents a useful Pb separation technique for samples with low to moderate Si contents as it is inexpensive, simple to implement, and the data are only marginally less accurate, especially when combined with a Pb double spike for mass bias correction.

New Tl, Pb, and Cd concentration and Tl, Pb isotope data are presented for enstatite as well as L- and LL-type ordinary chondrites, with additional Cd stable isotope results for the former. All three chondrite suites have Tl and Cd contents that vary by more than 1-2 orders of magnitude but Pb concentrations are more uniform, as a result of terrestrial Pb contamination. Model calculations based on Pb isotope compositions indicate that for more than half of the samples, more than 50% of the measured Pb contents are due to addition of modern terrestrial Pb. In part, this is responsible for the relatively young and imprecise Pb-Pb ages determined for EH, L, and LL chondrites, which are hence only of limited chronological utility. In contrast, four particularly pristine EL chondrites define a precise Pb-Pb cooling age of 4559 +/- 6Ma. The enstatite chondrites (ECs) have highly variable epsilon Cd-114/110 of between about +3 and +70 due to stable isotope fractionation from thermal and shock metamorphism. Furthermore, nearly all enstatite meteorites display epsilon Tl-205 values from -3.3 to +0.8, while a single anomalous sample is highly fractionated in both Tl and Cd isotopes. The majority of the ECs thereby define a correlation of epsilon Tl-205 with epsilon Cd-114/110, which suggests that at least some of the Tl isotope variability reflects stable isotope fractionation rather than radiogenic ingrowth of Tl-205 from Pb-205 decay. Considering L chondrites, most epsilon Tl-205 values range between -4 and +1, while two outliers with epsilon Tl-205-10 are indicative of stable isotope fractionation. Considering only those L chondrites which are least likely to feature Pb contamination or stable Tl isotope effects, the results are in accord with the former presence of live Pb-205 on the parent body, with an initial Pb-205/Pb-204=(1.5 +/- 1.4)x10(-4), which suggests late equilibration of the Pb-Tl system 26-113Ma after carbonaceous chondrites (CCs). The LL chondrites display highly variable epsilon Tl-205 values from -12.5 to +14.9, also indicative of stable isotope effects. However, the data for three pristine LL3/LL4 chondrites display an excellent correlation between epsilon Tl-205 and Pb-204/Tl-203. This defines an initial Pb-205/Pb-204 of (1.4 +/- 0.3)x10(-4), equivalent to a Pb-205-Tl-205 cooling age of 55+12/-24Ma (31-67Ma) after CCs.

Copper and Zn are trace metal micronutrients whose stable isotope systematics are receiving increasing attention as possible paleoenvironmental tracers. However, to realise this potential, their behaviour during chemical weathering must be better constrained. We present coupled Cu and Zn isotope data for a well-characterised Indian laterite weathering profile, which includes a full suite of samples from unaltered greywacke bedrock to indurated lateritic duricrust. This sample set provides an exceptional opportunity to interrogate Cu and Zn isotope compositions during an extreme example of chemical weathering. Despite their occurrence in different host phases within the parent greywacke, Cu and Zn isotopes behave coherently during weathering. We observe preferential loss of heavy isotopes at increasing degrees of alteration, with 0.6‰ total variability in δ66Zn and 0.9‰ in δ65Cu. Given the absence of evidence for CuS or ZnS phases in the parent lithology, we attribute the liberation of heavy isotopes to organic complexation in the aqueous phase and/or incorporation of light isotopes in secondary aluminous Fe-oxides. Strong enrichment of both metals is also associated with a peak in Mn at a previously identified paleo-water table horizon. This dataset confirms that weathering under oxygenated conditions releases isotopically heavy Cu, regardless of the host phase. Meanwhile, Zn isotopes are only fractionated to any significant extent at the most extreme degrees of chemical weathering reached during lateritization. We conclude that the isotopic composition of the weathering-derived input of Zn to rivers should be largely insensitive to climate change on geological timescales.

The often high Cd concentrations of cacao beans are a serious concern for producers in Latin America due to the implementation of stricter Cd limits for cocoa products by the European Union in 2019. This is the first investigation to employ coupled Cd isotope and concentration measurements to study soil - cacao systems. Analyses were carried out for 29 samples of soils, soil amendments and cacao tree organs from organic farms in Ecuador that harvest three distinct cacao cultivars. The majority of soils from 0-80 cm depth have very similar delta Cd-114/110 of about -0.1 parts per thousand to 0 parts per thousand. Two 0-5 cm topsoils, however, have high Cd concentrations coupled with heavy Cd isotope compositions of delta Cd-114/110 approximate to 0.2%, possibly indicating Cd additions from the tree litter used as organic fertilizer. Whilst cacao leaves, pods and beans are ubiquitously enriched in Cd relative to soils there are distinct Cd isotope signatures. The leaves and pods are isotopically heavier than the soils, with similar Delta Cd-114/110(leaf-soil) values of 0.22 +/- 0.07 parts per thousand to 0.41 +/- 0.09 parts per thousand. In contrast, the data reveal differences in Delta Cd-114/110(bean-leaf) that may be linked to distinct cacao cultivars. In detail, Delta Cd-114/110(bean-leaf) values of -0.34 parts per thousand to -0.40 parts per thousand were obtained for Nacional cacao from two farms, whilst CCN-51 hybrid cacao from a third farm showed no fractionation within error (-0.08 +/- 0.13 parts per thousand). As such, further work to investigate whether Cd isotopes are indeed useful for tracing sources of Cd enrichments in soils and to inform genetic efforts to reduce the Cd burden of cocoa is indicated.

Improving the geochemical database available for characterising potential natural and anthropogenic aerosol sources from South America and Southern Africa is a critical precondition for studies aimed at understanding trace metal controls on the marine biogeochemical cycles of the South Atlantic Ocean. We here present new elemental and isotopic data for a wide range of sample types from South America and Southern Africa that are potentially important aerosol sources. This includes road dust from Buenos Aires and lichen samples from Johannesburg, soil dust from Patagonia, volcanic ash from the Andean volcanic belt, and aerosol samples from São Paulo. All samples were investigated for major (Al, Ca, Fe, Mg, Na, K, Mn) and trace element (Cd, Co, Cr, Cu, Ni, Pb, REE, Sc, Th, Y, V, Zn) concentrations and Nd and Pb isotopic compositions. We show that diagrams of 208Pb/207Pb vs. εNd, 208Pb/207Pb vs. Pb/Al, 1/[Pb], Zn/Al, Cd/Al, Cu/Al, and εNd vs. Pb/Al, and 1/[Nd] are best suited to separate South American and South African source regions as well as natural and anthropogenic sources. A subset of samples from Patagonia and the Andes was additionally subjected to separation of a fine (

Isotopes of the actinide elements protactinium (Pa), thorium (Th), and uranium (U), and the lanthanide element neodymium (Nd) are often used as complementary tracers of modern and past oceanic processes. The extraction of such elements from low abundance matrices, such as seawater and carbonate, is however labor-intensive and requires significant amounts of sample material. We here present a combined method for the extraction of Pa, Th, and Nd from 5 to 10 L seawater samples, and of U, Th, and Nd from

During isotopic analysis of Cd by MC-ICP-MS, organic resin residue can perturb instrumental mass fractionation. These organic compounds can be removed by a liquid–liquid extraction procedure using heptane., Organic compounds released from resins that are commonly employed for trace element separations are known to have a detrimental impact on the quality of isotopic analyses by MC-ICP-MS. A recent study highlighted that such effects can be particularly problematic for Cd stable isotope measurements (M. Gault-Ringold and C. H. Stirling, J. Anal. At. Spectrom., 2012, 27, 449–459). In this case, the final stage of sample purification commonly applies extraction chromatography with Eichrom TRU resin, which employs particles coated with octylphenyl-N,N-di-isobutyl carbamoylphosphine oxide (CMPO) dissolved in tri-n-butyl phosphate (TBP). During chromatography, it appears that some of these compounds are eluted alongside Cd and cannot be removed by evaporation due to their high boiling points. When aliquots of the zero-ε reference material were processed through the purification procedure, refluxed in concentrated HNO3 and analyzed at minimum dilution (in 1 ml 0.1 M HNO3), they yielded Cd isotopic compositions (ε114/110Cd = 4.6 ± 3.4, 2SD, n = 4) that differed significantly from the expected value, despite the use of a double spike technique to correct for instrumental mass fractionation. This result was accompanied by a 35% reduction in instrumental sensitivity for Cd. With increasing dilution of the organic resin residue, both of these effects are reduced and they are insignificant when the eluted Cd is dissolved in ≥3 ml 0.1 M HNO3. Our results, furthermore, indicate that the isotopic artefacts are most likely related to anomalous mass bias behavior. Previous studies have shown that perchloric acid can be effective at avoiding such effects (Gault-Ringold and Stirling, 2012; K. C. Crocket, M. Lambelet, T. van de Flierdt, M. Rehkämper and L. F. Robinson, Chem. Geol., 2014, 374–375, 128–140), presumably by oxidizing the resin-derived organics, but there are numerous disadvantages to its use. Here we show that liquid–liquid extraction with n-heptane removes the organic compounds, dramatically improving quality of the Cd isotope data for samples that are analyzed at or close to minimum dilution factors. This technique is quick, simple and may be of use prior to analysis of other isotope systems where similar resins are employed.

Meteorite fusion crust formation is a brief event in a high-temperature (2000- 12,000 K) and high-pressure (2-5 MPa) regime. We studied fusion crusts and bulk samples of 10 ordinary chondrite falls and 10 ordinary chondrite finds. The fusion crusts show a typical layering and most contain vesicles. All fusion crusts are enriched in heavy Fe isotopes, with d 56 Fe values up to +0.35& relative to the solar system mean. On average, the d 56 Fe of fusion crusts from finds is +0.23&, which is 0.08& higher than the average from falls (+0.15&). Higher d 56 Fe in fusion crusts of finds correlate with bulk chondrite enrichments in mobile elements such as Ba and Sr. The d 56 Fe signature of meteorite fusion crusts was produced by two processes (1) evaporation during atmospheric entry and (2) terrestrial weathering. Fusion crusts have either the same or higher d 18 O (0.9-1.5&) than their host chondrites, and the same is true for D 17 O. The differences in bulk chondrite and fusion crust oxygen isotope composition are explained by exchange of oxygen between the molten surface of the meteorites with the atmosphere and weathering. Meteorite fusion crust formation is qualitatively similar to conditions of chondrule formation. Therefore, fusion crusts may, at least to some extent, serve as a natural analogue to chondrule formation processes. Meteorite fusion crust and chondrules exhibit a similar extent of Fe isotope fractionation, supporting the idea that the Fe isotope signature of chondrules was established in a high-pressure environment that prevented large isotope fractionations. The exchange of O between a chondrule melt and an 16 O-poor nebula as the cause for the observed nonmass dependent O isotope compositions in chondrules is supported by the same process, although to a much lower extent, in meteorite fusion crusts.

Biological reference materials with well-characterised stable isotope compositions are lacking in the field of ‘isotope biochemistry’, which seeks to understand bodily processes that rely on essential metals by determining metal stable isotope ratios. Here, we present Zn stable isotope data for six biological reference materials with certified trace metal concentrations: fish muscle, bovine muscle, pig kidney, human hair, human blood serum and human urine. Replicate analyses of multiple aliquots of each material achieved reproducibilities (2sd) of 0.04–0.13‰ for δ66/64Zn (which denotes the deviation of the 66Zn/64Zn ratio of a sample from a pure Zn reference material in parts per 1000). This implies only very minor isotopic heterogeneities within the samples, rendering them suitable as quality control materials for Zn isotope analyses. This endorsement is reinforced by (i) the close agreement of our Zn isotope data for two of the samples (bovine muscle and human blood serum) to previously published results for different batches of the same material and (ii) the similarity of the isotopic data for the samples (δ66/64Zn ≈ –0.8 to 0.0‰) to previously published Zn isotope results for similar biological materials. Further tests revealed that the applied Zn separation procedure is sufficiently effective to enable accurate data acquisition even at low mass resolving power (M/ΔM ≈ 400), as measurements and analyses conducted at much higher mass resolution (M/ΔM ≈ 8500) delivered essentially identical results. Electronic supplementary material The online version of this article (doi:10.1007/s00216-017-0240-y) contains supplementary material, which is available to authorized users.

“Two-dimensional voltammetry” using arrays of variable-sized gold channel microband electrodes in combination with variable flow rate measurements together with independent gold rotating disk electrode (RDE) data is applied to characterize the oxidation mechanism of l-ascorbic acid (AH2) to dehydro-l-ascorbic acid in aqueous solutions. At pH 2.1 and very low mass transport conditions the reaction is consistent with a CECE mechanism, while at higher mass transport conditions an ECfastCE mechanism is followed. At pH 6.7, the results are again consistent with an ECE mechanism. The following mechanism is proposed: AH2 ⇌ AH- + H+ (kCEE), AH- → AH• + e, AH• → A• - + H+ (kECE), A• - → A + e (CECE); AH2 ⇌ AH2+ + e, AH2+ → AH• + H+(fast), AH• → A• - + H+ (kECE), A• - → A + e (ECfastCE); where, only the first pathway applies at pH 6.7, AH- being the starting species. Values of 3.4 × 103 s-1 and 500 s-1 are found for the rate constants kCEE and kECE, respectively.

The design, construction, and application of a miniature channel electrode operating with very high flow conditions, of up to ca. 10 cm3 s-1, are reported. The channel cell has approximate cross-section dimensions of 0.2 cm × 100 μm so that the axial velocity of the solution through the channel can reach values as high as 75 m s-1 (270 km h-1, 167 mi h-1) at the channel center. The electrode takes the form of a microband electrode presently of length ca. 5-10 μm. With this arrangement voltammetry can be performed under flow conditions where the mass transport coefficient approaches 1.0 cm s-1. Voltammetric measurements utilizing the new cell are reported, and the mass transport is shown to be quantitatively consistent with a model in which the dominant transport is by diffusion normal to the electrode and by convection axially through the cell. Axial diffusion effects are relatively insignificant. The cell is applied to the study of ECE processes, and it is shown that homogeneous rate constants as high as 105 s-1 are readily measureable from steady-state experiments. © 1995 American Chemical Society.

Microwave activation of electrochemical processes has recently been introduced as a new technique for the enhancement and control of processes at electrode|solution (electrolyte) interfaces. This methodology is extended to processes at glassy carbon and boron-doped diamond electrodes. Deposition of both Pb metal and PbO2 from an aqueous solution of Pb2+ (0.1 M HNO3) are affected by microwave radiation. The formation of PbO2 on anodically pre-treated boron-doped diamond is demonstrated to change from kinetically sluggish and poorly defined at room temperature to nearly diffusion controlled and well defined in the presence of microwave activation. Calibration of the temperature at the electrode|solution (electrolyte) interface with the Fe3+/2+ (0.1 M HNO3) redox system allows the experimentally observed effects to be identified as predominantly thermal in nature and therefore consistent with a localized heating effect at the electrode|solution interface. The microwave-activated deposition of PbO2 on boron-doped diamond remains facile in the presence of excess oxidizable organic compounds such as ethylene glycol. An increase of the current for the electrocatalytic oxidation of ethylene glycol at PbO2/ boron-doped diamond electrodes in the presence of microwave radiation is observed. Preliminary results suggest that the electrodissolution of solid microparticles of PbO2 abrasively attached to the surface of a glassy carbon electrode is also enhanced in the presence of microwave radiation.

A channel flow cell suitable for the study of reactions at insulator | liquid interfaces is described, in which a pair of electrodes are located downstream of the solid of interest and used to monitor the release of ionic species by means of impedance measurements made at variable frequencies. Theory is given which enables the measured impedance resulting from the spatially inhomogeneous ion distribution within the flow cell, and its flow rate dependence, to be related to the rate process at the solid | liquid interface. The method is applied to the hydrolytic dissolution of solid triphenylmethyl chloride in aqueous solutions of low ionic strength and leads to the inference that the hydrolysis occurs at the solid | liquid interface rather than in bulk solution after the prior dissolution of the solid.

The reduction of the dye crystal violet in acetonitrile solution at platinum electrodes has been investigated using in situ electrochemical e.s.r. and a channel electrode flow cell. In the dark, in the rigorous absence of oxygen, a one-electron reversible reduction takes place, producing the stable crystal violet radical, the e.s.r. spectrum of which was recorded. The behaviour in the presence of oxygen is also discussed. On irradiation with light of wavelength ca. 400 nm the radical is thought to undergo a chemical reaction with the solvent, and the electrode reduction process has the characteristics of an EC mechanism. The nature of this reaction is deduced from the e.s.r. signal strength/current/electrolyte flow rate data together with pure electrochemical measurements, and kinetic parameters are reported.

Self-focusing of intense microwave radiation at the tip of a 25 microm diameter platinum disk microelectrode immersed into the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM(+)PF(6)(-)) containing 1 mM ferrocene causes dramatically (two orders of magnitude) enhanced voltammetric current signals and temperatures in excess of 600 K (at the electrode surface)--extreme conditions sufficient for condensed phase pyrolysis processes to occur.

The current transients arising after the sudden heating of an electrode by high-power laser irradiation have been studied. The method has been applied to a Au(111) single-crystal electrode in contact with perchloric and sulfuric acid solutions. The current transient can be explained as due to the recovery of the double layer capacity after its decrease due to the sudden rise of the temperature. It has been found that there is a Correlation between the sign of the current transient and the sign of the double layer charge, and there is a coincidence between the potential where the transient vanishes and the potential of zero charge. This allows its use as a general method for determination of the potential of zero charge of solid electrodes.

The application of fast-scan linear sweep voltammetry methods to a high-speed wall-tube electrode (HWTE) is reported. Experiments are reported for the oxidation of N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) in propylene carbonate solution containing 0.10 M tetrabutylammonium perchlorate for a 24 μm radius platinum microdisk electrode housed within the HWTE using a range of scan rates from 200 to 3000 V s-1 and average flow jet velocities from 0.24 to 9.4 m s-1 (corresponding to volume flow rates of 0.003-0.12 cm3 s-1, and centre-line jet velocities from 0.5 to 18.9 m s-1). Linear sweep voltammograms (LSVs) are analysed for a simple electron transfer under high volume flow rates, by curve fitting. Analysis of the transient LSVs yielded values for k0, α, and Ef0 for TMPD of (5.9±2.4)×10-2 cm s-1, 0.46±0.08 and 0.217±0.019 V (vs. Ag), respectively. This is in good agreement with independent experiments conducted using the high-speed channel electrode which yielded the results: k0=(6.3±0.4)×10-2 cm s-1, α=0.52±0.01, and Ef0=0.234±0.005 V (vs. Ag). The range of applicability of this method for measuring k0 was also investigated and compared with existing channel electrode techniques. © 2003 Elsevier B.V. All rights reserved.

We have applied the temperature jump method to the study of the properties of the electrochemical double layer formed in contact with platinum stepped surfaces vicinal to the (111) orientation. High power laser light (∼1 MW cm-2) has been used to increase the surface temperature (by ca. 15 K) of the electrode suddenly over very short time periods (∼10 ns). The resulting change of the open circuit potential has been monitored and analysed in terms of the entropies of double layer formation. The observation of two potentials where the change of the open circuit potential induced by the laser illumination is zero indicates the existence of two local maxima in the entropy of the formation of the double layer. We explain this inference in terms of the existence of cooperative effects in the formation of the structure of the adsorbed water layers, which are disrupted at the potentials where the local contributions of the step and the terrace sites to the overall entropy of formation are maximal. $ 2003 Elsevier B.V. All rights reserved.

Systems involving one and two electron redox reactions were studied under hydrothermal conditions using a novel hydrodynamic method based on a conventional channel flow cell where the working electrode was heated by radio frequency radiation. The diffusion activation parameters obtained with the radio frequency channel cell were compared with independent data from microelectrode high temperature experiments and analysed in terms of the Stokes-Einstein equation. © 2001 Elsevier Science B.V.

In situ microwave activation has been applied to the electro-deposition and stripping of palladium metal (which is widely used as a catalyst) at cavitation resistant boron-doped diamond electrodes. Focused microwave radiation leading to heating, boiling, and cavitation is explored as an option to improve the speed and sensitivity of the analytical detection procedure. The deposition and anodic stripping of palladium by linear sweep voltammetry in 0.1 M KCl (pH 2) solution and at boron-doped diamond electrodes is shown to be strongly enhanced by microwave activation due to both (i) the increase in mass transport and (ii) the increase in the kinetic rate of deposition and stripping. The temperature at the electrode surface is calibrated with the reversible redox couple Fe(CN)64−/Fe(CN)63− and found to be reach 380 K. In the presence of microwave radiation, the potential of onset of the deposition of palladium is strongly shifted positive from −0.4 to +0.1 V versus SCE. The optimum potential for deposition in the presence of microwaves is −0.4 V versus SCE and the anodic stripping peak current is shown to increase linearly with deposition time. Under these conditions, the stripping peak current varies linearly with the palladium concentration down to ca. 2 μM. At concentration lower than this a logarithmic variation of the stripping peak current with concentration is observed down to ca. 0.1 μM (for 5 min pre-concentration in presence of microwave radiation).

The application of steady-state and fast-scan linear sweep voltammetry to a high-speed wall-tube electrode (HWTE) is reported in different solvents to investigate the response of the HWTE over a wide range of Reynolds' numbers (Re). Experiments are reported for the oxidation of N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) in propylene carbonate (PC), water, butyronitrile (BN), acetonitrile (AN), and acetonitrile-water mixture solutions containing 0.10 M supporting electrolyte for a 24 μm radius platinum microdisk electrode housed within the HWTE using a range of average flow jet velocities from 0.03 to 19.8 m s-1 (corresponding to volume flow rates of 0.003-0.25 cm3 s-1 and center-line jet velocities from 0.05 to 39.5 m s-1). Fast scan linear sweep voltammetry is presented for the oxidation of TMPD in PC and of 9,10-diphenylanthracene (DPA) in AN. Theoretical results are derived using finite element methods for both one- and two-dimensional mass transport models. It is found that, for solvents with a kinematic viscosity above ca. 7.5 × 10-3 cm2 s-1, the hydrodynamic behavior for Re < 2000 is as expected with current responses in accordance with those predicted for a laminar, parabolic inlet flow profile. In low viscosity solvents, where Re < 2000, currents are lower than expected, indicating a departure from laminar flow in practical cells even at low Re. The HWTE is compared to the channel electrode in the light of the experimental results, theoretical limits of electron-transfer rate detectable, and conclusions drawn that the channel electrode is more reliable for kinetic measurements.

The effect of applied temperature was studied on various non-aqueous one- and two-electron systems of ferrocene, tris(4-bromophenyl)amine and N,N,N′,N′-tetramethyl-1,4-phenylenediamine in acetonitrile solvent at both radio frequency channel cell (RFCC) and microdisk electrode apparatus. Experimentally obtained diffusion coefficients (Dc) and activation energies (EA) for both RFCC and microelectrode experiments are in excellent agreement with each other and published data. Analysis of the data in terms of the Stokes-Einstein equation is also presented. This expands on previous work done in this area to incorporate not only solvent-based systems in addition to simple aqueous electrochemistry, but also more mechanistically complex electrode processes with coupled homogeneous kinetics such as ECE reactions. The application of the RFCC as a tool for mechanistic studies is discussed with the investigation of the well characterised ECE reaction of m-iodo-nitrobenzene in acetonitrile, giving a value of 80 ± 5 kJ mol-1 for the activation energy of the rate constant for the decomposition of the m-iodo-nitrobenzene radical anion. This represents, to the authors' knowledge, the first example of a quantitative, fully modelled investigation of a mechanistically complex electrochemical process at a locally heated electrode. © 2001 Elsevier Science B.V. All rights reserved.

The design and operation of the first ever in situ EPR cell for studying charge-transfer processes accompanying polarisation of the liquid/liquid interface is presented as well as EPR absorption data obtained from the reduction of TCNQ (to TCNQ. - ) and the oxidation of TTF (to TTF. + ) by the ferro–ferri-cyanide redox couple at the water/1,2-dichloroethane interface.

Using FIDAP, a finite element method simulation package, investigations into the effect of inlet wall thickness on the flow pattern occurring in the wall tube electrode or microjet electrode have been carried out. Simulation results show that vortex formation, observed above minimum solution velocity thresholds and missing from analytical treatments describing the flow, can have a critical effect on the hydrodynamics and hence on measured limiting currents. In addition, the current response for different-sized ring electrodes has been simulated at a range of speeds and suggests that the thickness of the jet tube wall and vortex formation can have an effect at both of these electrodes and radially offset microdisks. The latter are often used experimentally via the empirical maximization of observed currents. The dangers of applying approximate theory to these surprisingly complex devices are stressed.

High intensity microwave radiation effects are demonstrated for electron transfer processes at 25 or 50-μm diameter platinum electrodes immersed in micellar sodium dodecylsulfate (SDS) solutions. First, a solution containing 2 mM Fe(CN) 63- and 2 mM Fe(CN) 64- in aqueous 0.1 M NaCl with and without SDS is employed to calibrate the electrode temperature and mass transport conditions. Addition of 0.1 M SDS has only a small effect on the microwave enhanced voltammetry for the Fe(CN) 63-/4- system. Next, two highly water-insoluble redox systems are studied. A solution of 1 mM tert-butylferrocene in aqueous 0.1 M NaCl containing 0.1 M SDS is shown to give no current response in the absence of microwaves. In the presence of focused microwaves at a platinum disc electrode, a strong current for the one electron oxidation of tert-butylferrocene is detected presumably due to localized disruption of the micellar solution. Concentrations of tert-butylferrocene down to the micromolar level are detected. α-Tocopherol, a lipophilic vitamin and antioxidant, is soluble in aqueous 0.1 M SDS/0.1 M NaCl. In the presence of microwave radiation, a strong and concentration dependent anodic current response consistent with the two-electron oxidation of α-tocopherol is observed. A heptode array of seven individual 50 μm diameter platinum microelectrodes placed in ca. 720 μm distance of each other is shown to allow microwave enhanced currents to be increased sevenfold with each electrode exhibiting the same microwave effect. © Springer-Verlag 2005.

An apparatus for the measurement of steady-state microelectrode voltammetry at elevated temperatures is described. The scope of this experimental approach as a method for the determination of diffusion coefficients at variable temperatures in the case of simple one-electron processes is demonstrated. Diffusion coefficients over a range of temperatures are derived for N,N,N′N′-tetramethylphenylenediamine in both acetonitrile and water solvents, tris-4-bromophenylamine in acetonitrile, and ferrocene in acetonitrile and dimethylformamide from which activation energies for diffusion are obtained. Diffusion coefficient values are used to derive Stokes-Einstein radii for each species in solution. The electroreductions of o-bromonitrobenzene in dimethylformamide and 9-chloroanthracene in acetonitrile are studied as a function of temperature and activation energies estimated for carbon-halide bond cleavage in the corresponding radical anions.

In situ microwave activation of electrochemical processes in a novel electrochemical cell, in which intense microwave radiation is focused locally into the region at the electrode surface-solution interface, is shown to allow high-temperature voltammetry experiments at 100 μm Pt disk electrodes. Factors such as the cell geometry and the deposition of a thin film of mercury are shown to influence the microwave effect. The detection of trace metals or impurities by anodic stripping voltammetry is a routinely applied procedure with applications especially in rapid online monitoring, in remote place analysis, or for extremely dilute samples. For cadmium detect on by anodic stripping voltammetry microwave radiation is demonstrated to strongly affect the accumulation process but not the stripping process. Calibration of the effects induced by microwave radiation on the experimentally observed voltammetric data, based on the equilibrium potentials for the Fe(CN)6/(4-/3-) and the Ru(NH3)6/(3+/2+) redox systems, demonstrates that the data obtained are consistent with a thermally enhanced process. The temperature achievable at the electrode-solution interface before boiling and cavitation occurs, is shown to be strongly dependent on the type of electrode material and surface morphology. At a mercury film electrode deposited on platinum temperatures in excess of 150°C can be applied in voltammetric experiments in a constant heating mode.

A novel approach to thermoelectrochemistry is presented which involves the direct heating of the working electrode in a channel flow cell system by eddy currents caused by 8 MHz radio frequency (Rf) radiation. For the model redox systems Fe(CN)63−/4− and Ru(NH3)63+/2+ it is shown that it is possible to perform electrochemical experiments with simultaneous thermal activation at temperatures close to the boiling point of the electrolyte solution. Quantitative analysis of data obtained from thermoelectrochemical studies in the Rf-heated channel flow system is possible with the help of a computer model. Numerical simulation results obtained with a finite element program (FIDAP™) for the complex heat and mass flow during voltammetric experiments at the heated electrode are shown to be in quantitative agreement with experimental data. Both the increase in the rate of diffusion as well as the change in the flow pattern in the heated low viscosity region of the channel are shown to contribute significantly to the enhanced mass transport. After confirming the quantitative agreement of the numerical model with the data obtained for the oxidation of Fe(CN)64− and the reduction of Fe(CN)63− in 0.1 M KCl, the activation energy for the Ru(NH3)63+/2+ redox system diffusion in 0.1 M KCl is determined.

Illumination of the surface of a Au(111) single-crystal electrode with short pulses of high-power laser light has been used to produce a sudden increase of its temperature. From the evolution of the open circuit potential during the temperature relaxation after the laser pulse, it is possible to obtain a relative measurement of the entropy of formation of the double layer. The electrode potential, where the potential transient is zero, has been identified with the potential of maximum entropy of formation of the double layer. This methodology has been applied to study the double layer formed between the Au(111) electrode and perchloric and sulfuric acid solutions. In both cases, it has been found that the potential of maximum entropy is located slightly negative to the potential of zero charge, corresponding to a negative contribution of the water-dipole moments to the electrode-solution potential drop. In addition, in the case of sulfuric acid solutions, a sharp increase of the relaxation time after the temperature change has been observed at potentials just below the phase transition to form the (√3 × √7) adlayer. This has been explained in terms of formation of sulfate islands of reduced mobility in this potential region.

The ohmic distortion of current-voltage curves for the wall-jet hydrodynamic electrode is investigated using a finite-element approach with the circuit analysis program spice . Simulated and experimental data are presented, showing the displacement of the half-wave potential and the potential-dependent error in the Tafel slope. Error curves are given as a guide to the maximum current levels which may be used in practice with different electrolyte concentrations.

A channel electrode array, with electrodes ranging in size from the millimeter to the submicrometer scale, is used for the amperometric interrogation of mechanistically complex electrode processes. In this way, the transport-limited current, measured as a function of both electrode size and electrolyte flow rate (convection), is shown to provide a highly sensitive probe of mechanism and kinetics. The application of "two-dimensional voltammetry" to diverse electrode processes, including E, ECE, ECEE, EC', and DISP2 reactions, is reported.

In situ microwave activation is applied to the electrochemical oxidation of thiourea at low surface area (polished polycrystalline) and at high surface area (electrodeposited mesoporous platinum coated) platinum microelectrodes. The one electron oxidation of thiourea to formamidine disulfide is monitored as a function of the different activation parameters. In the absence of microwaves (ambient temperature, low mass transport) increasing the surface area (roughness) increases the thiourea oxidation response predominantly due to adsorption effects. In the presence of high microwave intensities, high mass transport and thermal effects further increase the oxidation current at mesoporous platinum. The most effective thickness of the mesoporous platinum film for the thiourea oxidation process is estimated as 3 μm independent of electrode diameter, temperature, or mass transport effects. © 2006 Wiley-VCH Verlag GmbH and Co. KGaA.

The Cd concentrations and isotopic compositions were determined for 19 water samples which cover the mixing zones of four major rivers with the coastal seas of the Siberian Shelf. The waters span salinities from about 1-32, with Cd concentrations of about 0.02-0.46nmol/kg and small but resolvable Cd isotope fractionations, with ε114/110Cd values of between +1.4 and +5.7. The data for the majority of the samples are in accord with the systematics expected for quasi-binary mixing of Arctic seawater (ε114/110Cd≈5.5±0.5 and Cd concentration between 0.1 and 0.25nmol/kg) with river waters characterized by ε114/110Cd≈+2±1 and low pristine Cd contents of about 0.02-0.06nmol/kg. The river values are similar to the inferred composition of the continental crust, which implies that weathering produces no or only limited Cd isotope fractionation. The results for five samples provide clear evidence for non-conservative behaviour of Cd, as the element is released from suspended riverine particles during mixing with seawater. The isotopic data furthermore show that the desorbed Cd is characterized by ε114/110Cd≈+3, in accord with a natural origin. This implies that the (natural) net riverine Cd fluxes of the Siberian rivers to seawater are also likely to be characterized by ε114/110Cd≈+2±1, a value that is either identical to or intermediate between the composition of the continental crust and marine deep waters. Additional data for the boreal Kalix River in Sweden contrasts with the results obtained for the Siberian rivers, as the former exhibits a much lighter Cd isotope composition of ε114/110Cd=-3.8 coupled with a much higher Cd content of ~0.24nmol/kg. These characteristics appear to be a consequence of the distinct hydro-geological setting of the Kalix drainage basin, which suggests that the riverine input of Cd isotopes to the oceans might display significant regional variability. In summary, our study underlines the important role that stable isotope analyses can play in biogeochemical investigations of trace metals. Here, the Cd isotope results provide important constraints, which are not available from concentration data alone, on the cycling of Cd in riverine and shelf environments. © 2012 Elsevier B.V.

One of the key activities during the initial phase of the international GEOTRACES program was an extensive international intercalibration effort, to ensure that results for a range of trace elements and isotopes (TEIs) from different cruises and from different laboratories can be compared in a meaningful way. Here we present the results from the intercalibration efforts on neodymium isotopes and rare earth elements in seawater and marine particles. Fifteen different laboratories reported results for dissolved 143Nd/144Nd ratios in seawater at three different locations (BATS 15 m, BATS 2000 m, SAFe 3000 m), with an overall agreement within 47 to 57 ppm (2σ standard deviation of the mean). A similar agreement was found for analyses of an unknown pure Nd standard solution carried out by 13 laboratories (56 ppm), indicating that mass spectrometry is the main variable in achieving accurate and precise Nd isotope ratios. Overall, this result is very satisfactory, as the achieved precision is a factor of 40 better than the range of Nd isotopic compositions observed in the global ocean. Intercalibration for dissolved rare earth element concentrations (REEs) by six laboratories for two water depths at BATS yielded a reproducibility of 15% or better for all REE except Ce, which seems to be the most blank-sensitive REE. Neodymium concentrations from 12 laboratories show an agreement within 9%, reflecting the best currently possible reproducibility. Results for Nd isotopic compositions and REE concentrations on marine particles are inconclusive, and should be revisited in the future.

This study reports the adsorption of arsenate, As(V), on goethite (α-FeO(OH)) and oil-coated goethite at experimental conditions chosen to mimic settings of wastewater from oil fields being released into marine and freshwater bodies. Similarities are evident between the As(V)–goethite and As(V)–oil–goethite systems: i) Adsorption is fast and saturation is achieved within 180 min, ii) Reaction rates approximate to a pseudo second order rate expression and range between 6.5 and 52.3 × 10−4 g/μmol/min, iii) Adsorption mechanisms are best described with a Langmuir model, and iv) Adsorption capacity rises with decreasing pH reflecting the increase of positive charges on the goethite surface. A difference is discernable in that the adsorption of As(V) is reduced significantly when the goethite is coated with oil. The similar experimental macroscopic observations for both systems, i.e., Langmuir model fits, reaction rates, and the effect of pH and ionic strength (I), suggest that the oil reduces the effective and/or reactive surface area. The zeta potential (ζ) indicates that the oil coating also changes the surface charge of the goethite, shifting the pH point of zero charge from 9.8 to about 3, thus contributing to the reduced As(V) adsorption. FTIR spectra show that As(V) interacts with the carbonyl functional groups of the oil. Our results suggest that oil-covered goethite significantly reduces the adsorption of As(V) and this points to a potentially significant indirect effect of oil on the cycling of As(V) and other oxyanions in oil polluted waters.

The 'characteristic function' is a two-parameter function relating precision or uncertainty in analytical results to the concentration of the analyte. In previous papers, in this series, it has been shown to provide a good model of precision measured: (a) under reproducibility conditions and (b) under 'instrumental' conditions. The present study shows that it is also a valuable model for precision estimated under repeatability conditions. The study data were large sets of duplicated results obtained for the purposes of quality control on typical test materials in routine analysis. As the analytes exhibited concentration ranges encompassing between one and three orders of magnitude, there was ample scope to demonstrate goodness of fit to the function under different circumstances.

Analysis of naturally occurring isotopic variations is a promising tool for investigating Zn transport and cycling in geological and biological settings. Here, we present the recently installed double-spike (DS) technique at the MAGIC laboratories at Imperial College London. The procedure improves on previous published DS methods in terms of ease of measurement and precisions obtained. The analytical method involves addition of a 64Zn–67Zn double-spike to the samples prior to digestion, separation of Zn from the sample matrix by ion exchange chromatography, and isotopic analysis by multiple-collector inductively coupled plasma mass spectrometry. The accuracy and reproducibility of the method were validated by analyses of several in-house and international elemental reference materials. Multiple analyses of pure Zn standard solutions consistently yielded a reproducibility of about ±0.05‰ (2 SD) for δ66Zn, and comparable precisions were obtained for analyses of geological and biological materials. Highly fractionated Zn standards analyzed by DS and standard sample bracketing yield slightly varying results, which probably originate from repetitive fractionation events during manufacture of the standards. However, the δ66Zn values (all reported relative to JMC Lyon Zn) for two less fractionated in-house Zn standard solutions, Imperial Zn (0.10 ± 0.08‰: 2 SD) and London Zn (0.08 ± 0.04‰), are within uncertainties to data reported with different mass spectrometric techniques and instruments. Two standard reference materials, blend ore BCR 027 and ryegrass BCR 281, were also measured, and the δ66Zn were found to be 0.25 ± 0.06‰ (2 SD) and 0.40 ± 0.09‰, respectively. Taken together, these standard measurements ascertain that the double-spike methodology is suitable for accurate and precise Zn isotope analyses of a wide range of natural samples. The newly installed technique was consequently applied to soil samples and soil leachates to investigate the isotopic signature of plant available Zn. We find that the isotopic composition is heavier than the residual, indicating the presence of loosely bound Zn deposited by atmospheric pollution, which is readily available to plants. Figure Zinc isotope ratio pools of bulk soil and the associated acid leach (estimated plant available pool) as measured by double-spike MC-ICPMS. δxZnLyon-JMC=(Rsample/RJMC-Lyon -1)x103, where Rsample and RJMC-Lyon denote the xZn/64Zn isotope ratio of the sample and standard (JMC-Lyon), respectively, and where x denotes either 66 or 68.

We combined micro computer tomography with Fe and Si isotope measurements of Mokoia, Allende and Grosnaja chondrules. Ten Mokoia chondrules contain 0.9 to 11.8 vol.% opaque phases (metal + sulfide), and 6 Allende chondrules contain 0.0 to 6.6 vol.% opaque phases. Hence, the Fe isotope composition of many chondrules is dominated by the Fe isotope composition of their opaque phases. We studied Fe isotopes of 35 bulk chondrules. The range is different for each of the three meteorites studied and largest for Allende with δ 56 Fe ranging from − 0.82 to + 0.37‰. Six out of seven chondrules analysed for their Si isotope composition in Mokoia and Grosnaja have similar δ 29 Si of around − 0.12‰. One anomalous chondrule in Mokoia has a δ 29 Si of + 0.58‰. We exclude isotopically heterogeneous chondrule precursors and different isotopic chondrule reservoirs as the source of the observed Fe isotope variation among bulk chondrules. We conclude that the observed bulk chondrule Fe isotope variation is the result of evaporation and re-condensation processes in a nebula setting with high dust densities, required to explain the comparatively low isotope fractionations. Subsequent parent body alteration slightly overprinted this pre-accretionary Fe isotope variation.

The impact of Sb(III) on the removal of As(III) from solution with activated alumina (AA), a widely employed low cost sorbent for various types of water treatments, was assessed. Adsorption isotherms were determined for binary element systems with As/Sb concentration ratios of 5:1, 9:1, and 12:1 to mimic conditions in water treatment facilities. These were compared to those established for single element systems. There was an increase in Sb(III) adsorption in the binary system compared to the Sb(III) only system. Conversely, in binary systems, As(III) adsorption decreased compared to the As(III) only system. These effects were similar at low and high As(III) concentrations (20 and 240 μg/mL, respectively) and at low and high pH (7.2 and 9.2). Adsorption in single element systems was well-modeled using Freundlich theory (R2 ≥ 0.92). For As: log qe = 0.521 log Ce − 0.064; Kf = 1.066, 1/n = 0.52. For Sb: log qe = 0.703 log Ce − 0.258; Kf = 0.552, 1/n = 0.70. The equation and constants determined for As(III) ...

The ‘characteristic function’ $$ \sigma = \sqrt {\alpha^{2} + \left( {\beta c} \right)^{2} } ,$$ with two empirically determined parameters α and β, is proposed as a general purpose function to describe the variation of precision (in terms of standard deviation σ), or uncertainty, with analyte concentration c (here denoting any compositional quantity), for specific analytical methods applied to a defined type of test material. In this study it is applied to examples of analytical data collected under ‘instrumental’ conditions for estimating precision. The function fitted the data well, with no systematic lack of fit. The study therefore extends the range of applications of this function.