Zinc Supply Affects Cadmium Uptake and Translocation in the Hyperaccumulator Sedum Plumbizincicola as Evidenced by Isotope Fractionation.

This study employs stable isotope analysis to investigate the mechanisms of cadmium (Cd) and zinc (Zn) interaction in the metal hyperaccumulating plant species Sedum plumbizincicola. To this end, the Cd and Zn isotope compositions of root, stem, leaf, and xylem sap samples were determined during metal uptake and translocation at different Cd and Zn concentrations. The enrichment of light isotopes of both elements in plants during uptake was less pronounced at low metal supply levels, likely reflecting the switch from a low-affinity to a high-affinity transport system at lower levels of external metal supply. The lower δ114/110Cd values of xylem sap when treated with a metabolic inhibitor decreasing the active Cd uptake further supports the preference of heavier Cd isotopes during high-affinity transport. The Δ66Znplant-initial solution or Δ66Znplant-final solution values were similar at different Cd concentrations, indicating negligible interaction of Cd in the Zn uptake process. However, decreasing Zn supply levels significantly increased the enrichment of light Cd isotopes in plants (Δ114/110Cd = -0.08‰) in low-Cd treatments but reduced the enrichment of light Cd isotopes in plants (Δ114/110Cd = 0.08‰) under high Cd conditions. A systematic enrichment of heavy Cd and light Zn isotopes was found in root-to-shoot translocation of the metals. The Cd concentrations of the growth solutions thereby had no significant impact on Zn isotope fractionation during root-to-shoot translocation. However, the Δ114/110Cdtranslocation values hint at possible competition between Cd and Zn for transporters during root-to-shoot transfer and this may impact the transport pathway of Cd. The stable isotope data demonstrate that the interactions between the two metals influenced the uptake and transport mechanisms of Cd in S. plumbizincicola but had little effect on those of Zn.

An investigation of zinc isotope fractionation in cacao (Theobroma cacao L.) and comparison of zinc and cadmium isotope compositions in hydroponic plant systems under high cadmium stress.

This study aims to establish whether zinc (Zn) and cadmium (Cd) share similar physiological mechanisms for uptake and translocation in cacao plants (Theobroma cacao L.). Multiple-collector ICP-MS was used to determine the Zn stable isotope compositions in the roots, stems and leaves of 19 diverse cacao genotypes grown in hydroponics with 20 µmol L-1 CdCl2. Additional plants of one genotype were grown in hydroponic solutions containing lower Cd concentrations (0 and 5 µmol L-1 added CdCl2). Regardless of the Cd concentration used in the exposures, the Zn stable isotope compositions show the same systematic patterns in plant organs, with δ66Znroot > δ66Znstem > δ66Znleaf (δ66Zn denotes relative differences in 66Zn/64Zn ratios in parts per thousand). The mean Zn stable isotope fractionation between the plants and the hydroponic solutions was ε66Znuptake = -1.15 ± 0.36‰ (2SD), indicating preferential uptake of isotopically light Zn by plants from the hydroponic solution. The mean  stable isotope fractionation factor associated with translocation of Zn from roots to shoots, ε66Znseq-mob = + 0.52 ± 0.36‰ (2SD), shows that isotopically heavy Zn is preferentially sequestered in the cacao roots, whilst isotopically light Zn is mobilised to the leaves. A comparison with the Cd stable isotope compositions of the same plants shows that both isotopically light Zn and Cd are preferentially taken up by cacao plants. In contrast to Zn, however, the cacao roots retain isotopically light Cd and transfer isotopically heavy Cd to the leaves.

Nucleosynthetic isotope anomalies of zinc in meteorites constrain the origin of Earth's volatiles.

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 stable isotope analysis reveals Zn dyshomeostasis in benign tumours, breast cancer, and adjacent histologically normal tissue.

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 < 0.0001), whereas δ66Zn is 0.17‰ lower in MT than HT (p = 0.017). Benign tumour Zn concentrations are also elevated compared to HT (p = 0.00013), but are not significantly elevated compared to NAT(BT) (p = 0.32). The δ66Zn of BT is 0.15‰ lower than in NAT(BT) (p = 0.045). The similar light δ66Zn of BT and MT compared to HT and NAT may be related to the isotopic compensation of increased metallothionein (64Zn-rich) expression by activated matrix metalloproteinase (66Zn-rich) in MT, and indicates a resultant 66Zn-rich reservoir may exist in patients with breast tumours. Zinc isotopic compositions thus show promise as a potential diagnostic tool for the detection of breast tumours. The revealed differences of Zn accumulation in healthy and tumour-adjacent tissues require additional investigation.

Evaluation of Optimized Procedures for High-Precision Lead Isotope Analyses of Seawater by Multiple Collector Inductively Coupled Plasma Mass Spectrometry.

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.

Cadmium isotope fractionation in the soil - cacao systems of Ecuador: a pilot field study.

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 δ114/110Cd of about -0.1‰ to 0‰. Two 0-5 cm topsoils, however, have high Cd concentrations coupled with heavy Cd isotope compositions of δ114/110Cd ≈ 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 Δ114/110Cdleaf-soil values of 0.22 ± 0.07‰ to 0.41 ± 0.09‰. In contrast, the data reveal differences in Δ114/110Cdbean-leaf that may be linked to distinct cacao cultivars. In detail, Δ114/110Cdbean-leaf values of -0.34‰ to -0.40‰ 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‰). 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.

High Precision Zinc Stable Isotope Measurement of Certified Biological Reference Materials Using the Double Spike Technique and Multiple Collector-ICP-MS.

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.

Improvements in Cd stable isotope analysis achieved through use of liquid-liquid extraction to remove organic residues from Cd separates obtained by extraction chromatography.

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.

Tracing anthropogenic thallium in soil using stable isotope compositions.

Thallium stable isotope data are used in this study, for the first time, to apportion Tl contamination in soils. In the late 1970s, a cement plant near Lengerich, Germany, emitted cement kiln dust (CKD) with high Tl contents, due to cocombustion of Tl-enriched pyrite roasting waste. Locally contaminated soil profiles were obtained down to 1 m depth and the samples are in accord with a binary mixing relationship in a diagram of Tl isotope compositions (expressed as ε(205)Tl, the deviation of the (205)Tl/(203)Tl ratio of a sample from the NIST SRM 997 Tl isotope standard in parts per 10(4)) versus 1/[Tl]. The inferred mixing endmembers are the geogenic background, as defined by isotopically light soils at depth (ε(205)Tl ≈ -4), and the Tl emissions, which produce Tl-enriched topsoils with ε(205)Tl as high as ±0. The latter interpretation is supported by analyses of the CKD, which is also characterized by ε(205)Tl ≈ ± 0, and the same ε(205)Tl value was found for a pyrite from the deposit that produced the cocombusted pyrite roasting waste. Additional measurements for samples from a locality in China, with outcrops of Tl sulfide mineralization and associated high natural Tl backgrounds, reveal significant isotope fractionation between soils (ε(205)Tl ≈ +0.4) and locally grown green cabbage (ε(205)Tl between -2.5 and -5.4). This demonstrates that biological isotope fractionation cannot explain the isotopically heavy Tl in the Lengerich topsoils and the latter are therefore clearly due to anthropogenic Tl emissions from cement processing. Our results thus establish that isotopic data can reinforce receptor modeling for the toxic trace metal Tl.

A new methodology for precise cadmium isotope analyses of seawater.

Previous studies have revealed considerable Cd isotope fractionations in seawater, which can be used to study the marine cycling of this micronutrient element. The low Cd concentrations that are commonly encountered in nutrient-depleted surface seawater, however, pose a particular challenge for precise Cd stable isotope analyses. In this study, we have developed a new procedure for Cd isotope analyses of seawater, which is suitable for samples as large as 20 L and Cd concentrations as low as 1 pmol/L. The procedure involves the use of a (111)Cd-(113)Cd double spike, co-precipitation of Cd from seawater using Al(OH)(3), and subsequent Cd purification by column chromatography. To save time, seawater samples with higher Cd contents can be processed without co-precipitation. The Cd isotope analyses are carried out by multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The performance of this technique was verified by analyzing multiple aliquots of a large seawater sample that was collected from the English Channel, the SAFe D1 seawater reference material, and several samples from the GEOTRACES Atlantic intercalibration exercise. The overall Cd yield of the procedure is consistently better than 85% and the methodology can routinely provide ε (114/110)Cd data with a precision of about ±0.5 ε (2sd, standard deviation) when at least 20-30 ng of natural Cd is available for analysis. However, even seawater samples with Cd contents of only 1-3 ng can be analyzed with a reproducibility of about ±3 to ±5 ε. A number of experiments were furthermore conducted to verify that the isotopic results are accurate to within the quoted uncertainty.

Measurement of zinc stable isotope ratios in biogeochemical matrices by double-spike MC-ICPMS and determination of the isotope ratio pool available for plants from soil.

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 (64)Zn-(67)Zn 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 δ(66)Zn, 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 δ(66)Zn 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 δ(66)Zn 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.

The effect of crude oil on arsenate adsorption on goethite.

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.

Accurate and precise zinc isotope ratio measurements in urban aerosols.

We developed an analytical method and constrained procedural boundary conditions that enable accurate and precise Zn isotope ratio measurements in urban aerosols. We also demonstrate the potential of this new isotope system for air pollutant source tracing. The procedural blank is around 5 ng and significantly lower than published methods due to a tailored ion chromatographic separation. Accurate mass bias correction using external correction with Cu is limited to Zn sample content of approximately 50 ng due to the combined effect of blank contribution of Cu and Zn from the ion exchange procedure and the need to maintain a Cu/Zn ratio of approximately 1. Mass bias is corrected for by applying the common analyte internal standardization method approach. Comparison with other mass bias correction methods demonstrates the accuracy of the method. The average precision of delta(66)Zn determinations in aerosols is around 0.05 per thousand per atomic mass unit. The method was tested on aerosols collected in Sao Paulo City, Brazil. The measurements reveal significant variations in delta(66)Zn(Imperial) ranging between -0.96 and -0.37 per thousand in coarse and between -1.04 and 0.02 per thousand in fine particular matter. This variability suggests that Zn isotopic compositions distinguish atmospheric sources. The isotopic light signature suggests traffic as the main source. We present further delta(66)Zn(Imperial) data for the standard reference material NIST SRM 2783 (delta(66)Zn(Imperial) = 0.26 +/- 0.10 per thousand).

Microwave-enhanced electro-deposition and stripping of palladium at boron-doped diamond electrodes.

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 0.1M 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)(6)(4-)/Fe(CN)(6)(3-) and found to be reach 380K. In the presence of microwave radiation, the potential of onset of the deposition of palladium is strongly shifted positive from -0.4 to +0.1V versus SCE. The optimum potential for deposition in the presence of microwaves is -0.4V 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. 2muM. At concentration lower than this a logarithmic variation of the stripping peak current with concentration is observed down to ca. 0.1muM (for 5min pre-concentration in presence of microwave radiation).

Microwave induced jet boiling investigated via voltammetry at ring-disk microelectrodes.

High intensity microwave radiation is (self-)focused at metal electrodes immersed in aqueous electrolyte solutions to generate highly localized superheating and convection effects. It is shown that, for an electrode pointing downward, low intensity microwave radiation causes density driven convective flow (upward), which at the onset of boiling abruptly switches to a fast jet of liquid moving away from the electrode surface (downward). This "jet-boiling" phenomenon allows extremely high rates of mass transport and mixing to be realized at the electrode surface. Cyclic voltammograms obtained at electrodes placed into a microwave field show very strong mass transport enhancement effects. Cyclic voltammograms recorded at a Pt/Pt ring-disk electrode system (r(1) = 25 microm, r(2) = 32 microm, r(3) = 32.4 microm) in the presence of microwave radiation are employed to further explore mass transport effects under microwave conditions. Mass transport coefficients, collection efficiencies, and temperatures are determined as a function of microwave intensity.

Investigations into the kinetics and thermodynamics of Sb(III) adsorption on goethite (alpha-FeOOH).

This study reports thermodynamic and kinetic data of Sb(III) adsorption from single metal solutions onto synthetic aqueous goethite (alpha-FeOOH). Batch equilibrium sorption experiments were carried out at 25 degrees C over a Sb:Fe molar range of 0.005-0.05 and using a goethite concentration of 0.44 g Fe/L. Experimental data were successfully modelled using Langmuir (R2 > or = 0.891) and Freundlich (R2 > or = 0.990) isotherms and the following parameters were derived from triplicate experiments: Kf = 1.903 +/- 0.030 mg/g and 1/n = 0.728 +/- 0.019 for the Freundlich model and b = 0.021 +/- 0.003 L/mg and Qmax = 61 +/- 8 mg/g for the Langmuir model. The thermodynamic parameters determined were the equilibrium constant, Keq =1.323 +/- 0.045, and the Gibb's free energy, DeltaG0 = -0.692 +/- 0.083 kJ/mol. The sorption process is very fast. At a Sb:Fe molar ratio of 0.05, 40-50% of the added Sb is adsorbed within 15 min and a steady state is achieved. The experimental data also suggest that desorption can occur within 24 h of reaction due to the oxidation of Sb(III) on the goethite surface. Finally, calculated pH of the aqueous solution using MINTEQ2 agrees well with the measured pH (3.9 +/- 0.7; n = 30). At pH 4, the dominant Sb species in solution are Sb(OH)3 and HSbO2 which both likely adsorb as inner sphere complexes to the positively charged goethite surface.

Microwave activation of the electro-oxidation of glucose in alkaline media.

The oxidation of glucose is a complex process usually requiring catalytically active electrode surfaces or enzyme-modified electrodes. In this study the effect of high intensity microwave radiation on the oxidation of glucose in alkaline solution at Au, Cu, and Ni electrodes is reported. Calibration experiments with the Fe(CN)(6)(3-/4-) redox system in aqueous 0.1 M NaOH indicate that strong thermal effects occur at both 50 and 500 microm diameter electrodes with temperatures reaching 380 K. Extreme mass transport effects with mass transport coefficients of k(mt) > 0.01 m s(-1)(or k(mt) > 1.0 cm s(-1)) are observed at 50 microm diameter electrodes in the presence of microwaves. The electrocatalytic oxidation of glucose at 500 microm diameter Au, Cu, or Ni electrodes immersed in 0.1 M NaOH and in the presence of microwave radiation is shown to be dominated by kinetic control. The magnitude of glucose oxidation currents at Cu electrodes is shown to depend on the thickness of a pre-formed oxide layer. At 50 microm diameter Au, Cu, or Ni electrodes microwave enhanced current densities are generally higher, but only at Au electrodes is a significantly increased rate for the electrocatalytic oxidation of glucose to gluconolactone observed. This rate enhancement appears to be independent of temperature but microwave intensity dependent, and therefore non-thermal in nature. Voltammetric currents observed at Ni electrodes in the presence of microwaves show the best correlation with glucose concentration and are therefore analytically most useful.

Microwave enhanced electroanalysis of formulations: processes in micellar media at glassy carbon and at platinum electrodes.

The direct electroanalysis of complex formulations containing alpha-tocopherol (vitamin E) is possible in micellar solution and employing microwave-enhanced voltammetry. In the presence of microwave radiation substantial heating and current enhancement effects have been observed at 330 microm diameter glassy carbon electrodes placed into a micellar aqueous solution and both hydrophilic and highly hydrophobic redox systems are detected. For the water soluble Fe(CN)(6)(3-/4-) redox system in micellar aqueous solutions of 0.1 M NaCl and 0.1 M sodium dodecylsulfate (SDS) at low to intermediate microwave power, thermal effects and convection effects are observed. At higher microwave power, thermal cavitation is induced and dominates the mass transport at the electrode surface. For the micelle-soluble redox systems tert-butylferrocene and 2,5-di-tert-butyl-1,4-benzoquinone, strong and concentration dependent current responses are observed only in the presence of microwave radiation. For the oxidation of micelle-soluble alpha-tocopherol current responses at glassy carbon electrodes are affected by adsorption and desorption processes whereas at platinum electrodes, analytical limiting currents are obtained over a wide range of alpha-tocopherol concentrations. However, for the determination of alpha-tocopherol in a commercial formulation interference from proteins is observed at platinum electrodes and direct measurements are possible only over a limited concentration range and at glassy carbon electrodes.

Microwave activation in ionic liquids induces high temperature-high speed electrochemical processes.

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.