Application Of tACS Research Articles

Neurophysiological aftereffects of 10 Hz and 20 Hz transcranial alternating current stimulation over bilateral sensorimotor cortex

Alpha (8–12 Hz) and beta (13–30 Hz) oscillations are believed to be involved in motor control. Their modulation with transcranial alternating current stimulation (tACS) has been shown to alter motor behavior and cortical excitability. The aim of the present study was to determine whether tACS applied bilaterally over sensorimotor cortex at 10 Hz and 20 Hz modulates interhemispheric interactions and corticospinal excitability. Thirty healthy volunteers participated in a randomized, cross-over, sham-controlled, double-blind protocol. Sham and active tACS (10 Hz, 20 Hz, 1 mA) were applied for 20 min over bilateral sensorimotor areas. The physiological effects of tACS on corticospinal excitability and interhemispheric inhibition were assessed with transcranial magnetic stimulation. Physiological mirror movements were assessed to measure the overflow of motor activity to the contralateral M1 during voluntary muscle contraction. Bilateral 10 Hz tACS reduced corticospinal excitability. There was no significant effect of tACS on physiological mirror movements and interhemispheric inhibition. Ten Hz tACS was associated with response patterns consistent with corticospinal inhibition in 57% of participants. The present results indicate that application of tACS at the alpha frequency can induce aftereffects in sensorimotor cortex of healthy individuals.

Synchronous Neural Oscillation Between the Right Inferior Fronto-Parietal Cortices Contributes to Body Awareness.

The right inferior fronto-parietal network monitors the current status of the musculoskeletal system and builds-up and updates our postural model. The kinesthetic illusion induced by tendon vibration has been utilized in experiments on the modulation of body awareness. The right inferior fronto-parietal cortices activate during the kinesthetic illusion. We aimed to determine the relationship between the right inferior fronto-parietal cortices and body awareness by applying transcranial alternating current stimulation (tACS) to exogenously modulate oscillatory neural activity in the right fronto-parietal cortices during the kinesthetic illusion. Sixteen young adults participated in this study. We counterbalanced the order in which participants received the three types of tACS (55 Hz enveloped by 6 Hz; synchronous, desynchronous, and sham) across the subjects. The illusory movement perception induced by tendon vibration of the left extensor carpi ulnaris muscle was assessed before and during tACS. Application of synchronous tACS over the right inferior fronto-parietal cortices significantly increased kinesthetic illusion compared with sham tACS. The kinesthetic illusion during desynchronous tACS decreased from baseline. There was no change in vibration sensation during any tACS condition. The modulation of oscillatory brain activity between the right fronto-parietal cortices alters the illusory movement perception without altering actual vibration sensation. tACS over the right inferior fronto-parietal cortices is considered to modulate the neural processing involved in updating the postural model when the stimulated muscle spindle sends kinesthetic signals. This is the first study that reveals that rhythmic communication between the right inferior fronto-parietal cortices has a causal role in body awareness.

Modulation of Working Memory Using Transcranial Electrical Stimulation: A Direct Comparison Between TACS and TDCS.

Transcranial electrical stimulation (TES) has been considered a promising tool for improving working memory (WM) performance. Recent studies have demonstrated modulation of networks underpinning WM processing through application of transcranial alternating current (TACS) as well as direct current (TDCS) stimulation. Differences between study designs have limited direct comparison of the efficacy of these approaches, however. Here we directly compared the effects of theta TACS (6 Hz) and anodal TDCS on WM, applying TACS to the frontal-parietal loop and TDCS to the dorsolateral prefrontal cortex (DLPFC). WM was evaluated using a visual 2-back WM task. A within-subject, crossover design was applied (N = 30) in three separate sessions. TACS, TDCS, and sham stimulation were administered in a counterbalanced order, and the WM task was performed before, during, and after stimulation. Neither reaction times for hits (RT-hit) nor accuracy differed according to stimulation type with this study design. A marked practice effect was noted, however, with improvement in RT-hit irrespective of stimulation type, which peaked at the end of the second session. Pre-stimulation RT-hits in session three returned to the level observed pre-stimulation in session two, irrespective of stimulation type. The participants who received sham stimulation in session one and had therefore improved their performance due to practice alone, had thus reached a plateau by session two, enabling us to pool RT-hits from sessions two and three for these participants. The pooling allowed implementation of a within-subject crossover study design, with a direct comparison of the effects of TACS and TDCS in a subgroup of participants (N = 10), each of whom received both stimulation types, in a counterbalanced order, with pre-stimulation performance the same for both sessions. TACS resulted in a greater improvement in RT-hits than TDCS (F(2,18) = 4.31 p = 0.03). Our findings suggest that future work optimizing the application of TACS has the potential to facilitate WM performance.

Non-invasive Brain Stimulation: A Paradigm Shift in Understanding Brain Oscillations.

Cognitive neuroscience set out to understand the neural mechanisms underlying cognition. One central question is how oscillatory brain activity relates to cognitive processes. Up to now, most of the evidence supporting this relationship was correlative in nature. This situation changed dramatically with the recent development of non-invasive brain stimulation (NIBS) techniques, which open up new vistas for neuroscience by allowing researchers for the first time to validate their correlational theories by manipulating brain functioning directly. In this review, we focus on transcranial alternating current stimulation (tACS), an electrical brain stimulation method that applies sinusoidal currents to the intact scalp of human individuals to directly interfere with ongoing brain oscillations. We outline how tACS can impact human brain oscillations by employing different levels of observation from non-invasive tACS application in healthy volunteers and intracranial recordings in patients to animal studies demonstrating the effectiveness of alternating electric fields on neurons in vitro and in vivo. These findings likely translate to humans as comparable effects can be observed in human and animal studies. Neural entrainment and plasticity are suggested to mediate the behavioral effects of tACS. Furthermore, we focus on mechanistic theories about the relationship between certain cognitive functions and specific parameters of brain oscillaitons such as its amplitude, frequency, phase and phase coherence. For each of these parameters we present the current state of testing its functional relevance by means of tACS. Recent developments in the field of tACS are outlined which include the stimulation with physiologically inspired non-sinusoidal waveforms, stimulation protocols which allow for the observation of online-effects, and closed loop applications of tACS.

Facilitated Event-Related Power Modulations during Transcranial Alternating Current Stimulation (tACS) Revealed by Concurrent tACS-MEG.

Non-invasive approaches to modulate oscillatory activity in the brain are increasingly popular in the scientific community. Transcranial alternating current stimulation (tACS) has been shown to modulate neural oscillations in a frequency-specific manner. However, due to a massive stimulation artifact at the targeted frequency, little is known about effects of tACS during stimulation. It remains unclear how the continuous application of tACS affects event-related oscillations during cognitive tasks. Depending on whether tACS influences pre- or post-stimulus oscillations, or both, the endogenous, event-related oscillatory dynamics could be pushed in various directions or not at all. A better understanding of these effects is crucial to plan, predict, and understand outcomes of solely behavioral tACS experiments. In the present study, a recently proposed procedure to suppress tACS artifacts by projecting MEG data into source-space using spatial filtering was utilized to recover event-related power modulations in the alpha-band during a mental rotation task. MEG data of 25 human subjects was continuously recorded. After 10-minute baseline measurement, participants received either 20 minutes of tACS at their individual alpha frequency or sham stimulation. Another 40 minutes of MEG data were acquired thereafter. Data were projected into source-space and carefully examined for residual artifacts. Results revealed strong facilitation of event-related power modulations in the alpha-band during tACS application. These results provide first direct evidence that tACS does not counteract top-down suppression of intrinsic oscillations, but rather enhances pre-existent power modulations within the range of the individual alpha (= stimulation) frequency.

Low systemic exposure and calcemic effect of calcipotriol/betamethasone ointment in rats with imiquimod-induced psoriasis-like dermatitis

Vitamin D3 (VD3) analogues-containing ointments are known to occasionally cause hypercalcemia in psoriasis patients, and the frequency of hypercalcemia is suggested to vary based on the VD3 analogue used. In this study, to address the differences in calcemic effects of VD3-containing ointments, the calcemic effects of marketed VD3-containing ointments, including calcipotriol (Cal), maxacalcitol (Max), tacalcitol (Tac), calcipotriol/betamethasone dipropionate (Cal/BDP) and maxacalcitol/betamethasone butyrate propionate (Max/BBP) ointments, were evaluated in a rat model of imiquimod-induced dermatitis. The topical application of Tac, Max and Max/BBP ointments, but not Cal and Cal/BDP ointments, to the imiquimod-induced skin lesions significantly induced an increase in the serum calcium level compared with the vaseline-treated group. Calcemic effect of VD3 analogues in rats treated with VD3-containing ointments was analyzed by evaluating the expression of vitamin D receptor target genes, such as Cyp24a1, Trpv5 and CalbindinD28k, in the intestine and kidney. Real-time reverse transcription PCR (RT-PCR) analysis showed that the renal and intestinal Cyp24a1 expressions in the Cal- and Cal/BDP-treated groups were significantly lower than those in the Tac-, Max- and Max/BBP-treated groups, suggesting that systemic exposure of VD3 analogues in the Cal- and Cal/BDP-treated groups were lower than those in the other ointment-treated groups. In addition, the renal Trpv5 and CalbindinD28k expressions, calcium-transporting genes, were increased in the Max- and Max/BBP-treated groups compared with the Cal- and Cal/BDP-treated groups. Thus, because of the low systemic exposure of VD3 analogues, Cal and Cal/BDP ointments have lower calcemic effect than the other VD3-containing ointments in rats with psoriasis-like dermatitis.

P007 Comparing the efficacy of transcranial alternating current stimulation (tACS) and transcranial random noise stimulation (tRNS) on the auditory temporal resolution in patients with dyslexia

The impaired processing of rapidly changing auditory temporal features has been suggested as one key factor in development dyslexia. Voice onset time (VOT), a short period between the release of closure and the start of voicing enables to distinguish categorically between voiced (i.e./da/) and voiceless stop-consonants (i.e./ta/). VOT thus requires the precise perception and categorization of rapidly changing temporal information in the speech signal and can be considered as an important acoustic cue for the encoding of linguistically relevant information. Recently, non-invasive transcranial electrical stimulation has been suggested as a valid tool to modulate VOT-processing in healthy subjects (Heimrath et al., 2015; Rufener et al., 2016). The current study strives to assess the potential of transcranial alternating current stimulation (tACS) and transcranial random noise stimulation (tRNS) on VOT-categorization in dyslexic participants. 16 adult dyslexics (age 20–50 years) with normal hearing acuity participated in this study. All participants received on three consecutive sessions either 20 min of tRNS (100–640 Hz), 40 Hz-tACS or sham stimulation over bilateral auditory cortex region while they performed an auditory phoneme categorization task. Subsequently, a passive MMN-paradigm with a standard stimulus (voiced/da/, VOT 20 ms), two within-category deviants (VOT 24 ms, VOT 28 ms) and to between-category deviants (voiceless/ta/, VOT 32 ms, VOT 36 ms) was performed. EEG-data were recorded from three midline electrodes (Fz, Cz, Pz) with the reference electrode at the tip of the nose. We found enhanced MMN-amplitudes at the Fz-electrode for both within-category deviants after 40 Hz-tACS compared to tRNS and sham. This finding indicates that tACS but not tRNS improves the auditory temporal resolution in patients with dyslexia. Our data provides first evidence for a superior effect of tACS compared to tRNS on VOT-processing in dyslexic participants. Of note, we found increased temporal precision of the auditory system after a single session of VOT-categorization accompanied by tACS. Our finding emphasizes the clinical application of tACS in the context of impaired speech processing.

Feasibility of Online Neuromodulation Using Transcranial Alternating Current Stimulation in Schizophrenia

Abnormalities in resting and event-related brain oscillations are known to be associated with cognitive deficits in schizophrenia. Transcranial alternating current stimulation (tACS) modulates these rhythms across the neuronal circuits and could have a potential therapeutic role in psychiatric disorders. In this report, we describe, for the first time, application of online tACS in a schizophrenia patient with working memory deficits. This case report supports the feasibility and potential utility of online tACS in schizophrenia, which needs further systematic research.

Frequency-specific insight into short-term memory capacity.

The digit span is one of the most widely used memory tests in clinical and experimental neuropsychology for reliably measuring short-term memory capacity. In the forward version, sequences of digits of increasing length have to be reproduced in the order in which they are presented, whereas in the backward version items must be reproduced in the reversed order. Here, we assessed whether transcranial alternating current stimulation (tACS) increases the memory span for digits of young and midlife adults. Imperceptibly weak electrical currents in the alpha (10 Hz), beta (20 Hz), theta (5 Hz), and gamma (40 Hz) range, as well as a sham stimulation, were delivered over the left posterior parietal cortex, a cortical region thought to sustain maintenance processes in short-term memory through oscillatory brain activity in the beta range. We showed a frequency-specific effect of beta-tACS that robustly increased the forward memory span of young, but not middle-aged, healthy individuals. The effect correlated with age: the younger the subjects, the greater the benefit arising from parietal beta stimulation. Our results provide evidence of a short-term memory capacity improvement in young adults by online frequency-specific tACS application.

40 Hz-Transcranial alternating current stimulation (tACS) selectively modulates speech perception

The present study investigated the functional relevance of gamma oscillations for the processing of rapidly changing acoustic features in speech signals. For this purpose we analyzed repetition-induced perceptual learning effects in 18 healthy adult participants. The participants received either 6Hz or 40Hz tACS over the bilateral auditory cortex, while repeatedly performing a phoneme categorization task.In result, we found that 40Hz tACS led to a specific alteration in repetition-induced perceptual learning. While participants in the non-stimulated control group as well as those in the experimental group receiving 6Hz tACS considerably improved their perceptual performance, the application of 40Hz tACS selectively attenuated the repetition-induced improvement in phoneme categorization abilities.Our data provide causal evidence for a functional relevance of gamma oscillations during the perceptual learning of acoustic speech features. Moreover, we demonstrate that even less than twenty minutes of alternating current stimulation below the individual perceptual threshold is sufficient to affect speech perception. This finding is relevant in that this novel approach might have implications with respect to impaired speech processing in dyslexics and older adults.

Transcranial alternating current stimulation. Entrainment and function control of neuronal networks

Transcranial alternating current stimulation (tACS) is a new technique for the modulation of oscillatory brain activity as measured in the electroencephalogram (EEG). In contrast to well-established stimulation techniques, such as transcranial direct current stimulation and transcranial magnetic stimulation, tACS applies a sinusoidal alternating current at a specific frequency. This enables the modulation of the amplitude and frequency of endogenous brain oscillations as well as related cognitive processes. Therefore, the use of tACS has the possibility to evaluate well-known correlations between brain oscillations and cognitive processes in terms of causality. Such causal relationships have been documented in numerous neurocognitive studies on sensory, motor and perceptual processes; however, the clinical application of tACS is still in its infancy. In principle, any pathology that can reliably be connected with brain oscillations of a defined frequency is treatable. A current main focus of clinical research is on symptoms of Parkinson's disease and to a lesser degree, tinnitus. For an effective application of tACS it is important to choose the electrode positions as well as the frequency, intensity and duration of the stimulation in a theory-based and symptom-related manner. A successful therapeutic intervention requires the persistence of the tACS effect after stimulation has ceased. A mechanism that offers not only an explanation to the origin of persistent tACS effects but is also of high therapeutic benefit is neural plasticity. Therefore, one current focus of research aims at a better understanding of tACS after effects.

Stimulation is never quite as simple as it seems.

Stimulation is never quite as simple as it seems.

A novel approach for the removal of tACS artifacts from high-density EEG recordings

Event Abstract Back to Event A novel approach for the removal of tACS artifacts from high-density EEG recordings Thiago Santos Monteiro1, Kirstin F. Heise1*, Stephan P. Swinnen1 and Dante Mantini1, 2 1 KU Leuven, Faculty of Kinesiology and Rehabilitation Science, Belgium 2 ETH Zurich, Department of Health Sciences and Technology, Switzerland Concurrent application of electroencephalography (EEG) and non-invasive brain stimulation with alternating electrical current (tACS) holds great potential for retrieving information about causal relationships between neural activity and behaviour (1). Principal component analysis (PCA) is the method currently used to separate neural activity and stimulation artifacts that are mixed in EEG recordings PCA (2). Importantly, the use of PCA may alter phase relationships between target areas. Furthermore, the approach has been developed for and applied to few EEG electrodes, and has not been implemented for high-density (hd-) EEG recordings. Based on a validation procedure using real resting-state hd-EEG data and a simulated tACS artefact we compared the performance of PCA with a novel combination of advanced filtering methods (Hampel filtering based on windowed version of autoregressive modelled artefact, wAR/HF) (3). While the wAR/HF approach is more precise in removing the excessive tACS artefact from the hd-EEG signal thereby retaining the frequencies of interest (figure 1A depicts deviation from original signal after artefact removal averaged across all channels, figure 1B indicates deviation in relative power distribution), the PCA is more stable for retaining the interregional phase relationships. This work constitutes a critical methodological step to allow for the application of concurrent tACS in hd-EEG, which may permit the study of causal relationship between oscillatory activity in the brain and behaviour. Figure 1

Safety of 5 kHz tACS

BackgroundSinusoidal transcranial alternating current stimulation (tACS) at 5 kHz applied for 10 min at 1 mA intensity over the hand area of the primary motor cortex (M1) results in sustained changes in cortical excitability as previously demonstrated. ObjectiveHere we have assessed safety aspects of this stimulation method by measuring neuron-specific enolase (NSE) levels, examining electroencephalogram (EEG) traces and analyzing anatomical data by using magnetic resonance imaging (MRI). MethodsAltogether 18 healthy volunteers participated in the study. tACS was applied at 5 kHz for a duration of 10 min over the left M1 at an intensity of 1 mA. ResultsAfter stimulation no significant changes were detected in NSE levels, no structural alterations were observed in the anatomical scans and no pathological changes were found in the EEG recordings. ConclusionsOur data imply that the application of tACS is safe at least within these parameters and with these applied protocols.

Pharmacokinetics of a self-microemulsifying drug delivery system of tacrolimus

This study evaluated the pharmacokinetics of tacrolimus (Tac) in a novel self-microemulsifying drug delivery system (SMEDDS) for improved oral administration. SMEDDS Tac consisted of ethyl oleate as the oily phase, Solutol HS 15 as the surfactant and glycofurol as the co-surfactant and contained 0.5mg/mL tacrolimus. Blood and tissue concentrations of tacrolimus from two study groups (oral application of SMEDDS Tac and Prograf®) were determined using ELISA technique following tacrolimus administration in rats. There was no difference between area under the whole blood concentration–time curve in the SEDDM Tac group and the Prograf® group. Maximum concentrations of the drug were three times higher (P<0.05) in the SEDDM Tac group accompanied by a 3-fold earlier peak time. Elimination half-life was significantly lower in the SEDDM Tac group. Application of SMEDDS Tac increased tissue accumulation. Already after 15min, Tac levels of small intestine, liver, kidney, spleen, heart and bone marrow were significantly higher in the SMEDDS Tac group than in the Prograf® group (P<0.05). However, the Tac concentration in the kidney was significantly lower in the SMEDDS Tac group. Formulation of SMEDDS did not affect blood-brain barrier function. The SMEDDS is a potentially useful method for a local delivery of Tac to target organs. The selection of the optimum SMEDDS Tac composition might have advantage as an alternative oral dosage form for Tac.

The chemical chaperone 4-phenylbutyric acid attenuates pressure-overload cardiac hypertrophy by alleviating endoplasmic reticulum stress

Evidence has shown that endoplasmic reticulum stress (ERS) is associated with the pathogenesis of cardiac hypertrophy. The aim of this study was to investigate whether direct alleviation of ER stress by 4-phenylbutyric acid (PBA), a known chemical chaperone drug, could attenuate pressure-overload cardiac hypertrophy in mice. The effects of orally administered PBA (100mg/kg body weight daily for a week) were examined using mice undergoing transverse aortic constriction (TAC-mice), an animal model to produce pressure overload. TAC application for 1week led to a 1.8-fold increase in the ratio of the heart weight over body weight (HW/BW) and up-regulation of the hypertrophy markers ANF and BNF accompanied by up-regulation of ERS markers (GRP78, p-PERK, and p-elF2α). The oral administration of PBA to the TAC-mice reduced hypertrophy (19%) and severely downregulated the fibrosis-related genes (transforming growth factor-β1, phospho-smad2, and pro-collagen isoforms). We conclude that ERS is induced as a consequence of remodeling during pathological hypertrophy and that PBA may help to relieve ERS and play a protective role against cardiac hypertrophy and possibly heart failure. We suggest PBA as a novel therapeutic agent for cardiac hypertrophy and fibrosis.

T1912 Calcineurine Inhibitors Accelerate Microvascular Thrombus Formation In Vivo

Thrombotic microangiopathy (TMA) is a fatal complication that occurs after combined pancreaskidney transplantation leading to allograft dysfunction and graft loss. Immunosuppressive drugs, such as calcineurin inhibitors, have been implicated in the development of nonimmune TMA. Tacrolimus has been shown to be associated with decreased NO-production, thus contributing to thrombus formation. ADMA acts as an endogenous NO-synthase inhibitor and is considered to be a marker of endothelial dysfunction. Aim of this study was to analyse the influence of different immunosuppressants on microvascular thrombus formation in vivo and to further examine the underlying endothelial function. Using the skin fold chamber in C57BL/6J mice, microvascular thrombus formation was induced photochemically and was quantitatively analyzed by intravital fluorescence microscopy. Mice were treated with tacrolimus (TAC: 10 mg/kg/d; n = 7), cyclosporine (CYA: 5 mg/kg/d) or sirolimus (RAPA: 1,5 mg/kg/d ip) on 3 consecutive days. Control mice received NaCl 0,9 % (10 ml/kg/d ip; n = 5). Drug plasma levels were examined to ensure therapeutic doses. Additionally, the systemic circulation of sPand sE-selectin as well as ADMA plasma levels were measured by ELISA. Application of immunosuppressants produced clinically relevant plasma levels (TAC: 8 ± 2 ng/ml, CYA: 214 ± 16 ng/ml; RAPA: 9 ± 1 ng/ml). Microvascular thrombus formation was significantly accelerated in mice receiving TAC compared to control mice (arteriolar and venular occlusion: 251 ± 101s and 179 ± 27 s vs. control 818 ± 221 s and 749 ± 231 s; p < 0,05). Application of CYA significantly increased thrombus formation only in venules (276 ± 49s; p < 0,05 vs. control), whereas RAPA had no significant effect on thrombosis induction. Plasma concentrations of sP-Selectin and sE-selectin were slightly reduced after TAC and CYA application. ADMA-levels however were significantly increased in mice receiving TAC (1,28 ± 0,16 μmol/l vs. control: 0,74 ± 0,13 μmol/l; p < 0,05). The present results show that clinically relevant plasma levels of cyclosporine enhanced thrombus formation only in venules whereas tacrolimus significantly accelerates thrombus formation in arterioles and venules. This effect could be explained by increased ADMA-levels in plasma resulting in impaired NO-bioavailability and increased thrombogenicity, thus presenting a new molecular mechanism in the development of transplant-thrombosis.

Structural Characteristics and Electrode Activities of Phosphorus Incorporated Tetrahedral Amorphous Carbon Films

Studies on structural properties and electrochemical behaviors of conductive phosphorus incorporated tetrahedral amorphous carbon (ta-C:P) films deposited using filtered cathodic vacuum arc technique with PH3 as the dopant source are presently reported. The structural characteristics of the films are characterized by X-ray photoelectron spectroscopy, Raman spectroscopy and Fourier transform infrared spectroscopy. The electrochemical reactivity of ta-C:P films are evaluated by cyclic voltammetry and differential pulse voltammetry. We find that phosphorus implantation enhances the clustering of sp2 sites dispersed in sp3 skeleton, develops the densities of π and π * states and improves the electrical and electrochemical behaviors of the films. It has been established that the inorganic films with amorphous structure appear excellent electrical conductivity and electrochemical activity similar to boron-doped diamond or nitrogen-doped amorphous carbon electrodes. These characteristics demonstrate greatly potential application of ta-C:P films as electrode materials in terms of its large electrochemical potential window, low background current, and a considerable electrochemical activity towards ferricyanide reduction and metal ions analysis.

Electrochemical Properties of Phosphorus Incorporated Tetrahedral Amorphous Carbon Film Electrode

Phosphorus incorporated tetrahedral amorphous carbon (ta-C:P) film was deposited by a filtered cathodic vacuum arc technology with PH3 as the dopant source. The composition and structural characteristics were investigated by X-ray photoelectron spectroscope and Raman spectroscope, and the electrochemical behaviors of ta-C:P film were examined by cyclic voltammetry and differential pulse voltammetry. Results indicate that phosphorus implantation does not remarkably change the amorphous structure of the film but enhances the clustering of sp 2 sites dispersed in sp 3 skeleton and the evolution of structrual ordering. Ta-C:P film pretreated by acid exhibits a large electrochemical potential window and a low background current in H2SO4 solution, a considerable electrochemical activity toward Cl − , quick electrode response and a high signal for Cu 2+ and Cd 2+ analysis. These characteristics greatly demonstrate a potential application of conductive ta-C:P film as electrodes for analysis and treatment of trace metal ions in waste water.

Kinetic study reveals weak Fe-binding ligand, which affects the solubility of Fe in the Scheldt estuary

The chemistry of dissolved Fe(III) was studied in the Scheldt estuary (The Netherlands). Two discrete size fractions of the dissolved bulk (< 0.2 μm and < 1 kDa) were considered at three salinities ( S = 26, 10 and 0.3). Within the upper estuary, where fresh river water meets seawater, the dissolved Fe concentration decreases steeply with increasing salinity, for the fraction < 0.2 μm from 536 nM at S = 0.3 to 104 nM at S = 10 and for the fraction < 1 kDa from 102 nM to 36 nM Fe. Further downstream, in the middle and lower estuary, this decrease in the Fe concentration continues, but is far less pronounced. For all samples, the traditionally recognised dissolved strong organic Fe-binding ligand concentrations are lower than the dissolved Fe concentrations. Characteristics of dissolved Fe-binding ligands were determined by observing kinetic interactions with adsorptive cathodic stripping voltammetry. From these kinetic experiments we concluded that apart from the well-known strong Fe-binding organic ligands (L, log K′ = 19–22) also weak Fe-binding ligands (P) existed with an α value (binding potential = K′ · [P]) varying between 10 11.1 and 10 11.9. The presence of this relatively weak ligand explained the high concentrations of labile Fe present in both size fractions in the estuary. This weak ligand can retard or prevent a direct precipitation after an extra input of Fe. The dissociation rate constants of the weak ligand varied between 0.5 × 10 − 4 and 4.3 × 10 − 4 s − 1 . The rate constants of the strong organic ligand varied between k d = 1.5 × 10 − 3 –17 × 10 − 2 s − 1 and k f = 2.2 × 10 8–2.7 × 10 9 M − 1 s − 1 . The dissociation rate constant of freshly amorphous Fe-hydroxide was found to be between 4.3 × 10 − 4 and 3.7 × 10 − 3 s − 1 , more labile or equal to the values found by Rose and Waite [Rose, A.L., Waite, T.D., 2003a. Kinetics of hydrolysis and precipitation of ferric iron in seawater. Environ. Sci. Technol., 37, 3897–3903.] for freshly precipitated Fe in seawater. Kinetic rate constants of Fe with the ligand TAC (2-(2-Thiazolylazo)- p-cresol) were also determined. The formation rate constant of Fe(TAC) 2 varied between 0.1 × 10 8 and 3.6 × 10 8 M − 1 s − 1 , the dissociation rate constant between 0.2 × 10 − 5 and 17 × 10 − 5 s − 1 for both S = 26 and S = 10. The conditional stability constant of Fe(TAC) 2 ( β Fe(TAC)2′) varied between 22 and 23.4 for S = 10 and S = 26 more or less equal to that known from the literature (log β Fe(TAC)2′ = 22.4; [Croot, P.L., Johansson, M., 2000. Determination of iron speciation by cathodic stripping voltammetry in seawater using the competing ligand 2-(2-Thiazolylazo)- p-cresol (TAC). Electroanalysis, 12, 565–576.]). However, at S = 0.3 the log β Fe(TAC)2′ was 25.3, three orders of magnitude higher. Apparently the application of TAC to samples of low salinity can only be done when the correct β Fe(TAC)2′ is known.