Differential Pulse Adsorptive Stripping Voltammetry Research Articles

Waste hazelnut shell based effective hydrothermal carbon/SnO2 nanoparticles: Towards electrochemical sensing of catechol in green tea, fruit juice, and urine samples

This study focused on the electrochemical detection of catechol (CC), a carcinogenic for humans and a periodic environmental pollutant found in consumed food and beverages and has low degradability and high toxicity in the ecological environment. Also, in this study, for the first time, a new and green electrochemical detection platform was developed for the detection of CC through green carbon material (HZ) recycled from waste hazelnut shells with the hydrothermal carbonization technique (HTC) and SnO2 nanoparticles (NPs). The morphology, surface chemistry, chemical structure, and physicochemical properties of the synthesized green-based functional carbon material and SnO2 NPs were thoroughly investigated and elucidated using different characterization techniques. Thus, a green perspective was contributed to the studies of researchers working on CC detection in designing new types of nanosensors and developing electrode modifications. On GCE with an HZ-SnO2 modification, the effects of pH, the supporting electrolyte, and the scan rate on the electrochemical behavior of CC were investigated. The limit of detection (LOD) of the proposed nanosensor for CC was determined as 8.51 nM and the linearity range was determined as 0.80–80 µM under optimal conditions using adsorptive stripping differential pulse voltammetry (AdsDPV).The developed new type, the green method, has been performed to detect the CC in green tea, fruit juice, and urine samples with sufficient accuracy and precision.

Biochar from sugarcane bagasse: Synthesis, characterization, and application in an electrochemical sensor for copper (II) determination

Biochar (BC) is a carbonaceous material obtained from the thermal decomposition of organic matter under limited oxygen supply that plays an attractive role in waste management. In this study, biochar was prepared from sugarcane bagasse, using pyrolysis temperatures from 300 to 700 °C, and chemically activated with HNO3. Structural characterizations showed that degradation increased as pyrolysis temperature increased. Furthermore, a higher number of functional groups were observed for the materials produced under the lowest temperatures. Chemical activation resulted in oxidation and nitration of carbonaceous structure, increasing the number of functional groups on the materials. All materials were evaluated for the construction of electrochemical sensors towards Cu2+ ions voltammetric determination. The material produced at 400 °C pyrolysis temperature and activated (BCA400) provided the most intense response, which can be related to the presence of one of the highest numbers of surface groups, such as oxygen groups, on it. A method for Cu2+ determination was successfully developed based on differential pulse adsorptive stripping voltammetry (DPAdSV). A linear dynamic range (LDR) from 1.0 to 15.0 μmol L−1 was achieved, with limit of detection (LOD) of 0.36 μmol L−1, and limit of quantification (LOQ) of 1.09 μmol L−1. The method was also adequate in terms of accuracy and precision, as well as selective against most cationic species commonly found in tap water. The analyte was determined in tap water samples, in natura and spiked with the maximum concentration allowed by Brazilian legislation, and successful recovery values were obtained. Therefore, biochar from sugarcane bagasse, an environmentally-friendly material, was successfully used to construct an electrochemical sensor and determining an environmental and health interest analyte.

A simple and reliable electrochemical method employing an unmodified boron-doped diamond electrode for the determination of triclocarban

Since the advent of the COVID-19 pandemic, triclocarban-containing cleaning products have been increasingly consumed. As triclocarban is an emerging compound, it is necessary to develop new sensors for its monitoring. So, a simple and reliable electroanalytical method for the determination of triclocarban using an unmodified boron-doped diamond electrode was developed. The application of a cathodic pretreatment (−2.0 V, 30 min, 0.5 mol L−1 H2SO4) on the electrode surface provided higher current intensities and lower resistance to charge transfer in contrast to the non-treated surface. On the diamond electrode surface, the triclocarban showed an irreversible behavior with two oxidation peaks at +1.10 and +1.40 V vs. Ag/AgCl, KCl(sat). The hypothesis for removing hydrogens of both amide groups of the triclocarban structure was supported by computational methodology which also explained the broadened oxidation peaks and the distance between them. The calibration curve for triclocarban, obtained by using differential pulse voltammetry in a supporting electrolyte composed of McIlvaine buffer (pH 3.0) and ethanol (80:20 v/v), covered a concentration range of 1.0 to 50 μmol L−1, and it exhibited a detection limit of 0.31 μmol L−1 under optimized experimental conditions. Using an accumulation time of 120 s at open circuit potential, a calibration curve by differential pulse adsorptive stripping voltammetry was constructed in a range of 0.05 to 20 µmol L−1 of triclocarban, with a detection limit of 18 nmol L−1. Triclocarban quantification assays were carried out on samples of antibacterial soaps and river water, and data were recorded with acceptable precision and accuracy.

Combined colorimetric and electrochemical screening method using 3D printed devices: Towards the selective detection of MDMA in forensic samples

This study introduces a new approach that combines the benefits of colorimetric and electrochemical techniques for the selective detection of 3,4-methylenedioxymethamphetamine (MDMA) in forensic samples using a 3D-printed electrochemical device. We propose and implement a two-step strategy integrating Simon's test with differential pulse adsorptive stripping voltammetry (AdSDPV). Simon's test employs sodium nitroprusside, acetaldehyde, and sodium carbonate, while the electrochemical analysis is performed using AdSDPV on a 3D-printed graphite/polylactic acid (Gr/PLA) electrode in a dual-cell configuration. Initially, MDMA is identified by a color shift from pink to dark purple in Simon's test and is subsequently confirmed by observing changes in the electrochemical behavior on the 3D-printed Gr/PLA electrode, both before and after the colorimetric reaction. MDMA exhibits two characteristic oxidation processes: O1 at +0.9 V and O2 at +1.1 V (vs. Ag pseudo-reference). Following Simon's test, an additional oxidation process emerges with a distinct peak potential (PSimon) at +0.38 V (vs. Ag pseudo-reference). Moreover, the peak currents of O1 and O2 decrease after the Simon's test reaction, further confirming the MDMA presence. The method demonstrates a broad linear range (1 to 175 µM) and a low limit of detection (0.1 µM) for MDMA. It achieves a good stability in electrochemical responses (RSD < 5 %) using either a single electrode (N = 5) or different electrodes (N = 3). The integrated approach, combining Simon's test and AdSDPV, effectively identifies MDMA, even in samples containing 3,4-methylenedioxyamphetamine (MDA). This method provides a robust, straightforward, and rapid selective screening tool for MDMA identification and quantification, leveraging three distinct responses: one colorimetric and two electrochemical (pre and post colorimetric reaction).

Voltammetric determination of genotoxic 4‐nitroindane at a mercury meniscus modified silver solid amalgam electrode

AbstractA silver solid amalgam electrode modified with mercury meniscus (m‐AgSAE) was used as a non‐toxic replacement of mercury electrodes in the voltammetric determination of genotoxic environmental pollutant 4‐nitroindane (4‐NI). The m‐AgSAE was used to characterize of the overall electrode process during the 4‐NI conversion using cyclic voltammetry (CV), and it was shown that the electrochemical reduction of 4‐NI is an irreversible process controlled by both diffusion and adsorption. Techniques of direct current voltammetry (DCV) and differential pulse voltammetry (DPV) at the m‐AgSAE were optimized for the development of a method for the sensitive determination of 4‐NI. The application of the more convenient DPV method was proven on authentic drinking and river water samples. Limits of quantification (LQs) obtained under the following optimal conditions were 0.1 μmol L−1 for DCV at the m‐AgSAE (Britton‐Robinson (BR) buffer pH 5.0–methanol (1 : 1); regeneration potentials E1,reg=−200 mV, E2,reg=−1100 mV) and 0.1 μmol L−1 for DPV at the m‐AgSAE (BR buffer pH 9.0–methanol (1 : 1); regeneration potentials E1,reg=−300 mV, E2,reg=−1300 mV). An attempt to decrease the LQ of the 4‐NI determination by differential pulse adsorptive stripping voltammetry at the m‐AgSAE was not successful. The LQs for DPV at the m‐AgSAE in authentic samples of drinking and river water were 1.0 μmol L−1 and 2.0 μmol L−1 (BR buffer pH 9.0–drinking or river water (1 : 9); regeneration potentials E1,reg=−300 mV, E2,reg=−1300 mV), respectively.

Voltammetric Determination of Metrafenone Using an Iridium Oxide Nanoparticle – Ionic Liquid Nanocomposite Modified Glassy Carbon Electrode

In this study, the first sensitive voltammetric nanosensor was developed for the determination of metrafenone. For this purpose, iridium oxide nanoparticles (IrOxNPs) were synthesized, and a nanocomposite was formed on the glassy carbon electrode with IrOxNPs and an ionic liquid (IL). The influence of pH on the metrafenone response was examined using phosphate and Britton-Robinson buffers as a function of pH. The influence of scan rate on the response to metrafenone was investigated in pH 7.0 phosphate buffer where the highest peak current was obtained and the peak shape was good. It was concluded that the oxidation occurred by the adsorption and diffusion mechanisms. According to cyclic voltammetry measurements for metrofenone, a single irreversible anodic peak was observed in all buffer solutions. Using the relationship between the peak potential and the logarithm of the scan rate, the electron number for the oxidation process was determined to be 2. Using adsorptive stripping differential pulse voltammetry, the detection limits for standard and the serum samples were 0.08 mg/L and 0.07 mg/L, respectively, and the calibration curve was linear up to 1.4 mg/L. The developed nanosensor was also employed to analyze to commercial preparations and good recovery values were obtained.

First Acyclovir Determination Procedure via Electrochemically Activated Screen-Printed Carbon Electrode Coupled with Well-Conductive Base Electrolyte.

In this work, a new voltammetric procedure for acyclovir (ACY) trace-level determination has been described. For this purpose, an electrochemically activated screen-printed carbon electrode (aSPCE) coupled with well-conductive electrolyte (CH3COONH4, CH3COOH and NH4Cl) was used for the first time. A commercially available SPCE sensor was electrochemically activated by conducting cyclic voltammetry (CV) scans in 0.1 mol L-1 NaOH solution and rinsed with deionized water before a series of measurements were taken. This treatment reduced the charge transfer resistance, increased the electrode active surface area and improved the kinetics of the electron transfer. The activation step and high conductivity of supporting electrolyte significantly improved the sensitivity of the procedure. The newly developed differential-pulse adsorptive stripping voltammetry (DPAdSV) procedure is characterized by having the lowest limit of detection among all voltammetric procedures currently described in the literature (0.12 nmol L-1), a wide linear range of the calibration curve (0.5-50.0 and 50.0-1000.0 nmol L-1) as well as extremely high sensitivity (90.24 nA nmol L-1) and was successfully applied in the determination of acyclovir in commercially available pharmaceuticals.

Voltammetric Analysis of Thiram with Bimetallic Nanosensor and Investigation of Adsorption Mechanism by DFT-D3 Method

In this study, to detect thiram electrochemically, a simple nanosensor based on a glassy carbon electrode (GCE) modified with green-synthesized Ag and Au nanoparticles was designed. AuNPs@AgNPs/GCE nanosensor gave considerably greater signal for 5 ppm thiram in pH 3.0 phosphate buffer solution using adsorptive stripping differential pulse voltammetry compared to bare GCE. Under ideal conditions, the nanosensor produced a linear concentration calibration curve extending from 0.2 to 1.4 ppm for thiram, with limits of detection and quantification of 0.033 ppm and 0.100 ppm, respectively. The developed electrochemical bimetallic nanosensor demonstrated high sensitivity and stability, showing that it is a novel and promising platform for thiram determination. Furthermore, the nanosensor was used to assess thiram in human serum and recovery was obtained as 103.6%. DFT-D3 results showed that covalent modification of GCE with AuNPs/AgNPs occurs with the electron transfer between the electrode surface and thiram by bonding sulfur atoms of thiram to AgNPs and AuNPs. Both experimental and theoretical analyses showed that the modification with Ag and Au, GCE appeared to be a key property to improve the electronic activity at the surface and increase the charge transfer that facilitates the adsorption of the selected guest.

Electrochemical Study of Sunset Yellow and its Determination in Soft Drink by Differential Pulse Adsorptive Stripping Voltammetry Using Ag-ErGO/GCE

The electrochemical behavior of sunset yellow on the glassy carbon electrode modified with silver and reduced graphene oxide has been investigated by cyclic and differential pulse adsorptive stripping voltammetry. The electrochemical behavior of sunset yellow was reversible and adsorptive on the working electrode. The optimal conditions were obtained as follows: Britton-Robinson (BR) buffer at pH 8.0; adsorption potential 0.4 V; adsorption time 50 s; sweep rate 50 mV/s; linearity range from 10-7 M to 10-6 M; the limits of detection and quantitation were 2.5 × 10­-8 M and 8.3 × 10­-8 M, respectively. The procedure was successfully applied to determine sunset yellow in soft drink samples.

Use of a lab-made screen-printed sensor with chemically deposited boron-doped diamond for simple and selective electrochemical detection of the synthetic cathinone N-ethylpentylone in forensic samples

N-ethylpentylone (NEP), also known as ephylone, is a synthetic cathinone (SC) that has been banned worldwide since 2019 due to alarming cases of intoxication. However, preliminary identification of this drug is of interest in the forensic scenario. Here, a new forensic application using a lab-made screen-printed sensor with chemically deposited boron-doped diamond electrode (LM-SP/BDDE) for the detection of SCs is presented. We present, for the first time, the electrochemical behavior of NEP and its detection in forensic samples using a versatile, robust, low-cost, and simple sensor that requires a small sample volume (30 µL) for the analysis. NEP presented three irreversible and independent redox processes (O1 at +0.88 V, R1 at –1.3 V and R2 at –1.45 V), and a dependent reduction R3 at –1.6 V vs. Ag/AgCl. The proposed method for NEP detection on LM-SP/BDDE was optimized by adsorptive stripping differential pulse voltammetry (AdSDPV). The use of LM-SP/BDDE with AdSDPV provided a good stability of NEP electrochemical responses using the same electrode (n = 5), with RSD < 4.0% for all redox processes. Furthermore, wide linear ranges for NEP determination (1.0 – 100.0 µmol L − 1) with a low LOD (0.66 µmol L − 1) were obtained. Interference studies have been performed for common adulterants and other illicit drugs (semi-synthetics, amphetamines, and other SCs), and a highly selective response for NEP detection was observed. Therefore, LM-SP/BDDE combined with AdSDPV is an alternative tool for selective screening of NEP in on-site forensic analysis, providing rapid and simple preliminary identification.

Electrochemistry of the synthetic tryptamine 5-MeO-MiPT at glassy carbon and screen-printed electrodes: A rapid and simple screening method for application in forensic analysis

5-Methoxy-N-methyl-N-isopropyltryptamine (5-MeO-MiPT), also known as moxy, is a synthetic tryptamine analogue used recreationally as a hallucinogenic drug. This work investigates the electrochemical behaviour of 5-MeO-MiPT using carbon electrodes for the first time. Although 5-MeO-MiPT showed only one irreversible oxidation process at a glassy carbon electrode, many electrochemical processes were exhibited on a graphite screen-printed electrode (SPE-Gr). The oxidation reaction of 5-MeO-MiPT on both carbon electrode surfaces involves an adsorption-controlled process with the loss of one electron and one proton. A voltammetric screening method for 5-MeO-MiPT was performed in 0.1 mol L−1 phosphate buffer solution at pH 7.0 on the SPE-Gr using differential pulse adsorptive stripping voltammetry (DPAdSV). The proposed method showed a wide linear range (0.05–30.0 µmol L−1) and a sufficiently low limit of detection (0.015 µmol L−1) for application to seized forensic samples containing 5-MeO-MiPT. Good stability of the electrochemical responses for 5-MeO-MiPT detection on SPE-Gr was obtained, using the same or different electrodes (N = 3) with a relative standard deviation of less than 4.0%. Interference studies with other drugs demonstrated that the proposed sensor is selective for electrochemical screening of 5-MeO-MiPT. In addition, 5-MeO-MiPT was identified in a biological sample of synthetic urine and in real seized samples by the proposed method and confirmed by GC-MS. The analytical performance of SPE-Gr with DPAdSV for 5-MeO-MiPT detection shows great potential as a simple, fast, and selective screening method in forensic scenarios.

Electrochemistry of 5F-MDMB-PICA synthetic cannabinoid using a boron-doped diamond electrode with short anodic-cathodic pretreatment: A simple screening method for application in forensic analysis

This work presents, for the first time, the electrochemical detection of methyl(2S)-2-{[1-(5-fluoropentyl)-1H-indole-3-carbonyl]amino}-3,3-dimethyl butanoate (5F-MDMB-PICA), which is one of the most reported synthetic cannabinoids (SCs) in seized forensic samples. The 5F-MDMB-PICA detection is based on adsorptive stripping differential pulse voltammetry (AdSDPV) using a boron-doped diamond electrode (BDDE) with short anodic-cathodic pretreatment. This SC exhibited an irreversible oxidation process at around +1.2 V on a BDDE (vs. Ag|AgCl|KCl(sat.)) in 0.1 mol L−1 H2SO4. The proposed method presents a wide linear range (1.0 to 100 µmol L−1) for 5-MDMB-PICA determination and a low limit of detection (0.09 µmol L−1). The selectivity for 5F-MDMB-PICA detection at the BDDE using AdSDPV was evaluated using six other SCs and no interference was observed. In addition, the BDDE showed a good stability of 5F-MDMB-PICA electrochemical responses. Addition-recovery studies in real seized samples presented results close to 100%. Therefore, the combination of BDDE with AdSDPV demonstrates a great potential for a simple and fast screening of 5F-MDMB-PICA and an on-site application in forensic analysis.

The validity of using bare graphite electrode for the voltammetric determination of paracetamol and caffeine

The validity of applying the readily available bare spectroscopic graphite electrode in the pharmaceutical analysis as a cost-effective, simple, and efficient alternative to the modified carbon-based electrodes was evaluated in this work using paracetamol and caffeine as test analytes. The cyclic voltammetry study on their electrochemical behavior revealed that paracetamol and caffeine display well-expressed oxidation peaks at potentials of typically 0.51 V and 1.36 V vs. Ag, AgCl/KClsat, correspondingly and that their oxidation is an adsorption-controlled process. Then the bare spectroscopic graphite electrode was applied for the separate and individual determination of the test analytes by differential pulse adsorptive stripping voltammetry. Under optimized experimental conditions (3 min accumulation time, pH 5.0) the electrode exhibited a linear response to paracetamol in the range from 5 μmol L−1 to 150 μmol L−1 and to caffeine in the range from 5 μmol L−1 to 60 μmol L−1. The detection limit achieved (0.2 μmol L−1 for each of the analytes) was found to be sufficient to carry out paracetamol and/or caffeine analysis in drugs. The results were validated by separate and individual paracetamol and caffeine determinations in commercial tablets with satisfactory recovery values (98.90–101.85 %). The presence of common pharmaceutical excipients did not affect the paracetamol and/or caffeine voltammetric response.

Sensitive and Selective Voltammetric Sensor Based on Anionic Surfactant-Modified Screen-Printed Carbon for the Quantitative Analysis of an Anticancer Active Fused Azaisocytosine-Containing Congener

3-(4-Nitrophenyl)-8-(2,3-dimethylphenyl)-7,8-dihydroimidazo[2,1-c][1,2,4]triazin-4(6H)-one (NDIT) is one of the most promising candidates for anticancer agents. Hence, a sensitive and selective sodium dodecyl sulfate-modified screen-printed carbon sensor (SPCE/SDS) was used for its quantitative analysis. The SPCE/SDS, in contrast to the SPCE, showed excellent behavior in the electrochemical reduction of NDIT by differential-pulse adsorptive stripping voltammetry (DPAdSV). Cyclic voltammetric (CV) studies reveal an irreversible, two-stage and not purely diffusion-controlled reduction process in 0.01 M HNO3. The sensor was characterized by CV and electrochemical impedance spectroscopy (EIS). Under the optimized conditions (t 45 s, ΔE 175 mV, ν 150 mV/s, and tm 5 ms), the DPAdSV procedure with the SPCE/SDS presented a very wide linear range from 1 to 2000 nM and a low detection limit of 0.29 nM. A 1000-fold excess concentration of potential interferents commonly present in biological samples did not significantly alter the peak current of NDIT. The practical application of the proposed DPAdSV procedure with the SPCE/SDS was successfully checked by analyzing spiked human serum samples.

A Zirconia‐Nanoparticles‐Modified Carbon Paste Electrode for Voltammetric Determination of Ibuprofen

AbstractZirconia‐modified carbon paste electrode (ZrO2/CPE) was prepared, characterized, and applied for efficient ibuprofen quantification by differential pulse adsorptive stripping voltammetry. The increased surface area of the modified electrode (up to 74 %), combined with the excellent zirconia adsorption performance allowed a 36 % signal increase to be achieved compared to bare CPE. Under optimized experimental conditions (69 : 1 w % graphite to ZrO2 ratio, 5 min accumulation time, pH 4.5) the ZrO2/CPE exhibited a linear response to ibuprofen in the range from 20 μmol L−1 to 250 μmol L−1. The LOD of 4 μmol L−1 (S/N=3) attained was found to be sufficient to perform ibuprofen analysis in pharmaceutical formulations. The results were validated by ibuprofen determination in commercial tablets with satisfactory recovery values (98.8–102 %). The presence of common pharmaceutical excipients did not affect the ibuprofen voltammetric response. The proposed sensor also demonstrated good reproducibility (RSD=2.84 %) and long term stability.

A portable smartphone-compatible ratiometric electrochemical sensor with ultrahigh sensitivity for anticancer drug mitoxantrone sensing

The development of reliable, sensitive, and highly stable electrochemical sensors with minimal extrinsic or intrinsic factors such as background noises, content of sensing materials, morphologies, and environmental changes is a difficult task. Here, a new sensitive nanocomposite (Ti3C2Tx-MXene) modified glassy carbon electrode (GCE) ratiometric electrochemical sensor coupled with an intrinsic built-in-correction has been developed through incorporating multi-walled carbon nanotubes (MWCNTs) to enhance conduction and methylene blue (MB) as an internal reference. Analysis of the electrochemical properties by cyclic voltammetry (CV) and adsorptive stripping differential pulse voltammetry (AdSDPV) showed an excellent electrocatalytic response for the anticancer agent mitoxantrone (MIT), even in serum and urine samples, in the linear range between 3.0 nM and 11.0 µM with a limit of detection as low as 79.15 pM, a rapid response of less than 120 s, and good anti-interference ability against multiple co-existing compounds. Additionally, no deterioration in sensitivity was observed in one month due to the strong adsorption capability of MXene towards the inner reference MB. However, GCE-modified electrodes have certain limitations, such as complicated setup and handling, electroactive material fouling, and extensive requirements for electrode washings, which cause these studies to be confined to laboratories and are not suitable for in-field use. To assist in point-of-care testing, we developed a portable, smartphone-compatible ratiometric sensor by depositing MB/Ti3C2Tx/MWCNTs on a paper substrate, which allowed the sensitive detection of MIT in serum and urine samples. The performances of GCE-modified and paper-based sensors were compared, and the advantages and disadvantages of each were discussed.

An Efficient, Simultaneous Electrochemical Assay of Rosuvastatin and Ezetimibe from Human Urine and Serum Samples.

The drug combination of rosuvastatin (ROS) and ezetimibe (EZE) is used to treat hypercholesterolemia. In this work, a simultaneous electrochemical examination of ROS and EZE was conducted for the first time. The electrochemical determination of ROS and EZE was carried out using adsorptive stripping differential pulse voltammetry (AdSDPV) on a glassy carbon electrode (GCE) in 0.1 M H2SO4. The effects of the pH, scan rate, deposition potential, and time on the detection of ROS and EZE were analyzed. Under optimum conditions, the developed sensor exhibited a linear response between 1.0 × 10-6 M and 2.5 × 10-5 M for EZE and 5.0 × 10-6 M, and 1.25 × 10-5 M for ROS. The detection limits for ROS and EZE were 3.0 × 10-7 M and 2.0 × 10-6 M, respectively. The developed sensor was validated in terms of linear range, accuracy, precision, the limit of determination (LOD), and the limit of quantification (LOQ), and it was evaluated according to ICH Guidelines and USP criteria. The proposed method was also used to determine ROS and EZE in human urine and serum samples, which are reported in terms of recovery studies.

Mixing and partially non-conservative behavior of molybdenum, uranium and vanadium along the salinity gradients of the Amazon and Pará estuaries and associated plume

The Amazon and the Pará are two major rivers that carry dissolved and suspended particulate trace metals to the Atlantic Ocean. In the dynamic mixing zone of the estuary, competing processes of trace metal sorption and release play a role, which might affect transport to the open ocean. Here we investigate the behavior of dissolved (<0.2 μm), soluble (<0.015 μm) and truly dissolved (<10 kDa and < 1 kDa) molybdenum (Mo), uranium (U), and vanadium (V) during estuarine mixing between river water (S < 1) and seawater (S > 35) end members during the high discharge period, as well as during aging of the plume in its northward flow along the coast. Molybdenum behaved conservatively during estuarine mixing and showed no colloidal fraction, suggesting Mo is solely present in the soluble or even truly dissolved fraction. Uranium behaved mostly conservatively but showed removal in the low salinity range (ca. S < 9). This is potentially due to colloidal flocculation at low salinities, as indicated by colloidal (0.015–0.2 μm) fractions of up to 30% for U but decreasing with increasing salinity until no significant difference could be discerned at S > 10. Vanadium shows a general conservative mixing, but with more scatter in the data than for Mo and U and potential removal at low to mid-salinities. Removal of V to the sediments is also indicated by surface sediment data from the mid-salinity region of the estuary but no size fractionation in the dissolved phase could be observed. Hence, V seems to be predominantly present in the soluble or even truly dissolved phase and export to the sediments might take place through particles >0.2 μm. No considerable removal or release of Mo, U and V was observed in their water column depth profiles, indicating a conservative behavior in the water column of the estuaries studied here. Additionally, we present a comparison of differential pulse adsorptive stripping voltammetry and inductively coupled plasma – mass spectrometry analyses for Mo and V, which showed excellent agreement within analytical uncertainty in this challenging sample material covering the full salinity range from freshwater to seawater.

Preparation of Multiwalled Carbon Nanotubes: Electrochemically Treated Pencil Graphite Electrodes for Nanomolar Detection of L‐Tryptophan in Complex Samples

AbstractThe present work reports a sensitive and simple sensor based on an electrochemically treated pencil graphite electrode (pre‐PGE) modified with multi‐walled carbon nanotubes (MWCNTs) for electrochemical determination of L‐tryptophan (L‐Try) detection in the presence of uric acid. Electrochemical and physical characterizations of the MWCNTs/pre‐PGE were investigated using cyclic voltammetry (CV), Electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) techniques. Under the optimized conditions, the linear working range was 0.030–200.0 μM with a limit of detection of 9.0 nM using the differential pulse adsorptive stripping voltammetry (DPAdSV) method. The proposed sensor exhibited good sensitivity, repeatability, reproducibility, and stability. The MWCNTs/pre‐PGE were successfully applied to L‐Try determination in commercial poly‐amino acid supplements with good recovery and accuracy.

Design and fabrication of a sensitive electrochemical sensor for uranyl ion monitoring in natural waters based on poly (brilliant cresyl blue).

New insights are proposed into enhancing detection of uranyl ions (UO22+) by electropolymerization brilliant cresyl blue-modified glassy carbon electrode (PBCB/GCE). The mercury-free PBCB/GCE sensor was applied to determine UO22+ in water samples by differential pulse adsorptive stripping voltammetry (DPAdSV). The unique combination of the PBCB/GCE and DPAdSV significantly improves sensitivity due to the polymer of high electroactive area and fast electron transfer rate. The DPAdSV current using a 3 mm diameter PBCB/GCE was proportional to the UO22+concentration in the range 2.0-90.0 μg·L-1 (- 0.113 V vs. SCE) with a detection limit of 0.650 μg·L-1, RSD = 3.1% (n = 10), and 4.5% reproducibility. In addition, the sensitivity for UO22+ determination was further improved at using an 1 mm diameter PBCB/GCE, which enhances the efficiency of UO22+ deposition due to its higher current density. The 1 mm diameter PBCB/GCE based on DPAdSV technique could be used to determine uranyl ions in the concentration range 0.20-2.0 μg·L-1 (- 0.113 V vs. SCE) with a detection limit of 0.067 μg·L-1, RSD = 5.7 % (n = 10) and 5.4% reproducibility. Hence, the PBCB/GCE is a suitable candidate to substitute the mercury electrode. Graphical abstract.