Inexpensive Electrochemical Sensor Research Articles

A simple eco‐friendly carbon paste modified electrode using chitosan‐CaO nanocomposite for the voltammetric detection of the antibiotic ornidazole in real samples

AbstractHerein, an eco‐friendly, simple, inexpensive electrochemical sensor for the antibiotic ornidazole (ORN) was developed based on a carbon paste electrode modified by chitosan‐CaO nanocomposite (Chi‐CaO‐NC/CPE). Eggshell waste was utilized to prepare CaO‐NPs which were then combined with chitosan (Chi) to obtain Chi‐CaO‐NC/CPE. The prepared Chi‐CaO‐NC/CPE was characterized by different techniques such as XRD, FTIR, SEM, and EDX. The produced sensor showed higher electrocatalytic activity toward ORN in (0.1 M) PBS (pH 7.0) than the unmodified CPE. The influence of pH and scanning rate on the reduction peak of ORN implies that the reduction process of ORN at the Chi‐CaO‐NC/CPE surface was a diffusion‐controlled reaction with four electrons and four protons. Additionally, under ideal conditions, differential pulse voltammetry (DPV) revealed that the cathodic current was directly proportional to ORN concentrations within two various detection ranges of 0.015–0.3 μM and 0.3–4.5 μM. The limit of quantification (LOQ), and the limit of detection (LOD) were 0.0138 μM and 4.13×10−3 μM, respectively. Moreover, the fabricated sensor provided acceptable selectivity towards ORN, good stability, and repeatable response, with recoveries ranging from 95.8 %–102.0 %; this electrode was also successful in detecting ORN in commercial tablets and milk samples.

One-step electrochemical preparation of platinum nanoparticle decorated self-healing reduced graphene oxide three-dimensional nanoarray for portable detection of bisphenol A

Highly selective and sensitive analysis of bisphenol A (BPA) in many plastic products remains its significance. We explored a simple, highly sensitive, and inexpensive electrochemical sensor based on a self-healing three-dimensional nanoarray (3DN) via a single-step electrochemical preparation of both platinum nanoparticles (PtNPs) and reduced graphene oxide (rGO) on a glassy carbon electrode for the portable detection of bisphenol (BPA) in plastic bottled waters. The structure of PtNPs/3DNrGO was confirmed by electron microscope and spectroscopic characterization. Electrochemical characteristics indicated that PtNPs/3DNrGO could decrease the oxidation overpotential due to the self-healing effect of the physical interaction between PtNPs and hydroxyl groups of rGO with an increase in the active surface area. The PtNPs/3DNrGO exhibited remarkably efficient electrocatalytic performance for the oxidation of BPA. The PtNPs/3DNrGO sensor for BPA demonstrated a wide linear range from 0.7 to 20 µM with a low limit of detection of 6 nM (S/N = 3) and effective performance including high sensitivity, high repeatability, and excellent selectivity. The developed sensor had been effectively implemented to assess BPA in plastic samples with desirable impacts. The interaction mechanism of both PtNPs and rGO was inferred by density functional theory. The proposed electrochemical sensor enabled the development of a portable, low-cost, and user-friendly monitoring of water quality, which will offer theoretical support for environmental monitoring.

Electrochemical Sensor Design Based on Silver Nanoparticles Modified Multiwalled Carbon Nanotubes Paste Electrode for the Sensitive Determination of Mepivacaine.

Mepivacaine, an amide-type local anesthetic drug widely used in regional anesthesia, was studied by some aspects such as electrochemical behavior, mechanism illumination, and analytical applications by cyclic voltammetry (CV) and different pulse voltammetry (DPV) methods. In this study, a novel, fast, simple, portable, and the inexpensive electrochemical sensor was developed for the determination of mepivacaine. This study was carried out by mepivacaine anodic direction detection for the first time. The modified sensor was fabricated with silver nanoparticles (AgNP) and multiwalled carbon nanotubes paste electrode (MWCNTPE) by using the drop-dry method. Different experimental parameters, such as pulse amplitude, step potential, and scanning rate in the DPV application module, were optimized. Under optimal operation conditions, the limit of detection (LOD) as low as 31 μg L-1 was found over the dynamic range (0.1-8.0 mg L-1). In contrast to its high response towards mepivacaine, the DPV exhibits negligible responses on modified AgNP/MWCNTPE when exposed to interfering species such as dopamine, uric acid, glucose, ascorbic acid, and some heavy metals. Exceptionally, the proposed DPV method on modified AgNP/MWCNTPE was successfully applied to pharmaceutical dosage form and synthetic human serum with a low relative standard deviation (RSD) of 1.35% and 2.02%, respectively.

Development of a sensitive and inexpensive electrochemical sensor for indigotin using poly(valine) modified carbon paste electrode

In this study, an electro-polymerized valine (VLN) stimulated carbon paste electrode (CPE) was used to create a straightforward, inexpensive, and renewable electrochemical sensor for accurate and selective indigotin (IGN) determination. Comparing the CPE, to the modified electrode, it exhibits excellent sensibility for the IGN oxidation-reduction reaction. Multiple techniques, including cyclic voltammetry (CV), differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) were utilized in this case to characterize the electrode materials. IGN was analyzed using CPE and poly(valine) modified carbon paste electrodes (P(VLN)MCPE) taking a 6.5 pH in 0.2 M phosphate buffer solution (PBS). Because it has more active spots than the CPE and a strong electrocatalytic nature, P(VLN)MCPE exhibits excellent electrochemical performance. The impact of pH, scan rate, numerous interferents, and fluctuation in analyte concentration were only a few of the important electrochemical factors that were investigated. The variation in scan rate proves that the IGN oxidation-reduction reaction on the surface of P(VLN)MCPE is as follows an adsorption-controlled pathway. The P(VLN)MCPE displays a good electrochemical nature for IGN in the 0.2 to 5.0 μM range, with a low limit of detection (LOD) is 0.0069 μM and a limit of quantification (LOQ) is 0.023 μM. P(VLN)MCPE shows good reproducibility, stability, and repeatability for the detection of IGN. Additionally, P(VLN)MCPE's analytical applicability for IGN detection in water sample was assessed with impressive recovery.

High-Performance Detection of Exosomes Based on Synergistic Amplification of Amino-Functionalized Fe3O4 Nanoparticles and Two-Dimensional MXene Nanosheets

Exosomes derived from cancer cells have been recognized as a promising biomarker for minimally invasive liquid biopsy. Herein, a novel sandwich-type biosensor was fabricated for highly sensitive detection of exosomes. Amino-functionalized Fe3O4 nanoparticles were synthesized as a sensing interface with a large surface area and rapid enrichment capacity, while two-dimensional MXene nanosheets were used as signal amplifiers with excellent electrical properties. Specifically, CD63 aptamer attached Fe3O4 nanoprobes capture the target exosomes. MXene nanosheets modified with epithelial cell adhesion molecule (EpCAM) aptamer were tethered on the electrode surface to enhance the quantification of exosomes captured with the detection of remaining protein sites. With such a design, the proposed biosensor showed a wide linear range from 102 particles μL-1 to 107 particles μL-1 for sensing 4T1 exosomes, with a low detection limit of 43 particles μL-1. In addition, this sensing platform can determine four different tumor cell types (4T1, Hela, HepG2, and A549) using surface proteins corresponding to aptamers 1 and 2 (CD63 and EpCAM) and showcases good specificity in serum samples. These preliminary results demonstrate the feasibility of establishing a sensitive, accurate, and inexpensive electrochemical sensor for detecting exosome concentrations and species. Moreover, they provide a significant reference for exosome applications in clinical settings, such as liquid biopsy and early cancer diagnosis.

Silver/graphene–polypyrrole composite for levosimendan detection

AbstractThis study used a facile method to develop a novel silver/Graphene–polypyrrole (Ag/G–PPy)‐modified electrode that can be used as an electrochemical sensor for levosimendan detection. The properties of the synthesized Ag/G–PPy‐modified electrode were examined through field‐emission scanning electron microscopy, x‐ray diffraction, and transmission electron microscopy. The Ag/G–PPy‐modified electrode exhibited satisfactory current signals toward levosimendan concentrations ranging from 0.21 to 6.88 μM and exhibited a low detection limit (0.12 μM). Accordingly, the proposed electrode can serve as a simple and inexpensive electrochemical sensor for levosimendan detection.

Epitope-imprinted polydopamine and reduced graphene oxide-based sensing interface for label-free detection of gliadin

Detection of gluten and its components in foods is paramount in ensuring safety of gluten-sensitive individuals. However, the conventional immunodetection methods including gold standard enzyme-linked immunosorbent assay (ELISA), polymerase chain reaction, and advanced proteomic methods suffer from high cost, complicated instrumentation and protocol, and slow assay turnaround time. Herein, we developed an inexpensive electrochemical sensor for gliadin (GLI) detection using electrochemically reduced graphene oxide for sensitivity enhancement and PQQPFPQQ epitope-imprinted polydopamine as selective recognition interface. The sensing performance was improved by optimizing key process factors including template/monomer ratio, pre-polymerization period, electropolymerization and electrochemical reduction cycles, elution time, and rebinding pH and time. The sensor shows a linear relationship between current response and GLI concentration in the 1–15 ppm range with high affinity to the epitope template (imprinting factor IF = 8.68) and target GLI (IF = 3.14), low limits of detection (0. 70 ppm) and quantification (2.33 ppm). The sensor also exhibits excellent selectivity against potential interferents including ovalbumin (selectivity factor SF = 0.15), folic acid (SF = 0.25), and casein (SF = 0.39) in buffered matrix. The obtained sensor-to-sensor reproducibility, repeatability, and stability ensure its sensitive determination of native GLI in rice flour matrix with coefficient of variance in the range of 2.52–4.27 %, and recovery rates of 99.1–101.9 %. The results fare better than those analyzed by traditional ELISA and similar methods. The developed sensor could be used as a reliable platform for rapid detection of allergic gluten components in processed food products.

Electrochemical investigation of Mn3O4/ZrO2 nanocomposite; a robust sensor platform for the sensitive determination of bisphenol A

ABSTRACT Electrochemical sensing of bisphenol A by Mn3O4/ZrO2 nanocomposite-modified screen printed graphite electrode (SPGE) was explored. Mn3O4/ZrO2 nanocomposite was prepared through a simple method. Field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) confirm the successful synthesis of this nanocomposite. The Mn3O4/ZrO2/SPGE exhibited good electrocatalytic performances towards bisphenol A with a sensitivity of about 0.0753 μA μM−1 and a low limit of detection (LOD) (9.0 nM) in the linear ranges of 0.03–375.0 μM. Besides this, the long-time performing stability, reproducibility and repeatability of the sensor are found to be reliable and good. The practical utility of this new sensor was substantially revealed for detecting bisphenol A in real samples. Considering the very good results, it seems that the Mn3O4/ZrO2/SPGE can be considered as a new method in the development of accurate and inexpensive electrochemical sensors.

Phenol monitoring in water samples using an inexpensive electrochemical sensor based on pencil electrodes modified with DTAB surfactant

Phenol (PNL) and phenolic compounds are major contaminants for water sources as they are used for the production of many industrial products. Herein, it is aimed to fabricate a novel voltammetric sensor platform for selective, sensitive, and practical detection of PNL. For this purpose, pencil graphite electrodes (PGEs) were modified with dodecyltrimethylammonium bromide (DTAB) surfactant as the first time in the literature. The optimizations of the experimental conditions for modification of DTAB at the surface of PGEs were done, then the oxidation signal of PNL was measured at +0.660 V using DTAB-PGEs. Enhanced PNL signal was obtained by using DTAB-PGEs and sensitive detection of PNL was achieved. PNL detection was successfully performed in not only buffer solution but also in tap water and industrial wastewater by reaching the detection limits as 0.16 µg/mL, 0.12 µg/mL, and 0.24 µg/mL, respectively. Moreover, DTAB-PGEs eliminated the interference effects of inorganic and organic compounds for the detection of PNL. This is the first study in the literature in terms of the development of DTAB-PGEs and non-enzymatic voltammetric detection of PNL by using DTAB-PGEs.

Electrochemical determination of rutin by using NiFe2O4 nanoparticles-loaded reduced graphene oxide.

A binary transition metal oxide containing nickel and iron (NiFe2O4) and hybridization of this nanomaterial with reduced graphene oxide (rGO) are synthesized by the hydrothermal method. X-ray diffraction (XRD) and Raman spectroscopy confirm the successful synthesis of these materials. Also, scanning electron microscope (SEM) and transmission electron microscope (TEM) images illustrated the particle morphology with the particle size of 20 nm. The synthesized material is then examined as a sensor on the surface of the glassy carbon electrode to detect a very small amount of rutin. Some electrochemical tests such as cyclic voltammetry, differential pulse voltammetry (DPV), and impedance spectroscopy indicate the remarkable accuracy of this sensor and its operation in a relatively wide range of concentrations of rutin (100 nM-100 µM). The accuracy of the proposed electrochemical sensors is approximately 100 nM in 0.1 M PBS, (pH = 3) which is relatively impressive and can be reported. Also, the stability rate after 100 DPV was about 95 %, which is a considerable and relatively excellent value. Considering the very good results, it seems that the NiFe2O4-rGO can be considered as a new proposal in the development of accurate and inexpensive electrochemical sensors.

An electrochemical sensor based on green tea extract for detection of Cd(II) ions by differential pulse anodic stripping voltammetry

In this study, a simple, selective and inexpensive electrochemical sensor was developed to detect Cd(II) ions. To this end, the bioextract (BioExt) obtained by ethanol extraction of dry green tea leaves was decorated with functionalized carbon nanotubes (MWCNTs), and the obtained nanobiocomposite (BioExt/MWCNTs) was immobilized to the glassy carbon electrode (GCE) surface. X-ray diffraction (XRD), scanning electron microscopy (SEM) and cyclic voltammetry (CV) characterizations were applied. Differential pulse anodic stripping voltammetry (DPASV) was preferred for the quantification of Cd(II) ions on GCE modified with BioExt/MWCNTs nanobiocomposite (BioExt/MWCNTs/GCE). Under optimal conditions, the peak currents depending on the Cd(II) ions concentrations on the BioExt/MWCNTs/GCE surface showed linearity between the range of 0.05 ~ 6.0 µM and the correlation coefficient (R2) was calculated as 0.9333, and the detection limit (LOD) as 1.01 nM. The proposed nanobiostructured-sensor (BioExt/MWCNTs/GCE) showed long-term stability, high selectivity, improved voltammetric behavior and good reproducibility. Cd(II) ions were successfully detected and quantified in both river and drinking water samples with this proposed nanobiostructured sensor using the standard addition method. It was observed that electrochemically obtained results were consistent with the results obtained with ICP-MS, which is a spectrometric comparison method.

Zinc Oxide-Carbon Cloth Nanosensors for Simultaneous Detection of Uric Acid, Epinephrine, and Ascorbic Acid

We present a flexible, inexpensive electrochemical sensor using zinc oxide (ZnO) grown directly on carbon cloth for the simultaneous detection of uric acid (UA), epinephrine (EP), and ascorbic acid (AA). The simultaneous detection of these biomolecules poses inherent challenges since their concentrations in the human body are low and the obtained signals are difficult to deconvolve. These limitations were overcome by using nanostructured ZnO on three dimensionally woven carbon fibers as a high surface area biosensing platform. Additionally, a differential pulse voltammetry (DPV) detection technique was used to overcome the bottleneck of clearly resolving signals from UA, EP and AA. The results obtained demonstrate the simultaneous detection of UA, EP and AA. The lowest simultaneously detected concentrations were 2.5 μM for UA, 4.0 μM for EP, and15 μM for AA, in the presence of the remaining two molecules at concentrations of 50 μM for UA and EP and 600 μM for AA. We have also successfully scaled down the biosensing platform to a single carbon fiber with ZnO to demonstrate similar results. Our results indicate that the prepared biosensor was robust, highly sensitive, and stable. Figure 1

Single Step Synthesis of MoSe2−MoO3 Heterostructure for Highly Sensitive Amperometric Detection of Nitrite in Water Samples of Industrial Areas

AbstractThe present work reports a simple and single‐step hydrothermal synthesis of MoSe2−MoO3 composite for highly sensitive and selective electrochemical oxidation of nitrite. FESEM of the MoSe2−MoO3 hybrid revealed the formation of composite as laminated structure of different sizes piled up together as finger‐like MoSe2 bars whilst other physico‐chemical characterizations (XRD, FTIR, UV‐Vis, XPS) confirmed that co‐existence of MoO3 as a major by‐product of hydrothermal synthesis. The as‐fabricated MoSe2−MoO3 composite based nitrite sensor showed remarkable selectivity and reproducibility with <3s of response time, excellent sensitivity and detection limit of 10.84 A M−1 cm−2 (R2=0.996) and 0.1 μM, respectively, in the range of 2.5–80 μM. The obtained sensitivity can be credited to the high surface area obtained from 1T phase MoSe2 and α phase MoO3 as the sensing material. The developed sensor was effectively evaluated for electrochemical recognition of nitrite in the water samples (potable and tap water) gathered from an industrial area. This new and efficient MoSe2−MoO3 based electrode material offers a new frontier for the progress of a novel composites by simple and single‐step approach which can be used for progress of non‐enzymatic and inexpensive electrochemical sensors for a wide range of analytical applications.

Template-cum-catalysis free synthesis of α-MnO2 nanorods-hierarchical MoS2 microspheres composite for ultra-sensitive and selective determination of nitrite

In this work, a novel composite constituted by α-MnO2 nanorods and hierarchical MoS2 microspheres is synthesized by a simple, template-cum-catalysis free two-step hydrothermal method for ultra-sensitive and selective detection of nitrite. The nitrite sensor (with optimal MnO2-MoS2 weight ratio) showed a limit of detection of 16 μM, the short response time (<5 s), outstanding selectivity, reproducibility, and sensitivity of 515.84 μA mM−1 cm−2 (R2 = 0.996) in the range of 100–800 μM in an optimized electrolytic pH of 4. The excellent sensing ability of the sensor can be attributed to the heterogeneous interface between two material constituents that results in unimpeded electrical transport due to the presence of intertwined nanosheets in MoS2 and 1D α-MnO2 nanorods, high number of active sites emanating from huge numbers of edges and defects in MoS2, high proportion of metallic (1T) phase than semiconducting (2H) phase in MoS2 and the combined effect of 1D α-MnO2 nanorods and MoS2 nanosheets. The fabricated sensor was also effectively assessed for the detection of nitrite in potable water. This novel, binder-free, MnO2-MoS2 composite based electrode material paves a new way for the development of simple, non-enzymatic and inexpensive electrochemical sensors for analytical applications.

A novel inexpensive electrochemical sensor for pyrazinoic acid as a potential tool for the identification of pyrazinamide-resistant Mycobacterium tuberculosis.

Tuberculosis (TB) is a significant cause of morbidity and mortality worldwide. The patient compliance with the long treatment regimens is essential for successful eradication. Pyrazinamide (PZA) shortens these regimens from 9 to 6 months, and therefore, improves treatment completion rates. Although PZA is a first-line medication for the treatment of TB, no simple or reliable assay to determine PZA resistance is yet available. In the presence of PZA, only susceptible Mycobacterium tuberculosis strains release pyrazinoic acid (POA). Therefore, the measurement and quantification of released POA is an indicator of PZA resistance. Two electrochemical sensors were constructed and tested with alternative working electrodes in conjunction with a portable potentiostat to measure the current produced when a potential difference of 2 V is applied to varying concentrations of POA in controlled solutions. The large (13.2 mm) electrochemical sensor was able to detect POA at a minimum concentration of 40 μM to a statistically significant level (P = 0.0190). Similar graphical trends were obtained when testing the electrochemical sensor in the supernatant of a negative microscopic observation drug susceptibility assay culture, irrespective of the presence of PZA. Inexpensive and reusable electrochemical sensors with a portable potentiostat are a promising tool for the detection of POA, a biomarker of PZA susceptible M. Tuberculosis.

Challenge Approach of an Inexpensive Electrochemical Sensor for Rapid Selective Determination of two Non‐classical β‐Lactams in Presence of Different Degradants and Interference Substances

AbstractAn inexpensive stability−indicating anodic voltammetric method for rapid determination of two non‐classical β‐lactam antibiotics; Meropenem (MP) and Ertapenem (EP) has been developed and validated. The method was based on the enhancement of voltammetric response at a disposable graphite pencil electrode (GPE). Differential pulse voltammetric (DPV) method was developed for quantification of both drugs in B−R buffer solution (pH 2.0) at GPE. The GPE displayed very good voltammetric behavior with significant enhancement of the peak current compared to glassy carbon electrode (GCE). Stress stability studies were performed using 0.5 M of either HCl or NaOH and H2O2. Mass and infrared spectroscopy were used for identification of degradants and their pathways were illustrated. Under optimal conditions, the peak currents showed a linear dependence with drug concentrations. The achieved limits of detection (LOD) were 1.23, 2.07 and 1.50 μM for MP and two waves of EP, respectively. The developed voltammetric method was successfully applied for direct determination of MP and EP in drug substances, pharmaceutical vials and in presence of either their corresponding hydrolytic, oxidative‐degradants or interfering substances with no potential interferences. The differential pulse voltammograms were highly advantageous and applicable in QC laboratories for rapid, selective micro‐determination of MP and EP.

New synthesis of poly ortho-methoxyaniline nanostructures and its application to construct modified multi-wall carbon nanotube/graphite paste electrode for simultaneous determination of uric acid and folic acid

Uric acid (UA) and folic acid (FA) are compounds of biomedical interest. In humans, about 70% of daily uric acid disposal occurs via the kidneys, and in 5–25% of humans, impaired renal (kidney) excretion leads to hyperuricemia. Folate is another form folic acid of which is known as, is one of the B vitamins. It is used as a supplement by women to prevent neural tube defects developing during pregnancy. Polyortho-methoxyaniline nanostructures (POMANS) was synthesized with a new two phase (organic-water) synthesis method. The POMANS was characterized using transmission electron microscopy (TEM) and Fourier transform IR (FTIR). This polymer was used to construct a modified multi-wall carbon nanotube, graphite paste electrode (POMANS-MWCNT/GPE). Linear sweep voltammograms (LSV), cyclic voltammetry (CV) and chronoamperometry were used to investigate the suitability of polyortho-methoxyaniline with multi-wall carbon nanotubes paste electrode as a modifier for the electrocatalytic oxidation of UA and FA in aqueous solutions with various pHs. The results showed that POMANS-MWCNT/GPE had high anodic peak currents for the electrooxidation of UA and FA in pH6.0.Under the optimized conditions, The catalytic peak currents obtained, was linearly dependent on the UA and FA concentrations in the range of 0.6–52 and 0.5–68μM with two segments and the detection limits 0.157 and 0.113μM for UA and FA were, respectively. Finally, the proposed method was also examined as a sensitive, simple and inexpensive electrochemical sensor for the simultaneous determination of UA and FA in real samples such as urine and serum.

Supramolecular interaction of 2,4-dichlorophenol and β-cyclodextrin functionalized ionic liquid and its preliminary study in sensor application

The supramolecular interaction of 2,4-dichlorophenol (2,4-DCP) and β-cyclodextrin functionalized ionic liquid, a mono-6-deoxy-6-(3-benzylimidazolium)-β-cyclodextrin tosylate (β-CD-BIMOTs) has been investigated. The inclusion complex of β-CD-BIMOTs-2,4-DCP complex was analyzed with conventional spectroscopic techniques and compared with native β-CD-2,4-DCP complex. The mechanism of the inclusion too was studied and discussed based on FTIR, 1H NMR and 2D NOESY analysis. β-CD-BIMOTs has a stronger binding affinity towards 2,4-DCP compared to native β-CD based on the formation constant value calculated. In this work, modified electrodes were fabricated by mixing β-CD-BIMOTs and carbon paste electrode (CPE) for determination of 2,4-DCP. The electrochemical behavior of 2,4-DCP at β-CD-BIMOTs/CPE exhibits higher electrochemical performance than that of native β-CD/CPE and CPE, revealing that CPE modified β-CD-BIMOTs not only displays good electrical properties of the ionic liquid but also exhibits high supramolecular recognition properties of β-CD-BIMOTs through the formation of an inclusion complex between β-CD-BIMOTs and 2,4-DCP molecules. This preliminarily study shows that β-CD-BIMOTs can act as an inexpensive electrochemical sensor that is suitable for the determination of 2,4-DCP.

Reversible Electrochemical Sensor for Detection of High-Charge Density Polyanion Contaminants in Heparin.

We present a simple, rapid, and inexpensive electrochemical sensor based on a reversible pulsed chronopotentiometric polyanion-selective membrane electrode for the detection and quantification of oversulfated chondroitin sulfate (OSCS) and other high charge-density polyanions that could potentially be used to adulterate heparin. The membrane is free of ion exchanger and is formulated with plasticized poly(vinyl chloride) (PVC) and an inert lipophilic salt, tridodecylmethylammonium-dinonylnaphthaline sulfonate (TDMA-DNNS). The neutral salt is used to reduce membrane resistance and to ensure reversibility of the sensor. More importantly, TDMA(+) is used as the recognition element for the polyanions. Here an anodic galvanostatic current pulse is applied across the membrane to cause the extraction of the polyanions from the sample into the membrane and potential is measured at the sample-membrane interface. The measured electromotive force (emf) is proportional to the concentration and the charge density of the polyanions. High charge-density polyanion contaminants and impurities in heparin can be detected using this method since the overall equilibrium potential response of polyions increases with increasing charge density of the polyions. Here, first the potential response of pure heparin is measured at a saturation concentration, the concentration beyond which further addition of heparin does not produce a change in potential response. Then the potential response of heparin tainted with different quantities of the high charge-density contaminant is measured at a fixed total polyion concentration (heparin concentration + contaminant concentration). The latter gives a greater negative potential response due to the presence of the high charge-density contaminant. The increase in the negative potential response can be used for detection and quantification of high charge-density contaminants in heparin. We demonstrate here that 0.3% (w/w) OSCS as well as 0.1% (w/w) dextran sulfate can be detected in heparin at 20-mg/mL total polyion concentration. It has also been shown that 1% (w/w) of dextran sulfate can readily be detected in heparin at only 2-mg/mL total polyanion concentration with a linear response (R(2) = 0.994).

Adsorptive Stripping Voltammetric Determination of 4‐Hexylresorcinol in Pharmaceutical Products Using Multiwalled Carbon Nanotube Based Electrodes

AbstractA sensitive electroanalytical method is presented for the determination of 4‐hexylresorcinol using adsorptive stripping voltammetry (AdsSV) at a multiwalled carbon nanotube modified basal plane pyrolytic graphite electrode (MWCNT‐BPPGE). This method is also extended to the use of a MWCNT modified screen‐printed electrode (MWCNT‐SPE), thereby demonstrating that this approach can easily be incorporated into a facile and inexpensive electrochemical sensor.