Comparison of different carbon nanostructures influence on potentiometric performance of carbon paste electrode

Recently, different carbon nanomaterials were introduced for construction of electrochemical sensors. In this study, the influence of carbon nanomaterial on performance of carbon paste potentiometric electrode was investigated. In this manner, different kinds of carbon nanomaterial, i.e., graphene, graphene oxide and carbon nanotube (CNT) were used as a conduction phase in carbon paste electrode. Then, potentiometric characteristics of the corresponding paste electrodes such as calibration slope, linear range, detection limit, response time and stability were compared with each other. The results appeared comprehensive findings about the role of electrode’s content in electrochemical performance.     

Simultaneous determination of l-thyroxine (l-T(4)), d-thyroxine (d-T(4)), and l-triiodothyronine (l-T(3)) using a sensors/sequential injection analysis system

Requirements of high purity and enantiopurity for the raw materials of active substances used for the pharmaceutical formulations involved utilization of high reliable analytical techniques for the analysis of the active compound. Sequential injection analysis system with electrochemical sensors as detectors proved to be a very good alternative for the chromatographic methods, as it is more reliable, not expensive, and faster. Drugs containing only l-thyroxine (l-T(4)) or both l-T(4) and l-triiodothyronine (l-T(3)) are formulated for the dysfunctions of thyroid. A sequential injection analysis system that can use two amperometric immunosensors (for the assay of l-T(3) and l-T(4)) and an amperometric biosensor (for the assay of d-thyroxine, d-T(4)) as detectors is proposed for the purity and enantiopurity tests of the raw materials used for the formulation of the drugs for thyroid. The system proved to be very reliable. The three compounds can be determined on-line in synthesis process control with a frequency of 20 samples per hour.     

Chemically modified electrodes with amperometric response in enantioselective analysis

Estimation of the enantiomeric purity of chiral biologically active compounds, as well as the determination of particular optical isomers, is very important for the control of medicines, food, and biological fluids. The main approaches to the development of electrochemical enantioselective sensors with the amperometric detection of the signal are considered in this review. Examples of the use of biochemical and supramolecular receptors providing enantiomer recognition and techniques of their inclusion into the corresponding sensors are given. The main characteristics of enantioselective sensors for the determination of optically active medicines, organic acids, aminoacids, carbohydrates, alcohols, and other biologically important compounds are considered.     

Flow Injection Analysis of Maleic Hydrazide Using an Electrochemical Sensor Based on Palladium‐Dispersed Carbon Paste Electrode

A new analytical methodology for the electrochemical detection of the herbicide maleic hydrazide (3,6‐dihydroxypyridazine) by flow injection analysis is presented. This method is supported by the novel application of a palladium‐dispersed carbon paste electrode as an amperometric sensor for this herbicide. Maleic hydrazide shows anodic electrochemical activity on carbon‐based electrodes (glassy carbon or carbon paste electrodes) in all the pH range. This electrochemical activity is enhanced using metal‐dispersed carbon paste electrodes, especially at Pd‐dispersed CPE which displays good oxidation signals at 690 mV (0.050 M phosphate buffer pH 7.0), 140 mV lower than at unmodified electrodes. Under the optimized conditions, the electroanalytical performance of Pd‐dispersed CPE in flow injection analysis was excellent, with good reproducibility (RSD 3.3%) and a wide linear range (1.9×10^?7 to 1.0×10^?4 mol L^?1). A detection limit of 1.4×10^?8 mol L^?1 (0.14 ng maleic hydrazide) was obtained for a sample loop of 100 μL at a fixed potential of 700 mV in 0.050 M phosphate buffer solution at pH 7.0 and a flow rate of 2.0 mL min^?1. The proposed method was applied for the maleic hydrazide detection in natural drinking water samples.     

Electrochemical detection coupled with high-performance liquid chromatography in pharmaceutical and biomedical analysis: a mini review

Recent advances in electrochemical detection techniques coupled with high-performance liquid chromatography (HPLC-ECD) in pharmaceutical and biomedical analysis are reviewed. ECD classification and modes including common amperometric, coulometric, conductimetric, and potentiometric detector, are outlined and the some typical examples of determinations in pharmaceutical and biomedical analysis are described. The electrochemical detection system can offer superior merits over other detectors commonly used with HPLC. These techniques have great potential owing to their prominent characteristics in high-throughput screening procedures of drugs in various matrices. Fundamental 67 references from last 5 years related with a field are cited in this review.     

Tellurite Carbon Paste Sensors: Microscopic Analysis Provides New Insights on the Nature of the Interaction Between the Ionophore and Analytical Species

In this work, scanning electron microscopy (SEM) was used for the characterization of chemically modified carbon paste sensors (CMCPSs), with the aim of understanding their chemical and electrochemical properties. The work also provides a microscopic study on the role of the binder, type of carbon, amount and nature of modifier, composition of the carbon paste and its impact on the electrochemical performance of the sensor. In addition, energy dispersive X‐ray spectroscopy (EDX) was utilized for the direct observation of the interaction between the chemical modifier and the carbon paste. This has enabled the fabrication of new sensitive and selective chemically modified carbon paste sensors that were successfully applied for the detection of tellurite ions in pure solutions, environmental and biological samples. This work provides new insights on the rational design and integration of carbon paste sensors for a variety of applications.     

Room Temperature Ionic Liquids (RTILs) and Multiwalled Carbon Nanotubes (MWCNTs) as Modifiers for Improvement of Carbon Paste Ion Selective Electrode Response; A Comparison Study with PVC Membrane

Room temperature ionic liquids (RTILs), 1‐n‐butyl‐3‐methylimidazolium tetrafluoroborate, [bmim]BF₄, and multiwalled carbon nanotubes (MWCNTs) were used for improvement of a praseodymium carbon paste ion selective sensor response. [bmim]BF₄ can be a better binder than mineral oils. MWCNTs have a good conductivity which helps the transduction of the signal in carbon paste electrode. The characteristics of these electrodes as potentiometric sensors were evaluated and compared with PVC membrane sensor. The results indicate that potentiometric sensor constructed with ionic liquid shows an increase in performance in terms of Nernstian slope, selectivity, response time, and response stability compared to Pr(III) PVC membrane sensor.     

Electrochemical detectors – tailormade techniques for liquid chromatography and capillary electrophoresis?

Electrochemical detectors for liquid chromatography and capillary electrophoresis are reviewed with special emphasis on electrode materials that allow the amperometric detection of otherwise non-electroactive compounds such as aliphatic alcohols, carbohydrates or amino acids. Noble metal electrodes can catalyze the oxidation of aliphatic compounds in alkaline media if multistep potential-time waveforms are employed. Various metal and metal oxide electrodes such as Ni, Cu or Co allow the detection of carbohydrates and similar compounds under constant potential conditions. Metallic copper electrodes operating in an amperometric mode or in a potentiometric mode can also serve as selective detectors for complexing species. A range of applications in combination with chromatography and electrophoresis is summarized. The current state of electrochemical detectors indicates that both amperometric and potentiometric detectors are on the verge of becoming tailormade detectors for micro-separation techniques.     

A new construction for a potentiometric, enantioselective membrane electrode--its utilization to the S-captopril assay

A novel potentiometric, enantioselective membrane electrode based on graphite paste (graphite powder and paraffin oil) has been constructed. The graphite paste is impregnated with 2-hydroxy-3-trimethylammoniopropyl-beta-cyclodextrin (as chloride salt) solution, 10(-3) mol l(-1). The potentiometric, enantioselective membrane electrode can be used reliable for S-captopril assay as raw material and from Novocaptopril tablets, using a chronopotentiometry (zero current) technique, in the 10(-6)-10(-2) mol l(-1) concentration range (detection limit 2 x 10(-7) mol l(-1)), with an average recovery of 99.99% (RSD=0.05%). The enantioselectivity was determined over R-captopril and D-proline. The response characteristics of the enantioselective, potentiometric membrane electrode were determined also for R-captopril. It was shown that only L-proline is the main interfering compound. The surface of the electrode can be regenerated by simply polishing, obtaining fresh surface ready to be used in a new assay.     

Preparation and characterization of implantable sensors with nitric oxide release coatings

The widespread use of miniaturized chemical sensors to monitor clinically important analytes such as PO₂, PCO₂, pH, electrolytes, glucose and lactate in a continuous, real-time manner has been seriously hindered by the erratic analytical results often obtained when such devices are implanted in vivo. One major factor that has influenced the analytical performance of indwelling sensors is the biological response they elicit when in contact with blood or tissue (e.g. thrombus formation on the device surface, inflammatory response, encapsulation, etc.). Nitric oxide (NO) has been shown to be a potent inhibitor of platelet adhesion and activation as well as a promoter of wound healing in tissue. Herein, we review recent work aimed at the development of hydrophobic NO-releasing polymers that can be employed to coat catheter-type amperometric oxygen sensors without interfering with the analytical performance of these devices. Such modified sensors are shown to exhibit greatly enhanced hemocompatibility and improved analytical performance when implanted within porcine carotid and femoral arteries for up to 16 h. Further, results from preliminary studies also demonstrate that prototype fluorescent oxygen sensors, catheter-style potentiometric carbon dioxide sensors and subcutaneous needle-type enzyme-based amperometric glucose sensors can also be fabricated with new NO-release outer coatings without compromising the analytical response characteristics of these devices. The NO-release strategy may provide a solution to the lingering biocompatibility problems encountered when miniature chemical sensors are implanted in vivo.     

Application of Carbon Nanotubes in the Extraction and Electrochemical Detection of Organophosphate Pesticides: A Review

Recent trends and challenges in developing carbon nanotubes (CNT) based sensors and biosensors for the detection of organophosphate (OP) pesticides and other organic pollutants in water are reviewed. CNT have superior electrical, mechanical, chemical, and structural properties over conventional materials such as graphite. At the same time CNT based sensors and biosensors are more efficient compared to the existing traditional techniques such as high-performance liquid chromatography or gas chromatography, because they can provide rapid, sensitive, simple, and low-cost on-field detection. The measurement protocols can be based on enzymatic and non-enzymatic detection. The enzyme acetylcholinesterase (AChE) is used with CNT for fabricating ultrasensitive biosensors for OP detection involving different immobilization schemes such as adsorption, crosslinking, and layer-by-layer self-assembly. This protocol relies on measuring the degree of enzyme inhibition as means of OP quantification. The other enzyme used along with CNT for OP detection is organophosphate hydrolase (OPH) which hydrolyzes the OP into detectable species that can be measured by amperometric or potentiometric methods. Different forms of CNT electrode materials can be used for fabricating such electrodes such as pure CNT and composite CNT. Due to their large surface area and hydrophobicity, CNT have also been used for the extraction and non-enzymatic electrochemical detection of OP with very high efficiency. The application of CNT and their novel properties for the adsorption and electrochemical detection of OP compounds is discussed in detail.     

Hybrid Electronic Tongue as a Tool for the Monitoring of Wine Fermentation and Storage Process

Hybrid electronic tongue based on potentiometric and voltammetric sensors was applied for the monitoring of wine production process. The sensor array formed by miniaturized ion‐selective electrodes and glassy carbon electrodes provided the analysis of the progress and correctness of wine fermentation and storage process, detection of the presence of disturbing factors and evaluation of the quality of final product. The efficiency of the proposed approach was compared with the monitoring of wine production carried out using standard reference methods. The results indicated that hybrid electronic tongue could be used as simple and reliable analytical tool dedicated to qualitative and quantitative assessment of wine production.     

A set up of a modern analytical laboratory for wastewaters from pulp and paper industry

The introduction of analytical techniques allowing rapid, selective, sensitive, and reliable determination of aqueous pollutants is of crucial importance for the protection of the environment. This critical review summarizes the advanced analytical techniques suggested over the last ten years together with already established methods, and evaluates whether they are fit for wastewater quality assessment considering the area of application, interferences, limit of detection, calibration function, and precision. The key parameters of wastewater quality assessment are: total organic carbon (TOC), chemical oxygen demand (COD), biochemical oxygen demand (BOD), organochlorines (AOX), nitrogen, phosphorus, sulfur, and toxicity. Chromatography and capillary electrophoresis, photocatalytic oxidation with semiconductor nanofilms and atomic emission spectrometry, optical fibre sensors and chemiluminescence, amperometric mediated biosensors and microbial fuel cells, respirometry and bioluminescence measurements are just part of the proposed wastewater analyst's toolkit. The diversity of fundamental phenomena and the captivating elegance of interdisciplinary applications involved in the development of wastewater analytical techniques should attract the interest of a wide scientific audience including analytical chemists, chemical physicists, microbiologists and environmentalists. To conclude, we suggest a laboratory set up for the analysis of wastewaters from the pulp and paper industry.     

All-solid-state electronic tongue and its application for beverage analysis

Disposable all-solid-state planar-type potentiometric electronic tongue has been developed with the carbon paste electrode array screen-printed on a polymeric substrate. Highly cross-sensitive solvent polymeric membranes based on different matrices [e.g. poly(vinyl chloride) (PVC), aromatic polyurethane, and polypyrrole (Ppy)] and doped with common electroactive components for potentiometric measurements (e.g. various plasticizers, and cation- and anion-selective ionophores) were deposited on the screen-printed carbon paste electrodes (SCPEs). It was observed that an incorporation of 10 wt.% of Prussian Blue (PB; Fe₄(III)[Fe(II)(CN)₆]₃) into a commercially available carbon paste and electrochemical preanodization of SCPEs in KCl solution at 1.6 V provide the all-solid-state planar-type electrodes with significantly improved potentiometric stability. The proposed fabrication method gives possibility for simple and reproducible mass-production of low-cost disposable electronic tongue microsystems. The practical utility of all-solid-state disposable electronic tongue chips has been demonstrated with a flow injection cell for the analysis of potable waters, soft drinks, and beers. It is shown that the potentiometric measurements with the SCPE-based all-solid-state chips and the combined use of chemometric methods (e.g. principal components analysis, partial least regression (PLS), and principal component regression (PCR)) for the analysis of obtained data sets successfully discriminate various types of samples according to their tastes.     

光电化学传感器的研究进展

光电化学传感器以光作为激发源,以光电流或光电压作为检测信号,具有响应快速、灵敏度高、设备简单等特点,目前已在环境、食品、医学等多个领域的分析测试中得到广泛应用。该文阐述了光电转换材料与光电化学传感器的制备方法,介绍了光电化学传感器的原理和分类。光电化学传感器包含光寻址电位型传感器和电流型光电化学传感器,其中,电流型光电化学传感器由于优良的光电性能、检出限低、所需材料低廉且易加工等优势而被广泛应用。文中着重介绍了电流型光电化学传感器在金属离子、有机污染物、核酸、蛋白质、细胞等方面的应用,并对光电化学传感器的发展前景进行了展望。     

Capillary batch injection analysis and capillary flow injection analysis with electrochemical detection: a comparative study of both methods

Capillary batch injection analysis (CBIA) and capillary flow injection analysis (CFIA) in combination with electrochemical detection as well as optical detection methods were studied and compared with respect to their performance. Despite the differences in technical equipment both techniques share the same idea of reproducible transport and washout of nanolitre samples over sensing surfaces. Thus the same electrochemical flow cell can be used for both CBIA and CFIA. The amperometric and potentiometric CBIA responses were studied under various experimental conditions in order to optimise the CBIA set-up. In particular, the density of the sample solution relative to that of the cell electrolyte had a remarkable effect on the hydrodynamic characteristics of CBIA. Dispersion in CFIA was investigated using on column UV-detection for electroosmotic flow (EOF) conditions as well as for gravity flow conditions. It is demonstrated for a 75 μm capillary that the relative band broadening of the sample plug under gravity flow is only about twice as large as under EOF. Furthermore, dispersion in a system that involves a chemical reaction between the sample and the carrier solution, namely CrO₇ ^2– and Fe²⁺ has been investigated by amperometric detection and exploited for the determination of dichromate microsamples.     

Ionic Liquids Modify the Performance of Carbon Based Potentiometric Sensors

A new type of potentiometric sensor based on a recently constructed carbon ionic liquid electrode (CILE) is described. Two kinds of ionic liquids, i.e., N‐octylpyridinium hexafluorophosphate (OPFP) and 1‐butyl‐3‐methylimidazoluim hexafluorophosphate (BMFP) were tested as binder for construction of the carbon composite electrode. The characteristics of these electrodes as potentiometric sensors were evaluated and compared with those of the traditional carbon paste electrode (CPE). The results indicate that potentiometric sensors constructed with ionic liquid show an increase in performance in terms of Nernstian slope, selectivity, response time, and response stability compared to CPE.     

Zeolite-modified solid carbon paste electrodes

New zeolite-modified carbon-based electrodes are described. They are based either on the physical anchoring of zeolite particles on the surface of solid carbon paste (the viscosity of which can be tuned by temperature change or controlled dissolution by an organic solvent), or on the dispersion of zeolite particles in the bulk of a carbon paste matrix containing solid paraffin as a binder. Both these systems display superior electrochemical performance in comparison to corresponding "classical" zeolite-modified carbon paste electrodes using mineral oil as binder. These well-described composites usually suffer from poor mechanical stability in stirred media as well as memory effects due to significant ingress of the external solution into the bulk electrode. Advantages of the zeolite-modified solid carbon paste electrodes are reported mostly on the basis of two electroanalytical applications: the voltammetric detection of Cu²⁺ ions after accumulation by ion exchange at open circuit, and the indirect amperometric detection of non-electroactive species (i.e. Na⁺) in flow injection analysis.     

Polypyrrole Nanoparticles Based Disposable Potentiometric Sensors

In this work polypyrrole nanoparticles of high electrochemical activity were used to prepare disposable, potentiometric sensors with a paper support. The paper support modified with polypyrrole nanoparticles served as electrical lead and ion‐to‐electron transducer and it was covered by a typical poly(vinyl chloride) based ion‐selective membrane. The properties of this arrangement were tested on example of potassium‐selective electrodes. The sensors prepared benefited from the properties of conducting polymer nanostructures: high electrical conductivity and electroactivity as well as absence of suspension stabilizing agent. The obtained electrodes were characterized with analytical parameters well comparable with those of classical ion‐selective electrodes.