Electrocatalytic determination of captopril using a modified carbon nanotube paste electrode: Application to determination of captopril in pharmaceutical and biological samples

A carbon paste electrode modified with carbon nanotube and benzoylferrocene (BF) was fabricated. The electrochemical study of the modified electrode, as well as its efficiency for electrocatalytic oxidation of captopril (CAP), was described. The electrode was employed to study the electrocatalytic oxidation of CAP, using cyclic voltammetry (CV), chronoamperometry (CHA) and square wave voltammetry (SWV) as diagnostic techniques. It has been found that the oxidation of CAP at the surface of modified electrode occurs at a potential of about 85 mV less positive than that of an unmodified CPE. SWV exhibits a linear dynamic range from 1.0 × 10⁻⁷ to 3.5 × 10⁻⁴ M and a detection limit of 3.0 × 10⁻⁸ M for CAP. Finally the modified electrode was used for determination of CAP in CAP tablet and urine sample.     

Electrochemical determination of sulfite and phenol using a carbon paste electrode modified with ionic liquids and graphene nanosheets: Application to determination of sulfite and phenol in real samples

Benzoylferrocene was used to construct a modified-graphene paste electrode. Also, hydrophilic ionic liquid (n-hexyl-3-methylimidazolium hexafluoro phosphate) was used as a binder to prepare the modified electrode. The electro-oxidation of sulfite at the surface of the modified electrode was studied using electrochemical approaches. This modified electrode offers a considerable improvement in voltammetric sensitivity toward sulfite, compared to the bare electrode. Square wave voltammetry (SWV) exhibits a linear dynamic range from 5.0 × 10⁻⁸ to 2.5 × 10⁻⁴ M and a detection limit of 20.0 nM for sulfite. The diffusion coefficient and kinetic parameters (such as electron transfer coefficient and the heterogeneous rate constant) for sulfite oxidation were also determined. The prepared modified electrode exhibits a very good resolution between the voltammetric peaks of sulfite and phenol that makes it suitable for the detection of sulfite in the presence of phenol in real samples.     

The design of polyaniline based sensor for the qualitative estimation of malonaldehyde

The detection of contaminated food in every stage of processing required new technology for fast identification and isolation of toxicity in food. Since effect of food contaminant are severe to human health, the need of pioneer technologies also increasing over last few decades. In the current study, MDA was prepared by hydrolysis of 1,1,3,3-tetramethoxypropane in HCl media and used in the electrochemical studies. The electrochemical sensor was fabricated with modified glassy carbon electrode with polyaniline. These sensors were used for detection of sodium salt of malonaldehyde and observed that a high sensitivity in the concentration range ∼1 × 10⁻¹ M and 1 × 10⁻² M. Tafel plots show the variation of over potential from − 1.73 V to − 3.74 V up to 10⁻⁵ mol/L indicating the lower limit of detection of the system.     

Potential step study of electrooxidation of methanol in 1-butyl-3-methylimidazolium tetrafluoroborate

A potential step method was used to characterize the electrooxidation of methanol on a chemically modified electrode in an ionic liquid solvent. Two major findings were reported from this study. Firstly, the oxidation was dominant 2.2 s after the potential step. Before that, the double layer charging and adsorption were dominant. Therefore, there should be a waiting time of a few seconds if a methanol sensor is developed with a potential step method. Secondly, the oxidation of methanol on the electrode was diffusion controlled. The concentration of methanol affected the diffusion. The diffusion constant D₀ was 8.37 × 10⁻¹⁷ m²/s when the concentration was lower than 0.5 M and was 2.66 × 10⁻¹³ m²/s when the concentration was higher than 1.0 M. This suggests that the methanol concentration should be kept higher than a threshold in an ionic liquid based fuel cell.     

A sensitive nanocomposite-based electrochemical sensor for voltammetric simultaneous determination of isoproterenol,acetaminophen and tryptophan

The electrooxidation of isoproterenol (ISPT), acetaminophen (AC) and tryptophan (Trp) and their mixture has been studied using an 8,9-dihydroxy-7-methyl-12H-benzothiazolo[2,3-b]quinazolin-12-one modified multiwall carbon nanotubes paste electrode (DMBQ-MCNTPE). The novel sensor exhibited potent and persistent electron mediating behavior followed by well separated oxidation peaks towards ISPT, AC and Trp with activation over-potential. The peak currents were linearly dependent on ISPT, AC and Trp concentrations using square wave voltammetry (SWV) method in the range of 0.04–400, 5.0–500, and 10.0–800 μmol L⁻¹, with detection limits of 0.009, 1.0, and 4.0 μmol L⁻¹, respectively. The modified electrode was used for the determination of ISPT, AC and Trp in biological and pharmaceutical samples.     

Rapid and simultaneous determination of tetracycline and cefixime antibiotics by mean of gold nanoparticles-screen printed gold electrode and chemometrics tools

The screen-printed gold electrode (SPGE) modified with the formation of self-assembly monolayer (SAM) of cysteine (Cys) on gold-nanoparticles (Au_nano) was utilized for rapid and simultaneous determination of tetracycline and cefixime antibiotics by square wave voltammetry (SWV). Electrochemical investigation and characterization of the modified electrode was achieved using cyclic voltammetry (CV) and scanning electron microscopy (SEM). A principal component artificial neural network (PCANN) with three layer back-propagation network was utilized for the analysis of the voltammogram data. It is possible to simultaneously determine the tetracycline and cefixime concentrations in the ranges of 10⁻⁵ and 10⁻³ mol L⁻¹, under the optimum conditions. Moreover the SPGE-Au_nano-Cys biosensor together with chemometrics tools was successfully applied to the determination of tetracycline and cefixime in biological fluids, which may provide a promising alternative in routine biosensing applications.     

Effect of SiC particles on the friction and wear behavior of Ti3Si(Al)C2-based composites

The non-lubricated, sliding friction and wear behavior of Ti₃Si(Al)C₂ and SiC-reinforced Ti₃Si(Al)C₂ composites against AISI 52100 bearing steel ball were investigated using a ball-on-flat, reciprocating tribometer at room temperature. The contact load was varied from 5 to 20 N. For monolithic Ti₃Si(Al)C₂, high friction coefficients between 0.61 and 0.90 and wear rates between 1.79 × 10⁻³ and 2.68 × 10⁻³ mm³ (N m)⁻¹ were measured. With increasing SiC content in the composites, both the friction coefficients and the wear rates were significantly decreased. The friction coefficients reduced to a value between 0.38 and 0.50, and the wear rates to between 2.64 × 10⁻⁴ and 1.93 × 10⁻⁵ mm³ (N m)⁻¹ when the SiC content ranged from 10 to 30 vol.%. The enhanced wear resistance of Ti₃Si(Al)C₂ is mainly attributed to the facts that the hard SiC particles inhibit the plastic deformation and fracture of the soft matrix, the oxide debris lubricate the counterpair, and the wear mode converts from adhesive wear to abrasive wear during dry sliding.     

Multi-range sensors for the measurement of liquid film thickness distributions based on electrical conductance

The paper presents an approach toward an enhancement of the measuring range of high-speed sensors for the measurement of liquid film thickness distributions based on electrical conductance. This type of sensors consists of electrodes mounted flush to the wall. The sampling of the current generated between a pair of neighboring electrode is used as a measure of the film thickness. Such sensors have a limited measuring range, which is proportional to the lateral distance between the electrodes. The range is therefore coupled to the spatial resolution. The proposed new design allows an extension of the film thickness range by combining electrode matrices of different resolution in one and the same sensor. In this way, a high spatial resolution is reached with a small thickness range, whereas a film thickness that exceeds the range of the high resolution measurement can still be acquired even though on the costs of a lower spatial resolution. A simultaneous signal acquisition with a sampling frequency of 3.2 kHz combines three measuring ranges for the characterization of a two-dimensional film thickness distribution: (1) thickness range 0–600 µm, lateral resolution 2×2 mm², (2) thickness range 400–1300 µm, lateral resolution 4×4 mm², and (3) thickness range 1000–3500 µm, lateral resolution 12×12 mm². The functionality of this concept sensor is demonstrated by tests in a horizontal wavy stratified air–water flow at ambient conditions. Using flexible printed circuit board technology to manufacture the sensor makes it possible to place the sensor at the inner surface of a circular pipe.     

A comparative study on the wear properties of coarse-grained Al6061 alloy and nanostructured Al6061–Al2O3 composites

Wear behavior of nanostructured Al6061 alloy and Al6061–Al₂O₃ nanocomposites produced by milling and hot consolidation were investigated. The samples were characterized by hardness test, pin-on-disk wear test, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Nanocomposites containing 3 vol% Al₂O₃ showed a maximum hardness of 235 HV and optimum wear rate of 4×10⁻³ mg/m. Increasing the amount of Al₂O₃ up to 5 vol% resulted in decrease in hardness values (∼112 HV) and a sharp rise in wear rate (∼18×10⁻³ mg/m).     

Uncertainty evaluation of a 10N·m dead weight torque standard machine and comparison with a 1kN·m dead weight torque standard machine

A 10N·m dead weight torque standard machine (10-N·m-DWTSM) has been developed and evaluated since 2006 at the National Metrology Institute of Japan (NMIJ), a part of the National Institute of Advanced Industrial Science and Technology (AIST). Previously, the lengths of a moment arm, made of a low-thermal-expansion alloy (Super Invar), and the sensitivity limit of the fulcrum were evaluated. However, it is known that mechanical parts made of Super Invar vary in size with time. Therefore, the sensitivity limit of the fulcrum should be investigated under real calibration conditions. In this study, the moment arm lengths and the sensitivity limit of the fulcrum were re-evaluated. The moment arm lengths were found to have increased by an average of 6.3 μm in five years. The relative combined standard uncertainty of the moment arm length, w_arm, was re-evaluated in consideration of the uncertainty of the secular length change and was found to be 1.8 × 10⁻⁵. The sensitivity limit of the fulcrum was investigated by using a highly accurate, small-rated-capacity torque measuring device. The relative combined standard uncertainty due to the sensitivity limit of the fulcrum was 2.5 × 10⁻⁵ in the 0.1–10N·m torque range. The uncertainty budget table of the 10-N·m-DWTSM was completed. The relative expanded uncertainty of torque realized by the 10-N·m-DWTSM, W_tsm, was evaluated in the 0.1–10N·m torque range and was found to be 6.6 × 10⁻⁵, with a coverage factor, k, being equal to 2. In addition, the 10-N·m-DWTSM was compared with the existing 1-kN·m-DWTSM at NMIJ by using small-rated-capacity torque measuring devices at 5N·m and 10N·m torque steps. Two loading conditions were adopted in this comparison. The comparison results showed good agreement within the uncertainties in all cases. Thus, the torque realized by the 10-N·m-DWTSM was shown to be equivalent to that achieved by the 1-kN·m-DWTSM.     

Electrochemical behaviors of benzoic acid at polyaniline/CuGeO3 nanowire modified glassy carbon electrode

20 wt.% polyaniline/CuGeO₃ nanowires have been used as glassy carbon electrode (GCE) modified materials for electrochemical determination of benzoic acid (BA) in neutral solution. The intensities of the anodic cyclic voltammogram (CV) peaks increase linearly with the increase of BA concentration and scan rate. The linear range is 0.001–2 mM and detection limit is 0.96 μM and 0.47 μM for cvp1 and cvp2, respectively at a signal-to-noise ratio of 3. 20 wt.% polyaniline/CuGeO₃ nanowire modified GCE exhibits good stability and reproducibility. Polyaniline plays an important role in the electrochemical responses of BA at polyaniline/CuGeO₃ nanowire modified GCE. The detection limit decreases to 0.64 μM and 0.28 μM for cvp1 and cvp2, respectively with the polyaniline content increasing to 40 wt.%. Polyaniline/CuGeO₃ nanowire modified GCE exhibit better electrochemical performance than traditional methods.     

Enhancing electrical conductivity and electrical thermal characteristics of a PEDOT:PSS thin layer by using solvent treatment and adding Ag nanoparticle solution

A method of enhancing the electrical conductivity of 3,4-ethylenedioxythiophene:poly styrene sulfonate (PEDOT:PSS) by combining solvent treatment (adding high polar solvent: 5 wt% ethylene glycol) and adding a small amount of silver (Ag) nanoparticles in a solution was investigated. The main purpose of this was to apply a PEDOT:PSS conductive layer to micro-thermal devices driven by electricity and, for this, to reduce the layer thickness (for low stiffness) while maintaining necessary high electrical conductivity. Layers with thicknesses of less than about 10 μm were examined for electrical conductivity and temperature when electricity was applied. The solvent treated PEDOT:PSS had suitable electrical resistance to generate appropriate temperature properties. The added Ag nanoparticles reduced the electrical resistance by 30–70% over the measured thickness range. The electric conductivity applied with this method was 200–260 Ω⁻¹ cm⁻¹ for thicknesses of 1–2 μm (conductive area: 12 mm × 10 mm) and the generated temperature increase was 20–50 °C at applied voltages of 3–5 V. These characteristics are considered to be suitable to use the conductive layer as a heating element. In addition, the method we used scarcely degraded the transparency of the layer. Measurements of the conductive area in a layer with conductive atomic force microscope (AFM) indicated that the added Ag nanoparticles contributed to increasing the conductive areas and distributing them more uniformly.     

Study of TiAlSiN coatings post-treated with N and C + N ion implantations. Part 2: The tribological analysis

Ion implantation has found to be an effective approach to modify surface properties of materials. The present research investigates the effect of (1) nitrogen (N), and (2) carbon subsequently with nitrogen (C + N) implantations on the mechanical and tribological properties of the titanium–aluminium–silicon–nitride (Ti–Al–Si–N) coatings. Superhard TiAlSiN coatings produced by magnetron sputtering, of approximately 2.5 μm thickness, were post-treated by implantations of N or C + N at an energy level of 50 keV. The dose range was between 5 × 10¹⁶ and 1 × 10¹⁸ ions cm^?2. After implantation, the tribological performance of the coatings was investigated by a ball-on-disk tribometer against WC–6 wt.%Co ball under dry condition in ambient air. The wear performance of the samples was examined by a variety of characterization techniques, such as secondary electron microscopy (SEM), 3D profilometry, atomic force microscopy (AFM), and micro-Raman. The results showed that the wear performance of the samples depended strongly on the implanted elements and doses. There was slight improvement on the samples implanted with N whereas significant improvement was found on the C + N implantations. Particularly, the friction coefficient of the sample with 5 × 10¹⁷ C⁺ cm^?2 and 5 × 10¹⁷ N⁺ cm^?2 could reach 0.1. In addition, the specific wear rate of the sample was extremely low (0.85 × 10^?7 mm³/Nm), which was nearly two orders of magnitude below that of the un-implanted coating. The speculation of the mechanical and tribological analyses of the samples indicates that the improvement of the N implanted and C + N implanted TiAlSiN samples could be due to a combined effect of improved hardness, plus enhanced adhesive and cohesive strength. In addition, the improved performance of the C + N implanted samples could be explained by the formation of lubricating implanted-layer, which existed mostly in sp² C–C and C–N forms. The formation of such implanted layer could lead to a change of wear mode from strong abrasive wear to mostly adhesive wear, and result in a drop of friction coefficient and wear rate.     

Small-capacity deadweight force standard machine compensating loading frame

The Korea Research Institute of Standards and Science (KRISS) has developed a 20 N deadweight force standard machine. The machine consists of a weight stack, a loading frame, a taring system, a main body and a control system. The taring system has the role of compensating the initial force generated by the loading frame. With two motors, a displacement sensor, several limit switches, and a synthetic control system consisting of a programmable logic controller and an operating PC, the machine can be operated almost fully automatically. The machine can generate a compressive force in the range of 0.5–22 N with a relative expanded uncertainty of 1.0 × 10^–4. The machine was compared with a 200 N deadweight force standard machine. In the comparison, the relative deviation was 5.8 × 10^–5, less than the declared expanded uncertainty of the force standard machines, therefore confirming the machine’s accuracy.     

Silver nanoparticles/polymethacrylic acid (AgNPs/PMA) hybrid nanocomposites-modified electrodes for the electrochemical detection of nitrate ions

AgNPs/PMA hybrid nanocomposite materials with different Ag loadings have been synthesized using a simple chemical route assisted by UV irradiation. The hybrid composites were characterized by means of SEM and TEM, UV–vis spectroscopy and XPS. The as synthesized hybrid samples, composed of small Ag nanoparticles (AgNPs) embedded within the PMA (poly-methacrylic-acid) matrix, have been used to modify the working electrode of disposable screen printed carbon electrodes (SPCEs). It has been observed that hybrid composite with the lowest Ag loading forms dendritic silver structures on the surface of working electrode, whereas at higher loadings massive structures were formed. The electrocatalytic properties of the AgNPs/PMA/SPCEs were investigated toward the reduction of nitrate at neutral pH. Based on these modified electrodes, both voltammetric and amperometric sensors were developed for the electrochemical sensing of nitrate. Voltammetric sensor showed a wide linear range (0–20 mM) and high sensitivity (130 μA mM⁻¹ cm⁻²).     

An investigation into the effect of film thickness on nanowear with amorphous carbon-based coatings

A sample oscillation module linked to a nanoindentation unit was used to perform nano-scale wear testing on a series of sputtered Cr doped amorphous C films deposited over a range of thicknesses (10, 20, 50, 150, and 2000 nm) under conditions relevant to MEMS and micro-scale engineering devices. A ruby sphere was used as the counter-body. Specific wear rates (defined as volume of worn material per unit applied load per unit of slid distance) were quantified and the effect of film thickness, applied load and test duration was investigated. Specific wear rate reduced exponentially with decreasing film thickness over the range of 10–2000 nm. The lowest wear rates were in the range of 0.1–6.1 × 10^?17 m³ N^?1 m^?1. Specific wear rate reduced with increased applied load over the range of 0.1–10 mN. The data scatter of replicated testing reduced along with the reduction of wear rate. A rapid reduction of specific wear rate was observed during the first 3000 oscillation cycles. This was analogous to the ‘running in’ process observed with macroscopic tribology systems.     

1-N-alkyl -3-methylimidazolium ionic liquids as neat lubricants and lubricant additives in steel–aluminium contacts

The influence of the alkyl chain length and of the anion on the lubricating ability has been studied for the room-temperature ionic liquids (IL) 1-n-alkyl-3-methylimidazolium X⁻ [X = PF₆; n = 6 (L-P106). X = BF₄; n = 2 (L102), 6 (L106), 8 (L108). X = CF₃SO₃; n = 2 (L-T102). X = (4-CH3C6H4SO3); n = 2 (L-To102)]. Neat IL have been used for AISI 52100 steel-ASTM 2011 aluminium contacts in pin-on-disk tests under variable sliding speed. While all IL give initial friction values lower than 0.15, real-time sharp friction increments related to tribochemical processes have been observed for L102 and L-P106, at room-temperature and at 100 °C. Electronic microscopy (SEM), energy dispersive (EDS) and X-ray photoelectron (XPS) spectroscopies show that wear scar surfaces are oxidized to Al₂O₃ and wear debris contain aluminium and iron (for L102) fluorides. For L-P106, the steel surface is covered with a P-containing tribolayer. A change of anion (L-T102; L-To102) reduces friction and wear, but the lowest values are obtained by increasing the alkyl chain length (L106; L108). When the more reactive L102 and L-P106 are used as 1 wt.% base oil additives at 25 °C, tribocorrosion processes are not observed and a friction reduction (69–75% for 1 wt.% L102) and a change from severe (10⁻³ mm³ m⁻¹) to mild wear (10⁻⁴ to 10⁻⁶ mm³ m⁻¹) is obtained with respect to the neat IL. 1 wt.% IL additives also show good lubricating performance at 100 °C.     

Determination of the thermal conductivity of composted material

The objective of this study was to develop a reliable method for the determination of the thermal conductivity of composted material using the TP08 probe. Study was set out to determine whether the selection of a signal fragment used to establish thermal conductivity (λ), has a significant influence on the results. Also minimum number of measurements was determined for every phase of the composting process. No significant differences were reported between results, but certain changes in the value of λ were noted. In successive stages of the process, thermal conductivity of composted material were: 0.31 ± 0.09, 0.45 ± 0.14, 0.27 ± 0.03 and 0.37 ± 0.17 W m⁻¹ K⁻¹.     

A comparison of tribological properties of evenly distributed and agglomerated diamond nanoparticles in lubricated high-load steel–steel contact

The tribological properties of evenly distributed and agglomerated nanodiamonds on steel contact surfaces were compared in ethylene glycol lubricated tests using a pin-on-disc tribometer with a steel counter ball. The nanodiamond distributions were studied on silicon and steel surfaces using scanning electron microscopy. Friction and wear decreasing effects were observed with both sprayed and agglomerated nanodiamonds. The average friction coefficient with pure ethylene glycol lubricated contacts decreased from 0.16 to 0.12 with agglomerated nanodiamonds when 100 N load was applied. A minimum for both disc wear rate (0.40×10⁻⁶ mm³/Nm) and ball wear rate (0.29×10⁻⁶ mm³/Nm) was observed with agglomerated nanodiamonds. One of the mechanisms of nanodiamond lubrication was observed to be the incorporation of nanodiamond particles in to the tribolayer.