Platinum Wire Surface Research Articles

Lab-made solid phase microextraction phases for off line extraction and direct mass spectrometry analysis: Evaluating the extraction parameters

The analyses of drugs and metabolites in complex matrices have been widely studied in recent years. However, due to high levels endogenous compounds and matrix complexity, these analyses require a sample pre-treatment step. To this aim, two lab-made extractive phases were integrated to probe electrospray ionization mass spectrometry (PESI-MS) technique for direct analysis of illicit drugs in biological fluids and phorbol esters in Jatropha curcas extract. The polypyrrole (PPy) phase was electropolymerized onto a platinum wire surface by cyclic voltammetry. The molecularly imprinted polymer (MIP) was synthesized and adhered onto a stainless-steel needle with epoxy resin. The PPy-PESI-MS method showed to be linear in a concentration range from 1 to 500 μg L−1, with accuracy values between -2.1 and 14%, and precision values between 0.8 and 10.8%. The MIP-PESI-MS method showed to be linear in a concentration range from 0.9 to 30 mg L−1, with accuracy values between -1.6 and -15.3%, and precision values between 4.1 and 13.5%.

Effect of the droplet size of an emulsion dispersion phase in nucleate boiling and emulsion boiling crisis

This paper presents the results of an experimental investigation of heat transfer in a boiling water/(vacuum oil VO-1C) emulsion at the surface of platinum wire 0.10mm in diameter and in a pipe with an inner diameter of 16mm. The influence of the diameter of a disperse phase droplet on the character of heat transfer in nucleate boiling and emulsion boiling crisis has been investigated.

Preparation of Solid Phase Microextraction (SPME) Probes through Polyaniline Multiwalled Carbon Nanotubes (PANI/MWCNTs) Coating for the Extraction of Palmitic Acid and Oleic Acid in Organic Solvents.

A fiber coating from polyaniline (PANI) was electrochemically prepared and employed for Solid phase micreoextraction (SPME). The PANI film was directly electrodeposited on the platinum wire surface using cyclic voltametry (CV) technique. The same method was applied for the preparation of SPME fiber coated by polyaniline multiwalled carbon nanotubes (PANI/MWCNTs) composite. The concentration of sulfuric acid for electropolymerization was 0.1 M in the presence of 0.045 M aniline in aqueous solution. For the electrodeposition of PANI/MWCNT composite, 4 μg/mL of MWCNTs was dispersed into the solution. Film coating was carried out on the platinum wire by repetitive cycling of potentials between 0 and 1.0 V at the scan rate of 0.05 V/s. The applicability of these coatings were assessed through employing a laboratory-made SPME injecting device and gas chromatography with mass spectrometry (GC-MS) for the extraction of palmitic acid and oleic acid from chloroform. The developed method proved to be simple and easy, offering high reproducibility. Both PANI coated and PANI/CNT coated probes had the ability to concentrate palmitic acid and oleic acid on their coating and produced strong signals in GC-MS chromatograms. In the meantime, PANI/CNT coated SPME probes produced signals which were stronger than those produced by PANI coated SPME probes. The amount of extracted palmitic acid and oleic acid from chloroform by the PANI/MWCNTs coating was about 6 and 12 times higher than the amount extracted by plane PANI SPME fibers respectively. It could be suggested that the composite material with CNTs has both an increased surface area and an elevated absorptive capacity which leads to this overall increase in extracted palmitic acid and oleic acid.

An aniline-based fiber coating for solid phase microextraction of polycyclic aromatic hydrocarbons from water followed by gas chromatography-mass spectrometry

A fiber coating from polyaniline (PANI) was electrochemically prepared and employed for solid phase microextraction (SPME) of some polycyclic aromatic hydrocarbons (PAHs) from water samples. The PANI film was directly electrodeposited on the platinum wire surface in sulfuric acid solution using cyclic voltammetry (CV) technique. The applicability of this coating was assessed employing a laboratory-made SPME device and gas chromatography with mass spectrometry (GC–MS) for the extraction of some PAHs from the headspace of aqueous samples. Application of wider potential range in CV led to a PANI with more stability against the temperature. The homogeneity and the porous surface structure of the film were examined by the scanning electron microscopy (SEM). The study revealed that this polymer is a suitable SPME fiber coating for extracting the selected PAHs. Important parameters influencing the extraction process were optimized and an extraction time of 40 min at 40 °C gave maximum peak area, when the aqueous sample was added with NaCl (20%, w/v). The synthesis of the PANI can be carried out conveniently and in a reproducible manner while it is rather inexpensive and stable against most of organic solvents. The film thickness of PANI can be precisely controlled by the number of CV cycles. The resulting thickness was roughly 20 μm after 20 cycles. At the optimum conditions, the relative standard deviation (RSD) for a double distilled water spiked with selected PAHs at ppb level were 8.80–16.8% ( n = 3) and detection limits for the studied compounds were between 0.1–6 pg mL −1. The performance of PANI was, also, compared with a commercial solid coated-based SPME fiber, carbowax/divinylbenzene (CW/DVB), under similar experimental conditions.

Electrolytic Reduction of Spent Nuclear Oxide Fuel as Part of an Integral Process to Separate and Recover Actinides from Fission Products

Bench‐scale tests were performed to study an electrolytic reduction process that converts metal oxides in spent nuclear fuel to metal. Crushed spent oxide fuel was loaded into a permeable stainless steel basket and submerged in a molten salt electrolyte of LiCl–1 wt% Li2O at 650°C. An electrical current was passed through the fuel basket and a submerged platinum wire, effecting the reduction of metal oxides in the fuel and the formation of oxygen gas on the platinum wire surface. Salt and fuel samples were analyzed, and the extent of fission product separation and metal oxide reduction was determined.

An electropolymerized aniline-based fiber coating for solid phase microextraction of phenols from water

An aniline-based polymer was electrochemically prepared and applied as a new fiber coating for solid phase microextraction (SPME) of some priority phenols from water samples. The polyaniline (PANI) film was directly electrodeposited on the platinum wire surface in sulfuric acid solution using cyclic voltammetry (CV) technique. The efficiency of new coating was investigated using a laboratory-made SPME device and gas chromatography with flame ionization detection for the extraction of some phenols from the headspace of aqueous samples. The scanning electron microscopy (SEM) images showed the homogeneity and the porous surface structure of the film. The results obtained proved the ability of this polymer as a suitable SPME fiber coating for trapping the selected phenols. Influential parameters affecting the extraction process were optimized and an extraction time of 50 min at 50 °C gave maximum efficiency, when the aqueous sample was saturated with NaCl and adjusted at pH 2. This new coating can be prepared easily in a reproducible manner and it is rather inexpensive and stable against most of organic solvents. The PANI thickness can be precisely controlled by the number of CV cycles. At the optimum conditions, the R.S.D. for a double distilled water spiked with phenol and chlorophenols at ppb level were 4.8–17% ( n = 3) and detection limits for the studied compounds were between 0.69 and 3.7 ng ml −1, except for phenol and 4-chlorophenol. The optimized method was successfully applied to some real-life water samples.

Evaluation of mass transfer coefficient and hydrogen concentration in supersonic flow by using catalytic reaction

The authors propose a new simple method to evaluate hydrogen concentrations in a hydrogen/air supersonic mixing layer without the need for costly apparatus. Catalytic reaction occurs on an electrically heated platinum wire in the supersonic flow of a hydrogen/air mixture. By adopting the technique of a constant-temperature hot-wire anemometer, the heat transfer coefficient and the catalytic heat release rate are measured. A series of experiments with different platinum wire temperatures shows that the platinum wire temperature does not affect the catalytic heat release rate, implying that the rate of mass transfer from the flow to the platinum wire surface is the controlling factor. This means that the catalytic heat release rate gives the mass transfer coefficient of the controlling species, which is hydrogen/oxygen in lean/rich mixtures. It is found that the effect of hydrogen concentration on the ratio of heat and mass transfer coefficients is very weak, suggesting that the mass transfer coefficient, is obtained with reasonable accuracy from the heat transfer coefficient by assuming the equivalent spatial distributions of heat and mass transfer. Based on this result, a method to translate the catalytic heat release rate into the hydrogen concentration of the flow is proposed. To prove the accuracy of this method, hydrogen concentrations of hydrogen/air premixed supersonic flows were measured successfully. Finally, one example applying this method to an actual supersonic mixing layer is presented.

Paraquat sensors containing membrane components of high lipophilicities

In the first part of this paper, the development of high-performance paraquat selective potentiometric sensors based on octamethylcyclotetrasiloxane is described. In the fabrication of these sensors, the use of highly lipophilic PVC-based membrane components, namely, plasticizer and anionic sites, is emphasized. The electrochemical characteristics of such sensors were evaluated and compared with earlier paraquat ion-selective electrodes (ISEs) that were based on the same sensing compound but with nitrophenyl octyl ether (NPOE) as plasticizing solvent and also based on dibenzo-30-crown-10. The use of bis(1-butylpentyl)decane-1,1-diyldiglutarate (BBDG) and tetra- n-undecyl 3,3′,4,4′-benzophenone tetracarboxilate (TBT) as plasticizer in conjunction with either sodium tetrakis[3,5-bis(trifluoromethyl)phenyllborate (NTB) or potassium tetrakis(4-chlorophenyl) borate (KTPB) as membrane additives all yielded functional paraquat selective chemical sensors of Nernstian slopes. Although the selectivity profile of these electrodes were slightly inferior as compared to a similar membrane system that uses NPOE as a plasticizer but was better than the earlier reported paraquat ISEs based on dibenzo-30-crown-10. A distinct advantage of the paraquat sensors described here was their resistance to fouling by surfactants as compared to earlier sensors that used NPOE as a plasticizer. The second part of this paper deals with the usage of the promising membrane systems described above when applied on the surface of platinum wire and subsequently used as a flow-through potentiometric detector. A brief description of the flow-through detector design and optimization of the flow-injection analysis (FIA) set-up were also presented. Analysis of 0.01–0.l mM paraquat dichloride in backgrounds of well, river and lake waters when performed in the FIA mode gave excellent recoveries. A throughput of 85 samples h −1 can be achieved with this system.

定温度熱線によるメタン‐空気予混合気の点火

Hot surface ignition of methane-air mixtures has been experimentally studied in normal gravity and microgravity. The primary aim of this research is to explain the effects of natural convection and catalytic reaction on the hot surface ignition in a closed vessel. The hot surfaces used are platinum wire for catalyst and nickel wire for non-catalyst. In order to define the initial condition and make the analysis simple, the following control unit was developed; which heats the wire to the setting temperature in a very short time, and maintains the wire temperature constant until ignition. From experimental results, ignition temperatures with platinum wire are higher than those with nickel wire by the catalytic inhibition of ignition due to the reactant depletion on the surface of the wire. Ignition temperatures with platinum wire are highest near the stoichiometric mixture ratio and decrease with equivalence ratio depart from stoichiometric mixture ratio, while those with nickel wire increase with equivalence ratio. Ignition temperatures in normal gravity are higher than those in microgravity. Natural convection supplies reactants to the platinum wire surface, and therefore reactants are consumed because of promoting catalytic reaction in normal gravity.

Simultaneous joule heating and potential cycling of cylindrical microelectrodes

An improved electrode design enabled to perform electroanalytical experiments in which a platinum wire electrode inside an aqueous electrolyte solution was continuously joule heated during dc polarization. The proposed symmetrical electrode arrangement allowed measurement of low magnitude electrochemical signals even when a high magnitude audio frequency current was used for heating. The new arrangement could open a way to amperometric sensing of sluggish reacting species without changing bulk solution temperature. The electrochemical behaviour of a platinum wire surface exposed to these conditions was considered. The heating effects are demonstrated by cyclic voltammograms of hexacyanoferrate(II)/(III) and by cathodic stripping of dissolved oxygen at the hot platinum surface.

An experimental and numerical investigation on the hot surface ignition of premixed gases under microgravity conditions

There have been many studies of hot surface ignition of premixed gases. However, using the experimentalresults obtained up to this time, it is difficult to understand the basic mechanism of ignition by heated surfaces because these experiments were made under the normal gravity condition, suffering from the effect of natural convection. In the present study, experiments were made on the ignition of mixtures by heated nickel, tungsten,and platinum wires under normal gravity and microgravity conditions. With a methane-oxygen mixture ignited by a heated tungsten wire, a strong gravity effect on the ignition delay is observed. On the contrary, there is almost no gravity effect observed with a methane-air mixture. Results of calculations show that ignition experiments under the microgravity condition are simulated successfully by this numerical model. It is shown from the numerical results that the ignition point in the methane-oxygen case is apart from the hot-wire surface, while, in the methane-air case, this point exists near the hot-wire surface. Therefore, natural convection has little effect on the ignition delay of a methane-air mixture. Experimental results of hydrogen-air mixtures ignited by heated platinum wires show that chemicalspecies are supplied to the platinum wire surface by natural convection, and therefore, the surface reaction is promoted under the normal gravity condition. Experimental and numerical results show that the surface reaction is the most energetic when the equivalence ratio of the mixture is 0.3, which conflicts with the result obtained by Coward and Guest that the rate of catalytic reaction attains a maximum at stoichiometric composition. This contradiction may be due partially to the gravity effect in their experiments.

Vapor Transport Reaction of MgO and SiO<sub>2</sub>

Vapor transport reaction of sintered polycrystalline MgO and quartz glass was examined using vapor transport couple. MgO and SiO2 were separated by 0.1mm platinum wire and firing was carried out at 1400°C for 24hrs.X-ray examination of the surface of MgO and SiO2 did not establish the development of reaction product. However, electron microprobe X-ray analysis proved the vapor transport of Si (or Si oxide) to the surface of MgO as well as that of Mg (or MgO) to the surface of SiO2. In addition, it was found that the amount of Si on the MgO surface was considerably larger than that of Mg on the SiO2 surface.Previous study using MgO-SiO2 contact diffusion couple indicated that the reaction product mainly developed on the SiO2 side. Therefore, it will be concluded that vapor transport did not play an important part on the development of the reaction product in the solid state reaction.Platinum wire had an shielding effect on the vapor transport of Mg, but, on the other hand, there was evidence of the rapid movement of MgO toward SiO2 along the surface of platinum wire.

Alkali cyanides in the iron blast-furnace

There have been many studies of hot surface ignition of premixed gases. However, using the experimentalresults obtained up to this time, it is difficult to understand the basic mechanism of ignition by heated surfaces because these experiments were made under the normal gravity condition, suffering from the effect of natural convection.In the present study, experiments were made on the ignition of mixtures by heated nickel, tungsten,and platinum wires under normal gravity and microgravity conditions. With a methane-oxygen mixture ignited by a heated tungsten wire, a strong gravity effect on the ignition delay is observed. On the contrary, there is almost no gravity effect observed with a methane-air mixture. Results of calculations show that ignition experiments under the microgravity condition are simulated successfully by this numerical model. It is shown from the numerical results that the ignition point in the methane-oxygen case is apart from the hot-wire surface, while, in the methane-air case, this point exists near the hot-wire surface. Therefore, natural convection has little effect on the ignition delay of a methane-air mixture.Experimental results of hydrogen-air mixtures ignited by heated platinum wires show that chemicalspecies are supplied to the platinum wire surface by natural convection, and therefore, the surface reaction is promoted under the normal gravity condition. Experimental and numerical results show that the surface reaction is the most energetic when the equivalence ratio of the mixture is 0.3, which conflicts with the result obtained by Coward and Guest that the rate of catalytic reaction attains a maximum at stoichiometric composition. This contradiction may be due partially to the gravity effect in their experiments.