1M H3PO4 Research Articles

Corrosion resistance of porous titanium surface prepared at moderate and high potentials in H3PO4/HF electrolytes

In this work a corrosion resistance study of porous layers formed on Ti in anodic oxidation process was shown. The anodic oxidation process was realized from moderate 30 V to high 240 V potentials. As the electrolytes, a mixtures of 2M H3PO4 and 0.2–2 wt % HF were applied. The corrosion resistance of the layers was investigated with respect to possible hard tissue implant applications, which means that surface, which provide porosity for osseointegration should possess high corrosion resistance, too. We have applied XRD and SEM techniques for surface characterization. The corrosion resistance was investigated in Ringer’s electrolyte using potentiodynamic method. For corrosion parameters determination, polarization curves were analyzed. Linking the structure, morphology and corrosion resistance gives conditions, which could be optimal for the implant surfaces. The structure, morphology and corrosion resistance of the anodized layers are strongly correlated with the processing conditions. We found that for possible hard tissue implant applications best morphology and corrosion resistance show Ti oxidized at 210 V in 2M H3PO4 + 0.2 wt % HF electrolyte.

Effect of the High Voltage Anodic Oxidation on the Titanium Corrosion Resistance

The paper describes anodic oxidation of titanium surface in a potential range from 30 to 240 V in a 2M H3PO4 electrolyte with the addition of 0÷2 % HF. The aim of the treatment was to form titanium oxide with a developed, rough morphology, useful for biomedical application. The morphology of the anodically oxidized samples was examined using SEM and AFM. The phase structure of the oxides was determined by XRD. One of the main parameters determining the suitability of that material for biomedical application is the corrosion resistance in an environment comparable to human body (Ringer’s solution). It has been observed that corrosion resistance of the anodized surfaces increases with the increase of the anodizing voltage for the samples oxidized in an electrolyte containing 0 % and 0.2 % HF. In electrolytes with the addition of 1 % and 2 % HF an inverse relationship was observed. The corrosion resistance of all tested surfaces was sufficiently high for the application as a biomaterial. The most promising anodizing treatment, providing best surface morphology and corrosion resistance was performed at 210 V in a 2M H3PO4 + 1 % HF electrolyte.

Anodic oxide film growth on thin magnetron sputter-deposited titanium layer

A ~100nm thick sputter-deposited titanium layer on electropolished aluminium is used for the investigation of anodic film growth in 1M H3PO4. It is found that the thin titanium layer could not provide sufficient current efficiency for titanium anodic film growth when anodized to the voltage over 80V due to the occurrence of oxygen evolution. The ruptures of titanium anodic film and the sputtering layer are induced by the development of oxygen bubbles. The penetrated phosphoric acid electrolyte in the ruptured regions of sputtering titanium layer contacts with the aluminium substrate, which is leading to the anodic oxide growth of aluminium. The thickness of the titanium anodic film increases from 10 to 100V, however, it is reduced from 100 to 150V due to the thinning of titanium layer. Over 80V, the sputtering layer at some regions where it is completely ruptured, the anodic film growth of titanium could not be created. A thicker aluminium anodic film is formed on such regions due to the direct connection with the electrolyte.

Control of nanotube shape and morphology on Ti–Nb(Ta)–Zr alloys by varying anodizing potential

Different applied potentials have been employed in a two-step anodization process, utilizing a 1M H3PO4 electrolyte and a solution containing this electrolyte and 0.8wt.% NaF, to control the shape and morphology of oxide nanotubes on coatings for ternary Ti–30Ta–xZr alloys. The ternary alloys were manufactured using an arc furnace, and corrosion testing was carried out using a potentiostat. The microstructures of the Ti–30Ta–xZr alloys had a needle-like structure, and the lath thickness of the α′ phase increased as the Zr content increased. The microstructures of Ti–30Nb–xZr alloys had equiaxed grains. The Ti–30Nb–xZr alloys showed smaller micropores and nanotubes compared to the Ti–30Ta–xZr alloys. The Ti–Nb(Ta)–Zr alloys tended to have improved corrosion resistance with increasing Zr content.

Electrochemical Formation of GaN Porous Structures Under UV-Light Irradiation for Photoelectrochemical Application

High-density array of semiconductor nanostructures have been widely investigated as building-blocks of energy conversion devices such as solar cells, photo-electrodes, bio-chemical sensors and so on. Among various semiconductor materials, GaN is getting a lot more attention lately because of their chemical stability and their potential to achieve direct photoelectrolysis by solar power. In this study, we investigated the structural and photoelectrochemical properties of GaN porous structures formed by the electrochemical process under UV-light irradiation.n-type GaN epitaxial layers (N D = 5 × 1016 ~ 5 × 1018 cm-3) grown on free-standing GaN substrates (N D ≧ 1 × 1018 cm-3) and on insulting sapphire substrates were used for the porous formation. The Au-ohmic contact was first made on the backside or topside of the substrate to supply the electrochemical current. The electrochemical process was performed using a standard cell with three electrodes in the electrolyte which is a mixture of 1M H2SO4 and 1M H3PO4. Photo-assisted anodization was carried out under UV light by comparing the back-sided irradiation (BSI) mode with the top-sided irradiation (TSI) mode.After the anodization for a few minutes, the high-density arrays of pores were formed in GaN layers on both free-standing substrate and sapphire substrate. From SEM observation, we found that the pore depth, wall thickness, and surface morphology of porous structures were strongly influenced by the way holes generated by the light irradiation were supplied. In the case of the BSI mode on the free-standing GaN substrates, the pore diameter and wall thickness were estimated to be about 20 nm and 50 nm, respectively. They were almost same sizes throughout all part of the porous layer from the top to the bottom. Furthermore, the pore depth was well controllable by the total electric charge whereas it has never been achieved by the TSI mode. This is because the electric holes were moderately supplied from the backside by using the BSI mode, where the top region of porous layer did not dissolve as seen in the TSI mode. As for the GaN layers grown on the insulating sapphire substrates, the anodic currents should be supplied from the top electrodes formed beside the reaction area. We found that the BSI mode was very effective even for such substrates to form the porous structures under the condition that holes were sufficiently generated and supplied from the back surface.We optimized the structural properties of GaN porous structures in view of the application as photoelectrodes and photosensors. As for such applications, the sufficiently-thick walls showing the good electrical conductivity and photoabsorption property are required as well as the deeper pores having a large surface area. From the photo-electrochemical measurements in a NaCl electrolyte, the photo-conversion efficiency degraded in the over-etched porous structures having thinner walls obtained by the TSI mode. On the other hand, the porous structures having thicker walls over 20 nm showed higher and depth-dependent efficiency. In addition to this, photorefelctance properties greatly influenced to the photo-conversion efficiency. As compared with the planar GaN surface, the porous surface showed a low photoreflectance with a high photoabsorption. The smallest reflectance was obtained from the sample with a largest porosity on the surface for both the BSI and TSI mode. These results indicate that the control of porous structural features such as surface morphology, thickness of pore walls, and pore depth is considered crucial to the improvement of the photoelectrochemical characteristics of GaN porous structures.

Morphology and properties of nanotubular oxide layer on the “Ti–13Zr–13Nb” alloy

The “Ti-13Zr-13Nb” alloy in solid and porous form was oxidised. The constant voltage 20V, oxidation time 0.5 and 1h, and 1M H3PO4 (orthophosphoric acid) with an addition of HF (hydrofluoric acid) as the test conditions were applied. SEM (Scanning Electron Microscope) examinations of surface, EDS (Energy Dispersive X-ray Spectroscopy) chemical analysis, nanohardness and nanoscratch tests, and corrosion potentiokinetic tests at various pH values were performed.Results show that an oxidation of this ternary alloy in acidic solution in the presence of fluoride ions results in the appearance of nanotubular oxide layer of high nanohardness, well adjacent to the base. Oxide film appears both on the surface and within the pores. Different colonies of nanotubes are observed. Obtained results prove that for such alloys, both as solid and porous material, nanotubular oxide layers of suitable morphology, high mechanical properties and enhanced bioactivity may be formed.

Inhibitive Action of Artemisia Plant Extract on the Copper Corrosion in Phosphoric Acid.

Effect of Artemisia plant Extract (APE) on the copper corrosion as a corrosion inhibitor in an aerated acidic solution of in 2M H3PO4 containing 3.10-1 M NaCl has been investigated using gravimetric and electrochemical techniques. A significant decrease in the corrosion rate of copper was observed in the presence of the Artemisia plant extract. The potentiodynamic polarization data indicated that the inhibitor was of mixed type. Impedance measurements showed that the charge transfer resistance increased and double layer capacitance decreased with increase in the inhibitor’s concentration. Also, some thermodynamic data for the activation are calculated and discussed. The results obtained from potentiodynamic polarization, impedance measurements and gravimetric method are in good agreement.

Surface Characteristics and Hydrophilicity of the as-Anodized Films Formed at High Current Density on Ti-6Al-4V in Different Electrolytes

Hydrophilicity of the as-anodized films is an important factor for improving the osseointegration of Ti implants and bone tissues. This study investigated the surface characteristics and the hydrophilicity of the as-anodized films formed on Ti-6Al-4V. The as-anodized films on Ti-6Al-4V were prepared using galvanostatic method in 1M H3PO4 or 1M MCPM as an electrolyte with different current densities (5, 20, 80 mA/cm2) and using potentiostatic method with different voltages (5, 100 and 150 V) for 30 minute at room temperature. The as-anodized films shows a significantly lower water contact angle compared to the untreated Ti-6Al-4V. The porous oxide films were fabricated on Ti-6Al-4V. Ti 2p spectra show that the as anodized films consist of TiO2 and O 1s present hydroxide (OH-) and adsorbed water (H2O) that effect to the hydrophilicity on the as-anodized film surface. These results demonstrate that the galvanostatic method at a high current density of 20 mA/cm2 and the potentiostatic at a high voltage of 150 V in MCPM could enhance both of the high surface roughness and appropriate surface species which is leading to good hydrophilicity on the as-anodized films.

Surface characteristics of hydroxyapatite coatings on nanotubular Ti–25Ta–xZr alloys prepared by electrochemical deposition

The surface characteristics of hydroxyapatite coatings on nanotubular Ti–25Ta–xZr alloys prepared by electrochemical deposition for dental implants have been investigated using various methods. The Ti–25Ta–xZr alloys were prepared by an arc melting furnace, homogenized for 12h at 1000°C in an argon atmosphere, and then water-quenched. Nanotubular structures were formed by an electrochemical method in 1M H3PO4 electrolytes containing 0.8wt.% NaF. Electrochemical deposition was carried out using a cyclic voltammetry method over a potential range of −1.5V to 0V at 80°C in a 5mM Ca(NO3)2+3mM NH4H2PO4 solution. Surface characteristics were observed by optical microscopy, X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, contact angle goniometer, and image analyzer software. Microstructures of the Ti–25Ta–xZr alloys changed from α″ phase to β phase, and the phases changed in morphology from a needle-like to an equiaxed structure with increasing Zr content. The arrangement of nanotubes changed from an irregular distribution to a high level of ordering surrounded by smaller tubes, and the occupied percentage of pore wall surface decreased from 28% to 23%, as the Zr content increased. HA precipitates also changed in morphology from a plate or leaf-like shape to a needle or flower-like shape as the Zr content increased.

Doping Control Analysis of 16 Non-Steroidal Anti-Inflammatory Drugs in Equine Plasma Using Liquid Chromatography-Tandem Mass Spectrometry

Non-steroidal anti-inflammatory drugs (NSAIDs) are classified as Class 4 agents by the Association of Racing Commissioners International and are banned in racehorses during competition in Pennsylvania (PA). To control the abuse of these agents in racehorses competing in PA, a forensic method for screening and confirmation of the presence of these agents is needed. Equine plasma (0.5 mL) was acidified with 75 μL 1M H3PO4 to increase recovery of the analytes by liquid-liquid extraction using methyl tert-butyl ether (MTBE). Extracted analytes were separated by reversed-phase liquid chromatography using a C8 column under gradient condition. All 16 analytes were detected, quantified and confirmed using a triple quadrupole tandem mass spectrometry with selected reaction monitoring (SRM) in both negative and positive electrospray ionization modes. The limit of detection, quantification and confirmation of the analytes were 1.0 - 5.0 ng/mL, 1.0 - 5.0 ng/mL and 1.0 - 20 ng/mL, respectively. The linear dynamic range of quantification was 5.0 - 200 ng/mL. The method is routinely used in anti-doping analysis to control the abuse of NSAIDs in racehorses competing in PA.

Hydroxyapatite precipitation on nanotubular films formed on Ti-6Al-4V alloy for biomedical applications

In this study, hydroxyapatite precipitation on nanotubular film-formed Ti-6Al-4V alloy for biomedical applications has been investigated using a variety of techniques. To prepare the substrate samples for hydroxyapatite (HA) deposition, the starting Ti-6Al-4V alloy was polished and heat-treated for 12h at 1050°C in an Ar atmosphere, followed by water-quenching at 0°C. Nanotube formation on the titanium alloy was performed using anodization with a DC power supply at 30V for 1h in 1M H3PO4+0.8 wt.% NaF at 25°C. Subsequent HA precipitation treatment was carried out by cyclic voltammetry over a potential range of −1.5V to 0V using a scanning rate of 100mV/s in 0.03M Ca(NO3)2∙4 H2O+0.018M NH4H2PO4 at 80°±1°C. Four different numbers of cycles were employed: 10, 20, 30, and 50. Surface morphology and structure were examined by field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy.The heat-treated Ti–6Al–4V alloy has a needle-like duplex microstructure containing the martensitic α′ phase and β phase. Plate-like precipitates were formed on bulk Ti–6Al–4V alloy, and the size of these precipitates increased with the number of deposition cycles. The HA precipitates on the nanotube surface showed a mixture of plate-like and flower-like particles with more deposition cycles. The deposited HA phase in the coated layer had an amorphous structure, with particle composition in good agreement with Ca10(PO4)6(OH)2.

Surface morphology of TiN-coated nanotubular Ti–25Ta–xZr alloys for dental implants prepared by RF sputtering

The surface morphology of TiN-coated nanotubular Ti–25Ta–xZr alloys prepared by radio-frequency sputtering for dental implants was investigated. Ti–25Ta–(0–15wt.%) Zr alloys were initially formed in an arc-melting vacuum furnace, homogenized for 12h at 1000°C, and water-quenched. Formation of a nanotubular structure was achieved on the alloys by anodization at room temperature in 1M H3PO4 electrolytes containing 0.8wt.% NaF. A TiN coating was then placed on the alloys using a radio-frequency magnetron sputtering technique. These depositions were performed on the alloy substrates using pure Ti targets. Surface morphologies of the nanotubular alloys were examined by a variety of instruments. The nanotube diameters on Ti–25Ta, Ti–25Ta–3Zr and Ti–25Ta–7Zr had irregular distribution, while the nanotubes on Ti–25Ta–15Zr had a more regular pattern of large tubes surrounded by several smaller tubes. As the Zr content in these alloys increased, the average thickness of the TiO2 nanotubes increased. At high Zr content, the surface of the nanotubes was covered with the TiN film. The Zr content affects the Ra and wettability, providing a hydrophilic property.

Surface characteristics of hydroxyapatite-coated layer prepared on nanotubular Ti–35Ta–xHf alloys by EB-PVD

In this study, we investigated the surface characteristics of hydroxyapatite (HA)-coated layers prepared by electron-beam physical vapor deposition (EB-PVD) on nanotubular Ti–35Ta–xHf alloys (x=3, 7, and 15wt.%). Ti–35Ta–xHf alloys were first prepared by arc melting. Formation of a nanotube structure on these alloys was achieved by an electrochemical method in 1M H3PO4+0.8wt.% NaF electrolytes. The HA coatings were then deposited on the nanotubular surface by an EB-PVD method. The surface characteristics were analyzed by field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction (XRD). The electrochemical behavior was examined using a potentiodynamic polarization test in 0.9% NaCl solution. The Ti–35Ta–xHf alloys had an equiaxed grain structure with α″+β phases, and the α″ phase disappeared with increases in Hf content. The Ti–35Ta–15Hf alloy showed higher β-phase peak intensity in the XRD patterns than that for the lower Hf-content alloys. A highly ordered nanotubular oxide layer was formed on the Ti–35Ta–15Hf alloy, and the tube length depended on Hf content. The HA coating surface formed at traces of the nanotubular titanium oxide layer and completely covered the tips of the nanotubes with a cluster shape. From the potentiodynamic polarization tests, the incorporation of Hf element and formation of the nanotubular structure were the main factors for achieving lower current density. In particular, the surface of the HA coating on the nanotubular structure exhibited higher corrosion resistance than that of the nanotubular titanium oxide structure without an HA coating.

Obtaining, structural and corrosion characterization of anodized nanolayers on Ti-20Zr alloy surface

The binary Ti–20Zr alloy was elaborated with the aim to be used as small diameter implant placed in narrow edentulous ridge. The alloy surface was galvanostatically anodized in 1M H3PO4 solution to increase its corrosion resistance and bioactivity. The results of energy dispersive X-ray spectroscopy, Raman spectroscopy, Fourier-transform infrared and X-ray photoelectron spectroscopy showed that the alloy surface was covered by a quasi-amorphous TiO2 oxide based nanolayer with very small crystalline nuclei of rutile-type structure that incorporated phosphorous ions. The anodized nanolayer revealed submicron surface features and nanoscale roughness measured by atomic force microscopy, and flake-like platelets observed by scanning electron microscopy. The electrodeposited nanolayer acted as a barrier against the diffusion of ions through it and reduced very much (about ten times lower) the corrosion and ion release rates, a good indicator of increased long-term alloy biocompatibility in Ringer's solutions/simulated body fluids. The main electrochemical parameters evinced a nobler behavior of the anodized alloy in comparison with bare one. Electrochemical impedance spectroscopy indicated that the anodization treatment provided the formation of a more stable, resistant nanolayer. Long-term experiments denoted the improvement over time of the protective properties of the anodized nanolayer by its thickening. Immersion of the anodized alloy in neutral and alkaline Ringer's solutions resulted in the deposition of nanostructured coatings with a morphology of entangled acicular n-HA nanocrystallites, while brushite coatings deposited in acid Ringer's solution. The anodized nanolayer obtained on the Ti–20Zr alloy surface endowed the substrate both with protection and bioactivity.

Hydroxyapatite coating on micropore-formed titanium alloy utilizing electrochemical deposition

The purpose of this study was to investigate hydroxyapatite coatings on micropore-formed titanium alloy, utilizing an electrochemical deposition method. A commercially pure titanium surface was used as a substrate for calcium phosphate (CaP) deposition on micropores formed after anodization. Prepared surfaces were anodized in 1M H3PO4 solution, and CaP deposition was performed with a potentiostat at cathodic potential in an electrolyte containing 0.042M Ca(NO3)2 and 0.025M NH4H2PO4. Micropores acted as growth sites for nanophase CaP crystals. Flake-like CaP and needle-like CaP were observed at 25°C and 85°C, respectively. If the specimen was not heat-treated, octacalcium phosphate and hydroxyapatite were observed, whereas slight CaP decomposition to tricalcium phosphate occurred with heat treatment at 700°C. The phenomena involved in CaP deposition were affected by the electrolyte temperature for both morphology and nucleation site.

Formation of titanium dioxide nanotubes on Ti–30Nb–xTa alloys by anodizing

The goal of this study was to investigate the formation of titanium dioxide nanotubes on the surface of cast Ti–30Nb–xTa alloys by anodizing. The anodization technique for creating the nanotubes utilized a potentiostat and an electrolyte containing 1M H3PO4 with 0.8wt.% NaF. The grain size of the Ti–30Nb–xTa alloys increased as the Ta content increased. Using X-ray diffraction, for the Ti–30Nb alloy the main peaks were identified as α″ martensite with strong peaks of β phase. The phases in the Ti–30Nb–xTa alloys changed from a duplex (α″+β) microstructure to solely β phase with increasing Ta content. The nanotubes that formed on the surface of the Ti–30Nb–xTa alloys were amorphous TiO2 without an evidence of the crystalline anatase or rutile forms of TiO2. Scanning electron microscopy revealed that the average diameters of the small and large nanotubes on the Ti–30Nb alloy not containing Ta were approximately 100nm and 400nm, respectively, whereas the small and large nanotubes on the alloy had diameters of approximately 85nm and 300nm, respectively. As the Ta content increased from 0 to 15wt.%, the average lengths of the nanotubes increased from 2μm to 3.5μm. Energy-dispersive X-ray spectroscopy indicated that the nanotubes were principally composed of Ti, Nb, Ta, O and F. Contact angle measurements showed that the nanotube surface had good wettability by water droplets.

Molecular characterization of lipid fractions from extremely water-repellent pine and eucalyptus forest soils

There is little information available about the molecular composition of organic fractions with a possible bearing in soil water repellency. Extremely water-repellent forest soils developed on granites or schists, under vegetation of pine or eucalyptus, were used for sequential isolation of two lipid fractions: free lipid extracted with petroleum ether and ‘bound’ lipid obtained with the same solvent after 2M H3PO4 pre-treatment. Soil water repellency tests were carried out, and lipids were analyzed by gas chromatography/mass spectrometry (GC–MS). Free lipids in soils under eucalyptus consisted mainly of sesquiterpenes (globulol, aromadendrene, eudesmol and ledene) whereas soils under pine included diterpene resin acids (mainly dehydroabietic, pimaric and seco-dehydroabietic) and phenol. Free alkanes (C15 to C37) displayed homologous series typical in epicuticular waxes, whereas free fatty acids series showed bimodal distribution.‘Bound’ lipids consisted almost exclusively of fatty acids (mainly C16 and C18 acids), and alkanes (maximum at C27 or C28 and no even-to-odd C-number preference). Major compounds related to soil water repellency are typically found in higher plants and are not synthesized by microorganisms. After removing free lipids, soil water repellency decreased slightly but remained extreme. After extraction of bound lipids, the repellency considerably decreased, but did not disappear completely. As regards the effect of the lipid fractions in soil water repellency, it was clear the dominant role of the vegetation type in the case of free lipid, whereas for bound lipid, repellency mainly represents an emergent property arising from strong interaction between organic matter and the geological material.The results suggest that soil lipids only explain a part of the soil water repellency, which also depends on surface properties of the soil matrix, i.e., not only depends on hydrophobic coatings but probably of diffusion of hydrophobic cements into micellar associations self-organized into zonal structures in humus–clay matrix.

Scan Rate and Fluoride Concentration Effect on the Anodic Growth of Self-Aligned Titanium Dioxide Nanotubes in Phosphates

Formation of titania nanotubes at different scan rates of polarization during the first stage of anodizing titanium in 1M H3PO4 with the addition of various amounts of HF (0.2–0.4 wt.%) which consisted of a potential ramp to 20V with a scan rates of 400-600 mV/s. Insight into current/voltage curves allowed to identify the incubation of nanotubes by examination of current transient slope changes. The lowest values of the oxide layer breakdown time tbreak were observed at 500mV/s and 0.3%wt.HF, when the most homogenous titania nanotube, as observed with SEM and EDS, were obtained. Also the concentrations of phosphates and fluorine in titania nanotubes (XPS) were the highest for that conditions. These results suggest that to reach the equilibrium between oxidation/dissolution processes, transport of fluorides in oxide may be crucial.

Apricot juice as green corrosion inhibitor of mild steel in phosphoric acid

The corrosion protection of mild steel in 1M H3PO4 solution by apricot juice was studied at different temperatures by weight loss technique. Adsorption, activation and statistical studies were addressed in this work. Adsorption studies showed that inhibitor adsorbed on metal surface according to Langmuir isotherm. Average value of heat of adsorption was −14.93kJ/mol indicates a spontaneous physical adsorption on metal surface. Activation parameters did not changed with addition of inhibitor indicates that there is no change in reaction mechanism. Analysis of variance (ANOVA) was also applied. This analysis showed that the corrosion rate influenced by temperature, inhibitor concentration and combined interaction of them.

A new and very simple procedure for the differential pulse polarographic determination of ultra trace quantities of tungsten using catalytic hydrogen wave and application to tobacco sample

In this work a new and very simple differential pulse polarographic method is established for the trace determination of tungsten using catalytic hydrogen peak. For its determination, polarograms have been taken in various electrolytes including Britton–Robinson buffer (pH=2.0, pH=4.0, pH=5.0 and pH=6.0), nitric acid, hydrochloric acid, perchloric acid and phosphoric acid. The highest peak was obtained in the presence of 0.01M H3PO4 +0.1M KCl (pH=2.0–2.5) which appeared at −1.1V. The effects of pH, phosphate concentration, type of electrolyte on this peak have been studied. The height of the hydrogen catalytic peak was increasing with the addition of Mo(VI). Formation of a heteropoly acid was responsible of the catalytic hydrogen peak. The best condition for the determination of 5×10−8MW(VI) was found to be 1×10−5M Mo(VI) and 1×10−2M H3PO4+0.1M KCl (pH=2.0–2.5).The interference effect of Cu(II), Pb(II), Sn(IV), Mo(VI), Se(IV), As(III) and Zn(II) have also been studied. Among these ions only in the presence of As(III), the catalytic hydrogen peak of tungsten (shown as Mo–W) overlapped with the hydrogen catalytic peak of arsenic (Mo–As). This interference could be eliminated by oxidizing As(III) into As(V) using HNO3. With the newly established method the limit of detection (LOD) was 1.3×10−9M (S/N=3). This method was applied successfully for the determination of tungsten in digested tobacco sample.