Mixture Of Phosphoric Acid Research Articles

Determination of stoichiometry of Li 1+ yCoO 2 materials by flame atomic absorption spectrometry and automated potentiometric titration

A rapid, accurate and precise analytical method to determine the stoichiometry of pure, excess lithium and magnesium-doped Li 1+ y CoO 2 materials is described. The method is based on the determination of lithium, cobalt and magnesium by flame atomic absorption spectrometry after dissolution of samples in dilute hydrochloric acid. Five-point calibration curves using aqueous standard solutions have been constructed for all the analytes. Relative standard deviation (R.S.D.) of five repeated measurements are better than 0.3% for all metals when the absorbance signal of analytes is set near the middle of the regression lines. The total oxygen content is indirectly determined by potentiometric titration of average oxidation state of cobalt. The Co 3+ present in the oxide powders is reduced to Co 2+ at room temperature with a known excess of 0.1 M Fe 2+ solution in 6 M sulphuric and phosphoric acid mixture. The samples completely dissolved in a few minutes developing a pink coloured and clear solution. The excess of Fe 2+ ions is back titrated with potassium dichromate standard solution using automated potentiometric end-point detection. The difference between the total cobalt content (found by AAS) and Co 3+ (found by potentiometric titration) gives the amount of Co 2+ present in the materials. The S.D. of the determined Co 3+ value has been estimated to be below 0.03 mg for samples of 10–20 mg. By the proposed method the LiCoO 2 is well characterised and can be applied as a standard reference material for use in lithium batteries technology.

Rapid, low cost thin-layer chromatographic screening method for the detection of ochratoxin A in green coffee at a control level of 10 microg/kg.

A thin-layer chromatographic (TLC) screening method was developed for the detection of ochratoxin A (OTA) in green coffee at a control level of 10 microg/kg. The method is based on extraction of OTA with a mixture of phosphoric acid and dichloromethane, purification by liquid-liquid partition into sodium hydrogen carbonate, separation by normal-phase TLC, and detection by visual estimation of fluorescence intensity under a UV lamp at 366 nm. The method was validated by performing replicate analyses of uncontaminated green coffee material spiked at 3 different levels of OTA (5, 10, and 20 microg/kg), and also by comparing results obtained on a series of test trial green coffees naturally contaminated with OTA (range 0.2 to 136.7 microg/kg) with those measured by a quantitative immunoaffinity/HPLC method. The agreement between the two methods was excellent, and neither false positive nor false negative results were recorded. This screening method is rapid, simple, robust, and very cheap, which makes it particularly well adapted for implementation in coffee-producing countries.

Determination of captopril in biological samples by high-performance liquid chromatography with ThioGlo 3 derivatization.

Captopril, a well-known angiotensin converting enzyme (ACE) inhibitor, is widely used for treatment of arterial hypertension. Recent studies suggest that it may also act as a scavenger of free radicals because of its thiol group. Therefore, the present study describes a rapid, sensitive and relatively simple method for the detection of captopril in biological tissues with reverse-phase HPLC. Captopril was first derivatized with ThioGlo 3 [3H-Naphto[2,1-b]pyran,9-acetoxy-2-(4-(2,5-dihydro-2,5-dioxo-1H-pyrrol-1-yl)phenyl-3-oxo-)]. It was then detected by fluorescence-HPLC using an Astec C(18) column as the stationary phase and a water:acetonitrile:acetic acid:phosphoric acid mixture (50:50; 1 mL/L acids) as the mobile phase (excitation wavelength, 365 nm; emission wavelength, 445 nm). The calibration curve for captopril was linear over a range of 10-2500 nM and the coefficient of variation acquired for the within- and between-run precision for captopril was 0.5 and 3.8%, respectively. The detection limit of captopril with this method was found to be 200 fmol/20 microL injection volume. Its relative recovery from biological samples was determined to the range from 93.3 to 105.3%. Based on these results, we believe that our method is advantageous for captopril determination.

Transmission Electron Microscopy Study of the Microstructure of Np- Etched CdTe Thin Films

Polycrystalline CdTe is a promising candidate for solar cells due to its nearly ideal band-gap, high absorption coefficient, and ease of film fabrication. Small-area CdTe/CdS cells with efficiencies of 16.0% have been demonstrated. The structure of a typical CdTe/CdS solar cell (Figure 1) consists of a glass superstrate, on which a thin layer of SnO2 is deposited (front contact), n-type CdS, p-type CdTe, and a back contact. Prior to applying the back contact to the CdTe, etching of the CdTe surface using a mixture of nitric and phosphoric (NP) acids is normally needed. It is known that the etching depletes a crystalline CdTe surface of Cd and creates a Te-rich layer. Two effects of the Te-rich layer has been proposed, namely, forming a Te-CdTe low-series-resistance contact and improving CdTe device stability by the gettering of Cu. Thus, the NP etching is an important process in the CdTe device fabrication. in this paper, we report on transmission electron microscopy (TEM) study of the microstructure of the surface of NP etched CdTe thin films.

High-performance liquid chromatographic method for the determination of di(2-ethylhexyl) phthalate in total parenteral nutrition and in plasma

A simple, rapid and sensitive reversed-phase high-performance liquid chromatographic method with UV detection was developed for the quantification of di(2-ethylhexyl) phthalate (DEHP) in parenteral nutrition admixtures containing fat emulsion and in plasma samples of children daily treated by total parenteral nutrition. The analyte and the internal standard, di- n-heptyl phthalate, were extracted twice using hexane and the organic layer separated and dried under nitrogen. The residues were reconstituted with acetonitrile and 20 μl was injected into a Waters Spherisorb C 18 column, the UV detector was set at 202 nm. The mobile phase was acetonitrile–aqueous buffer (triethylamine 0.08% adjusted to pH 2.8 with 1 M phosphoric acid) mixture (88:12, v/v) and it was pumped at 1 ml/min. Average recoveries were 97% or greater. This method was successfully used to investigate the amounts of DEHP which can leach from bags and tubing into fat emulsion and which could contaminate children under long-term parenteral nutrition. On the other hand, the circulating DEHP concentrations were estimated in four children under regular long-term parenteral nutrition.

Adamantylazoles: IV* acid-catalyzed adamantylation of pyrazoles

Pyrazoles with pKBH+ no more than 0.8 and having substituents in 3(5) position with effective van der Waals radii not exceeding 2 A in a mixture of phosphoric and acetic acids at weight ratio 4:1 (H0 -1,8) react with 1-adamantanol to afford the corresponding 1-(1-adamantyl)- or 1,4-di(1-adamantyl)pyrazoles.

Improved Phosphoric Acid Mixtures for Nitride Strip

Improved Phosphoric Acid Mixtures for Nitride Strip

A kinetic study of phospholipid extraction by degumming process in sunflower seed oil

AbstractDuring the refining process of vegetable oils (degumming), phospholipids are eliminated by thermal treatment with water (hydratable phospholipids, HP) and other degumming agents such as phosphoric acid, citric acid, or acid mixtures (nonhydratable phospholipids, NHP). Samples of pressed crude sunflower oils were degummed with water and acids, and the corresponding pellets (gums) and supernatant oils were obtained by centrifugation. During the water degumming process, a decrease of more than 98% in the phosphatidylcholine (PC) content was achieved in 5 min; phosphatidylethanolamine (PE) was the most difficult compound to be removed. Phosphatidylserine, phosphatidic acid, and phosphatidylinositol (PI) presented an intermediate behavior. The optimal contact time for quantitative extraction of the most important HP (PC, PI, and PE) in crude sunflower oils was 35 min. For acid treatments, a rapid elimination of the residual levels of PC was registered (5 min); the optimal contact times for the quantitative removal of the NHP were 35 min for phosphoric acid und acid mixture, and 25 min for citric acid. Taking into account that PE was the most difficult component to be removed, its level could be used as a monitor to evaluate the efficiency of the degumming process.

Studies on uranium extraction from phosphoric acid using di-nonyl phenyl phosphoric acid-based synergistic mixtures

During acidulation of phosphate rock with sulphuric acid to produce phosphoric acid for fertilizer application, the uranium values contained in the rock also become solubilised. The phosphoric acid produced by the ‘di-hydrate’ process, containing 26–30% P 2O 5, called the ‘weak phosphoric acid’ (WPA), is concentrated to >50% P 2O 5 grade, known as ‘merchant grade acid’ (MGA). The ‘hemi-hydrate’ process directly yields acid of high P 2O 5 content. The uranium concentration varies with acid concentration, provided oxidising conditions are maintained so that selective precipitation of uranium does not take place. Depending on the rock used, the acid produced can contain 0.0050–0.05 g U 3O 8/L. Separation of uranium by solvent extraction employing a novel synergistic combination of organo-phosphorus reagents is reported in this paper. In particular, the solvent mixture of di-nonyl phenyl phosphoric acid (DNPPA) with di-butyl butyl phosphonate (DBBP) in an aliphatic diluent has been found to be a stronger extractant than the commonly used combination of di-(2-ethyl hexyl) phosphoric acid (DEHPA) with tri- n-octyl phosphine oxide (TOPO). The DNPPA–TOPO mixture is an even stronger extractant. Results on extraction from both WPA and MGA are reported. Stripping of uranium from the organic phase was achieved with concentrated phosphoric acid in the presence of Fe +2 reducing agent at elevated temperature. Stripped uranium was subjected to a second cycle of extraction-stripping and recovered as a peroxide precipitate of high purity. Brief results on allied areas of acid pre-treatment and post-treatment are included.

Phosphato complexes of beryllium(II): a 31P and 9Be nuclear magnetic resonance study

31P and 9Be NMR spectra of mixtures of beryllium(II) and phosphoric acid have been interpreted to support the speciation previously proposed on the basis of potentiometric measurements. Nine 31P lines were observed at ≈0.4, −3.67, −4.51, −5.57, −6.5, −7.08, −8.81, −9.3 and −11.0 ppm relative to 85% phosphoric acid as external standard. The signal in the range 0.36–0.56 was assigned to rapidly exchanging H 3PO 4, H 2PO 4 − with a further contribution from Be 3O(H 2PO 4) 6 2−. The peaks at −3.67 and −4.51 ppm were ascribed to isomers of Be(H 2PO 4) 2. The species Be(H 2PO 4) + also gives a signal centred at −4.51 ppm. The peak at −6.5 ppm was assigned to Be 3(OH) 3(H 2PO 4) 3. The peaks at −5.58, −8.81 and −9.3 ppm are tentatively assigned to isomers of the complex Be 2(OH)(H 2PO 4) 2+. Signals observed at −7.08 and −11.0 ppm could not be assigned to any of the complexes proposed by potentiometry. The 9Be NMR data are also consistent with the model previously proposed.

Synthèse et étude structurale par RMN 31P et 183W d’un octadécatungstomonophosphate de type Dawson [H4PW18O62]7– et de deux de ses dérivés, [H4PW17O61]11– et [Zn(H2O)(H4PW17O61)]9–

Abstract Syntheses and 31P and 183W NMR structural characterization of a novel Dawson-type tungstophosphate [H4PW18O62]7– and of its lacunary and zinc-substituted derivatives [H4PW17O61]11– and [Zn(H2O)(H4PW17O61)]9–. Three novel polyoxotungstophosphates have been synthesized as potassium salts: a Dawson-type octadecatungstomonophosphate, K7[H4PW18O62] and its lacunary and zinc-substituted derivatives K11[H4PW17O61] and K9[Zn(H2O)(H4PW17O61]. The saturated compound was obtained by refluxing for 60 h a mixture of sodium tungstate and phosphoric acid (W/P=20) at pH 2.2. 31P-NMR spectroscopy showed the formation of a single product only after prolonged heating, while a mixture of three isomers was initially obtained. The derivatives were obtained by controlled alkaline degradation as usual for Dawson-type compounds. The structure of [H4PW18O62]7– (abbreviated as PW18) and of its derivatives was inferred from the comparison of their spectroscopic and electrochemical features with those of [P2W18O62]6– (P2W18). The 31P-NMR spectrum of each of these species displays a unique signal at −6.7 ppm for PW18, −2.05 ppm for PW17 and −2.95 ppm for PW17Zn. When compared with P2W18 (−12.45 ppm), with the PW8 unit of α2-P2W17 (−7.1 ppm) and the PW8Zn unit of α2-P2W17Zn (−8.6 ppm), the data for PW17 and PW17Zn are consistent with the removal or the replacement of one tungsten atom in a PW9 half-unit. Moreover, in the region of the PO stretching vibrations the IR spectra of PW17 and PW17Zn exhibit only one band, which is in favour of the removal of a tungsten atom from the cap of the PW9 unit. The 183W-NMR spectrum of PW18 exhibits four resonances at −181.3 (6W; d, 2JWOP=1.46 Hz) and −144.9 ppm (3W; d, 2JWOP=1.26 Hz) assigned to the PW9 unit, and at −127.8 ppm (6W; s) and −135.7 ppm (3W; s) assigned to the HnW9 unit. The three homonuclear 2JWOW coupling constants are in the range 20–27 Hz, which further confirms that the PW18 anion, like P2W18 consists of two A-type half-anions. Attempts to locate the four protons by 1H-NMR and to solve the crystal structure of PW18 by X-ray diffraction have been so far unsuccessful; however the isolated compound is probably the α isomer and the two minor products could be the β or γ isomers. The related tungstoarsenates were also obtained in similar conditions. © 2000 Academie des sciences / Editions scientifiques et medicales Elsevier SAS polyoxometalates / Dawson-type tungstophosphates / 31P NMR / 183W NMR

Binding of phosphate with a simple hexaaza polyammonium macrocycle.

A mixture of dihydrogen phosphate and phosphoric acid has been crystallized with a hexaprotonated 26-membered polyammonium macrocycle, 1,4,7,14,17,20-hexaazacyclohexacosane, as the counterion. The complex crystallizes in the monoclinic space group P2(1)/c with unit cell parameters of a = 10.006(2) A, b = 12.525(1) A, c = 19.210(2) A, beta = 102.91(1) degrees, and V = 2346.6(5) A3. The hexaprotonated macrocycle is located on a crystallographic center of inversion and is surrounded by eight phosphate anions. Six of the phosphates are dihydrogen phosphates (H2PO4-), and the other two are neutral phosphoric acid molecules. Intricate hydrogen-bonding networks, involving the anionic and neutral phosphates and the protonated macrocycle, dominate the crystal lattice. Potentiometric studies using NaCl as the supporting electrolyte indicate high formation constants for the triprotonated macrocycle, H3L3+, with PO4(3-) at pH approximately 9.5 (log K = 4.55(4)), for the tetraprotonated macrocycle, H4L4+, with monohydrogen phosphate, HPO4(2-), at pH approximately 8.0 (log K = 6.01(3)), and for ditopic complexes with H5L5+ and H6L6+ and dihydrogen phosphate, H2PO4-, at pH approximately 4.0 (log K = 6.16(6)) and pH approximately 2.5 (log K = 6.44(5)), respectively. The ditopic behavior in the simple polyazamacrocycle receptor is a somewhat unusual occurrence, as is the finding of phosphoric acid species in the crystal structure.

A study of the back contacts on CdTe/CdS solar cells

Conventional back contacts on CdTe/CdS solar cells are commonly made with Cu/Au or Cu/graphite. Often the contact limits the solar cells efficiency and the performance degrades because of Cu diffusion to the junction. In order to get stable and ‘non-rectifying’ back contacts Sb has been applied. Pre-deposition etching treatments, post-deposition annealing, influence of Sb layer thickness and stability issues have been studied. Different etchants not only clean the CdTe surface but they also produce a conducting Te layer on the grain boundaries. Using a mixture of nitric and phosphoric acid and Sb/Au as a back contact, 12.5% efficiency cells are obtained. The stability of solar cells depends on the etching solution. Stability tests under continues 1 sun illumination suggest that under optimum condition stable cells with Sb/Au contact can be developed. A comparative analysis of the photovoltaic properties of solar cells with different back contacts will be presented.

アルミニウムのアルカリ性化学研磨液における浴組成と光沢度，表面構造との関係について

Chemical polishing solutions for aluminum based on mixtures of phosphoric and nitric acid cause air pollution with hazardous gaseous emissions, such as NOx, during the chemical polishing process, and cause water pollution due to the effluent of wastewater that contains phosphates and nitrates. Hence, the authors attempted to polish aluminum in an alkaline solution containing sodium hydroxide as an alkaline agent and sodium persulfate as an oxidizing agent. In this process, exceptionally bright surfaces of aluminum were obtained; that is, the brightness of the surface polished in the alkaline solution was comparable with that of the surface polished in an acid chemical polishing solution. The composition of the alkaline solution that had the least polishing effect had a concentration of sodium hydroxide in a range of 0.5 to 1.5% by weight for pure aluminum and a range of 1.0 to 2.0% by weight for commercially pure aluminum, while the concentration of sodium persulfate was 35% by weight. At with a high magnification on a scanning electron microscope (SEM), network patterns were observed over the entire polished surface of the aluminum polished in the alkaline solution and that in the acid chemical polishing solution. On the surface of the commercially pure aluminum polished in the alkaline solution, very small projections were observed by SEM, that were identified by electron probe microanalysis (EPMA) as insoluble phases that included foreign elements such as Fe and Si in the aluminum. On the other hand, on the surface of the aluminum polished in the acid chemical polishing solution, very small pits were observed, formed by dissolution of the phases in the acid solution. Also, use of x-ray photoelectron spectroscopy (XPS) and fourier transform infrared spectroscopy (FT-IR) indicated that the oxide films formed on the surface of the aluminum polished in the alkaline solution were thicker and contained a larger amount of hydroxyl radicals than those on the surface polished in the acid chemical solution.

In vitro aging of a calcium phosphate cement.

Cement samples made of beta-tricalcium phoshate (beta-TCP), phosphoric acid (PA) and water mixtures were incubated in several aqueous solutions to determine their stability over time. The effects of the cement composition and the incubating temperature were investigated in more detail. The cement samples contained mostly dicalcium phosphate dihydrate (DCPD) and remnants of beta-TCP crystals. Depending on the initial cement composition, a certain amount of dicalcium phosphate (DCP) crystals were formed. The larger the initial PA concentration, the larger the DCP amount. After setting, the cement composition was stable for at least 16 days up to 60 degrees C. Above that temperature, the DCPD crystals decomposed into DCP crystals. The latter reaction provoked a decrease of the pH of the incubation solution, phenomenon expected for a cement sample containing an excess of PA. As the cement samples contained an excess of beta-TCP, it was postulated that beta-TCP crystals became so covered by DCP or DCPD crystals during setting that the setting reaction was stopped prematurely. The latter phenomenon gave a good explanation for the low pH values measured in the incubation solutions.

COMPARATIVE STUDY ON THE CONSTITUTENTS OF SOUND AND DISEASE AFFECTED SISSOO (DALBERGIA SISSOO ROXB) WOOD

A comparative study has been conducted on the constituents of sissoo (Dalbergia sissoo) wood to find out the effect of causal agent of massive mortality. Ten ideal pieces of affected and four pieces of sound wood were collected from different plantations. The sawdust of both sound and affected wood was freed from extractives with alcohol benzene mixture in a soxhlet apparatus. Cellulose and hemicellulose were determined by treatment of 10% sodium hydroxide, acetic acid and ethyl alcohol, and lignin by 72% sulfuric acid and phosphoric acid mixture. Distinct variations were found among the constituents of sound and affected sissoo wood. Hemicellulose and lignin content of affected wood were found 5.5 and 7.5% lower than those of sound wood respectively. The causal agent of massive mortality brought about these differences on account of the degradation and decomposition of lignin and hemicellulose.

Removing as from converter dust by a hydrometallurgical method

Research has been conducted at the Faculty of Metallurgy, Technical University, Kosice, to develop a hydrometallurgical method for removing arsenic from copper converter dust. The process consists of a selective leaching of the flue dust in which arsenic is dissolved in sodium-sulfide solution and then removed by precipitation methods using various agents: copper sulfate, a mixture of phosphoric acid with calcium hydroxide, calcium oxide, and ferrous or ferric sulfate. In principle, arsenic can be removed as a marketable product (copper arsenate for wood preservation) or as stable precipitate compounds suitable for safe landfill disposal under existing U.S. Environmental Protection Agency regulations.

A new method for enhancing the performance of red mud as a hydrogenation catalyst

A new method is presented for improving the performance of red mud as a hydrogenation catalyst (a residue from the production of alumina by the Bayer process that contains iron oxides), based on the method developed by K.C. Pratt and V. Christoverson, Fuel 61 (1982) 460. The activation method consists essentially in dissolving red mud in a mixture of aqueous hydrochloric and phosphoric acids, boiling the resulting solution, adding aqueous ammonia until pH=8, and filtering, washing, drying and calcining the resulting precipitate. The catalyst thus obtained is characterised, and after sulphidation, tested (activity and life) for the hydrogenation of a light fraction of an anthracene oil. The catalytic performance is compared with that of sulphided untreated red mud and sulphided red mud activated by the method of Pratt and Christoverson. This activation method has proved to be more effective in improving the performance of red mud as a hydrogenation catalyst than the method of Pratt and Christoverson, since the activated catalyst presents a slightly higher level of activity and a markedly extended active life.

Determination of succinylcholine in human plasma by high-performance liquid chromatography with electrochemical detection

An alternative HPLC method for the quantification of the depolarizing neuromuscular blocking agent succinylcholine in human plasma is described. Drug spiked plasma and patient plasma samples were extracted using a C 1 solid-phase cartridge. Succinylcholine was separated on a Cyano column and quantitated using electrochemical detection at a potential of 450 mV and 750 mV. Mobile phase consisted of a mixture of phosphoric acid–acetonitrile–methanol (45:35:25) adjusted to an apparent pH of 5. Standard curves for the quantitation were linear in the range of 250–8000 ng/ml. Between-day and within-day relative standard deviations were 5.1% and 1.7%, respectively. Mean drug recovery and accuracy was 68% and 104%, respectively.

Surface Finishing of High Speed Print Bands: II. An Electrochemical Process for Microfinishing of Hardened Fe‐13Cr Stainless Steel

An electrochemical process has been developed to obtain microfinishing of hardened Fe‐13Cr stainless steel. The electrolyte is a mixture of phosphoric acid, sulfuric acid, and glycerol. Optimum conditions have been determined that lead to mirror finishing of the work piece over a wide range of current density. The process operates at ambient temperature and is insensitive to slight variations in temperature of the electrolyte. The beneficial effects of glycerol is due to its influence on the transport properties of the electrolyte and the diffusing species. The process is suitable for surface finishing of high speed print bands.