Sodium Hydroxide Medium Research Articles

Spectrophotometric determination of metoclopramide hydrochloride in pharmaceutical tablets, by diazotization-coupling method with 1-naphthol as the coupling agent

Simple, rapid and sensitive spectrophotometric method was proposed for the analysis of metoclopramide hydrochloride (MPH) in pure form as well as in pharmaceutical tablets. The method is based on the diazotization reaction of MPH with sodium nitrite in hydrochloric acid medium to form diazonium salt, which is coupled with 1-naphthol in sodium hydroxide medium to form azo dye, showing absorption maxima at 550 nm. Beer’s law is obeyed in the concentration range of 0.4 – 18 µg mL-1 of MPH with detection limit 0.5448 µg mL-1. The molar absorptivity and Sandell’s sensitivity are 3.4969 × 104 L mol-1 cm-1 and 0.0101 µg cm-2, respectively. The method was successfully applied to the determination of MPH in pharmaceutical tablets without any interference from common excipients used as additives in tablets. The results agree favorably with the official British Pharmacopoeia method.

Formation and stabilization of tetragonal phase in sol–gel derived ZrO2 treated with base-hot-water

Zirconia (ZrO 2 ) nanoparticles have been prepared by sol–gel route. Low temperature crystallization using base-hot-water treatment (BHWT) was conducted for the sol–gel derived ZrO 2 gel powders at 90 °C and at pH 14 for various periods of time. Single phase nanocrystalline tetragonal ZrO 2 (t-ZrO 2 ) was successfully obtained by immersing the dry gel powders into hot, basic condition water and kept at rest for given time. BHWT at pH 14 with sodium hydroxide (NaOH) medium by digestion for 12 h and then continuing with stirring for 12 h resulted in the formation of t-ZrO 2 with surface area of 292 m 2 /g and crystal size of 7 nm. Study on base solution medium, using NaOH, shows that the sodium ions play an important role for the formation of t-ZrO 2 by incorporating into the crystal structure during the treatment. BHWT also effectively removed organic groups of the sol–gel derived ZrO 2 nanoparticles.

A comparative study of vanadium extraction by Aliquat-336 from acidic and alkaline media with application to spent catalyst

A comparative study of the solvent extraction of vanadium(V) from hydrochloric acid and sodium hydroxide media was separately carried out using Aliquat-336 (methyltrioctylammonium chloride) extractant dissolved in kerosene containing 10% n-octanol as phase modifier. The different parameters affecting the extraction process including acid, alkali, extractant, metal concentrations, phase ratio and loading capacity as well as the temperature were separately investigated. Vanadium(V) species were suggested to be (H 2V 10O 28) 4 − and (VO 3OH) 2 − in acidic and alkaline solutions, respectively. Based on the obtained results, the extraction equilibria were deduced and the optimum conditions for the extraction of vanadium were proposed. The method was applied for treatment of the spent catalyst used in the manufacture of sulphuric acid industry giving a recovery of 93.0% for vanadium in the whole process.

Direct room-temperature synthesis of methyl-functionalized Ti-MCM-41 nanoparticles and their catalytic performance in epoxidation

Methyl-functionalized Ti-MCM-41 nanoparticles with a size of 80 to 160 nm (Me-Ti-MCM-41 NP) were directly prepared via a dilute solution route by the co-condensation of tetraethoxysilane and methylalkoxysilanes in sodium hydroxide medium at room temperature. The characterization results showed the existence of ordered hexagonal mesoporous structure and tetrahedral Ti species in the nanoparticles. In the epoxidation of cyclohexene with tert-butyl hydroperoxide and aqueous H 2O 2, Me-Ti-MCM-41 NP samples displayed higher turnover frequencies (TOFs) for cyclohexene and initial reaction rates compared to Ti-MCM-41 and methyl-functionalized Ti-MCM-41 with normal particle size and to non-functionalized Ti-MCM-41 nanoparticles. Simultaneously, a higher selectivity for cyclohexene epoxide was observed in the case of aqueous H 2O 2, suggesting that the hydrolysis of cyclohexene epoxide with water is reduced on Me-Ti-MCM-41 NP samples. The improved catalytic behavior of Me-Ti-MCM-41 NP is discussed both in terms of the nanosize and methylation of the surface of the catalyst particles. The regeneration of Me-Ti-MCM-41 NP with tert-butyl hydroperoxide solution was evaluated via washing and calcination approaches.

Determination of terbutaline sulfate by capillary electrophoresis with chemiluminescence detection

A novel capillary electrophoresis (CE) with chemiluminescence (CL) detection method for determination of terbutaline sulfate has been developed. This method is based on the chemiluminescence reaction of potassium ferricyanide with luminol in sodium hydroxide medium sensitized by terbutaline sulfate. With the peak height as a quantitative parameter applying optimum working conditions, terbutaline sulfate is determined over the range of 7.0 × 10 −8 to 3.6 × 10 −6 M with a detection limit of 3.0 × 10 −8 M. The relative standard deviation (RSD) was 4.6% for 6.0 × 10 −7 M terbutaline sulfate ( n = 11). The proposed method has been applied to determination of terbutaline sulfate in commercial terbutaline sulfate drug and spiked in human urine with satisfactory results.

Chemiluminescence determination of gossypol at trace levels using flow injection as sample introduction techniques

A simple and sensitive flow injection method with chemiluminescence (CL) detection is developed for the determination of gossypol at trace levels. The method is based on the reaction of luminol with ferricyanid in a sodium hydroxide medium sensitized by gossypol. Under the optimum conditions, the CL intensity is proportional to the concentration of gossypol over the range of 1.11 × 10−17 − 2.78 × 10−16 M in an acidic solution and 8.00 × 10−11 − 7.39 × 10−8 M in a neutral solution with correlation coefficients of 0.9983 and 0.9905, respectively. The detection limit is 1.48 × 10−18 M (3σ). The proposed method has been applied to the determination of gossypol in cottonseeds and pharmaceutical preparations with satisfactory results. The CL mechanism is discussed by examining the CL emission spectrum and the effect of various free radical scavengers on the CL emission intensity.

Mechanistic aspects for the oxidation of sunset yellow dye by chloramine-T in presence of perchloric acid and in sodium hydroxide medium catalyzed by Os(VIII): A spectrophotometric kinetic approach

The kinetics of oxidation of sunset yellow (SY) by sodium- N-chloro- p-toluenesulfonamide or chloramine-T (CAT) was studied spectrophotometrically in HClO 4 and NaOH media with Os(VIII) as a catalyst in the latter medium at 298 K and 303 K, respectively. In acid medium, the experimental rate law is −d[CAT]/d t = k[CAT] 0[SY] 0[HClO 4] −0.46. Alkali accelerates the rate of reaction and the rate law takes the form −d[CAT]/d t = k[CAT] 0[SY] 0[NaOH] 0.23[OsO 4] 0.84. The solvent isotope effect was studied using D 2O. Benzenesulfonic acid and 1,2-naphthoquinone-6-sulfonic acid were characterized as the oxidation products of SY. Under identical set of experimental conditions in alkaline medium, Os(VIII) catalyzed reaction is about seven-fold faster than the uncatalyzed reaction. Activation parameters for the overall reaction and also with respect to catalyst have been evaluated. The observed results have been explained by plausible mechanisms and the related rate laws have been deduced.

Interfacial chemistry of organic conversion film on AZ61 magnesium alloy surface

The anodic electrochemical behavior of AZ61 magnesium alloy in sodium hydroxide medium in the absence and presence of p-nitro-benzene-azo-resorcinol (PNBAR) was studied using electrochemical techniques. In the presence of PNBAR, organic conversion film formed on the surface of magnesium alloy. The nature of chemical mechanisms, bonds, and structures at the interface of PNBAR/magnesium alloy was investigated by using energy dispersive spectrometer (EDS) analysis and Fourier transform infrared spectroscopy. An in situ electrochemical deposition was evidenced to produce a corrosion protective barrier by the formation of organic conversion film of magnesium-PNBAR complex and to enhance film adhesion by the covalent bonds of Mg O N linkage. The linear sweep voltammetry experiments and the score tests were used to investigate the adhesion and evaluate the potential of corrosion resistance of organic conversion film. The results indicated the corrosion resistance of magnesium alloy was improved, the organic conversion film showed excellent adhesion not only to the substrate but also to the outer paint coatings.

SPECTROPHOTOMETRIC DETERMINATION OF MINOXIDIL IN PURE FORM AND ITS PHARMACEUTICAL PREPARATIONS

Four simple, accurate, sensitive and economical procedures (A-D) for the estimation of minoxdil, both in pure form and in pharmaceutical formulations have been developed The first method (A) is based on the Oxidatton of the studied drug by a known excess of potassium permanganate in sulfuric acid medium directly .followed by measuring the decrease in absorption of KMnO4 , (A method ) at 525.6 nm. The second method (B) is based on the same principle with subsequent determination of unreacted potassium permanganate using methylene blue dye in the same acid medium at a suitable 66- am. The third method is based on measuring manganate produced from the reaction of minoxidil with potassium permanganate in sodium hydroxide medium at ʎmax 610 nm. While the fourth method is based on oxidation of the drug by Fe3+ in the presence of bipyridyl (bipy) in acetate buffer of pH 4.22 resulting in the formation of tris-complex which demonstrated at ʎmax 530 nm. Regression analysis of Beer-lambert plots showed good correlations in the concentration ranges 8 0-40 . 2.0-20 and 2.0- 10 g ml respectively. Molar absorptivity and Sandell's sensitivity were calculated for each method the optimum reaction conditions and other analytical parameters were evaluated. The proposed methods were applied to the determination of this drug in laboratory prepared tablets which contains the same contents of Loniten tablets .produced by ( Pharmacia and Upjohn). The influence of the substances commonly employed as excipients with this drug were studied. The suggested methods were compared with reference one results have demonstrated that the methods are equally accurate and reproducible as the reference method

Studies on the behavior of Co 2+ and Zn 2+ in the conversion from FeOOH to magnetite in NH 3 (NaOH)–Fe 2+, Co 2+–H 2O medium under hydrothermal conditions

Crystalline FeOOH and Zn(II) doped FeOOH samples were prepared by a co-precipitation method using ferrous sulphate heptahydrate, zinc sulphate heptahydrate, ammonia, 3% hydrogen peroxide at 80 °C and pH value 3.0. These samples were characterized by XRD and were also chemically analyzed. The XRD patterns of pure FeOOH matched with that of Zn(II) doped FeOOH sample and showed no shift in their d-values, which indicated that Zn 2+ ions were adsorbed on the surface of FeOOH or on the surface of the crystalline lattice, and were not captured into the ferrite lattice. Chemical analysis showed that the molar ratio of Zn(II)/Fe in Zn(II) doped FeOOH sample was only 0.038 when this ratio was 0.5 in an initial reaction solution. These samples were treated in ammoniacal or sodium hydroxide medium in the presence of ferrous sulphate or cobalt sulphate under hydrothermal conditions. The converted products were analyzed both for ferrous, total iron, cobalt and zinc. Characterization was carried out using instrumental techniques such as SEM, FT-IR, XRD and magnetization characterization. Though the XRD patterns of the converted products showed presence of only magnetite in the NH 3–Fe 2+, Co 2+–H 2O converted medium, the FT-IR spectra and chemical analysis showed an un-reacted FeOOH in the converted product. Even though, the saturation magnetization of this magnetite was higher to 97.489 emu g − 1 . Furthermore, higher temperature increased the concentration of Co 2+ captured into spinel structure. The conversion were restrained in NH 3 concentration of less than 12 g/L and more than 25 g/L. However, increasing of Fe 2+/Co 2+ ratio in the NH 3–Fe 2+, Co 2+–H 2O medium made no distinct difference in the introduction of Co 2+ into spinel structure when concentration of Fe 2+ was enough. Compared with Zn-free FeOOH, it was difficult for Zn-doped FeOOH to convert to magnetite in the NH 3 (NaOH)–Fe 2+–H 2O medium. Furthermore, alkali species were critical in the above conversion. The content of Zn 2+ which was out of Zn-doped FeOOH solid state and entered into the outer solution was more in the NH 3 medium than that of the NaOH medium, but conversion from Zn–FeOOH into magnetite was easy in the NaOH medium. The explanations of above facts were given in the text.

Synthesis and catalytic activity of Ti-MCM-41 nanoparticles with highly active titanium sites

Ti-MCM-41 nanoparticles 80–160 nm in diameter (Ti-MCM-41 NP) were successfully prepared by a dilute solution route in sodium hydroxide medium at ambient temperature. Ti-MCM-41 NP were characterized by X-ray diffraction, nitrogen adsorption/desorption isotherms, SEM, TEM, FT-IR, and UV–vis spectroscopy. The characterization results showed the existence of highly ordered hexagonal mesoporous structure and tetrahedral Ti species in Ti-MCM-41 NP. In the epoxidation of cyclohexene with aqueous H 2O 2, Ti-MCM-41 NP displayed higher conversion and initial reaction rate than a Ti-MCM-41 sample with normal particle size (Ti-MCM-41 LP). Diffusion of the reactants was accelerated and the accessibility to the catalytic Ti species was enhanced in the shorter channels in Ti-MCM-41 NP samples. Ti-MCM-41 NP showed much higher selectivity for cyclohexene oxide compared with Ti-MCM-41 LP, suggesting reduced hydrolysis of cyclohexene oxide with water in the former case. The increased selectivity for cyclohexene oxide can be attributed to the lower concentration of residual surface silanols in Ti-MCM-41 NP and the shorter residence time of epoxide in the shorter mesoporous channels. Ti-MCM-41 NP also appears to be a suitable catalyst in the epoxidation of a bulky substrate, like cholesterol, with tert-butyl hydroperoxide.

Determination of trace amounts of cobalt in foods by polymer-phase fluorophotometry with thiamine

A selective and sensitive method for the determination of trace amounts of cobalt has been developed by polymer-phase fluorophotometry with thiamine as an emission reagent. The method is based on the fact that cobalt reacts with thiamine to form a strong fluorescent compound in 0.65% sodium hydroxide medium. The fluorescence intensities show a good linearity with the concentration of cobalt in the range of 2–56 μg/L. The fluorescence intensities were measured in 5-mm quartz cells with excitation and emission wavelengths at 375 and 438 nm, respectively. The detection limit is 0.61 μg/L and the RSD is 1.70%. The sensitivity of the method is four times the conventional fluorophotometry in solution. The fluorescent life of thiamine is longer in polymer than that in solution. The general coexisting ions have no interference to the reaction of cobalt and thiamine except for copper and iron ions. The proposed method was applied to the determination of trace amounts of cobalt in food samples with satisfactory results.

Photo-induced chemiluminescence-based determination of diphenamid by using a multicommuted flow system

This manuscript deals with the application of molecular connectivity calculations to predict the photo-induced chemiluminescent behaviour of the family of herbicides grouped as amides. Several compounds of this group were theoretically studied by means of a general discriminant equation formerly obtained, being 18 of them (plus eight from the chloroacetanilide sub-group) predicted with a high probability as photo-induced chemiluminescent. Empirical confirmation of the chemiluminometric behaviour was performed with some few commercially available amide herbicides. On the basis of these results, a new multicommutation-photo-chemiluminescent method is proposed for the determination of the diphenamid. The method is based on the photodegradation of the pesticide and then the resulting photo-fragment solutions are oxidized by K 3[Fe(CN) 6] in sodium hydroxide medium, at room temperature and 80 °C, for the photodegradation and chemiluminometric oxidation, respectively. The studied calibration up to 5.0 mg l −1, revealed a linear dynamic graph up to 20 mg l −1. The reproducibility between days resulted in a R.S.D. (in slope %) of 2.8 ( n = 5) and the repeatability with a %R.S.D. ( n = 20) of 4.3. LOD (s/n = 3) of 1 μg l −1 and sample throughput of 20 h −1. The influence of foreign compounds is also tested and the optimized flow assembly is applied to different kind of samples.

A new sensitive flow‐injection chemiluminescence method for the determination of H2‐receptor antagonists

Based on the chemiluminescence (CL) intensity generated from the potassium ferricyanide [K(3)Fe(CN)(6)]-rhodamine 6G system in sodium hydroxide (NaOH) medium, a new sensitive flow-injection chemiluminescence (FI-CL) method has been developed, validated and applied for the determination of three kinds of H(2)-receptor antagonists: cimetidine (CIMT), ranitidine (RANT) hydrochloride and famotidine (FAMT). Under the optimum conditions, the linear range for the determination was 1.0 x 10(-9)-7.0 x 10(-5) g/ml for CIMT, 1.0 x 10(-9)-5.0 x 10(-5) g/mL for RANT hydrochloride and 5.0 x 10(-9)-7.0 x 10(-5) g/mL for FAMT. During 11 repeated measurements of 1.0 x 10(-6) g/mL sample solutions, the relative standard deviations (RSDs) were all <5%. The detection limit was 8.56 x 10(-10) g/mL for CIMT, 8.69 x 10(-10) g/mL for RANT hydrochloride and 2.35 x 10(-9) g/mL for FAMT (S:N = 3). This method has been successfully implemented for the analysis of H(2)-receptor antagonists in pharmaceuticals.

Synthesis and Photocyclization of 1,2,4‐Triazole‐3‐thiones.

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Compressive properties and degradability of poly(ε‐caprolatone)/hydroxyapatite composites under accelerated hydrolytic degradation

Hydroxyapatite (HA) was incorporated as filler into polycaprolactone (PCL) matrix to improve the bioactivity as well as the compressive properties of the polymer composites that can be typically used in tissue engineering scaffolds. The compressive properties of five PCL/HA composites of different compositions were investigated in conjunction with the study of their rate of degradation. As PCL has a slow degradation rate, the experiment was conducted in a concentrated 5M sodium hydroxide medium to accelerate the degradation process. The compressive strength and modulus of all PCL/HA compositions were observed to decrease as the degradation experiment progressed, with samples having high HA content degraded most significantly as compared with samples with lower HA content. Pure PCL samples, however, were found to retain their mechanical properties comparatively well in the same degradation experiments. Although the addition of HA as filler into the PCL matrix was shown to have improved mechanical properties and bioactivity initially, these results do raise concerns of material properties being compromise during hydrolytic degradation.

Determination of the dissociation constants of some newly synthesized derivatives of 1,2,4-triazoline-3-thione in sodium hydroxide media

The behaviour of some newly synthesized derivatives of 1,2,4-triazoline-3-thione (4-butyl-5-octyl-2,4-dihydro-3 H -1,2,4-triazoline-3-thione, 4-allyl-5-octyl-2,4-dihydro-3 H -1,2,4-triazoline-3-thione, 4-phenyl-5-octyl-2,4- dihydro-3 H -1,2,4-triazoline-3-thione) was studied in aqueous sodium hydroxide solutions at different pH values with UV spectroscopy. The measurements were carried out immediately after preparation of the solutions, in the wavelength range from 190 nm to 360 nm, on a Varian Cary UV spectrophotometer. When the p H value of the solution increased from 5 to 9, the measured value of the absorbance decreased, while the absorption maximum shifted towards lower wavelengths. The dissociation constants were determined using the equation p KBH = log I + p H ( I = c (BH)/ c (B – )). The ionic strength of the solutions of 0.10 mol/dm 3 was adjusted with addition of NaClO 4 . The calculations were derived from the values of the absorbance from the spectra obtained experimentally and from the spectra reconstructed by using the method of characteristic vector analysis (CVA). The absorbance values were measured at four wavelengths, on and around the absorption maxima for each investigated compound. Also, the p KBH values were determined graphically and they were in good agreement with those obtained numerically. The obtained values of the p KBH were in the range from 7.45 to 7.54 and they were in a good agreement with the expected ones for this kind of compounds.

Synthesis and Photocyclization of 1,2,4-Triazole-3-thiones

Irradiation of thienyl and other substituted triazolothiones in a thin film reactor at 254 nm in an acetonitrile-dilute sodium hydroxide medium, furnished the respective triazolobenzothiazoles and, in some cases, the desulfurized product. The irradiation of anilinomethyl-, and aryloxymethyltriazolothiones under the above conditions also furnished the respective cyclized products and desulfurized compounds. Irradiation of benzyl substituted triazole thiones in the presence of triethylamine in benzene furnished the corresponding triazolothiazine and triazolodibenzazepine. Reaction of glycine hydrazide with aryl isothiocyanates furnished the triazolothiones, wherein glycine hydrazide functioned as a hydrazine-transferring agent. Irradiation of o-chlorophenyl substituted thione in basic acetonitrile medium furnished triazolodibenzdiazepine, whereas, the benzyl derivative furnished the triazolobenzothiazine.

Second Chemiluminescence Behavior of Fe2+, Fe3+ and Cr3+ in the Luminal-KMnO4 System

A novel flow injection chemiluminescence (CL) method has been developed for the determination of three metal ions, namely Fe2+, Fe3+ and Cr3+, based on the second CL (SCL) signal of the mixture of luminal with KMnO4 in a sodium hydroxide medium by the catalysis of Fe2+, Fe3+ or Cr3+. The possible CL mechanism of the systems, the influencing factors, and the optimum conditions for the reactions were investigated based upon the kinetic curve of the CL reaction, CL spectra, UV-visible spectra and some other experiments. Under the optimum conditions, the SCL intensity was directly proportional to the concentration of these metal ions in solution in the range of 0.10 - 100.00 mg l(-1) for Fe(2+), 0.50 - 7.50 and 7.50 - 200.00 mg l(-1) for Fe3+, 0.01 - 0.25 and 0.25 - 10.00 mg l(-1) for Cr3+. The detection limits (3 sigma/s) were 9.87 x 10(-6) g l(-1), 2.71 x 10(-6) g l(-1) and 5.25 x 10(-7) g l(-1) for Fe2+, Fe3+ and Cr3+, respectively.

Kinetics of sodium borohydride direct oxidation and oxygen reduction in sodium hydroxide electrolyte: Part I. BH 4− electro-oxidation on Au and Ag catalysts

The direct oxidation of sodium borohydride in concentrated sodium hydroxide medium has been studied by cyclic and linear voltammetry, chronoamperometry and chronopotentiometry for silver and gold electrocatalysts, either bulk and polycrystalline or nanodispersed over high area carbon blacks. Gold and silver yield rather complete utilisation of the reducer: around 7.5 electrons are delivered on these materials, versus 4 at the most for platinum as a result of the BH 4 − non-negligible hydrolysis taking place on this latter material. The kinetic parameters for the direct borohydride oxidation are better for gold than for silver. A strong influence of the ratio of sodium hydroxide versus sodium borohydride is found: whereas the theoretical stoichiometry does forecast that eight hydroxide ions are needed for each borohydride ion, our experimental results prove that a larger excess hydroxide ion is necessary in quasi-steady state conditions. When the above-mentioned ratio is unity (1 M NaOH and 1 M NaBH 4), the tetrahydroborate ions direct oxidation is limited by the hydroxide concentration, and their hydrolysis is no longer negligible. The hydrolysis products are probably BH 3OH − ions, for which gold displays a rather good oxidation activity. Additionally, silver, which is a weak BH 4 − oxidation electrocatalyst, exhibits the best activity of all the studied materials towards the BH 3OH − direct oxidation. Finally, carbon-supported gold nanoparticles seem promising as anode material to be used in direct borohydride fuel cells.