The effect of sodium benzoate and sodium 4-(phenylamino)benzenesulfonate on the corrosion behavior of low carbon steel

Abstract  

The effect of sodium benzoate (SB) and sodium 4-(phenylamino)benzenesulfonate (SPABS) on the corrosion behavior of low carbon steel has been investigated using gravimetric method in the temperature range of 30–80 °C, velocity range of 1.44–2.02 m s⁻¹ and concentration range of 6.94 × 10⁻⁴ to 4.16 × 10⁻³ mol dm⁻³ SB and 3.69 × 10⁻⁴ to 2.06 × 10⁻³ mol dm⁻³ SPABS. Optimization of temperature, fluid velocity, and inhibitors concentration has been made. The obtained results indicate that the inhibition efficiency (w _IE %) at 1.56 m s⁻¹ is not in excess of 81.5% at 4.16 × 10⁻³ mol dm⁻³ SB and 84.4% at 2.06 × 10⁻³ mol dm⁻³ SPABS. The inhibitive performance of these compounds showed an improvement with increasing concentration up to critical values of SB and SPABS; beyond these concentrations no further effectiveness is observed. These inhibitors retard the anodic dissolution of low carbon steel by protective layer bonding on the metal surface. The adsorption of SB and SPABS on the low carbon steel surface was found to obey the Freundlich isotherm model. The FT-IR spectroscopy was used to analyze the surface adsorbed film.     

Low-concentration aqueous solutions of undecenoic acid and sodium undecenoate

The behaviors of low-concentration aqueous solutions of 10-undecenoic acid and its sodium salt were studied by several techniques. The acid does not have a critical micelle concentration, but gives an emulsion of very small droplets at (0.8–1) ×  10⁻⁴ mol dm⁻³. The emulsion was clearly visible by eye at 0.002 mol dm⁻³. The sodium salt has a stepwise aggregation process, giving premicellar aggregates at 0.023 ± 0.008 mol dm⁻³, which grow to form micelles at 0.117 ± 0.007 mol dm⁻³. The compositions of the solution and the micelles were also studied. Received: 25 February 1999 Accepted in revised form: 21 June 1999     

The aggregation of sodium dehydrocholate in water

 We used a battery of different methods to study the association in aqueous sodium dehydrocholate (NaDHC) solutions. This salt associates by a stepwise mechanism. Below (9.6 ± 4.2) × 10⁻⁴ mol dm⁻³ there is a molecular solution with some strongly insoluble dehydrocholic acid produced by hydrolysis. Between (9.6 ± 4.2) × 10⁻⁴ and (5.2 ± 2.2) × 10⁻³ mol dm⁻³, an aggregate similar to acid soap (NaDHC.HDHC) appears and its amount and the aggregate's size increase with concentration. At =(2.20 ± 0.85) × 10⁻² mol dm⁻³ the aggregates formed have properties usually associated with true micelles, such as solubilisation of water-insoluble dyes. These aggregates increase in size with concentration and change their shape at 8 × 10⁻² mol dm⁻³, giving nonsymmetrical aggregates. The changes in the solution physicochemical properties at these concentrations may be misinterpreted and this explains the different values of the critical micelle concentration reported in the literature for substances with similar structure, such as bile salts. Received: 14 May 2001 Accepted: 10 August 2001     

Application of the catalytic properties of N-methylthiourea to the determination of In(III) at low levels by square wave voltammetry

Abstract  

This article proposes a simple and fast method of In(III) determination in the presence of Cd(II) and Pb(II). The catalytic activity of N-methylthiourea was used in the In(III) electroreduction, which also had a slight effect on the electroreduction process of Cd(II) and Pb(II). By applying square wave voltammetry it was possible to determine 3 × 10⁻⁷ mol dm⁻³ In(III) in the presence of 5 × 10⁻⁵ mol dm⁻³ Cd(II) and 1 × 10⁻⁴ mol dm⁻³ Pb(II) in 5 mol dm⁻³ NaClO₄ at pH 2. The calibration curve for In(III) was linear from 3 × 10⁻⁷ to 5 × 10⁻⁴ mol dm⁻³. The relative standard deviation for In(III) determination was about 3.0%.     

Kinetics and mechanism of interaction of hexaaquachromium(III) with <Emphasis Type="SmallCaps">l</Emphasis>-Dopa in aqueous medium: comparative antiparkinsonian studies

The kinetics and mechanism of the substitution reaction between [Cr(H₂O)₆]³⁺ and l-Dopa in aqueous medium has been studied over the range 1.8 ≤ pH ≤ 2.6, 1.68 × 10⁻² mol dm⁻³ ≤ [Dopa] ≤ 5.04 × 10⁻² mol dm⁻³, I = 0.1 mol dm⁻³ (KNO₃) at 50 °C. The reaction takes place via an outer sphere association between Cr³⁺ and l-Dopa followed by chelation. The product was characterized by physicochemical and infrared spectroscopic methods. The antiparkinsonian activity of the product was found to be higher than that of l-Dopa.     

Electroreduction and Quantification of Furazolidone and Furaltadone in Different Media

 Adsorptive cathodic stripping voltammetry was used for the determination of furazolidone (FZ) and furaltadone (FD) in borax and phosphate buffers, respectively, using HMDE as working electrode. The influence of different factors upon the peak current response such as accumulation potential, scan rate, preconcentration time, pH and other variables was studied. Furazolidone and furaltadone showed an adsorption character on HMDE in presence of borax and phosphate buffers, respectively. A single cathodic peak at −0.36 V in borax (pH = 9.5) was observed for FZ, while FD gave a cathodic peak at −0.32 V in phosphate buffer (pH = 8.5). The calibration graph showed a linear behavior over the range 3×10⁻⁹–9×10⁻⁸ mol dm⁻³ for furazolidone. In the case of FD, concentrations from 3×10⁻⁹ to 2×10⁻⁷ mol dm⁻³ gave a linear relationship with the peak current. A detection limit of 2×10⁻⁹ mol dm⁻³ and 1×10⁻⁹ mol dm⁻³ was obtained for furazolidone and furaltadone, respectively. This method was applied to determine these drugs in pharmaceutical formulations, urine and serum samples. Received December 15, 1998. Revision February 4, 2000.     

The kinetics of the reduction of tetraoxoiodate(VII) by <Emphasis Type="Italic">n</Emphasis>-(2-hydroxylethyl)ethylenediaminetriacetatocobaltate(II) ion in aqueous perchloric acid

The stoichiometries, kinetics and mechanism of the reduction of tetraoxoiodate(VII) ion, IO₄ ⁻ to the corresponding trioxoiodate(V) ion, IO₃ ⁻ by n-(2-hydroxylethyl)ethylenediaminetriacetatocobaltate(II) ion, [CoHEDTAOH₂]⁻ have been studied in aqueous media at 28 °C, I = 0.50 mol dm⁻³ (NaClO₄) and [H⁺] = 7.0 × 10⁻³ mol dm⁻³. The reaction is first order in [Oxidant] and [Reductant], and the rate is inversely dependent on H⁺ concentration in the range 5.00 × 10⁻³ ≤ H⁺≤ 20.00 × 10⁻³ mol dm⁻³ studied. A plot of acid rate constant versus [H⁺]⁻¹ was linear with intercept. The rate law for the reaction is:

Application of the Specific Ion Interaction Theory → the Solubility Product and First Hydrolysis Constant of Europium

The specific ion interaction theory (SIT) was applied to the first hydrolysis constants of Eu(III) and solubility product of Eu(OH)₃ in aqueous 2, 3 and 4 mol⋅dm⁻³ NaClO₄ at 303.0 K, under CO₂-free conditions. Diagrams of pEu_aq versus pC_H were constructed from solubilities obtained by a radiometric method, the solubility product log₁₀ K_{sp, Eu(OH)3}^I {Eu(OH)_3(s) Eu_aq³⁺+ 3OH_aq⁻ } values were calculated from these diagrams and the results obtained are log₁₀ K_sp,Eu(OH)3^I = − 22.65 ± 0.29, −23.32 ± 0.33 and −23.70 ± 0.35 for ionic strengths of 2, 3 and 4 mol⋅dm⁻³ NaClO₄, respectively. First hydrolysis constants {Eu_aq³⁺+H₂O Eu(OH)_(aq)²⁺+H⁺ } were also determined in these media by pH titration and the values found are log₁₀β_Eu,H^I = − 8.19 ± 0.15, −7.90 ± 0.7 and −7.61 ± 0.01 for ionic strengths of 2, 3, and 4 mol⋅dm⁻³ NaClO₄, respectively. Total solubilities were estimated taking into account the formation of both Eu³⁺ and Eu(OH)²⁺ (7.7 < pC_H < 9) and the values found are: 1.4 × 10⁻⁶ mol⋅dm⁻³, 1.2 × 10⁻⁶ mol⋅dm⁻³ and 1.3 × 10⁻⁶ mol⋅dm⁻³, for ionic strengths of 2, 3 and 4 mol⋅dm⁻³ NaClO₄, respectively. The limiting values at zero ionic strength were extrapolated by means of the SIT from the experimental results of the present research together with some other published values. The results obtained are log₁₀ K_{sp, Eu(OH)3}^o = − 23.94 ± 0.51 (1.96 SD) and log₁₀β_Eu,H⁰ = − 7.49 ± 0.15 (1.96 SD).     

Voltammetric investigation and amperometric detection of the bisphosphonate drug sodium alendronate using a copper nanoparticles-modified electrode

The electrochemical behavior of sodium alendronate on copper microparticle- and copper nanoparticle-modified carbon paste electrodes was investigated. In the voltammograms recorded using microparticles, a single anodic oxidation peak appeared, while using nanoparticles, two anodic peaks appeared. The anodic currents were related to the electrocatalytic oxidation of alendronate via the active species of Cu(III). The catalytic rate constant for the electrocatalytic oxidation process and the diffusion coefficient of alendronate were obtained to be 1.57 × 10³ cm³ mol⁻¹ s⁻¹ and 2.44 × 10⁻⁶ cm² s⁻¹, respectively. A sensitive and time-saving detection procedure was developed for the analysis of alendronate, and the corresponding analytical parameters were reported. Alendronate was determined with a limit of detection of 11.26 μmol L⁻¹ with a linear range of 50–6,330 μmol L⁻¹. The proposed amperometric method was applied to the analysis of commercial pharmaceutical tablets, and the results were in good agreement with the declared values.     

Cathodic Adsorptive Stripping Voltammetry for Estimation of the Forest Area Pollution with Nickel and Cobalt

 Necessary conditions were established for simultaneous nickel and cobalt determination in environmental samples, such as oak wood and soil, based on cathodic adsorptive stripping voltammetry. Ni(II) and Co(II), complexed with dimethylglyoxime, were determined using a hanging mercury drop electrode. Optimum conditions were found to be: accumulation time 90 s, accumulation potential −0.80 V vs. SCE, supporting electrolyte 0.2 mol dm⁻³ ammonia-ammonium chloride buffer (pH = 9.4) + 0.05 mol dm⁻³ NaNO₂ and dimethylglyoxime 2 × 10⁻⁴ mol dm⁻³. A linear current-concentration relationship was observed up to 7.51×10 ⁻⁷ mol dm⁻³ for Ni(II) and 7.0 × 10⁻⁷ mol dm⁻³ for Co(II). Excess amounts of zinc(II) interfering with cobalt peaks were masked by complexation with EDTA. Wood and soils were mineralized by applying a microwave digestion system, using the mixtures H₂O₂ + HNO₃ or HNO₃ + HF, respectively. The developed procedure was tested by analysing international reference materials (BCR 62 Olive Leaves and GBW 08302 Tibet Soil). The developed procedure was used to determine pollution of oak stand with nickel and cobalt in different regions of Poland. Received August 10, 2000. Revision May 22, 2001.     

Simple sensor for simultaneous determination of dihydroxybenzene isomers

A simple sensor based on bare carbon ionic liquid electrode was fabricated for simultaneous determination of dihydroxybenzene isomers in 0.1 mol L⁻¹ phosphate buffer solution (pH 6.0). The oxidation peak potential of hydroquinone was about 0.136 V, catechol was about 0.240 V, and resorcinol 0.632 V by differential pulse voltammetric measurements, which indicated that the dihydroxybenzene isomers could be separated absolutely. The sensor showed wide linear behaviors in the range of 5.0 × 10⁻⁷–2.0 × 10⁻⁴ mol L⁻¹ for hydroquinone and catechol, 3.5 × 10⁻⁶–1.535 × 10⁻⁴ mol L⁻¹ for resorcinol, respectively. And the detection limits of the three dihydroxybenzene isomers were 5.0 × 10⁻⁸, 2.0 × 10⁻⁷, 5.0 × 10⁻⁷ mol L⁻¹, respectively (S/N = 3). The proposed method could be applied to the determination of dihydroxybenzene isomers in artificial wastewater and the recovery was from 93.9% to 104.6%.     

Kinetic Determination of Nanogram Levels of Manganese(II) by Naphthol Blue Black–Potassium Periodate–1,10-Phenanthroline System

 The catalytic effect of manganese(II) on the oxidation of Naphthol Blue Black, with potassium periodate in the presence of 1,10-phenanthroline in weakly acidic media is studied. The reaction is followed spectrophotometrically by measuring the decrease in the absorbance of the dye at 618 nm. Under the optimum conditions (3 × 10⁻⁵ mol dm⁻³ Naphthol Blue Black, 6 × 10⁻⁴ mol dm⁻³ potassium periodate, 1 × 10⁻⁴ mol dm⁻³ 1,10-phenanthroline, 0.1 mol dm⁻³ acetate buffer – pH 4.0, 60 °C, 5 min) manganese(II) in the range 0.08–4 ng cm⁻³ can be determined by the fixed-time method with a detection limit of 0.025 ng cm⁻³. The influence of foreign ions on the accuracy of the results is investigated. The developed method is highly sensitive, selective, and simple. The method was applied successfully to the determination of manganese in cucumbers, garlic cloves and parsley leaves. Received June 12, 2000. Revision December 12, 2000.     

CO<Subscript>2</Subscript> corrosion inhibition of X-70 pipeline steel by carboxyamido imidazoline

The corrosion inhibition of X-70 pipeline steel in saltwater saturated with CO₂ at 50 °C with carboxyamido imidazoline has been evaluated by using electrochemical techniques. Techniques included polarization curves, linear polarization resistance, electrochemical impedance, and electrochemical noise measurements. Inhibitor concentrations were 0, 1.6 × 10⁻⁵, 3.32 × 10⁻⁵, 8.1 × 10⁻⁵, 1.6 × 10⁻⁴, and 3.32 × 10⁻⁴ mol l⁻¹. All techniques showed that the best corrosion inhibition was obtained by adding 8.1 × 10⁻⁵ mol l⁻¹ of carboxyamido imidazoline. For inhibitor concentrations higher than 8.1 × 10⁻⁵ mol l⁻¹ a desorption process occurs, and an explanation has been given for this phenomenon.     

Dyeing behaviour of lyocell fabric: effect of NaOH pre-treatment

To understand the effect of alkali pre-treatment on the dyeing of lyocell fabrics, samples are pre-treated with 0.0–7.0 mol dm⁻³ NaOH using a pad-batch process and then dyed with different types of reactive dyes. Exhaustion, fixation, and visual colour strength (K/S values) are measured. It is observed that sodium hydroxide pre-treatment significantly improves the colour yield, exhaustion, and fixation for all dyes used. Highest K/S values are obtained when the fabrics are pre-treated with 2.0–2.5 mol dm⁻³ NaOH. Cross-sectional analysis shows that below this optimum concentration the core fibres in the yarn are not dyed; at optimum concentration all fibres in yarn cross-section are homogeneously dyed. Cross-sectional analysis shows that as the pre-treatment concentration of NaOH increases above 2.5 mol dm⁻³, the fibres change progressively from a circular to angular cross-section, forming a solid unit. The decrease in K/S above the treatment concentration of 2.5 mol dm⁻³, though the %E and %F remains almost constant, is attributed to the distribution of dye over a larger surface area of the outer fibres in the yarn cross section, forcing the K/S at λ_max to decrease. This paper was presented at the 2nd International Cellulose Conference, Tokyo, Japan, 24th October 2007.     

Behavior of cadmium(II) in irradiated aqueous solutions

Behavior of cadmium(II) in aqueous solutions irradiated by accelerated electrons was studied. A concentration of 8.8 × 10⁻⁴ mol L⁻¹ of cadmium dissolved from Cd(NO₃)₂ requires dose of 15 kGy to be effectively removed from the system containing 1 × 10⁻² mol L⁻¹ of HCOOK as a scavenger of OH radicals. The positive effect of deaeration with N₂O or N₂ was observed in the range of lower doses. The addition of solid modifiers (bentonite, active carbon, zeolite, Cu₂O, NiO, TiO₂ and CuO) reduced the effectivity of radiation removal of cadmium. Product of irradiation is CdCO₃. On the contrary, in the system with cadmium dissolved from CdCl₂ radiation reduction takes place. Systems contained organic complexants (ethylene diamine tetraacetic acid–EDTA, citric acid) were also studied. The solutions of Cd(NO₃)₂ containing initial concentration 2.37 × 10⁻⁴ mol L⁻¹ of Cd^II were mixed with 3 × 10⁻⁴ mol L⁻¹ EDTA. In this system the efficient degradation proceeds up to 90% at a dose of 45 kGy with addition of 5 × 10⁻³ mol L⁻¹ carbonate (pH 10.5). The product of irradiation is CdCO₃. The presence of 1 × 10⁻² mol L⁻¹ of HCOOK in the solution is necessary for radiation removal of cadmium complexed with citric acid (1 × 10⁻³ mol L⁻¹) at pH 8. With increasing concentration of HCOOK (up to 5 × 10⁻² mol L⁻¹) decreases the pH value necessary for the radiation induced precipitation of cadmium. The best result was obtained in the system containing zeolite as a solid modifier.     

A novel lariat crown compound as ionophore for construction of a mercury(II)-selective electrode

Abstract  

The construction, performance, and application of a new PVC membrane electrode for determination of the mercury(II) ion, based on 8,17-bis(pyren-1-ylmethyl)-6,7,8,9,15,16,17,18-octahydrodibenzo[f,m][1,8,4,11]dithiadiazacyclotetradecine as an ionophore, is described. The effects of factors such as membrane composition, the nature and amount of the plasticizers and additives, and pH for the improved sensitivity of the electrode were studied. The electrode had a Nernstian response for mercury(II) ions over the concentration range 1.0 × 10⁻²–1.0 × 10⁻⁶ mol dm⁻³ with a slope of 27.6 ± 0.6 mV/pHg. The detection limit for mercury(II) was 7.9 × 10⁻⁷ mol dm⁻³. The response time of the electrode was between 5 and 15 s, depending on the concentration of mercury, and it can be used in a pH range 4.0–4.5 for approximately 4 months without any substantial divergence of the response characteristics. It showed higher selectivity for mercury(II) ions than for several common alkali, alkaline earth, and transition metal ions except silver(I). The proposed electrode was successfully applied to direct determination of mercury in a dental filling amalgam alloy as a real sample with a complex matrix and as an indicator electrode in complexation titrations.     

Kinetic determination of silver at trace level based on its catalytic effect on a ligand substitution reaction

It is observed that Ag(I) catalyzes the rate of substitution of phenylhydrazine (PhNHNH₂) into hexacyanoferrate(II), producing a cherry red colored complex, [Fe(CN)₅PhNHNH₂]³⁻. The reaction was monitored at 488 nm leading to the formation of the complex under the conditions: [Fe(CN)₆]⁴⁻ (5.0 × 10⁻³ mol dm⁻³), PhNHNH₂ (2.0 × 10⁻³ mol dm⁻³), temperature (25 ± 0.1 °C), pH (2.8 ± 0.02), and ionic strength, I (0.02 mol dm⁻³), (KNO₃). Under optimum conditions, absorbance at fixed times (A _t ) is linearly related to Ag(I) in the concentration range 10.79–97.08 ng cm⁻³, in the presence of several diverse ions. The highest percentage error and relative standard deviations in the entire range of Ag(I) determination are found to be 2.5% and 0.16, with a detection limit of 8.75 ng cm⁻³ of silver(I). The experimental accuracies expressed in terms of percentage recoveries are in the range of 97.87–102.50. The method was successfully applied for the determination of Ag(I) in a few synthetic samples and found to be in good agreement with those obtained from atomic absorption spectrophotometry (AAS). The validity of the proposed method has also been tested for Ag(I) determination in spiked drinking water samples. The present catalytic kinetic method (CKM) is highly sensitive, selective, reproducible, and inexpensive. A review of recently published catalytic spectrophotometric methods for determination of Ag(I) has also been presented for comparison.     

Direct electrochemistry and electrocatalysis of nitrite based on nano-alumina-modified electrode

Simple and sensitive electrochemical method for the determination of nitrite, based on a nano-alumina-modified glassy carbon electrode (GCE), is described. Nitrite yields a well-defined oxidation peak whose potential is 0.74 V at the nano-alumina-coated GCE in 0.1 mol L⁻¹ phosphate buffer (pH 5.0). Compared with bare GCE, the nano-alumina-modified GCE has evident catalytic effect towards the oxidation of nitrite, and its peak current can be significantly enhanced. Some of the experimental parameters were optimized for the determination of nitrite. The oxidation peak current was proportional to nitrite concentration in the range of 5.0 × 10⁻⁸–1.1 × 10⁻³ mol L⁻¹, and a detection limit of 1.0 × 10⁻⁸ mol L⁻¹ was obtained. This method has been successfully used to the determination of nitrite in sausage sample. Furthermore, results obtained by the method have been compared with spectrophotometric method.     

Sensitive voltammetric sensor of dihydromyricetin based on Nafion/SWNT-modified glassy carbon electrode

A novel voltammetric sensor, based on single-walled carbon nanotubes (SWNT) dispersed in Nafion and modified glassy carbon electrode (GCE), was fabricated and used to determine the trace amounts of dihydromyricetin (DMY). The electrochemical behavior of DMY at this sensor was investigated in 0.1 mol L⁻¹ sulfuric acid solutions + 0.1 mol L⁻¹ NaCl by cyclic voltammetry and squarewave voltammetry. Compared with bare GCE, the electrode presented an excellent response of DMY through an adsorption-controlled quasi-reversible process. Under the optimum conditions, the response peak currents were linear relationship with the DMY concentrations in the range of 1.0 × 10⁻⁷–1.0 × 10⁻⁵ mol L⁻¹ with a detection limit of 9 × 10⁻⁸ mol L⁻¹. Based on this voltammetric sensor, a simple and sensitive electroanalytical method for DMY was proposed and applied to quantitative determination of DMY in Ampelopsis grossedentata samples. In addition, the oxidation mechanism was proposed and discussed, which could be a reference for the pharmacological action of DMY in clinical study.     

Kinetic spectrophotometric determination of hydrazine

A kinetic spectrophotometric method for hydrazine determination in the range of 9.36×10⁻⁷ to 4.37×10⁻⁵ mol dm⁻³, based on the inhibitory effect of hydrazine on the oxidation of Victoria Blue 4- R by KBrO₃, was developed and validated. Kinetic parameters are reported for both the indicating and the inhibiting reaction. The detection limit was established as 9.98×10⁻⁸ mol dm⁻³. The selectivity of the proposed method was tested considering the influence of different ions that may be present in real samples. The method was successfully applied for hydrazine determination in various samples (very pure water from the water-steam system of a power plant and Isoniazid tablets, a pharmaceutical product).