Rapid dissolution of chromite with sulphuric acid-lithium sulphate mixture containing ceric sulphate, manganese dioxide or periodate, and spectrophotometric determination of chromium

Cr(2)O(3) and chromite ore can be dissolved in H(2)SO(4)Li(2)SO(4)Ce(SO(4))(2) (20/10/1 v/w/w), H(2)SO(4)Li(2)SO(4)MnO(2) (20/10/1 v/w/w) and H(2)SO(4)Li(2)SO(4)KIO(4) (20/10/2 v/w/w) mixtures. The turbid solution produced can be clarified by treatment with H(2)O(2) or solvent extraction and the chromium determined spectrophotometrically at 614 nm.     

A complete dissolution procedure for SnPb solders using nitric and hydrochloric acids with simultaneous determination of major and trace elements by ICP/OES

A complete and fast dissolution procedure for tin and lead based solders is described. Trace and major elemental concentrations are determined by inductively coupled argon plasma emission (ICP) spectroscopy. One gram solder samples in the concentration range of 40-63 wt % tin are completely dissolved using nitric and hydrochloric acids. ICP analyses of certified reference materials prepared by this dissolution method are reported and compared to reference values. Based on comparison, the sample preparation method discussed is successful for quantitative analysis of trace and major elements in tin-lead solders.     

On-line dilution and determination of the amount of concentrated hydrochloric acid in the final products from a hydrochloric acid production plant using a sequential injection titration system

An on-line sequential injection titration system for the determination of the concentration of concentrated hydrochloric acid as final product from a hydrochloric acid production plant is described. The system involves on-line dilution of the concentrated hydrochloric acid solution to an acceptable range for direct measurement by merging the sample stream with a de-ionized water diluent stream, followed by mixing in a dilution coil, before aspiration into the sequential injection system. Concentrated standard solutions were treated in exactly the same way as the samples. The system was evaluated for reproducibility, linearity, accuracy, and sample throughput. A linear relationship between peak width and logarithm of acid concentration was found in the range 5.934–8.995 mol l⁻¹ and a concentration of 0.005 mol l⁻¹ NaOH solution was used as titrant. Samples from the production plant showed excellent agreement when compared with the manual and automated batchwise titrations. The relative standard deviation was found to be less than 0.4% with a sample frequency of 30 samples per hour.     

Novel electrochemical procedure for the determination of metamitron

In this paper, a chronopotentiometric method for the determination of herbicide metamitron (MTM) using a glassy carbon electrode (GCE) and a thin film mercury electrode (TFME) as working electrodes is presented. MTM provided a well-defined reductive peak in the Britton–Robinson buffer on both working electrodes. Instrumental and chemical factors such as pH of the buffer, initial potential and reduction current influencing MTM chronopotentiometric response were optimised with the Box–Behnken experimental design. Under the optimal combination of factors, the analytical signal was linear in the MTM concentration range of 0.8–30 mg/L, with a detection limit of 68.53 µg/L using a TFME, and in the concentration range of 1–30 mg/L, with a detection limit of 92.91 µg/L using a GCE. The precision of the method was estimated as a function of repeatability and reproducibility, with the value of relative standard deviation lower than 2.6%. The applicability of the method was verified by direct analysis of MTM in spiked water samples and commercial pesticide formulations. The obtained results were in good agreement with those obtained using liquid chromatography/tandem mass spectrometry (LC-MS/MS) method, or with those labelled by the manufacturer. By using chronopotentiometry, neither extraction nor preconcentration procedures are necessary, thus making this method simple, cost-effective and more feasible for analytical routine analysis.     

Carbon dioxide hydrogenation to formic acid by using a heterogeneous gold catalyst

AUROlite, consisting of gold supported on titania (picture shows extrudates in a steel net cage), is a robust catalyst for the production of catalyst-free HCOOH/NEt(3) adducts from H(2), CO(2), and neat NEt(3). Pure HCOOH is freed from the adducts by amine exchange.     

New convenient dissolution of iron-rhodium alloys using hydrochloric acid containing a small amount of nitric acid without heating for an ICP-AES analysis.

A new convenient dissolution method for Fe-Rh alloys has been developed. Aqua regia has been used for the dissolution of rhodium alloy samples. However, it is difficult to dissolve high-concentration rhodium (more than 50 mass%) in aqua regia, because a rhodium-passivity on the alloys surface occurs with nitric acid. By using hydrochloric acid containing a small volume of nitric acid, Fe-Rh (24-64 mass%) alloys could be completely decomposed and dissolved under mild experimental conditions. The principal advantages of this method are simplicity and time-saving compared with other dissolution methods.     

A study of dissolution kinetics of a Nigerian galena ore in hydrochloric acid

The results of experimental investigation on the study of dissolution kinetics of a Nigerian galena ore in hydrochloric acid solution were discussed. The influence of acid concentration, temperature, particle size, stirring speed and solid/liquid ratio on the extent of dissolution was examined. The elemental analysis by XRF showed that the galena ore is composed mainly of PbS with metals such as Sn, Fe and Zn occurring as minor elements and Mn, Rb, Sr and Nb as traces. The XRD analysis indicated galena as the dominant mineral phase, with the presence of associated minerals, such as α-quartz (SiO₂), sphalerite (ZnS), cassiterite (SnO₂), pyrite (FeS₂) and manganese oxide (MnO₂).Results of leaching studies showed that galena dissolution in HCl solution increases with increasing acid concentration and temperature; while it decreases with particle diameter and solid/liquid ratio at a fixed stirring rate of 450 rpm. The study showed that 94.8% of galena was dissolved by 8.06 M HCl at 80 °C within 120 min with initial solid/liquid ratio of 10 g/L. The corresponding activation energy, E_a was calculated to be 38.74 kJ/mol. Other parameters such as reaction order, Arrhenius constants, reaction and dissociation constants were calculated to be 0.28, 73.69 s^?1, 1.73 ± 0.13 × 10³ and 1.37 ± 0.024 × 10⁴ mol L^?1 s^?1, respectively. The mechanism of dissolution of galena was established to follow the shrinking core model for the diffusion controlled mechanism with surface chemical reaction as the rate controlling step for the dissolution process. Finally, the XRD analysis of the post-leaching residue showed the presence of elemental sulphur, lead chloride and α-quartz.     

Proposal for a mercury isolation procedure using cold vapor method in combination with voltammetric determination using a rotating gold electrode

The optimal process of pre-treatment and activation of gold rotating disc electrode (AuRDE) before voltammetric determination of mercury is proposed. This treatment encompasses polishing of the electrode surface, electrochemical cycling, and activation. This procedure both increases determination sensitivity as well as improves determination reproducibility. The detection limit on the working electrode achieved using this approach amounted to 8.26·10⁻¹⁰ mol L⁻¹for direct mercury determination in water solution (applying 200 s running accumulation). The procedure of the quantitative mercury isolation from complicated sample matrix was developed as well. It provides better selectivity and significant increase of sensitivity of mercury determination. In case of mercury isolation from one liter of water the detection limit is 6.23·10⁻¹¹ mol L⁻¹ (analyzing a greater sample volume the determined concentration could be lower).      

Spectrophotometric determination of copper with hydrochloric acid

A procedure is proposed whereby copper may be determined spectrophotometrically by means of the very near infrared absorption of its complex ion with hydrochloric acid. Only stannous and ferrous ions are serious interferences and they may be oxidized with nitric acid or with ammonium persulfate to avoid such interference. The method is simple and rapid and is capable of reasonably good precision and accuracy.     

Atomic absorption spectrometry for the automatic indirect determination of ascorbic acid based on-the reduction of manganese dioxide.

A new and simple flow injection method followed by atomic absorption spectrometry has been developed for the indirect determination of ascorbic acid. The proposed method is based on oxidation of ascorbic acid to dehydroascorbic acid using a solid-phase manganese dioxide (30% m/m suspended on silica gel beads) reactor. The flow of the sample through the column reduces the MnO2 to Mn(II) in an acidic carrier stream of 6.3 mM HNO3 (pH 2.2) with flow rate of 4.0 ml/min at room temperature; Mn(II) is measured by atomic absorption spectrometry. The absorbance of Mn(II) is proportional to the concentration of ascorbic acid in the sample. The calibration curve was linear up to 30 mg/L, with a detection limit of 0.2 mg/L for a 220 microL injected sample volume. The developed procedure was found to be suitable for the determination of AsA in pharmaceuticals and foods with a relative standard deviation better than 1.09% and a sampling rate of about 95 h(-1). The results exhibit no interference from the presence of large amounts of organic compounds. The reliability of the method was established by parallel determination against the 2,6-dichlorophenol-indophenol methods.     

Rapid chromite dissolution using manganese dioxide-lithium-sulphate-sulphuric acid mixture-estimation of alumina in chromite for quality control assessment

Proposed in this paper is a less labour-intensive method involving a mixture (0.3 g MnO₂ + 1.0 g Li₂SO₄ + 10 mL H₂O + 20 mL of 36M H₂SO₄ for 0.2 g sample) to decompose chromites for accurate and precise estimation of alumina in chromite matrices for quality control (QC) assessment. Several international chromite samples, namely, CHR-BKg, CHR-Pt, IGS-30 and BCS-308 were analysed. Intermethod comparison studies reveal that the probability of results being different is less than (slight variation in case of CHR-BKg) 99% when two methods [ethylenediamine tetraacetic acid (EDTA) titration and spectrophotometry using ammonium aurinitricarboxylate (aluminon)] were compared. It also shows that the proposed method yields better results than the most conventional route involving HClO₄ decomposition used for similar purpose; hence can be used for QC programme and in the evaluation of reference materials.     

Optical and electrochemical-mediated detection of ascorbic acid using manganese porphyrin and its gold hybrids

The developments concerning new hybrids based on porphyrin derivatives and colloids destined for the detection of ascorbic acid (AA) in the relevant range for medical investigations are presented. Mn(III) tetratolylporphyrin chloride (MnTTPCl), spherical gold colloid (n-Au), and their hybrid (MnTTPCl/n-Au) were chosen to be comparatively investigated by ultraviolet–visible spectroscopy in the presence of AA. The hybrid material (MnTTPCl/n-Au) has the best capacity to detect concentrations of AA in the range of 2.6 × 10^?6–4.38 × 10^?5 M. Modified glassy carbon (GC) electrodes were obtained by thin film deposition of MnTTPCl, n-Au alone, and in successive mixed thin films, comparing their response during the electrochemical oxidation of AA. The electrocatalytic effect of the MnTTPCl on the AA oxidation is justified both by the increase in the peak current density and by the shift toward more negative potentials (0.024 V). The GC/MnTTPCl electrode has the best electrocatalytic effect for the AA oxidation and is promising for sensor applications.     

Selective determination of uric acid in the presence of ascorbic acid using a penicillamine self-assembled gold electrode

The electrochemical behaviors of uric acid (UA) at the penicillamine (Pen) self-assembled monolayers modified gold electrode (Pen/Au) have been studied. The Pen/Au electrode is demonstrated to promote the electrochemical response of UA by cyclic voltammetry (CV). The diffusion coefficient D of UA is 6.97 × 10⁻⁶ cm² s⁻¹. In differential pulse voltammetric (DPV) measurements, the Pen/Au electrode can separate the UA and ascorbic acid (AA) oxidation potentials by about 120 mV and can be used for the selective determination of UA in the presence of AA. The detection limit was 1 × 10⁻⁶ mol L⁻¹. The modified electrode shows excellent sensitivity, good selectivity and antifouling properties.     

The study of a membrane for extracting gold(III) from hydrochloric acid solutions

A membrane is described consisting of Aliquat 336 chloride immobilized in poly(vinyl chloride) (PVC) which extracts gold(III) selectively from hydrochloric acid solutions in the presence of a 500-fold higher concentration of copper(II). Gold is recovered from the membrane by stripping with a thiourea solution. The stability of the membrane is reported in terms of the extent of leaching of the reagent from the membrane in aqueous solutions.     

气相色谱法测定甘油与盐酸反应过程的混合物

采用气相色谱方法分析了甘油与盐酸反应过程中的主要物质. 使用KB-WAX毛细管柱及FID检测器, 以乙二醇作内标和甲醇定容, 并用内标法计算. 结果表明, 在程序升温下, 气相色谱内标法能使GLY, DCP, CPD等几种物质达到基线分离, 该方法能满足测试要求.     

Effect of methanol on the dissolution of neodymium oxide in hydrochloric acid solutions

The effect of methanol on the solubility of Nd₂O₃ in HCl medium in the temperature range of 25–55°C were studied. HCl-CH₃OH was observed to be a better solvent than HCl-CH₃OH-H₂O and hydrochloric acid for the dissolution of Nd₂O₃ mainly due to prevention of neodymium hydroxide and dissolution increased with increase of HCl concentration even at high HCl concentrations. Presence of methanol in the medium was determined to cause corresponding decreases in conductivity, E_SCE, pH values with corresponding increase in E_R values. Neodymium compounds formed in HCl-CH₃OH medium at 25°C were isolated and identified using X-ray diffraction, thermal and chemical analysis methods and their thermal behaviour were investigated between 25–1100°C. NdCl₃ × x ₁CH₃OH and NdCl₃ × x ₂CH₃OH × 4.14H₂O (x ₁ + x ₂ = 2.8) were formed in non-aqueous medium and these compounds were converted into NdCl₃, NdCl_2.37 and NdCl₃ × 0.47CH₃OH with complete and partial loss of water and methanol around 240°C respectively. Methanol was completely removed around 390°C with formation of NdCl_2.37 (77.5%) and NdOCl (22.5%) and NdOCl was detected as the major stable phase above 700°C.     

A new indirect spectrophotometric procedure for determination of sulphur dioxide

An operationally inexpensive and sensitive spectrophotometric procedure for sulphur dioxide is proposed. The reagent 5,5-dimethyl-1,2,3-cyclohexanetrione-1,2-dioxime-3-thiosemicarbaz one is used to determine trace amounts of sulphur dioxide indirectly by means of the reduction of Fe(III) to Fe(II). The method can determine down to 0.032 microg/ml of sulphur dioxide in the final solution and recoveries are better than 98%. The method can be applied to the determination of atmospheric SO(2) provided that interfering gases such as nitrogen dioxide and hydrogen sulphide are eliminated.     

Voltammetric determination of uric acid by using gold nanotubule electrode

Gold nanotubule membranes were prepared by using electroless deposition of gold within the pores and surfaces of polycarbonate track-etched membranes.And the gold nanotubule membrane was used as an electrode for determination of uric acid in urine samples for the first time.In Britton-Robinson buffer of pH 4.56,uric acid exhibited well-defined differential pulse voltammograms.And the interference between coexistent ascorbic acid and uric acid was overcome owing to the attractive ability of the gold nanotubule electrode to yield a large anodic peak difference ca.0.404 V(vs.SCE).The proposed method was then applied to the determination of uric acid in urine without any pretreatment.