Solvent bar microextraction combined with electrothermal vaporization inductively coupled plasma mass spectrometry for the speciation of inorganic arsenic in water samples

A new method of solvent bar microextraction (SBME) combined with electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) for the speciation of As(III) and As(V) in water samples was developed. The method is based on the chelation of As(III) and ammonium pyrrolidine dithiocarbamate (APDC) under the selected conditions, and the As(III)-PDC complex could be extracted into the organic phase, while As(V) remained in aqueous solution. The post-extraction organic phase was directly injected into ETV-ICP-MS for determination of As(III) with the use of iridium as permanent chemical modifier. As(V) was reduced to As(III) by L-cysteine and was then subjected to SBME prior to total As determination. The assay of As(V) was based on subtracting As(III) from total As. The factors affecting on the SBME, such as organic solvent, sample pH, chelating reagent concentration, stirring rate and extraction time, and chemical modification of iridium in ETV-ICP-MS have been studied. Under the optimized conditions, the enrichment factor of 220-fold could be achieved in 15 min extraction, the limit of detection (LOD) for As(III) was 0.32 pg mL^− 1, and the relative standard deviation (RSD) was 8.8% (0.1 ng mL^− 1, n = 9). Compared with hollow fiber liquid phase microextraction (HF-LPME), SBME has a higher enrichment factor and faster extraction kinetics. In order to validate the accuracy of the method, a Certified Reference Material of GSBZ50004-88 (No. 200420) water sample was analyzed and the results obtained were in good agreement with the certified values. The developed method was also applied to the speciation of inorganic As in environmental waters with satisfactory results.     

Study on Determination of Trace Copper by Spectrophotometry after Flotation Separation Using Microcrystalline Adsorption System

The paper presents a novel method for the flotation separation of Cu²⁺ using microcrystalline adsorption system prior to the determination by spectrophotometry. The effects of different parameters, such as the dosages of NH₄SCN and octadecyl trimethyl ammonium bromide (OTMAB), various salts on the flotation yield of Cu2+ have been investigated to select the optimum experimental conditions. The possible flotation separation mechanism of Cu²⁺ was discussed. The results showed that under the optimum conditions, octadecyl trimethyl ammonium bromide cation (OTMAB⁺) reacted with SCN^‐ to produce the microcrystalline matter (Ms‐M) of (OTMAB⁺·SCN^‐), the water‐insoluble ternary association complex of [Cu(SCN)₄] (OTMAB)₂ which produced by Cu²⁺ and SCN^‐, OTMAB⁺ was quantificationally adsorbed on the surface of Ms‐M of (OTMAB²⁺·SCN^‐) and was floated above water phase, the liquid‐solid phases were formed with clear interface. In this condition, K⁺, Na⁺, Ca²⁺, Mg²⁺, Al³⁺, Fe²⁺, Mn²⁺, Ni²⁺, Cd²⁺ and Co²⁺ could not be floated. Therefore, Cu²⁺ was separated completely from the above metal ions. A new method of determination of trace copper by flotation separation was established. The proposed method has been successfully applied to the determination of Cu²⁺ in plating waster water, and the results agreed well with AAS method. The recoveries were 93.3%～107.8%, and the RSD was 1.9%～2.1%.     

同多酸和染料探针共振光散射法测定蛋白质

在酸性条件下,铬黑T、钼酸铵与蛋白质形成聚合物,使体系的共振光散射明显增强。据此建立了利用共振光散射技术测定总蛋白含量的新方法。在最佳条件下,体系的最大散射峰位于555nm处。共振光散射增强的程度与蛋白质的浓度呈良好的线性关系。牛血清白蛋白和人血清白蛋白的线性范围分别为0.20～10.0μg/mL和0.10～8.0μg/mL,检出限为0.050μg/mL和0.039μg/mL。方法已用于人血清样品的分析,并与考马斯亮蓝的测定结果进行了比较,两者无显著性差异。     

T-X Br phase diagram for the NH4Br x Cl1−x system

In this study using a mean field model we calculate the phase line equations for the β-δ, β-γ and γ-δ phase transitions in the NH₄Br_xCl_{1 x} system. We then fit our phase line equations to the experimentally observed T-X _Br phase diagram for this system. Our calculated phase diagram agrees well with the observed one for the NH₄Br_xCl_{1 x} system.     

Proton conductivity and ferroelectric phase transition in hydrogen-bonded ferroelectric NH4IO3

We report on the ac dielectric permittivity (ε) and the electric conductivity (σ_ω), as function of the temperature 300?K?T4IO₃. The main feature of our measured parameters is that, the compound undergoes a ferroelectric phase transition of an improper character, at (368?±?1)K from a high temperature paraelectric phase I (Pm2₁ b) to a low temperature ferroelectric phase II (Pc21n). The electric conduction seems to be protonic. The frequency dependent conductivity has a linear response following the universal power law (σ_{( ω )}?=?A(T)ω ^{s (T)}). The temperature dependence of the frequency exponent s suggests the existence of two types of conduction mechanisms.     

Effect of Ammonium Salts on the Volumetric and Viscometric Behavior of D(+)-Glucose,D(−)-Fructose and Sucrose in Aqueous Solutions at 25°C

Apparent molar volumes, V _φ, and viscosity, η, of D(+)-glucose, D(−)-fructose and sucrose in water and in 0.02, 0.05, 0.5, 1.0 and 2.0 mol·kg⁻¹ aqueous solutions of ammonium bromide, tetraethylammonium bromide and tetra-n-butylammonium bromide have been determined at 25 °C from density and efflux time measurements by using a vibrating-tube digital densimeter and a capillary viscometer, respectively. Partial molar volumes, , at infinite dilution that were extrapolated from the V _φ data were used to obtain the corresponding transfer volumes, , for saccharides from water to different aqueous solutions of co-solutes. The Jones-Dole equation viscosity B-coefficients were obtained from the viscosity data. Positive values of were obtained for the saccharides in the presence of ammonium bromide, whereas both positive and negative values were obtained in the presence of tetraethylammonium and tetra-n-butylammonium bromides. The negative values at very low concentrations have small magnitudes. Volumetric interaction coefficients have been calculated by using the McMillan-Mayer theory and Gibbs energies of activation of viscous flow have been calculated by using Feakin’s transition-state theory equation. The parameters obtained from the volumetric and viscometric studies were used to understand various mixing effects due to the interactions between saccharides and ammonium salts in aqueous solutions.     

Application of Membrane-Selective Electrodes for the Determination of Pioglitazone Hydrochloride in the Presence of Its Acid Degradant or Metformin Hydrochloride in Tablets and Plasma

Abstract

Polyvinyl chloride (PVC) membrane sensors for the determination of pioglitazone hydrochloride (PIO) and metformin hydrochloride (MET) were described by using the ion association complexes between these drugs with either sodium tetraphenyl-borate (TPB) or ammonium reineckate (RNC) counter ions. The performance characteristics of the sensors were evaluated according to IUPAC recommendations, reveal a fast, stable and linear response over the concentration range 3.162 × 10^?5 ? 1 × 10^?2 M for PIO and 1 × 10^?3 ? 1 × 10^?1 M for MET. The sensors are used for determination of PIO and MET in tablets and plasma. The developed method was found to be simple, accurate and precise when compared with the reported method.     

Optical Urea Biosensor Based On Ammonium Ion Selective Membrane

ABSTRACT

An optical urea biosensor was developed by immobilizing an urease enzyme layer on a thin ammonium-selective polymer membrane. The ammonium optical membrane utilized dichlorofluorescein octadecyl ester (DCFOE) as anionic chromophore and nonactin as neutral ionophore. The urease layer was coated on the top of the ammonium layer by gelatin entrapment combined with glutaradehyde cross-linking. Hydrolysis of urea catalyzed by urease produced ammonium ion, which was extracted into the-polymer film to form complexes with nonactin. A proton was released which resulted in a color change of the optical membrane due to charge neutrality principle. The biosensor     

A novel bioglycerol-based recyclable carbon catalyst for an efficient one-pot synthesis of highly substituted imidazoles

The new bioglycerol-based carbon catalyst acts as an efficient, readily available, and reusable catalyst for the synthesis of 2,4,5-trisubstituted imidazoles/1,2,4,5-tetrasubstituted imidazoles, when aromatic aldehyde, ammonium acetate/amine, and 1,2-diketone are reacted in acetonitrile.