Centri-voltammetric study with amberlite XAD-7 resin as a carrier system

Centri-voltammetry is a novel method, which allows combining the advantages of centrifugation and voltammetry. The method offers a practical way for application of coprecipitation in trace analysis allowing direct voltammetric scan hence prevents the loss of the analyte, which usually is the case for other preconcentration techniques. The performance of the method was successfully tested using trace amounts of Pb²⁺ ions in aqueous solution in a vessel specially designed to be compatible to both centrifugation and voltammetry. XAD-7 resin was used as the carrier material and the parameters related to the carrier material and medium characteristics as well as the centrifugation settings were investigated. The sensitivity of the method was found comparable to that of stripping techniques and the detection limit for lead ions was calculated as 5.2 × 10⁻⁹ M with mercury coated gold sphere electrode. The precision of the method depends on the configuration of the working electrode and better reproducibility was obtained with mercury coated plate electrodes (R.S.D. 3.3%, n = 6).     

Radical scavenging and antioxidant activity of tannic acid

Tannic acid, a naturally occurring plant polyphenol, is composed of a central glucose molecule derivatized at its hydroxyl groups with one or more galloyl residues. In the present paper, we examines the in vitro radical scavenging and antioxidant capacity of tannic acid by using different in vitro analytical methodologies such as 1,1-diphenyl-2-picryl-hydrazyl free radical (DPPH) scavenging, 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging activity, total antioxidant activity determination by ferric thiocyanate, total reducing ability determination using by Fe³⁺–Fe²⁺ transformation method, superoxide anion radical scavenging by riboflavin–methionine-illuminate system, hydrogen peroxide scavenging and ferrous ions (Fe²⁺) chelating activities. Also, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), α-tocopherol and trolox, a water-soluble analogue of tocopherol, were used as the reference antioxidant radical scavenger compounds.Tannic acid inhibited 97.7% lipid peroxidation of linoleic acid emulsion at 15 μg/mL concentration. On the other hand, the above mentioned standard antioxidants indicated an inhibition of 92.2%, 99.6%, 84.6% and 95.6% on peroxidation of linoleic acid emulsion at 45 μg/mL concentration, respectively. In addition, tannic acid had an effective DPPH scavenging, ABTS⁺ radical scavenging, superoxide anion radical scavenging, hydrogen peroxide scavenging, Fe³⁺ reducing power and metal chelating on ferrous ions activities. Also, those various antioxidant activities were compared to BHA, BHT, α-tocopherol and trolox as references antioxidant compounds. The present study shows that tannic acid is the effective natural antioxidant component that can be used as food preservative agents or nutraceuticals.     

溴氧化法测定五倍子中单宁的研究

提出了五倍子中单宁的溴氧化紫外光度分析法。本法用过量溴氧化单宁,剩余的溴与I-作用生成I2。该I2在乙醇溶液中289nm波长下测定。其线性范围为0～2.0mg L,表观摩尔吸光系数为6.8×105L·moL-1·cm-1,相对标准偏差为2.3%。已用于五倍子中单宁的测定。     

Synthesis of amberlite XAD-2-PC resin for preconcentration and determination of trace elements in food samples by flame atomic absorption spectrometry

A new chelating sorbent has been developed using Amberlite XAD-2 resin anchored with pyrocatechol through –N=C– group. This sorbent, characterised by elemental analysis and infrared (IR) spectra, was used as packing for the minicolumn in an on-line system preconcentration system for cadmium, cobalt, copper and nickel determination. Metal ions were sorbed in the minicolumn, from which it could be eluted directly to the nebulizer–burner system of the flame atomic absorption spectrometer (FAAS). Elution of all metals from minicolumn can be made with 0.50 mol L^− 1 HCl or HNO₃. The enrichment factors obtained were 16 (Cd), 24 (Co), 15 (Cu) and 19 (Ni), for 60 s preconcentration time, and 39 (Cd), 69 (Co), 36 (Cu) and 41 (Ni), if used 180 s preconcentration time. Under the optimum conditions, the proposed procedure allowed the determination of cadmium, cobalt, copper and nickel with detection limits of 0.31, 0.32, 0.39 and 1.64 μg L^− 1, respectively, when used preconcentration periods of 180 s. The accuracy of the developed procedure was sufficient and evaluated by the analysis of the certified reference materials NIST 1515 apple leaves and NIST 1570a spinach leaves. The method was applied to the analysis of food samples (spinach, black tea and rice flour).     

Determination of tannic acid by direct chemiluminescence in a FIA assembly

The determination of tannic acid is performed in a FIA assembly on the basis of the analytical output obtained by oxidation of the acid. The analyte solution was daily prepared in a mixture of quinine as sensitiser and perchloric acid and it was injected into a pure water stream acting as a carrier. This solution merges with the mixture potassium permanganate in perchloric medium and the resulting chemiluminescence is monitored. The method was applied over the range 0.5–20 mg l⁻¹ of tannic acid with a LOD 100 μg l⁻¹. The reproducibility was 2.1% and the sample throughput 54 h⁻¹. The influence of foreign substances was studied and the new method is applied to the determination of tannic acid in pharmaceutical and galenic formulations in human urine and surface waters.     

Determination of Gold and Palladium in Manganese and Nickel Compounds by Atomic Absorption Spectrometry After Separation by Use of Amberlite XAD-7 Resin

Abstract

A method for preconcentration and determination of traces of Au and Pd from manganese, nickel and their compounds is described. The trace elements are preconcentrated at a small column filled with Amberlite XAD-7 resin. After their eluation the elements are determined by flame AAS. The relative standard deviations (N=10) were found to be lower than 5%; the detection limit (3s, N=20) for Au and Pd in metal samples is 0.07 μg/g.     

氨基修饰超高交联树脂对没食子酸的吸附性能

以亲水性小分子有机酸没食子酸作为研究对象,研究了氨基修饰超高交联树脂对没食子酸的吸附行为和机理.结果表明,氨基修饰超高交联树脂WJN-10对没食子酸有较高的吸附容量和吸附作用力;π-π共轭作用是树脂WJN-10吸附没食子酸主要作用力;WJN-10吸附没食子酸是物理吸附主导;吸附速率主要受控于颗粒内扩散过程;WJN-10对没食子酸有较好的吸附-脱附性能.     

A detailed investigation for determination of tannic acid by anodic stripping voltammetry using porous electrochemical sensor

The electrochemical responses of tannic acid have been obtained at porous pseudo-carbon paste electrode (PPCPE), polypyrrole modified carbon paste electrode (PCPE), SBA-15 modified CPE (SBA-MCPE) and carbon paste electrode (CPE) under same conditions, respectively. The results show that the sensitivity of PPCPE is the highest among all the checked electrodes. The detection limit at PPCPE is 0.01 μM, which is about 10 times lower than that at CPE and is about 5 times lower than that at PCPE or SBA-MCPE. The developed electrode PPCPE possesses a few obvious advantages and no binding reagents are needed. The surface area of PPCPE is 59.26 m² g⁻¹ with pores ranging from 2 to 5 μm in diameter. The PPCPE is easy to preserve and has good reusability, which affords a nice electrochemical platform for detecting tannic acid.     

Determination of some trace elements in high-purity aluminium, zinc and commercial steel by AAS after preconcentration on amberlite XAD-1180 resin

The determination of trace metals, e.g. Bi, Cd, Pb, in high-purity aluminium, zinc and commercial steel by flame or graphite furnace atomic absorption spectrometry following their preconcentrations as iodo complexes on XAD-1180 resin by means of a short column system is described. The recoveries are quantitative (95%). The relative standard deviations varies between 6% and 10%. The relative errors are less than 8% in a concentration range of 1 × 10^–3 –4 × 10^–5%. Detection limits for flame AAS and GFAAS were in the ranges of 0.002–0.110 g/ml and 0.0003–0.004 g/ml or in the ranges of 0.08–4.40 g/g and 0.012–0.16 g/g with respect to the solid samples, respectively.     

Preconcentration and determination of ultra-trace amounts of U(VI) and Th(IV) using titan yellow-impregnated Amberlite XAD-7 resin

A simple and sensitive method for the determination of ultra trace amounts of U(VI) and Th(IV) ions by spectrophotometric method after solid-phase extraction on a new extractant-impregnated resin (EIR) has been reported. The new EIR was synthesised by impregnating a weakly polar polymeric adsorbent, Amberlite XAD-7, with titan yellow (TY) as extractant. The analytical method is based on the simultaneous adsorption of analyte ions in a mini-column packed with TY/XAD-7 and performing sequential elution with 0.5% (w/v) Na₂CO₃ for uranium and 2.0 M HCl for thorium. The influences of the analytical parameters including pH, salting out agent and sample volume were investigated. The interference effects of foreign ions on the retention of the analyte ions were also explored. The limits of detection for U(VI) and Th(IV) were as low as 50 and 25 ng L^?1, respectively. Relative standard deviations (n = 7) for U(VI) and Th(IV) were 3.1% and 2.9%, respectively. The method was successfully applied to the determination of ultra trace amounts of U(VI) and Th(IV) in different real matrices including industrial wastewater samples and environmental waters. The proposed method was validated using three certified reference materials and the results were in good agreement with the certified values.     

On the liquid chromatography and identification of the flavonoids,present in the “sumach tannic acid” extracted fromRhus coriaria

Summary The leaves ofRhus coriaria contain about 15–20% polyphenolic compounds. These are mostly hydrolysable tannins, with a central glucose unit, to which several gallic acid rests are bound depsidically. 5 to 10% of the total polyphenolic fraction however, consists of condensed tannins or flavonoids. This work studies the identity and the liquid chromatographic behaviour of these flavonoids. The presence of the dimeric flavonoids agathisflavone, amenthoflavone and hinokiflavone is proved. A new dimeric flavanoid (Sumaflavone) is tentatively identified.     

The comparison of physic-chemical properties of chitosan/collagen/hyaluronic acid composites with nano-hydroxyapatite cross-linked by dialdehyde starch and tannic acid

Scaffolds based on chitosan, collagen and hyaluronic acid, cross-linked by dialdehyde starch with hydroxyapatite were obtained with the use of the freeze-drying method. Scaffolds were cross-linked by tannic acid or dialdehyde starch addition. Composites were characterized by different analyses, e.g. SEM images, porosity, density, liquid uptake, and mechanical tests. In addition, the adhesion and proliferation of human osteosarcoma SaOS-2 cells were examined on the obtained scaffolds.The results showed that the properties of the scaffolds based on chitosan, collagen, and hyaluronic acid can be modified by cross-linkers addition. The compressive modulus for the scaffolds cross-linked by dialdehyde starch was higher than for those cross-linked by tannic acid. The porosity of scaffolds cross-linked by starch was higher than those in which tannic acid was applied. However, the former presented lower density. SEM images showed the homogeneous scaffold structure with interconnected pores. Scaffolds cross-linked by tannic acid exhibited higher biocompatibility than those cross-linked by dialdehyde starch. However, the results showed that both scaffolds, cross-linked by dialdehyde starch and by tannic acid can provide the support required in tissue engineering and regenerative medicine. The scaffolds presented here may be easily operated to fit such small bone defects without causing adverse reactions.     

Morphological and mechanical properties of tannic acid/PAAm semi-IPN hydrogels for cell adhesion

A series of hydrogels were fabricated from tannic acid (TA), a typical plant polyphenol widely present in wood, and polyacrylamide (PAAm) by semi-IPN and cryogelation techniques. The introduction of TA into the PAAm network endows the system with enhanced cell adhesion properties. The cryogels with open interconnected macropores had a superfast swelling rate and a high swelling ratio, as well as high elasticity in response to compression. The degradation of the hydrogels can be tuned by modulating the content of cross-linker poly(ethylene glycol) diacrylate (PEGDA). Cytotoxicity results revealed that the hydrogels were non-toxic to COS-7 cells. All these results suggested that TA/PAAm semi-IPN hydrogels have great potential for applications in tissue engineering.     

Electrochemistry and voltammetric determination of tannic acid on a single-wall carbon nanotube-coated glassy carbon electrode

The voltammetric behavior of tannic acid (TA) on a single-wall carbon nanotubes (SWNTs) modified glassy carbon electrode has been investigated by cyclic voltammetry. TA can generate a well-defined anodic peak on the modified electrode at around 0.42 V (vs. SCE) in 0.10 M phosphate buffer solutions (pH = 4.0). The electrochemical reaction involves 1e transfer, accompanied by one proton. The electrode process is controlled by adsorption. The parameters affecting the response of TA, such as solution pH, accumulation time and accumulation potential are optimized for the determination of TA. Under the optimum conditions, the peak current changes linearly with the TA concentration in the range of 5.0 × 10⁻⁸–1.0 × 10⁻⁶ M. The lowest detectable concentration of TA is 8.0 × 10⁻⁹ M after 180 s accumulation. This method has been successfully applied to the determination of TA in tea and beer samples. In addition, the influence of potential interferents is examined. In the presence of bovine serum albumin, the peak current of TA decreases linearly due to the formation of a super-molecular complex.     

2-噻吩乙酸在三种不同树脂上的吸附热力学和动力学研究

通过静态吸附实验,研究了XAD-4,NDA-100和ND-90吸附树脂对水溶液中2-噻吩乙酸的吸附热力学及动力学特性,结果表明,2-噻吩乙酸在XAD-4树脂上是单层吸附,符合Langmuir等温吸附方程,吸附过程符合准一级动力学吸附方程.2-噻吩乙酸在NDA-100和ND-90树脂上的吸附也能用Langmuir等温吸附方程表示,但并不只是单层吸附,而主要是由毛细管凝聚和微孔填充作用造成的吸附,吸附过程可分为大孔和中孔区的吸附以及微孔区的吸附两个阶段,两个阶段都符合准一级动力学吸附方程.     

树脂相分光光度法测定水中微量铁

在ｐＨ９６０氨性介质中，巯基乙酸与铁（Ⅲ）生成紫红色络合阴离子，与强碱性阴离子交换树脂交换，将有色络合物富集于树脂相上，用树脂相分光光度法测定微量铁，其最大吸收波长位于５３０ｎｍ；表观摩尔吸光系数ε为６７×１０４Ｌ·ｍｏｌ－１·ｃｍ－１；铁含量在０～１４ｍｇ／Ｌ范围内符合比耳定律；测定内蒙地段黄河水和呼和浩特地区自来水中微量铁，相对标准偏差分别为４６％和３２％。     

Synthesis, physical studies and uptake behavior of: copper(II) and lead(II) by Schiff base chelating resins

Two new chelating resins possessing multiple functional groups capable of coordinating with several metal ions are reported. The resins were synthesized by condensing Schiff bases derived from 2-aminophenol, 2-hydroxy-5-chloroaniline and terephthaldehyde with formaldehyde in an alkaline medium. The effects of pH and contact time of the Cu(2+) and Pb(2+) in aqueous solutions on the uptake behavior of the resins were studied. The metal ion uptake behavior of the resins was investigated by the batch method. Both the uptake and the selectivity of the resins towards the investigated metal ions were related to the structure of the resins, type of the metal ion and the uptake conditions. The resins showed maximum uptake capacity for Cu(2+) and Pb(2+) at pH 10. Cu(2+) was seen to undergo preferential adsorption in separate and mixture solutions of Cu(2+) and Pb(2+). Kinetic studies for the resins using Langmiur equation were also performed. The Schiff base monomers and their formaldehyde resins were characterized by elemental analyses, FTIR and (1)H NMR spectroscopy. The thermal stability of the resins was studied using TGA/DTG analysis.     

Green, effective chemical route for the synthesis of silver nanoplates in tannic acid aqueous solution

Silver nanoplates, with average size tunable from 50 to 500 nm, have been synthesized via a simple room-temperature tannic acid (TA) solution-phase chemical reduction method. The synthesis was a seedless process in which tannic acid was used as a reducing as well as a capping agent, and did not need any other surfactant or capping agent to direct the anisotropic growth of the silver nanoparticles. The morphology of silver nanoplates has been confirmed by transmission electron microscopy, the growth process of nanoplates has been studied by UV/vis spectroscopy. Control experiments have been explored for a more thorough understanding of the growth mechanism. It was found that both the concentrations of TA and the pH of solution were the key elements to control the morphology silver nanoplates. The optical in-plane dipole plasmon resonance bands of these silver plates could be tuned from 520 to 1100 nm.     

Studies on synthesis and application of XAD-4-salen chelate resin for separation and determination of trace elements by solid phase extraction

The use of chemically modified XAD-4-salen chelating resin had been studied for the separative concentration of metal ions from an aqueous solution. XAD-4-salen was synthesized by diazonium coupling reaction of salen[N,N′-bis(salicylidene)ethylenediamine] and Amberlite XAD-4 resin. The distribution coefficient at various pH values and adsorption capacities were obtained with respect to Cu(II), Pb(II) and Bi(III). Trace elements were pre-concentrated on the synthesized XAD-4-salen by batch method for atomic absorption spectrometric determination. Some conditions, such as the pH of aqueous solution, amount of XAD-4-salen, kinds and concentration of acids were optimized for the analytical application of XAD-4-salen. For the pre-concentration of metal ions, the pH of the aqueous solution was adjusted to approximately 5.5, and then it was stirred 30 min after the addition of 50 mg of pulverized XAD-4-salen. The adsorbed metal ions were desorbed by 10 mL of 1.0 M HNO₃. The desorption efficiency of Bi(III) was enhanced by the addition of 30 mg/L of Pd(II). The addition of Pd(II) as a matrix modifier could improve the reproducibility and sensitivity in the Atomic Absorption Spectroscopy (AAS) determination of volatile lead and bismuth. In the present study, this procedure has been applied for the determination of Cu(II), Pb(II) and Bi(III) in real samples of five kinds of river water, using a standard calibration curve method. Recoveries of 85–120% were obtained in the spiked samples in which given amount of analytes were added.     

单宁酸与牛血红蛋白相互作用的光谱研究

利用荧光光谱技术研究了单宁酸与牛血红蛋白分子的相互作用。实验结果表明:单宁酸分子与BHb发生反应生成基态复合物,导致BHb内源荧光的猝灭,该猝灭属于静态猝灭。测定了不同温度下该反应的表观结合常数、结合位点数及结合热力学参数,热力学参数的变化表明上述作用过程是一个熵增加、自由能降低的自发分子间作用过程,单宁酸与BHb之间以疏水和氢键作用力为主;根据Frster能量转移理论,测得供体与受体间结合距离r和能量转移效率E;并用同步荧光光谱法探讨了单宁酸对BHb构象的影响。