Solid-phase spectrophotometric determination of trace amounts of vanadium using 2,3-dichloro-6(3-carboxy-2- hydroxynaphthylazo)quinoxaline

Solid-phase spectrophotometry (SPS) has been applied to analysis for trace amounts of vanadium in several environmental water (potable and polluted), biological samples (human blood and urine), and soil samples. Vanadium was sorbed in a styrene-divinylbenzene-type anion-exchanger Dowex 1-X8 as a vanadium--2,3-dichloro-6(3-carboxy-2-hydroxynaphthylazo)quinoxaline. Resin phase absorbances at 606 and 800 nm were measured directly which allowed the determination of vanadium in the range 0.03-2.2 ng ml(-1) with a relative standard deviation (R.S.D.) of 1.4%. The comparison of the SPS method and the gallic acid persulphate method shows that the linearity, analytical sensitivity, and precision were better for the SPS method, and that the latter method has lower detection and quantification limits compared with the gallic acid persulphate method.     

Elimination of the interferences of anions in the kinetic spectrophotometric determination of vanadium (V) solution

Accurate determination of vanadium (V) in industrial waste water is of great importance in environmental, biological and toxicological studies. Most of kinetic spectrophotometric methods based on the catalytic effect of vanadium (V), when applied to real samples for determination of trace levels of vanadium (V) lack the satisfactory sensitivity and selectivity. This may be attributed to the serious interferences of various anions which are common pollutants in industrial waste water. The oxidation of gallic acid by ammonium persulphate, catalysed by vanadium (V) was chosen for our study. The effect of the serious interferences of various anions such as chloride, bromate, bromide, chromate, iodide, iodate, molybdate, carbonate and sulphate on the net absorbance given by 4 microg l(-1) of vanadium (V) solution were studied. The minimum concentrations of citric acid, EDTA, ascorbic acid and oxalic acid as leveling off agents required to level off interfering effects due to the aforementioned anions in the kinetic determination of vanadium (V) were 50, 70, 80 and 120 microg ml(-1), respectively. In the presence of optimum concentrations of effective leveling off agents, the dynamic range can be extended and sensitivity increased as compared with the proposed method without levelling off agents. The proposed method is a rapid, sensitive and selective method for the determination of ultra trace amounts of vanadium (V) in real samples with satisfactory results.     

High-performance thin-layer chromatography densitometric method for the simultaneous determination of three phenolic acids in Syzygium aromaticum (L.) Merr. & Perry

A simple, precise, and rapid high-performance thin-layer chromatographic (HPTLC) method has been developed for the simultaneous determination of 3 phenolic acids, i.e., gallic acid, caffeic acid, and syringic acid, in the dried buds of Syzygium aromaticum, commonly known as clove. HPTLC was performed on silica gel 60F254 plates with toluene-ethyl acetate-formic acid (8 + 2 + 1) mobile phase and densitometric scanning at 280 nm. The method was validated for selectivity, linearity, precision, and repeatability. Instrumental precision coefficient of variation (CV) was 0.88, 0.93, and 0.98% and repeatability of the method (CV) was 0.76, 0.64, and 0.69% for gallic acid, caffeic acid, and syringic acid, respectively. The linear concentration ranges were 400-3200 ng/spot with a correlation coefficient of 0.993 for gallic acid, 440-3520 ng/spot with a correlation coefficient of 0.994 for caffeic acid, and 400-4000 ng/spot with a correlation coefficient of 0.993 for syringic acid. The average recoveries of gallic acid, caffeic acid, and syringic acid were 96.3, 95.7, and 92.4%, respectively. Gallic acid, caffeic acid, and syringic acid were present at levels of 1.58, 0.06, and 0.05% (w/w), respectively, in S. aromaticum. This method is simple, accurate, precise, and economical and can be used for routine quality control.     

Oxidants for the colorimetric determination of pindolol

A simple, sensitive and accurate colorimetric method is described for the quantitative determination of pindolol either in the pure form or in its tablets. The method is based on the oxidation of the indole moiety in pindolol with potassium persulphate or hydrogen peroxide-in acid medium-to give a highly coloured product that exhibits maximum absorption at 535 nm and 570 nm, respectively. Beer's law is obeyed over concentrations ranging from 0.07-0.35 mg/10 ml for potassium persulphate and 0.1-0.5 mg/10 ml for hydrogen peroxide with mean recoveries of 99.6+/-0.6 and 99.8+/-0.9%, respectively. The method is applied for the assay of pindolol tablets without any interference due to tablet fillers.     

没食子酸在电活化玻碳电极上的电化学行为及测定

采用循环伏安法和线性扫描伏安法对没食子酸在电活化玻碳电极上的电化学行为进行了研究。玻碳电极在pH7.0的磷酸盐缓冲溶液中,用恒电位法在1.7 V电位阳极氧化400 s。然后在pH3.0的柠檬酸盐缓冲溶液中,没食子酸在0.479 V和0.442 V处有一良好的氧化还原峰,在0.02～0.40 V s-1范围内,其氧化峰电流与扫描速率呈良好线性关系,表明电极过程为受吸附控制的准可逆过程。线性循环伏安法的氧化峰电流与没食子酸浓度1×10-6～1×10-4mol L-1范围内呈良好的线性关系(r=0.980 6),检出限为7.6×10-7mol L-1(S/N=3)。该方法操作简便,重现性较好,并应用此法分析了健民咽喉片剂中的没食子酸的含量。     

A silver nanoparticle-based method for determination of antioxidant capacity of rapeseed and its products

A novel silver nanoparticle-based (AgNP) method and two modified procedures, ferric reducing antioxidant power (FRAP) and 2,2'-diphenyl-1-picrylhydrazyl (DPPH), were used for determination of antioxidant capacities of the ethanolic, methanolic, methanolic-aqueous (1?:?1 v/v) and aqueous extracts of rapeseed and its products. The AgNP method based on the electron-transfer reaction between silver ions and antioxidants in an optimized ammonium buffer medium (pH = 8.4) and determination of silver nanoparticle formation has been elaborated. The novel AgNP method was validated using sinapic acid, gallic acid, caffeic acid, ascorbic acid and quercetin as standard antioxidant solutions in concentration ranges of 0.03-0.21 μmol mL(-1), 0.02-0.20 μmol mL(-1), 0.01-0.18 μmol mL(-1), 0.03-0.30 μmol mL(-1) and 0.001-0.009 μmol mL(-1). The calculated detection (DL = 0.01, 0.02, 0.009, 0.02 and 0.0004 μmol mL(-1) for sinapic, gallic, caffeic, ascorbic acids and quercetin, respectively) and quantification limits (QL = 0.04, 0.06, 0.03, 0.08 and 0.001 μmol mL(-1) for sinapic, gallic, caffeic, ascorbic acids and quercetin, respectively) confirm linearity concentration ranges for determination of antioxidant capacity by AgNP assay. The average antioxidant capacities of the studied rapeseed samples ranged between 14.7 and 126.2 μmol sinapic acid per gram for the proposed AgNP method, 7.4-112.7 μmol sinapic acid per gram for the FRAP method and 39.1-339.8 μmol sinapic acid per gram for DPPH assay. The methanol-water mixture (1:1 v/v) was the most efficient solvent for extraction of antioxidants from the studied rapeseed samples. There are significant, positive correlations between the novel AgNP and the modified FRAP, DPPH and FC methods for all extracts of the studied rapeseed samples (r = 0.7564-0.8516, p < 0.001). Satisfactory values of precision (RSD = 1.2-4.4%) and accuracy (recovery = 95.6-104.6%, except methanolic extracts) demonstrate the benefit of the proposed AgNP method for analysis of the antioxidant capacity of rapeseed samples. Results of the principal component analysis (PCA) indicate that there are differences between the total amounts of antioxidants in rapeseed samples extracted by different solvents.     

Cyclic and stripping voltammetry of tin at mercury hanging drop and film electrodes in acidic o-diphenol media in the presence of lead and cadmium

The influence of catechol, gallic acid and tiron on the voltammetric behaviour of tin(IV) in the presence of lead(II) and cadmium(II) was investigated at hanging drop and mercury film electrodes in perchloric acid, oxalic acid and formate supporting electrolytes. Under cyclic conditions, well separated peaks of tin, lead and cadmium are obtained in oxalic acid and formate solutions containing gallic acid or catechol; tiron suppresses the tin peaks significantly. The efficiency of the deposition of tin in the presence of catechol or gallic acid is less than that of lead, particularly at long deposition time. The best separation of the stripping peaks of tin, lead and cadmium is obtained in oxalic acid solution containing gallic acid or catechol. In perchloric acid solution containing gallic acid or catechol the second peak corresponding to tin oxidation is useful for determinations of tin in the presence of lead. Tin(IV) at the 10^-8 mol l^-1 level can be detemined in various salt solutions and in water samples in the presence of five-fold amounts of lead and cadmium.     

Studies on the interaction of gallic acid with human serum albumin in membrane mimetic environments

In this study the interaction between gallic acid and human serum albumin (HSA) in AOT/isooctane/water microemulsions was characterized for the first time using fluorescence quenching technique in combination with UV absorption spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, circular dichroism (CD) spectroscopy and dynamic light scattering (DLS) technique. In water-surfactant molar ratio (omega(o))=20 microemulsions fluorescence data revealed the presence of one binding site of gallic acid on HSA and its binding constants (K) were (1.18+/-0.02)x10(4), (1.13+/-0.02)x10(4), (1.03+/-0.02)x10(4), (0.95+/-0.02)x10(4), (0.87+/-0.02)x10(4) and (0.82+/-0.03)x10(4)M(-1) at 282, 289, 296, 303, 310 and 317 K, respectively. The affinities in microemulsions were much higher than that in buffer solution. FT-IR and CD data suggested that the protein conformations were altered with the reductions of alpha-helices from 54-56% for free HSA in buffer to 40-41% for free HSA in microemulsion. After binding with gallic acid, the alpha-helices of HSA in microemulsion increased 2-7% for different drug-protein molar ratio. The thermodynamic functions standard enthalpy (Delta H(0)) and standard entropy (DeltaS(0)) for the reaction were calculated to be -8.10 kJ mol(-1) and 49.42 J mol(-1)K(-1). These results indicated that gallic acid bound to HSA mainly by hydrophobic interaction and electrostatic interaction in microemulsions. In addition, the displacement experiments confirmed that gallic acid could bind to the site I of HSA, which was approved by the molecular modeling study. Furthermore, the DLS data suggested that HSA may locate at the interface of the microemulsion and gallic acid could interact with them.     

Determination of Gallic Acid by Flow Injection Analysis Based on Luminol‐AgNO3‐Ag NPs Chemiluminescence System

A novel flow injection procedure has been developed for the determination of gallic acid based on the enhancement function for luminol‐AgNO₃‐Ag NPs chemiluminescence (CL) system by gallic acid. The enhancement mechanism was proposed for the reinforcing effect of the gallic acid on the CL system. The UV‐vis absorption spectrum and CL emission spectrum were applied to confirm the mechanism. The method is simple, rapid and sensitive with a detection limit of 5×10^?10 g·mL^?1 and a linear range of 8.0×10^?10–1.0×10^?7 g·mL^?1. The relative standard deviation (RSD) is 1.3% for eleven measurements of 5×10^?8 g·mL^?1 gallic acid. The method has been successfully applied to the determination of gallic acid in Chinese proprietary medicine–Jianmin Yanhou tablets and synthesized samples.     

Determination of vanadium in refractory metals, steel, cast iron, alloys and silicates by extraction of an NBPHA complex from a sulphuric-hydrofluoric acid medium

A method for determining up to 0.15% of vanadium in high-purity niobium and tantalum metals, cast iron, steel, non-ferrous alloys and silicates is described. The proposed method is based on the extraction of a red vanadium(V)-N-benzoyl-N-phenylhydroxylamine complex into chloroform from a sulphuric-hydrofluoric acid medium containing excess of ammonium persulphate as oxidant. The molar absorptivity of the complex is 428 l.mole(-1).mm(-5) at 475 nm, the wavelength of maximum absorption. Interference from chromium(VI) and cerium(IV) is eliminated by reduction with iron(II). Common ions, including large amounts of titanium, zirconium, molybdenum and tungsten, do not interfere.     

Adsorption and radical stabilization of humic-Acid analogues and Pb2+ on restricted phyllomorphous clay

Humic acids have stable radicals that are indigenous to their structure. Hydroxybenzoic acid derivatives such as gallic acid (GA) and protocatechuic acid are appropriate models for the radical properties of humic acids. Here we show that the adsorption or intercalation of gallic acid in Laponite clay results in a significant thermodynamic stabilization of gallic acid radicals. Moreover, the formed organoclay shows enhanced stability against acid dissolution. The structural details of the association of gallic acid with Laponite depend on the GA/Laponite loading. At low GA/Laponite ratios (approximately 10(-6) M of gallic acid per gram of clay), gallic acid is adsorbed at the variable charge sites of Laponite. This adsorption can be adequately described by surface complexation modeling. At higher GA/Laponite ratios (approximately 10(-3) M of gallic acid per gram of clay), X-ray diffraction data show that gallic acid is intercalated at the interlamellar sites of Laponite. In the presence of Pb2+ ions, the formed GA/Pb complex is associated with Laponite in an analogous structural manner, that is, adsorption at variable charge sites or intercalation at the interlamellar sites of Laponite, depending on the loading. Laponite stabilizes the GA/Pb radicals. At prolonged exposure to ambient O2, Laponite promotes the formation of stable oligomeric GA/Pb radical species, which are intercalated into interlamellar sites.     

高速逆流色谱法分离制备中药诃子中的没食子酸

利用高速逆流色谱法从100 mg诃子醇提物中一次性分离制备得到8.6 mg没食子酸。通过分析型高速逆流色谱对5种溶剂系统进行筛选,确定以正己烷-乙酸乙酯-甲醇-水(体积比为1:5:1:5)为两相溶剂体系并放大到制备型上,以上相为固定相,下相为流动相,在主机转速850 r/min、流动相流速2 mL/min、检测波长254 nm的条件下进行分离制备,获得4个分离峰(组分Ⅰ、Ⅱ、Ⅲ、Ⅳ)。经高效液相色谱检测,按照面积归一法计算,其中组分Ⅲ的纯度达96.40%。经电喷雾电离质谱分析,并结合与没食子酸标准品的高效液相色谱测定结果的对比,确定组分Ⅲ为没食子酸。该方法简便、快速、重复性好,适合于诃子中没食子酸的分离制备。     

Evaluation of oxidant media for the determination of lead in food slurries by hydride generation atomic absorption spectrometry

Several oxidant media were evaluated for the generation of lead hydride from slurry samples and their application to the determination of lead in vegetables and fish by hydride generation atomic absorption spectrometry. Three oxidant - acid media were compared: hydrogen peroxide - nitric acid, ammonium persulphate - nitric acid and potassium dichromate - lactic acid. The powdered samples were suspended in Triton X-100 and shaken with 10.0 g of blown zirconia spheres until a slurry was formed. The potassium dichromate - lactic acid medium was the most satisfactory for the determination of lead in fish and vegetables, providing the lowest detection limits as a result of its high sensitivity and low blank values. The ammonium persulphate - nitric acid medium gave good accuracy, precision and selectivity for vegetables (1-2 p.p.m. of lead); however, with fish (0.1-1 p.p.m. of lead) it was only a semi-quantitative medium for the determination of lead owing to its lack of sensitivity and selectivity. The hydrogen peroxide - nitric acid medium was unsatisfactory for the generation of lead hydride from slurry samples because of decomposition of hydrogen peroxide by the organic matter in the sample.     

Flow injection chemiluminescence determination of the total phenolics levels in plant-derived beverages using soluble manganese(IV)

This study established a flow injection (FI) methodology for the determination of the total phenolic content in plant-derived beverages based on soluble manganese(IV) chemiluminescence (CL) detection. It was found that mixing polyphenols with acidic soluble manganese(IV) in the presence of formaldehyde evoked chemiluminescence. Based on this finding, a new FI-CL method was developed for the estimation of the total content of phenolic compounds (expressed as milligrams of gallic acid equivalent per litre of drink) in a variety of wine, tea and fruit juice samples. The proposed method is sensitive with a detection limit of 0.02 ng mL⁻¹ (gallic acid), offers a wide linear dynamic range (0.5-400 ng mL⁻¹) and high sample throughput (247 samples h⁻¹). The relative standard deviation for 15 measurements was 3.8% for 2 ng mL⁻¹ and 0.45% for 10 ng mL⁻¹ of gallic acid. Analysis of 36 different samples showed that the results obtained by the proposed FI-CL method correlate highly with those obtained by spectrophotometric methods commonly used for the evaluation of the total phenolic/antioxidant level. However, the FI-CL method was found to be far simpler, more rapid and selective, with almost no interference from non-phenolic components of the samples examined.     

HPLC法测定怀菊花中没食子酸的含量

为建立HPLC法测定怀菊花中没食子酸含量测定方法,采用Agilent C18柱(150 mm×4.6mm,5μm),以V(甲醇)+V(超纯水+0.1%磷酸)=25+75为流动相,流量:0.5 mL·min1;柱温为25℃,检测波长:258 nm;进样量:10μL,进行测定。结果表明,回归方程为y=3.054 2 x-2.207 1,r2=0.999 1(n=6),线性范围0～20μg,平均回收率97.28%,RSD为3.39%。样品中没食子酸质量分数为3.17 mg/g。方法快速、简便、准确、重现性较好,结果可靠,可为怀菊花中没食子酸的质量评价提供依据。     

Rise in the pH of an unfrozen solution in ice due to the presence of NaCl and promotion of decomposition of gallic acids owing to a change in the pH

Oxidative decomposition of gallic acid occurs in alkaline solutions but hardly arises in acidic solutions. We have found that the addition of sodium chloride promotes the decomposition of gallic acid caused by freezing even under neutral and acidic conditions. Even at pH 4.5, gallic acid was decomposed by freezing in the presence of NaCl; however, in the absence of NaCl, it was hardly decomposed by freezing at pH lower than 7. Chloride ions are more easily incorporated in ice than sodium ions when the NaCl solution is frozen. The unfrozen solution in ice becomes positively charged, and as a result, protons transfer from the unfrozen solution to the ice. We measured the pH in the unfrozen solution which coexists with single-crystal ice formed from a 5 mmol dm(-3) NaCl solution and determined the pH to be 8.6 at equilibrium with CO(2) of 380 ppm or 11.3 in the absence of CO(2) compared to pH 5.6 in the original solution. From the model calculation performed for gallic acid solution in the presence of 5 mmol dm(-3) NaCl, it can be estimated that the amount of OH(-) transferred from the ice to the solution corresponds to 1.26 x 10(-5) mol dm(-3). The amount of OH(-) transferred is concentrated into the unfrozen solution and affects the pH of the unfrozen solution. Therefore, the pH in an unfrozen gallic acid solution in ice becomes alkaline, and the decomposition of gallic acid proceeds. It is expected that other base-catalyzed reactions in weakly acidic solutions also proceed by freezing in the presence of NaCl without the need for any alkaline reagents.     

Validated high-performance thin-layer chromatographic method for quantification of gallic acid and ellagic acid in fruits of Terminalia chebula,Phyllanthus emblica,and Quercus infectoria

A simple and rapid high-performance thin-layer chromatographic method for quantification of gallic acid and ellagic acid in dried fruits of Terminalia chebula, Phyllanthus emblica, and Quercus infectoria has been developed. The chromatographic development was carried out on precoated silica gel 60 F₂₅₄ plates in a mixture of toluene:ethyl acetate:chloroform:formic acid (4:8:1:3 v/v/v/v). The plate was scanned densitometrically at a wavelength of 280 nm. The retention factor value of gallic acid and ellagic acid was found to be 0.63 ± 0.2 and 0.53 ± 0.1, respectively. The developed method was validated in terms of linearity, precision, accuracy, sensitivity, robustness, specificity and stability as per the international conference of harmonization guidelines. The method showed good linear relationship over a range of 100–600 ng/band (gallic acid) and 100–500 ng/band (ellagic acid) with a regression coefficient (r²) of 0.997 (gallic acid) and 0.996 (ellagic acid). The method showed high accuracy (99.65%–100.85%). The percentage relative standard deviation of intra-day and inter-day precision studies was not more than 2%. The method is highly robust and has displayed high specificity. The developed method is new, simple, and accurate and can be successfully employed in routine analysis of raw materials and formulations containing gallic acid and ellagic acid.     

Determination of Gallic Acid by Flow Injection with Electrochemiluminescent Detection

ABSTRACT

Potential dependent inhibition and enhancement effects of gallic acid on the electrochemiluminescence (ECL) of luminol in alkaline solutions were found. On the basis of the enhancement effect, a flow injection method was developed for the determination of gallic acid. The method was simple, convenient and sensitive. A detection limit of 1.8×10^?8 mol/L, linear range of 3.0×10^?8 - 1.0×10^?4 mol/L, relative standard deviation of 1.0% for eleven measurements of 5.0×10^?6 mol/L of gallic acid was found. This method was successfully applied to determine the content of gallic acid in Chinese gall (moshizi).     

在线扫集-毛细管胶束电动色谱法对石榴与石榴叶中没食子酸含量的测定

建立了一种在线扫集-胶束电动色谱法测定没食子酸的新方法。考察了背景溶液pH值、十二烷基硫酸钠(SDS)浓度、样品基体组成和进样时间对富集效果的影响。使用未涂层的毛细管柱(48.5 cm×75μmi.d.,有效柱长40 cm),pH9.0的20 mmol/L硼酸盐+50 mmol/LSDS为背景溶液,在紫外检测波长272 nm、运行电压18 kV的条件下,200 s内的富集倍数可达20倍。线性范围为0.62~10.30 mg/L(r=0.999),检出限(S/N=3)为0.08 mg/L,平均回收率为104%。没食子酸迁移时间和峰面积的相对标准偏差分别为1.2%和1.6%。方法快速、准确可靠、灵敏度高、重复性好,可检测石榴不同部位和石榴叶以及饮料中没食子酸的含量。     

Validated HPTLC method for quantitative determination of gallic acid in stem bark of Myrica esculenta Buch.-Ham. ex D. Don, myricaceae

A simple, rapid, and precise HPTLC method was developed for quantitative estimation of gallic acid in stem bark of Myrica esculenta, family Myricaceae. Separation was performed on silica gel 60F254 HPTLC plates using toluene-ethyl acetate-formic acid-methanol (3 + 3 + 0.6 + 0.4, v/v/v/v) mobile phase for separation of the extracted components. The determination was carried out in the UV densitometric absorbance-reflection mode at 280 nm. The amount of gallic acid in free and combined form in the stem bark powder was found to be 0.276 and 0.541%, respectively, on a dry weight basis. The method was validated in terms of linearity, accuracy, precision, and specificity according to International Conference on Harmonization guidelines. Gallic acid response was found to be linear over a broad concentration range of 0.4-2.0 microg/band. LOD and LOQ were 0.103 and 0.312 microg/spot, respectively. The developed method is capable of quantifying amounts of gallic acid in stem bark powder of M. esculenta.