Rapid and sensitive determination of protein by light-scattering technique with Eriochrome Blue Black R

Based on the interaction between Eriochrome Blue Black R (EBBR) and proteins, which causes a strong light-scattering signal with the maximum scattering peak located at 398 nm, a simple, rapid, sensitive and selective method is developed for the determination of proteins by the light-scattering technique using a common spectrofluoremeter. Under proper experimental conditions, the protein determination can be performed in the range of 0.1-25, 0.1-20 and 0.25-25 μg ml⁻¹ for bovine serum albumin (BSA), human serum albumin (HSA) and human immunoglobulin G (IgG), respectively. The detection limit, calculated as 3 times the S.D. of nine blank measurements, are 33 μg l⁻¹ for BSA, 25 μg l⁻¹ for HSA and 38 μg l⁻¹ for IgG. Moreover, there is no significant difference among the scattering signals yielded by HSA, IgG and BSA, and almost no interference of many amino acids and metal ions. The method has been satisfactorily applied to the direct determination of the total protein in human serum, saliva and urine samples. The results obtained from the studies on the binding characteristics of EBBR to BSA indicated that an electrostatic force existed in the binding system, and the binding constant (K) and the number of the binding sites (n) at 25 °C are 1.69×10⁵ l mol⁻¹ and 0.946, respectively.     

Inorganic complexation of nickel and cobalt in natural waters

The distribution of nickel and cobalt species has been computed, based on the pH-dependent model of Zirino and Yamamoto. The media used in the pH range of 7 to 9 are natural waters like fresh water, sea water and a mixture of them at different compositions, at 25°C temperature and 1 atm pressure. In fresh water, both nickel and cobalt dominate as free cations at lower pH, and as carbonato complexes at higher pH. In sea water, chloro complexes are significant. In mixtures of the two kinds of water, as might be found in a totally mixed estuary, chloro complexes are important, varying slowly with pH. Sea water plays an important role in complexation. The present results are in excellent agreement with experimental data obtained by the resin exchange method.     

Rapid determination of aluminum by UV-vis diffuse reflectance spectroscopy with application of suitable adsorbents

Diffuse reflectance spectroscopy (DRS) can be used as a rapid and sensitive method for the quantitative determination of low amounts of aluminum. In this analytical technique, the analyte in samples are extracted onto a solid sorbent matrix loaded with a colorimetric reagent and then quantified directly on the adsorbent surface. Alternatively, colored aluminum complexes formed in solution can also be immobilized onto adsorbent surface and be measured by DRS technique. Octadecyl silica disk, methyltrioctylammonium chloride–naphthalene and MCM-41 were examined as adsorbents. Eriochrome cyanine R and quinalizarin were used as coloring reagents. Optimal sorption conditions were found for each system of analyte–reagent–adsorbent. The concentration of analyte is determined using the appropriate form of the Kubelka–Munk function. We obtained for each of the aluminium–reagent–adsorbent system a calibration curve by plotting the absorbance versus the log 10²[Al³⁺] μg ml⁻¹. The linear dynamic range extends over two orders of magnitude within 0.01–15 μg ml⁻¹ with little differences in the range and in the correlation coefficients among the adsorbents. We consider that for a rapid determination of aluminum a spot-test-DRS combination with a detection limit of 1.0 × 10⁻² μg ml⁻¹ is the more facile and preferred technique.     

Development of a cloud point extraction and preconcentration method for determination of trace aluminum in mineral waters by FAAS

A cloud point extraction (CPE) method has been developed for the preconcentration of trace aluminum prior to its determination by flame atomic absorption spectrometry (FAAS). The CPE method is based on the complex of Al(III) with Xylidyl Blue (XB) and then entrapped in non-ionic surfactant Triton X-114. The main factors affecting CPE efficiency, such as pH of sample solution, concentration of XB and Triton X-114, equilibration temperature and time, were investigated in detail. An enrichment factor of 50 was obtained for the preconcentration of Al(III) with 50 mL solution. Under the optimal conditions, the detection limit of this method for Al(III) is 1.43 μg L^− 1, and the relative standard deviation is 2.7% at determination of 100 μg L^− 1 Al(III). The proposed method has been applied for determination of trace amount of aluminum in mineral water samples with satisfactory results. Also, the proposed method was applied to the certified reference materials. The results obtained were in good agreement with certified values.     

Resonance Rayleigh scattering determination of trace amounts of Al in natural waters and biological samples based on the formation of an Al(III)-morin-surfactant complex

A novel method for the determination of trace amounts of Al(III) based on resonance Rayleigh scattering (RRS) has been developed. In the presence of some surfactants, Al(III) can react with morin and form an Al(III)-morin-surfactant complex, which results in the enhancement of RRS intensity and the appearance of the corresponding RRS spectral characteristics. Their maximum scatter peaks are at 476 nm for the cetyltrimethylammonium bromide (CTAB) system, 489 nm for the cetylpyridinium chloride (CPC) system, 474 nm for the Triton X-100 system, and 473 nm for the Tween-20 system. The enhanced RRS intensity is directly proportional to the concentration of Al(III). The detection limits are in the range of (0.50-1.2)×10⁻⁷ mol l⁻¹ depending on the surfactant. The characteristics of RRS spectra of the complexes, the optimum conditions of these reactions and the influencing factors have been investigated. The method has high selectivity, and was successfully applied to the determination of Al(III) in natural and biological samples. Furthermore, according to different complexation capacity of Al(III)-morin-CTAB system under two pH conditions, speciation analysis of Al(III) in natural waters was explored. The labile monomeric Al fraction (mainly inorganic Al, Al_i) is determined at acidic pH and the total monomeric Al fraction (Al_a) is determined at alkaline pH. The results are in agreement with those obtained by Driscoll’s 8-hydroxyquinoline extraction-ion exchange method.     

Separation and preconcentration of trace amounts of aluminum ions in surface water samples using different analytical techniques

A separation/preconcentration of aluminum (III) (Al³⁺) has been developed to overcome the problem of high matrix species, which may interfere with the determination of trace quantity of Al³⁺ in natural water samples. The separation of Al³⁺ in water samples was carried out from interfering cations by complexing them with 2-methyle 8-hyroxyquinoline (quinaldine) on activated silica. Whereas the separated trace amounts of Al³⁺ was preconcentrated by cloud point extraction (CPE), as prior step to its determination by spectrofluorimetry (SPF) and flame atomic absorption spectrometry (FAAS). The Al³⁺ react with 8-hydroxyquinoline (oxine) and then entrapped in non-ionic surfactant Triton X-114. The main factors affecting CPE efficiency, such as pH of sample solution, concentration of oxine and Triton X-114, equilibration temperature and time period for shaking were investigated in detail. The validity of separation/preconcentration of Al³⁺ was checked by certified reference material of water (SRM-1643e). After optimization of the complexation and extraction conditions, a preconcentration factor of 20 was obtained for Al³⁺ in 10 mL of natural water samples. The relative standard deviation for 6 replicates containing 100 μg L⁻¹ of Al³⁺ was 5.41 and 4.53% for SPF and FAAS, respectively. The proposed method has been applied for determination of trace amount of Al³⁺ in natural water samples with satisfactory results.     

Competing ligand exchange-solid phase extraction method for the determination of the complexation of dissolved inorganic mercury (II) in natural waters

A method employing dual competitive ligand exchange followed by solid phase extraction (CLE-SPE) for characterizing the complexation of inorganic Hg(II) in natural waters is described. This method employs parallel use of two competing ligands: diethyldithiolcarbamate (DEDC), which forms hydrophobic complexes with Hg(II), and thiosalicylic acid (TSA), which forms hydrophilic complexes with Hg(II). Inorganic mercury complexed by natural and competing ligands are separated based on hydrophobicity using C₁₈ solid phase extraction columns.Data modeling allows for the calculation of the concentration and conditional stability constants of natural ligands capable of complexing Hg(II) in both the operationally defined hydrophilic and hydrophobic fractions. The use of multiple ligand concentrations, and thus multiple analytical windows, to characterize different ligand classes within both of these two fractions is described. Studies of the kinetics of the ligand exchange involved, potential for changes in the stability of natural ligands during freezing and thawing, potential breakthrough during solid phase extraction, as well as the method's precision and estimation of error, are presented and discussed.Results from the application of the method to natural freshwaters demonstrated that in the limited samples collected over 99.99% of the ambient inorganic mercury is strongly complexed by ligands with conditional stability constants (, Hg²⁺) on the order of 10³⁰, values similar to that of reduced sulfur ligands. At ambient conditions 85-90% of the mercury exists in hydrophobic complexes in these freshwaters, but strong Hg-binding ligands exist in both the hydrophobic and hydrophilic fractions.     

Speciation of chromium(III) and chromium(VI) by in situ separation and sequential determination with electrothermal vaporization inductively coupled plasma atomic emission spectrometry

A novel method for the speciation of chromium(III) and chromium(VI) by in situ separation and sequential determination with electrothermal vaporization-inductively coupled plasma-atomic emission spectrometry (ETV-ICP-AES) was developed. The reaction conditions between Cr(III) and 8-hydroxyquinoline (8-Ox) and the vaporization behavior of the chelate formed were investigated in detail. It was found that the Cr(III)-8-Ox chelate could be formed at room temperature and vaporized from graphite furnace under controlled experimental conditions, therefore, an in situ separation of Cr(III) from Cr(VI) was achieved. The retained Cr(VI) in graphite tube was then determined by using fluorination vaporization ETV-ICP-AES with PTFE slurry as chemical modifier. Under optimum experimental conditions, the detection limits for Cr(III) and Cr(VI) are 8.6 ng/ml and 11.3 ng/ml, and the relative standard deviations (R.S.D.s) are 3.8% and 4.1% (c=0.1 μg/ml, n=6), respectively. The linear ranges of the calibration curve for both Cr(III) and Cr(VI) covered three orders of magnitude. The proposed method has been applied to the speciation of Cr(III) and Cr(VI) in water samples with the satisfactory results.     

8-羟基喹啉动态有序介孔SiO_2涂层毛细管微萃取与ICP-MS在线联用分析天然水中铝的形态

本文采用溶胶-凝胶方法合成SiO_2溶胶,制备了8-羟基喹啉改性的有序介孔SiO_2涂层毛细管,建立了毛细管微萃取-电感耦合等离子体质谱(CME-ICP-MS)在线联用技术分析铝形态的新方法.选择游离态铝和Al-柠檬酸络合物为不同铝形态的代表物,详细探讨了不同实验参数对铝形态分离的影响.结果表明:8-羟基喹啉改性的有序介孔SiO_2涂层毛细管在pH为5.0～8.0的范围内可以有效地分离试样中的稳定态单核铝(柠檬酸铝)和非稳定态无机单核铝(游离态铝).方法的富集倍数为10,检出限为0.34 ng·mL~(-1).该法应用于湖水、池塘水和长江水中铝的组形态分析,所得结果与8-羟基喹啉负载硅胶微柱分离所得结果吻合很好.     

A sequential injection method for the determination of aluminum in drinking water using fluorescence enhancement of the aluminum-morin complex in micellar media

A robust and simple sequential injection (SI) method for the assay of aluminum ions in natural water is described. The method is based on the enhancement of the fluorescence of the aluminum-morin complex in the presence of a non-ionic surfactant (Tween-20). The fluorescence of the complex is monitored at an emission wavelength of 495 nm with excitation at 425 nm. The pH, morin concentration and the aspirated sample volume were optimized simultaneously using a chemometric method. The optimum operating conditions are: 150 μl aspirated sample volume, 20 μM morin concentration, a pH of 4.5 and 0.8% Tween-20. Using these optimum conditions a linear calibration curve was obtained from 50 to 1000 ppb. The detection limit was 3 ppb and the maximum relative standard deviation (n=5) of the method was 2.9%. The method was successfully applied for the determination of aluminum ions in natural water samples.     

Spectrofluorimetric determination of aluminum in drinking waters by sequential injection analysis

A selective procedure for the determination of Al³⁺ in drinking and natural waters is proposed. The analytical procedure is based both on the complex formation between Al³⁺ and 8-hydroxyquinoline-5-sulfonic acid (HQS) and on a fluorimetric detection of the complex. The reaction was carried out in presence of thioglycolic acid as a masking agent. This procedure has been adapted to a sequential injection analysis (SIA) system. Operative conditions both for batch and SIA procedures were investigated including reagent concentration, volumes, pH and wavelengths used for the fluorimetric detection. Batch procedure allows determination of Al³⁺ at ppb level (LOQ: 2.8 μg l⁻¹) within a working range of 2.2-300 μg l⁻¹. The SIA procedure was successfully employed for the determination of Al³⁺ in several commercial drinking and tap waters.     

铬蓝黑R-示波计时电位法快速测定天然水中不同形态的铝浓度

本文报道铬蓝黑 R-示波计时电位法快速测定天然水中不同形态的铝。在 0 .5mol/L 乙酸 -乙酸铵 - 1× 1 0 - 3mol/L铬蓝黑 R( p H4.6)底液中 ,铝 -铬蓝黑 R铬合物在 - 0 .80 V电位处产生灵敏切口 ,切口深度与铝浓度成正比 ,线性范围为 8× 1 0 - 7～6× 1 0 - 5mol/L,检测下限为 6× 1 0 - 7mol/L,相对标准偏差为 4.8% ( n=1 0 ,4× 1 0 - 5mol/L Al)。应用该法测定了天然水中不同形态的铝浓度 ,并同 Driscoll的 MIBK-GF/AAS法进行了比较 ,结果基本一致     

虎杖提取物中白藜芦醇的荧光分析研究

建立了一种荧光检测虎杖提取物中白藜芦醇的新方法,探讨了白藜芦醇荧光检测的最佳条件,其激发波长和发射波长分别是336和380nm。白藜芦醇荧光强度与浓度在0～1.68×10-5mol L的范围内具有良好的线性关系,相对标准偏差为2.39%～4.45%。检出限为8.84×10-10mol L。     

一种天然显色剂在光度法测定铝中的应用

自紫甘蓝中提取的花青素与Al3+发生络合反应的产物颜色与花青素本身不同,利用该性质可以建立一种定量测定Al3+的新方法.花青素在pH4.7的乙酸-乙酸钠缓冲体系中与Al3+显色,络合物最大吸收波长580nm.Al3+含量在0.1～1.0mg/25mL范围内与吸光度呈良好的线性关系,相关系数R2=0.9995,络舍物摩尔吸光系数236L·mol-1·cm-1,铝离子浓度为25μg/mL时方法相对标准偏差2.1％,定量检出限0.059mg/25mL.方法应用于国家土壤标准样品(GBW07408)的测定,土壤样品加标回收率在98％～109％之间.方法可用于低常量和微量铝的定量测定.     

Investigation into sorption processes in the anodic stripping voltammetric speciation of Cu in natural waters

In the anodic stripping voltammetric speciation of copper significant errors may be introduced as a result of sorption of Cu²⁺ onto active surfaces of the voltammetric cell assembly. A correction method was developed based on monitoring of the total copper concentration in solution using a -radiotracer; additionally this allowed us to study sorption phenomena in the voltammetric cell assembly.For copper speciation in a fresh water sorption-corrected complexing capacity data (total natural ligand concentration and conditional stability constant of formed complex) showed considerable discrepancies with uncorrected data. From the same sorption data it could be deducted that this was accountable to the presence of two active surface sites in the voltammetric cell assembly.     

Effects of various competing ligands on the kinetics of trace metal complexes of Laurentian Fulvic Acid in model solutions and natural waters

The objective of this work was to study the effects of the following Ligands: Chelex-100, Dowex MAC-3 and Dowex 50WX-8 using Competing Ligand Exchange Method. This objective was achieved by investigating complex dissociation kinetics of trace metals: Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Mn(II) and Pb(II) of a well-characterized Laurentian Fulvic Acid (LFA) in model solutions and in a natural waters of Lake Heva (Québec, Canada). The effects of variation in the competing ligands (including their quantities) on the complex dissociation kinetics were quantitatively characterized by their first-order dissociation rate coefficients. The kinetic lability of the metal complexes varied with the metal-to-LFA ratio, as expected from the theory of metal complexes of the chemically and physically heterogeneous complexants, LFA. The general trend in the metal-binding by the above competing ligands was: Dowex 50WX-8 > Chelex-100 > Dowex MAC-3. However, no difference was found between the Dowex 50WX-8 and Chelex-100 for Cd(II), Zn(II), and Co(II). The results revealed the importance of the quantity of Chelex-100 as a competing ligand in the metal(II)-LFA complexation, on the dissociation kinetics of these complexes in model solutions. By developing Competing Ligand Exchange Method as an analytical technique, for studying the relative affinities of the above competing ligands for metals complexation in natural waters this work has made a substantial contribution to analytical chemistry.     

Combination of ionic liquid-based dispersive liquid-liquid micro-extraction with stopped-flow spectrofluorometry for the pre-concentration and determination of aluminum in natural waters, fruit juice and food samples

In this research, we combined ionic liquid-based dispersive liquid-liquid micro-extraction (IL-based DLLME) with stopped-flow spectrofluorometry (SFS) to evaluate the concentration of aluminum in different real samples at trace level. 1-Hexylpyridinium hexafluorophosphate [Hpy][PF₆] ionic liquid and 8-hydroxyquinoline (oxine), which forms a highly fluorescent complex with Al³⁺, were chosen as the extraction solvent and chelating agent, respectively. The hydrophobic Al-oxine complex was extracted into the [Hpy][PF₆] and separated from the aqueous phase. Then, the concentration of the enriched aluminum in the sediment phase was determined by SFS. Some effective parameters that influence the SFS signals and the micro-extraction efficiency, such as the suction and sending time, the concentration of the chelating agent, pH, the amount of the ionic liquid, the type of disperser solvent and diluting agent, ionic strength, extraction time, equilibration temperature and centrifugation time were investigated and optimized. In the optimum experimental conditions, the limit of detection (3 s) and enrichment factor were 0.05 μg L⁻¹ and 100, respectively. The relative standard deviation (RSD) for six replicate determinations of 6 μg L⁻¹ Al was 1.7%. The calibration graph using the pre-concentration system was linear in the range of 0.06-15 μg L⁻¹ with a correlation coefficient of 0.9989. The developed method was validated by the analysis of certified reference materials and applied successfully to the determination of aluminum in several water, fruit juice and food samples.     

Determination of free copper concentrations in natural waters by using supported liquid membrane extraction under equilibrium conditions

A method is described for measurement of freely dissolved copper concentrations in natural water samples using supported liquid membrane (SLM) extraction under equilibrium conditions, a technique denoted equilibrium sampling through membranes (ESTM). For this purpose, 1,10-dibenzyl-1,10-diaza-18-crown-6 as neutral carrier and oleic acid were used in the membrane phase. The main variables optimised were the carrier used to form the metal complexes, the organic solvent used in the membrane, the countercation, pH, the ligand used in the acceptor phase, the extraction time, and the flow rate of the donor phase. After the optimisation process an enrichment factor of 18.5 was obtained. Equilibrium conditions were reached after extraction for 60 min if a flow rate of 1.0 mL min^–1 or greater was used. When different ligands such as humic acids, phthalic acid, and EDTA were added to the sample solution, and sample pH ranged from 6 to 8, the results obtained for freely dissolved copper concentrations were in a good agreement with results from speciation calculations performed with Visual Minteq V 2.30, Cheaqs V L20.1, and WinHumic V. The developed technique was applied to analysis of stream and leachate water.Electronic Supplementary Material Supplementary material is available for this article at     

Examination of the range of copper complexing ligands in natural waters using a combination of cathodic stripping voltammetry and computer simulation

Knowledge of the detection capabilities of speciation techniques, gained by calculation and computer simulation, can be combined with experimental measurements to arrive at an understanding of trace metal speciation which is less dependent on operational factors than other approaches. Examples of the application of this means of measuring copper speciation to samples from the Humber Estuary are given. Although concentrations of total dissolved copper can approach the estuarine Environmental Quality Standard value of 5 μg 1^?1, there is evidence for a substantial excess of complexing ligands at all locations except the outer estuary, where copper levels are much reduced by dilution. Dissolved copper is therefore present almost totally in the form of organic complexes. The range of different types of ligand is also assessed. In sea water, there appears to be a range of ligands of differing affinities for copper; the complexing capacity ranges from 20 nM [conditional stability constant of the copper complex (K′) > 10¹⁴] to 70 nM (K′) > 10⁸). For estuarine samples, ligands with a high affinity for copper seem to be predominant and the overall complexing capacity rises to over 200 nM. In freshwater samples, it is likely that the potential for varying combinations of weak and strong complexes will depend on the water quality, but a capacity to complex over 200 nM copper is not unusual.     

Determination of As(III) and arsenic(V) in natural waters by cathodic stripping voltammetry at a hanging mercury drop electrode

A simple, fast and quantitative method was developed for the determination of As(III) and total inorganic arsenic (As (total)) in natural spring and mineral waters using square wave cathodic stripping voltammetry (SWCSV) at a hanging mercury drop electrode (HMDE). In the determination of As(III), pre-concentration was carried out on the electrode from a solution of 1 mol/l HCl in the presence of 45 ppm of Cu(II) at a potential of −0.39 V versus Ag/AgCl, and the deposited intermetallic compound was reduced at a potential of about −0.82 V versus Ag/AgCl. In the determination of As (total) the pre-concentration was carried out in 1 mol/l HCl in the presence of 400 ppm of Cu(II) at a potential of −0.40 V versus Ag/AgCl, and the intermetallic compound deposited was reduced at a potential of about −0.76 V versus Ag/AgCl. For determination of As(III) the quantification limit was 0.2 ppb for a deposition time of 40 s, and the relative standard deviation (R.S.D.) was calculated to be 6% (n=13) for a solution with 8 ppb of As(III). For As (total), the quantification limit was 2 ppb for a deposition time of 3 min, and the R.S.D. was calculated to be 3% (n=10) for a solution with 8 ppb of As(V). The method was validated by application of recovery and duplicate tests in the measurements of As(III) and As (total) in natural spring and mineral waters. For As (total), the results of the SWCSV method were compared with the results obtained by optical emission spectrometry with ICP coupled to hydride generation (OES-ICP-HG) good correlation being observed.