Removal, preconcentration and spectrophotometric determination of U(VI) from water samples using modified maghemite nanoparticles

Arsenazo III modified maghemite nanoparticles (A-MMNPs) was used for removing and preconcentration of U(VI) from aqueous samples. The effects of contact time, amount of adsorbent, pH and competitive ions was investigated. The experimental results were fitted to the Langmuir adsorption model in the studied concentration range of uranium (1.0 × 10^?4–1.0 × 10^?2 mol L^?1). According to the results obtained by Langmuir equation, the maximum adsorption capacity for the adsorption of U(VI) on A-MMNPs was 285 mg g^?1 at pH 7. The adsorbed uranium on the A-MMNPs was then desorbed by 0.5 mol L^?1 NaOH solution and determined spectrophotometrically. A preconcentration factor of 400 was achieved in this method. The calibration graph was linear in the range 0.04–2.4 ng mL^?1 (1.0 × 10^?10–1.0 × 10^?8 mol L^?1) of U(VI) with a correlation coefficient of 0.997. The detection limit of the method for determination of U(VI) was 0.01 ng mL^?1 and the relative standard deviation (R.S.D.) for the determination of 1.43 and 2.38 ng mL^?1 of U(VI) was 3.62% and 1.17% (n = 5), respectively. The method was applied to the determination of U(VI) in water samples.     

Preconcentration and spectrophotometric determination of low concentrations of malachite green and leuco-malachite green in water samples by high performance solid phase extraction using maghemite nanoparticles

A novel and sensitive extraction procedure using maghemite nanoparticles (γ-Fe₂O₃) modified with sodium dodecyl sulfate (SDS), as an efficient solid phase, was developed for removal, preconcentration and spectrophotometric determination of trace amounts of malachite green (MG) and leuco-malachite green (LMG). Combination of nanoparticle adsorption and easily magnetic separation was used to extraction and desorption of MG and LMG. The adsorption capacity was evaluated using both the Langmuir and Freundlich adsorption isotherm models. Maghemite nanoparticles were prepared by co-precipitation method and their surfaces were modified by SDS. The size and properties of the produced maghemite nanoparticles was determined by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and BET analysis. MG and LMG became adsorbed at pH 3.0. LMG was oxidized to MG by adsorption on maghemite nanoparticles. The adsorbed MG was then desorbed and determined spectrophotometrically. The calibration graph was linear in the range 0.50-250.00 ng mL⁻¹ of MG and LMG with a correlation coefficient of 0.9991. The detection limit of the method for determination of MG was 0.28 ng mL⁻¹ and the relative standard deviation (R.S.D.) for 10.00 and 50.00 ng mL⁻¹ of malachite green was 1.60% (n = 3) and 0.86% (n = 5), respectively. A preconcentration factor of 50 was achieved in this method. The Langmuir adsorption capacity (q_max) was found to be 227.3 mg g⁻¹ of the adsorbent. The method was applied to the determination of MG in fish farming water samples.     

Spectrophotometric determination of trace amounts of uranium(VI) in water samples after mixed micelle-mediated extraction

A cloud point extraction process using mixed micelle of the cationic surfactant CTAB and non-ionic surfactant TritonX-114 to extract uranium(VI) from aqueous solutions was investigated. The method is based on the color reaction of uranium with pyrocatechol violet in the presence of potassium iodide in hexamethylenetetramine buffer media and mixed micelle-mediated extraction of complex. The optimal extraction and reaction conditions (e.g. surfactant concentration, reagent concentration, effect of time) were studied and the analytical characteristics of the method (e.g. limit of detection, linear range, preconcentration, and improvement factors) were obtained. Linearity was obeyed in the range of 0.20-10.00 ng mL⁻¹ of uranium(VI) ion and the detection limit of the method is 0.06 ng mL⁻¹. The interference effect of some anions and cations was also tested. The method was applied to the determination of uranium(VI) in tap water, waste-water and well water samples.     

Micellar effect on the sensitivity of spectrophotometric Mo(VI) determination based on the formation of gallic acid complex providing evidence for the polyoxoanion structure of molybdate ions

In this study effects of anionic (sodium dodecyl sulfate, SDS), cationic (cetyltrimethylammonium bromide, CTAB) and nonionic (Triton X-100, TX100) micelles on the sensitivity of spectrophotometric molybdenum(VI) (Mo) determination based on the formation of a binary complex with gallic acid (GA) were investigated.

Micellar CTAB was found to enhance the formation of Mo–GA complex. SDS micelles exerted an inhibitory effect while TX100 micelles had no effect on the complex formation. By the optimization of experimental conditions, the determination limit of the method suggested in the literature was lowered from 5.2 × 10⁻⁵ to 4.6 × 10⁻⁶ and to 5.7 × 10⁻⁷ M, in the absence and presence of CTAB, respectively.

The mechanism of the effect of CTAB was investigated by spectrophotometric titrations and it was concluded that CTAB did not form a ternary complex with Mo and GA. The stoichiometry of the complex, deduced from the results of spectrophotometric titrations, provided evidence for the formation of para-Mo₇O₄⁶⁻ polyanions at pH 4.5, indicating to the formation of a charge transfer complex between these ions and GA in micellar medium.     

Direct voltammetric determination of Mo(VI) in plants: the need for a multivariate study of interferences

A multivariate modelling procedure using a second order composite design showed that the adsorptive stripping voltammetry (AdSV) technique used for molybdenum determination in a N,N-dimethylformamide (DMF)-ethanol-water homogeneous ternary solvent system (HTSS) using α-benzoinoxime (αBO) as the complexing agent and a sodium acetate-acetic acid buffer as the supporting electrolyte is much more tolerant to the presence of phosphorous (as phosphate) and iron than it could be presumed. Instead of the concentration ratios of P/Mo=100 and Fe/Mo=500, determined by univariate experiments, these values were respectively raised to 97,500 and 4200 when the phosphate and Fe(III) levels are varied simultaneously from 0.625 to 2.500 and from 0.006 to 0.150 mg l⁻¹, respectively, in the voltammetric cell, keeping the molybdenum concentration constant at 3.00 μg l⁻¹. This allowed us to propose a straightforward AdSV-HTSS procedure for the determination of Mo(VI) in plants. The AdSV results compared favourably with those obtained by using graphite furnace atomic absorption spectrometry (GFAAS) and with the results of samples from the International Plant-Analytical Exchange (IPE) programme of Wageningen University (The Netherlands).     

Solid phase extraction-spectrophotometric determination of fluoride in water samples using magnetic iron oxide nanoparticles

A new, sensitive, fast and simple method using magnetic iron oxide nanoparticles (MIONs), as an adsorbent has been developed for extraction, preconcentration and determination of traces of fluoride ions. The determination method is based on the discoloration of Fe(III)-SCN complex with extracted fluoride ions which was subsequently monitored spectrophotometrically at λ_max = 458 nm. Various parameters affecting the adsorption of fluoride by the MIONs have been investigated, such as pH of the solution, type, volume and concentration of desorbing reagent, amount of adsorbent and interference effects. A linear response for the determination of fluoride was achieved in the concentration range of 0.040-1.250 μg mL⁻¹. The limit of detection (LOD) and limit of quantification (LOQ) for fluoride based on 3 times and 10 times the standard deviation of the blank (3S_b, 10S_b) were 0.015 and 0.042 μg mL⁻¹ (n = 20) for fluoride ion, respectively. A preconcentration factor of 50 was achieved in this method. The proposed procedure has been applied for determination of fluoride concentration in various water samples. The results obtained from this method were successfully compared with those provided by standard SPADNS method.     

Cloud-point extraction,preconcentration, and spectrophotometric determination of palladium in water samples

The possibility of using Thio-Michler's Ketone (TMK), 4,4′-bis(dimethylamino) thiobenzophenone, for palladium(II) concentrated by micellar extraction at the cloud-point temperature, and later spectrophotometric determination, was investigated. Under the optimum conditions, preconcentration of 50?mL of water samples in the presence of 0.1% (w/v) octylphenoxy polyethoxy ethanol (Triton X-114), 2?×?10^?6?mol?L^?1?TMK and 1?×?10^–3?mol?L^?1 buffer solution (pH?=?3.0) gave the limit of detection of 0.47?ng?mL^?1, and the calibration graph was linear in the range of 2–50?ng?mL^–1. The recovery under optimum working conditions was higher than 97%. The proposed method has been applied to the spectrophotometric determination of palladium(II) in natural water samples after cloud-point extraction with satisfactory results.     

介孔二氧化硅纳米球对水中Mo(VI)的吸附研究

本研究制备了介孔二氧化硅纳米球(MSN),并用之吸附脱除水中的Mo(VI)。应用扫描电镜、介孔分析仪、红外光谱等对MSN进行了表征。考察了pH、吸附时间、MSN投加量和温度对水中Mo(VI)脱除率的影响,并在单因素试验基础上通过正交试验法确定了Mo(VI)的最佳脱除条件：pH=3,MSN投加量为 8.5g/L,吸附时间为36h。在优化吸附试验条件下MSN对加标水中Mo(VI)的脱除率为93.6% ~ 97.3%。     

A new experimental approach for liquid-liquid extractive spectrophotometric determination of chromium(VI) in tannery wastewater and alloy samples

In this research work, a new approach is developed for the extractive determination of chromium. The principle of this approach is based on the complexation reaction between 4-(4?-chlorobenzylideneimino)-3-methyl-5-mercapto-1,2,4-triazole (CBIMMT) in dichloromethane as a complexing reagent and chromium(III) in presence of potassium iodide to form a yellow coloured complex at room temperature. The 1:2:2 [Cr(III)-CBIMMT-iodide] ternary complex was quantitatively extracted in dichloromethane from 2.5 mol L^?1 of hydrochloric acid medium which showed maximum absorption intensity at λ_max 411 nm and was stable for more than 72 h. The values of molar absorption coefficient and Sandell’s sensitivity of the complex were found to be 0.7019 × 10⁴ L mol^?1 cm^?1 and 0.00748 µg cm^?2, respectively. The system adheres to Beer’s law from 1.5 to 6.0 µg mL^?1; however, Ringbom’s plot suggests optimal concentration range was 1.8–5.8 µg mL^?1. The limit of detection and limit of quantification of the approach is 0.26 and 0.79 µg mL^?1. This approach was successfully used for the determination of chromium from wastewater effluents from the tannery industries (Kolhapur, MS, India), alloy samples and for separation of it from synthetic mixtures. The present experimental approach is apparently much simpler than the conventional method comprising multistep processes.     

Chemically selective membrane optode for Cr(VI) determination in aqueous samples

A methodology for simultaneous preconcentration and determination of Cr(VI) from aqueous samples was developed using a membrane optode formed by physical inclusion of a Cr(VI) selective chromophore 1,5-diphenylcarbazide (DPC) into a plasticized cellulose triacetate matrix. The inclusion of an anion exchanger (Aliquat-336) was found to be effective for immobilization of both DPC and Cr(VI)-DPC complex in the optode matrix itself. The proportionality in intensity of the magenta color on the optodes loaded with varying amounts of Cr(VI) suggests its potential applications for screening of Cr(VI) in aqueous samples by visual colorimetry. On loading high amounts of Cr(VI) in the membrane optode, its color changes from magenta to yellow, which indicates the possibility of using it as a threshold detector for Cr(VI). The membrane optode was optimized in terms of obtaining maximum preconcentration efficiency for Cr(VI) and subsequent stable optical response proportional to the amount of Cr(VI) in the membrane optode sample. The membrane optodes were tested for Cr(VI) determination in tap water and seawater samples. Using this optode, Cr(VI) even at levels of 13.6 ppb could be quantitatively detected. The optodes developed in the present work were found to be stable, cost effective, easy to prepare and efficient for direct preconcentration and determination of Cr(VI) in a variety of aqueous samples using spectrophotometry. However, this membrane optode is for one time use only as the reaction of Cr(VI) with DPC is irreversible.     

Removal of humic matter interference in the determination of Cr(VI) in soil extracts by the diphenylcarbazide method

Alkaline digestion of soil samples, which is recommended for minimizing Cr(III)–Cr(VI) interconversions during the extraction of Cr(VI), may also solubilize humic matter (HM). The latter is responsible for both positive and negative interference in the analysis of Cr(VI) in the extract by the diphenylcarbazide (DPC) method. Humic compounds indeed absorb light at 540 nm as the Cr-DPC product and are also able to rapidly reduce Cr(VI) under the pH conditions of the standard DPC method. To prevent any risk of interference and make the DPC method applicable to soil extracts, a new protocol is proposed. This consists of three successive steps: (1) extraction of Cr(VI) by the U.S.EPA method 3060A in the presence of Mg²⁺; (2) batch removal of solubilised HM by the XAD-7 sorbent at pH 3.0 ± 0.1 with 3–5 min contact time; (3) analysis of Cr(VI) with the DPC method at pH 3.0 ± 0.1. The application of this new protocol to the soil product SQC-012 Lot 4 certified by R.T. Corporation (RTC, USA) gave significantly lower Cr(VI) concentrations and smaller variability compared to certified values (46.5 ± 2.3 instead of 153 ± 32.6 mg/kg). The new protocol was validated by Cr(VI) and Cr(III) spikes either to the soil/extractant suspension or to the exctract. Cr(VI) results in the wide range of acceptance limits (104–202 mg/kg) reported by RTC were only obtained when the U.S.EPA method 3060A without the addition of Mg²⁺ and DPC analysis at pH 1.0 were applied. The latter procedure appears questionable since it leads to largely variable results which reflect the complex role played by humic matter in the determination of Cr(VI) and the instability of Cr(III) during the extraction.     

Kinetic Determination of Nanogram Amounts of Mo(VI) in Solution

A new inhibitory reaction is proposed and a kinteic method developed for the determination of ultra‐micro amounts of Mo(VI) on the basis of its inhibitory activity in oxidation of trimethylenediamine ‐N,N,N′,N′‐tetraacetic acid (TDTA) by KMnO₄ in the presence of hydrochloric acid. Under optimal conditions the sensitivity of the method is 0.5 ng/cm³. The probable relative error is 2.9–3.5% for the concentration range 7.5–2.0 ng/cm³ of Mo(VI). The effect of certain foreign ions upon the reaction rate were determined for the assessment of the selectivity of the method. The selectivity of the method is relatively good. Kinetic equations were proposed for the investigated process. A method has been applied for determination of Mo(VI) in a certain kind of steel.     

Spectrophotometric determination of Chromium(VI) using cyclam as a reagent

A simple, rapid, sensitive, and inexpensive method for spectrophotometric determination of chromium(VI), based on the absorbance of its complex with 1,4,8,11-tetraazacyclotetradecane (cyclam) is presented. The complex showed a molar absorbtivity of 1.5?×?10⁴?L?mol^?1?cm^?1 at 379?nm. Under optimum experimental conditions, a pH of 4.5 and 1.960?×?10³?mg?L^?1 cyclam were selected, and all measurements were performed 10?min after mixing. Major cations and anions did not show any interference; Beer's law was applicable in the concentration range 0.2–20?mg?L^?1 with a detection limit of 0.001?mg?L^?1. The standard deviation in the determination is ±0.5?mg?L^?1 for a 15.0?mg?L^?1 solution (n?=?7). The described method provides a simple and reliable means for determination of Cr(VI) in real samples.     

Removal of Cr(VI) from water by cork waste

The biosorption by cork powder is considered as a promising method for heavy metal removal from industrial waste waters such as chromium tanning factories. The aim of this study is to evaluate the efficiency extent of this method using cork powder as a biosorbent for Cr(VI). The Fourier Transform Infrared spectroscopy (FTIR) analysis permits to distinguish the type of functional groups likely to participate in metal binding. A linear form of BET isotherms for all the three used temperatures (i.e., 25, 35 and 45 °C) and a pseudo-second-order equation of adsorption kinetics are obtained. Other experimental results highlight the meaningful influence of parameters such as contact time, pH, concentration of Cr(VI) and the adsorbent particle size on Cr(VI) adsorption. 97% of Cr(VI) has been removed under definite conditions particularly a particle size of diameter d < 0.08 mm and pH of 2–3 values.     

Structural analysis of several W(VI) and Mo(VI) complex perovskites prepared by the polymeric precursors method

We describe in this work the synthesis by the Pechini method of five Mo(VI)- and W(VI)-containing complex perovskites and their structural characterisation by HREM and XRD. The compounds studied, Ba(B_2/3′B_1/3″)O₃ (B′=In and Y; B″=W and Mo) and Sr(In_2/3W_1/3)O₃, were obtained after firing the precursor powders for 8 h at 1200°C. Thermal analysis showed that the formation mechanism of the five perovskites is similar and implies the formation of barium carbonate and barium tungstates or molybdates of different stoichiometries as intermediate phases. Interesting enough, these similar mechanisms yield to materials of a quite different structure. Indeed, Ba(In_2/3Mo_1/3)O₃ and Sr(In_2/3W_1/3)O₃ were found to be disordered perovskites (unit cells: a_p×a_p×a_p and , respectively); on the other hand, two phases coexist in the sample Ba(In_2/3W_1/3)O₃ at the synthesis conditions: an ordered predominant phase (unit cell: 2a_p×2a_p×2a_p) and, as a minor phase, a disordered perovskite (unit cell: a_p×a_p×a_p). Finally, the two yttrium-containing compounds were found to be ordered perovskites (2a_p×2a_p×2a_p).     

Selective flow injection analysis of ultra-trace amounts of Cr(VI), preconcentration of it by solvent extraction, and determination by electrothermal atomic absorption spectrometry (ETAAS)

A rapid, robust, sensitive and selective time-based flow injection (FI) on-line solvent extraction system interfaced with electrothermal atomic absorption spectrometry (ETAAS) is described for analyzing ultra-trace amounts of Cr(VI). The sample is initially mixed on-line with isobutyl methyl ketone (IBMK). The Cr(VI) is complexed by reaction with ammonium pyrrolidine dithiocarbamate (APDC), and the non-charged Cr(VI)–PDC chelate formed is extracted into IBMK in a knotted reactor made from PTFE tubing. The organic extractant is separated from the aqueous phase by a gravity phase separator with a small conical cavity and delivered into a collector tube, from which 55 μl organic concentrate is subsequently introduced via an air flow into the graphite tube of the ETAAS instrument. The operations of the FI-system and the ETAAS detector are synchronously coupled. A significant advantage of the approach is that matrix constituents, such as high salt contents, effectively are eliminated. The extraction procedure was optimized by a simplex approach. A central composite design was subsequently employed to verify the estimated operational optimum. An 18-fold enhancement in sensitivity of Cr(VI) was achieved after preconcentration for 99 s at a sample flow rate of 5.5 ml min⁻¹, as compared to direct introduction of 55 μl of sample, yielding a detection limit (3σ) of 3.3 ng l⁻¹. The sampling frequency was 24.2 samples h⁻¹. The proposed method was successfully evaluated by analyzing a NIST Cr(VI)-reference material, synthetic seawater and waste waters, and waste water samples from an incineration plant and a desulphurization plant, respectively.     

Simultaneous determination of molybdenum(VI) and tungsten(VI) and its application in elemental analysis of polyoxometalates

Spectrophotometric determination of molybdenum(VI) and tungsten(VI) with application of Artificial Neural Networks is proposed and it was applied for elemental analysis of solid polyoxometalates. Better results in comparison with previously those achieved by previous published method were demonstrated. MALDI-TOF Mass Spectrometry was tested for possible determination of molecular weight of polyoxometalates utilizing different matrices. Phenomena observed during desorption-ionisation processes are discussed. LDI-TOF MS was found to be suitable for the determination of Mo:W ratio in polyoxometalates as a rapid screening method to follow synthetic procedure.     

X-ray structurally characterized Mo (VI), Fe (III) and Cu (II) complexes of amide-imine conjugate: (bio)catalytic and histidine recognition studies

An amide-imine conjugate, (E)-N′-((2-hydroxybenzen-1-yl) methylene)-4-methylbenzohydrazide (H₂L^PTASAL), derived from 4-methyl-benzoic acid hydrazide (PTA) and 2-hydroxybenzaldehyde is used to prepare Mo (VI), Cu (II) and Fe (III) complexes. The X-ray structurally characterized complexes have been explored as catalyst for amine assisted asymmetric ring opening (ARO) of epoxide, carbon-heteroatom cross-coupling and ethyl benzene oxidation. In addition, their catecholase like activities have thoroughly been investigated. Moreover, the Cu (II) complex selectively recognizes histidine by fluorescence spectroscopy.     

石墨烯负载零价纳米铁材料的合成及去除水中Cr(VI)的研究

以石墨粉为原料,采用改良Hummers方法合成石墨烯,然后通过液相还原法制备出石墨烯负载纳米铁材料(Graphene-supported nanoscale zero-valent iron,G-nZVI),借助扫描电子显微镜(SEM)、红外光谱分析仪(FTIR)进行表征,并以G-nZVI为反应材料,研究其对水体中Cr(VI)的去除效率,结果显示:室温下,当G-nZVI投加量为0.4g/L,Cr(VI)的初始浓度为20 mg/L,初始pH值为3.0时,Cr(VI)的去除率在2h内可以达到95%以上。G-nZVI具有磁性,使用后可通过外加磁力除去,以防对水体的二次污染,具有较好的应用前景。     

Metal chelates in adsorption polarography I: Mo(VI) and derivatives of oxine

The formation of complexes between Mo(VI) and 8-hydroxy-quinoline (oxine) and four oxine derivatives were investigated by multiwavelength molecular absorption spectrometry, potentiometry, and polarography. The following pK_OH- and pK_NH- values of the ligands and logK ₂₁₁-values of the complexes MoO₂(OH)₂L ^x– (x=1 or 2) were obtained at 25° C and an ionic strength of 1M(NaClO₄): 5,7-dinitro8-hydroxyquinoline 4.59, <0, 14.50; 7-nitro-8-hydroxyquinoline-5-sulfonic acid 5.34, 0.41, 15.70; 7-iodo-8-hydroxyquinoline-5-sulfonic acid 6.98, 2.62, 17.65; 8-hydroxyquinoline-5-sulfonic acid 8.33, 4.13, 18.71; and 8-hydroxyquinoline 9.62, 5.28, 19.69. A good linearity was found between logK ₂₁₁ and the sum of the pK-values of the OH- and NH⁺-groups. The dependence of the peak current of Mo(VI)-determinations by adsorption polarography of the 7-nitro-8-hydroxyquinoline-5-sulfonate complex of Mo(VI) MoO(OH)₃L^– can quantitatively be described at pH 0.8–2 using the corresponding pK-values and the log K₃₁₁ of 18.54±0.03, determined by polarography.