The polarographic determination of copper and zinc in plants and soils

A method is described whereby the extraction and polarisation of copper and zinc with maximum, sensitivity is possible. Interference from cobalt is prevented by extracting with dithizonc in the presence of dimethylglyoxime.The supporting electrolyte used is dccimolar potassium hydrogen phthalate which permits satisfactory waves for both copper and zinc (with greater sensitivity for copper, than is the case with the ammonia-ammonium chloride electrolyte).     

Sequential extraction for the speciation of some heavy metals in soils

The five step sequential extraction for speciation of copper and nickel originally designed for sediments has been applied to soil samples. The extractant solutions were: 1 mol/l ammonium acetate, 1 mol/l hydroxylammonium chloride in 25% acetic acid (1∶1), 0.1 mol/l hydrochlorid acid, 0.5 mol/l sodium hydroxide and 8 mol/l nitric acid. The residue was decomposed by HF and HNO₃. Using this procedure the metal fraction bound to the organic matter can be distinguished. The concentrations of analytes were determined in the soil extracts by FAAS and ETAAS. Accuracy was assessed by comparing the sum of the contents of copper and nickel in soil extracts with the total certified values of CRMs of soils. The overall recovery values for nickel was 84–105% and for copper 105–114%.     

Spectroscopic method for the determination of crystallinity of hematite

The thermal transformation of goethite to hematite and the temperature dependence of the degree of crystallinity have been investigated using transmission and diffraction electron microscopy and infrared spectroscopy. The electron microscopy results reveal that the treatment of natural goethite by NaOH or citrate dithionite-bicarbonate (CDB) has no effect on its structure but leads to increase in the crystallinity of the ore. On the other hand, heat treatment of the untreated or treated sample is found to convert goethite ore to hematite with increase in its crystallinity. An infrared spectroscopic technique is applied for quantitative calculation of the crystallinity changes.     

Validation of the methods for heavy metal speciation in soils and sediments

The knowledge of the chemical forms of metals is used to assess their availability and uptake by plants, and in sediments the forms of metals determine their transport and mobility in the aquatic media. This information may be obtained by determining chemical forms of metals (speciation) or different phases in which the metals are bound, obtained by applying extraction schemes. The analytical methods used include different steps and all of them must be validated. We report here the recommendations to minimize the errors in this kind of analysis. For validation the use of Certified Reference Materials (CRMs) and the participation in interlaboratory exercises are highly recommended.     

Analytical protocol for investigation of zinc speciation in plant tissue

A specific procedure is proposed for investigating the chemical speciation of zinc (Zn) in plant tissues, viz., the extraction of Zn compounds from Plantago lanceolata L. followed by the chromatographic separation and inductively coupled plasma mass spectrometry (ICP-MS) identification of these compounds. In order to separate the Zn compounds, both size-exclusion (SEC) and ionexchange liquid chromatography (IC) were used in direct sequential and reverse sequential modes. In the direct sequential mode, the entire extract undergoes SEC separation and then the individual fractions are injected onto the ion-exchange column. The molecular size distribution is evaluated by SEC coupled on-line to the UV detector. In the reverse sequential mode, the entire extract undergoes the ion-exchange chromatographic separation and then the individual fractions are injected onto the size-exclusion column. The identification of Zn incorporated into the compounds is further performed using ICP-MS. This procedure is particularly useful in speciation studies when identification of the individual components of the element is problematic due to the lack of suitable standard substances, as is the case for Zn compounds. The proposed procedure facilitates assignment of the signals to the individual components of the fractions for both types of chromatography, thus rendering the chemical speciation of Zn possible when the lack of suitable standard substances impedes the identification of individual components.     

Use of a modified, high-sensitivity, anodic stripping voltammetry method for determination of zinc speciation in the North Atlantic Ocean

Zinc speciation is considered to be an important determinant of the biological availability of zinc. Yet in oceanic surface waters, characterization of zinc speciation is difficult due to the low concentrations of this essential micronutrient. In this study, an anodic stripping voltammetry method previously developed for the total determination of cadmium and lead was successfully adapted to the measurement of zinc speciation. The method differs from previous zinc speciation anodic stripping voltammetry methods in that a fresh mercury film is plated with each sample aliquot. The fresh film anodic stripping voltammetry method was compared to competitive ligand exchange cathodic stripping voltammetry in a profile from the North Atlantic Ocean. Results using the fresh film anodic stripping voltammetry method were similar to those determined using the cathodic stripping voltammetry method, though ligand concentrations determined by fresh film anodic stripping voltammetry were generally slightly higher than those determined by cathodic stripping voltammetry. There did not seem to be a systematic difference between methods for the estimates of conditional stability constants. The ligand concentration in the North Atlantic profile ranged from 0.9 to 1.5 nmol L⁻¹ as determined by fresh film anodic stripping voltammetry and 0.6 to 1.3 nmol L⁻¹ as determined by cathodic stripping voltammetry. The conditional stability constants determined by fresh film anodic stripping voltammetry were 10^9.8-10^10.5 and by cathodic stripping voltammetry were 10^9.8-10^11.3.     

The polarographic determination of zinc and manganese in plant and animal tissues and soils

A method is proposed whereby microgram quantities of zinc and manganese may be simultaneouly extracted with excess sodium diethyldithiocarbamate in the presence of tartrate at pH 5.5, the extracts decomposed and the metals polarographed in a lithium chloride supporting electrolyte. Iron must first be removed with cupferron, and the interference by cobalt and nickel is overcome by the use of dimethylglyoxime prior to the extraction. The method may be applied to the digests of animal tissues, plant materials or soils.     

Nature of the HCl-soluble sulfate in the sequential extraction for sulfur speciation in soils

Thirty soils collected from different regions of China were used to investigate the nature of HCl-soluble sulfate (HCl-S) and to evaluate the importance of HCl-S for sulfur speciation in soils. The soils were first extracted with NaH₂PO₄ solution to remove water-soluble and adsorbed sulfate, followed by extraction in 1 mol/l HCl at room temperature, minimizing the hydrolysis of organic sulfur into sulfate. Excellent linear correlations (r = 0.986) were found between the HCl-S and the carbonate contents in these soils, indicating HCl-S was mainly the carbonate-occluded inorganic sulfate in calcareous soils, averaging for 39% of total sulfur. However, the traditionally recognized major form of soil sulfate (water-soluble and adsorbed sulfate) only account for 7.5% of total sulfur. The non-calcareous soils were also found to contain some of HCl-S (6.9% of total sulfur). Large errors will occur in the determination of ester sulfur if HCl-S is not subtracted from the HI-reducible sulfur, especially in calcareous soils and soils containing little organic matter, which was the common practice in sulfur speciation studies. The reasonableness of including HCl-S in the subtraction method to determine ester sulfur was further verified by the good correlations between ester sulfur and organic carbon content in the soils Received: 21 February 1996 / Revised: 10 June 1996 / Accepted: 14 June 1996     

Spectroscopic study of protoporphyrin IX zinc(II) encapsulated in sol-gel glass

Previous studies indicated that the organization of native porphyrins and their intentionally designated derivatives in solid substrates is of current interest because of the biological and practical importance of these compounds. In this paper, we report herein for the first time the incorporation of a functionalized diacid, protoporphyrin IX Zn(II) (Zn-pp-IX), successfully in a silica based transparent organic-inorganic hybrid material by choosing proper alkoxy silane containing amino-group via the sol-gel method. The entrapped guest was diagnosed using UV-vis sectrophotometry, emission spectroscopy, and infrared spectrometry; the properties of the encapsulated porphyrin were compared to those of the compound in solution. The results indicate that Zn-pp-IX is well distributed and homogeneously in the glass.     

Chemical speciation of radionuclides through the microbial process in soils

Environmental factors (nutrients and pH) influence the retention of Sr, Cs, and Ba as analogue of long-lived radionuclides by the microorganism. The effect of pH and concentration of organic nutrients are proved to be significant factors for retention of cations (Sr, Cs and Ba) by the microorganisms inoculated from surface soil. Microorganisms can affect the speciation of Sr, Cs, and Ba in the environment. Concentration of organic nutrients and pH are indicated to be the important environmental factors in the consideration of the migration of the radionuclides through microbial processes in the terrestrial environment.     

Advanced quality control for zinc speciation investigations in human breast milk

Summary Information is provided about the reliability of results obtained in Zn-speciation analyses of human milk. For such analyses, convenient techniques have already been given in an earlier paper [1], comprising mass balances of metal and ligand, purity of analytes, etc. Here, however, the influence of the eluent was checked in an extended manner. For this series of experiments, bi-distilled water was compared with different buffers as the eluent. Water proved to be a more suitable mobile phase than buffers with regard to contamination. Moreover, a method was developed to investigate the possibility of a transfer of Zn among the proteins during size exclusion chromatography. For these experiments, casein and metallothionein were chosen as competitive Zn-ligands, showing extremely different affinities to Zn. A possible Zn-transfer from one protein to the other was examined in combining a Zn-containing protein with a Zn-free one. No change of the Zn-status of the proteins was detected, indicating a stable protein-metal complex under the experimental conditions. Zn and protein mass balances (injected/eluted) were calculated and found to be 100%.     

Time-resolved XANES speciation studies of chromium on soils during simulated contamination

Time-resolved synchrotron X-ray absorption near edge structure (XANES) spectroscopy was used to study changes of chromium speciation in soils upon soil–water interaction. The time resolution was 30–45 min. In a flow-column apparatus operated near the synchrotron beamline, two different types of soil were treated with potassium-dichromate solution, and soil samples were taken and directly analysed by XANES. The results provide insight into different equilibrium times of a few hours, depending on the type of soil. The XANES speciation analyses, based on a model comprising insoluble Cr(III) and Cr(VI) compounds, show how the fate of Cr species on soils can be followed close to real-time. Since the method allowed the soils to be investigated close to real-time, sampling in the field and preservation before analysis were made redundant. This study benefits the development of corresponding in situ remediation techniques.     

Spectroscopic identification towards tunable mesoscale aggregates of zinc tetraphenylporphyrin for materials

We present a study of spectroscopic identification towards the molecular aggregates of zinc tetraphenylporphyrin(ZnTPP) illustrating how the energy states and intermolecular interactions determine the tunable properties of functional materials in condensation processes. Distinguishable fingerprints of ZnTPP nanorods and nanosheets are addressed utilizing X-ray diffraction(XRD), Raman and UV-vis absorption spectroscopies. Although these ZnTPPs are assigned to J-aggregation at different extent, the spectral analysis reveals a significant role of the intermolecular interactions associated with varying mesoscale architectures. Energy decomposition analysis(EDA) revealed that the varied ZnTPP aggregates are stabilized by altered dispersion interactions due to the dominant π…π stacking between the monomers.     

Sorption-fluorimetric determination of zinc

The sorption of ions of zinc on carriers modified by 8-oxychinoline and its derivative is investigated. The optimum parameters of sorption are revealed, based on which silochrome S-60 with immobilized 8-oxychinoline (pH 7.1, time of contact 30 min, weight of sorbent 0.3 g, capacity of sorbent on the modifier 60 μmol/g) is chosen. A yellow-green fluorescence sorbate arises on irradiation by ultra-violet light in a phase sorbent. The spectrum of fluorescence represents a wide unstructured strip with a maximum at 505 nm. In the construction of a calibrated graph, Cu(II), Cd(II), Pb (II), Bi(III), and Fe(III) do not prevent the determination of 5–50 μg of zinc; however, equal amounts of Al(III) (50–100 μg) do prevent it. The technique is applied for the sorption-fluorimetric determination of zinc in river and waste water. The relative standard deviation does not exceed 0.05 (n = 5).     

Extraction and speciation of arsenic in plants grown on arsenic contaminated soils

A sequential arsenic extraction method was developed that yielded extraction efficiencies (EE) that were approximately double those using current methods for terrestrial plants. The method was applied to plants from two arsenic contaminated sites and showed potential for risk assessment studies. In the method, plants were extracted first by 1:1 water-methanol followed by 0.1 M hydrochloric (HCl) acid. Total arsenic in plant and soil samples collected from contaminated sites was mineralized by acid digestion and detected by inductively coupled plasma-atomic emission spectrometry (ICP-AES) and hydride generation-atomic absorption spectrometry (HG-AAS). Arsenic speciation was done by high performance liquid chromatography coupled with HG-AAS (HPLC-HGAAS) and by HPLC coupled with ICP-mass spectrometry (HPLC-ICP-MS). Spike recovery experiments with arsenite (As(III)), arsenate (As(V)), methylarsonic acid (MA) and dimethylarsinic acid (DMA) showed stability of the species in the extraction processes. Speciation analysis by X-ray absorption near edge spectroscopy (XANES) demonstrated that no transformation of As(III) and As(V) occurred due to sample handling. Dilute HCl was efficient in extracting arsenic from plants; however, extraction and determination of organic species were difficult in this medium. Sequential extraction with 1:1 water-methanol followed by 0.1 M-HCl was most useful in extracting and speciating both organic and inorganic arsenic from plants. Trace amounts of MA and DMA in plants could be detected by HPLC-HGAAS aided by the process of separation and preconcentration of the sequential extraction method. Both organic and inorganic arsenic compounds could be detected simultaneously in synthetic gastric fluid extracts (GFE) but EEs by this method were lower than those of the sequential method. The developed sequential method was shown to be reliable and applicable to various terrestrial plants for arsenic extraction and speciation.     

New analytical method for determination and speciation of forms of carbon

A new analytical method is presented, allowing the identification and determination of various forms of carbon (elemental and combined) present in materials. The method is based on temperature-controlled heating of the sample in oxygen or an inert atmosphere, with continuous recording of the amount of carbon oxides evolved, as a function of temperature. The application of the method is demonstrated with typical examples (cast iron, artificial diamond, carbides isolated from steel, electrographite).     

Separation of uranium from soils for its determination

A method has been developed for the determination of microamounts of uranium in soils, which is based on application of the rapid and effective removing of luminescence quenchers from liquid preparations with subsequent uranium determination by laser-induced luminescence registration of its polysilicate complexes. To remove the luminescence quenchers, they were precipitated in strongly basic carbonate medium in the presence of activated charcoal (as a collector of the precipitate).     

Separation of zinc and copper with cyanoacetamide in the determination of zinc

The new use of cyanoacetamide as a selective masking agent for copper in the determination of microgram amounts of zinc with zincon is described. It is very possible that the unique masking action of this compound may have importance in eliminating the interference of copper in other spectrophotometric and titrimetric procedures for zinc thereby reducing the time required to complete the analysis by decreasing or eliminating laborious separation or extraction techniques. The possibility of using cyanoacetamide as a masking agent for other ions should not be overlooked.     

Spectroscopic and HPLC methods for the determination of alendronate in tablets and urine

Two methods (spectrophotometric and HPLC) have been developed and validated for the analysis of alendronate sodium in tablet dosage form. Both methods depend on the ability of alendronate sodium to react with o-phthalaldehyde (OPA) at basic pH to produce a light-absorbing derivative. The derivative was found to possess absorption maximum at 330 nm where neither the derivatizing agent nor the analyte had any absorption. Thus, spectroscopic method was based on the derivatization-induced absorption of alendronate sodium at 333 nm. The HPLC method was based on separation of the formed derivative from other ingredients in tablets with detection at 333 nm. Both methods were satisfactory with regard to accuracy, prescion and linearity. Moreover, a HPLC method with fluorescence detection (HPLC-FD) was developed for the quantification of alendronate sodium in urine. The method was also based on the derivatization of alendronate with OPA, but fluorescence detection was employed. Linearity, recovery, selectivity, prescision and sensitivity were satisfactory for the proposed HPLC-FD method. Yet a new quantification limit (0.6 ng ml⁻¹) for alendronate in urine was achieved.     

Chromatographic determination of copper speciation in jet fuel

A method is described that allows one to distinguish and quantitate two different classes of copper compounds in the same hydrocarbon sample. This will enable the study of the effects of different copper compounds on the performance and stability of petroleum samples. Copper N,N'-disalicylidene-1,2-propylenediamine (CuDMD) and several copper carboxylates were preconcentrated from a hydrocarbon matrix using a column packed with polyvinylpyrrolidone, (C(6)H(9)NO)(x), a novel polymeric stationary phase. The copper complexes were then sequentially eluted using a step gradient program beginning with hexane/isopropyl alcohol as the eluent and ending with an acetic acid/isopropyl alcohol eluent. The copper complexes were detected by serial UV absorbance and flame atomic absorbance (FAA) detection. With on-column preconcentration and FAA detection, the limits of detection were 7 and 40 ppb copper for CuDMD and the copper carboxylates respectively. With this method, it was possible to distinguish between the two different classes of copper compounds in the same hydrocarbon sample, which will help to provide an understanding of the catalytic activity of different copper compounds, leading to a better understanding of the factors causing fuel instability. The method promises to be a valuable tool in the analysis and characterization of copper compounds in petroleum samples.