Simultaneous determination of cadmium(II), lead(II) and copper(II) by using a screen-printed electrode modified with mercury nano-droplets

We are presenting a strategy for the fabrication of disposable screen-printed electrodes modified with mercury nano-droplets and capable of sensing heavy metal ions. They were prepared by coating electrodes with a mixture of multi-walled carbon nanotubes and chitosan, this followed by adsorption of mercury. The resulting sensor was characterized by cyclic voltammetry and impedance spectroscopy. Also the effects caused by adsorption of mercury were investigated. It is shown that square wave anodic stripping voltammetry enables simultaneous determination of cadmium(II), lead(II) and copper(II), for which detection limits of 12, 23 and 20 nM, respectively, are found. Relative standard deviations for ten determinations at 0.6 µM concentrations of these ions are in the range of 3.0 to 5.7%. The applicability was tested by analyzing river water and showed recoveries between 94.1 and 104.6%, thus demonstrating its utility for in-field monitoring of these heavy metal ions.     

Voltammetric determination of cadmium(II) using a chemically modified electrode

An 1-(pyridylazo)-2-naphthol modified glassy carbon electrode has been investigated as sensor for the measurement of trace levels of Cd²⁺. Cd²⁺ is deposited on the surface of a PAN modified glassy carbon electrode at –1.10 V (vs. SCE) via forming Cd²⁺–PAN and subsequent reduction at the electrode. In the following step, Cd-PAN is oxidized, and voltammograms are recorded by scanning the potential in a positive direction. Calibration plots were found to be linear in the range 2 × 10^–8 mol/L to 8 × 10^–7 mol/L. The detection limit was 5 × 10^–10 mol/L, and the coefficient of variation, determined on one single electrode at a concentration of 5 × 10^–7 mol/L, was calculated to be 3.2% (n = 5). Using this new kind of modified electrode, trace levels of Cd(II) in water samples were determined; the average recovery was calculated to be 98.78%. Received: 17 August 2000 / Revised: 19 December 2000 / Accepted: 27 December 2000     

Voltammetric determination of cadmium(II) using a chemically modified electrode

An 1-(pyridylazo)-2-naphthol modified glassy carbon electrode has been investigated as sensor for the measurement of trace levels of Cd2+. Cd2+ is deposited on the surface of a PAN modified glassy carbon electrode at -1.10 V (vs. SCE) via forming Cd2+-PAN and subsequent reduction at the electrode. In the following step, Cd-PAN is oxidized, and voltammograms are recorded by scanning the potential in a positive direction. Calibration plots were found to be linear in the range 2 x 10(-8) mol/L to 8 x 10(-7) mol/L. The detection limit was 5 x 10(-10) mol/L, and the coefficient of variation, determined on one single electrode at a concentration of 5 x 10(-7) mol/L, was calculated to be 3.2% (n = 5). Using this new kind of modified electrode, trace levels of Cd(II) in water samples were determined; the average recovery was calculated to be 98.78%.     

Metallatriazadiphosphorines of zinc(II), cadmium(II) and mercury(II)

Metallatriazadiphosphorine complexes corresponding to [{N(PPh₂NR)₂}M(OAc)] and [{N(PPh₂NR)₂}₂M], (R = Ph or SiMe₃; M = Zn, Cd or Hg) have been synthesized under strictly anhydrous and inert conditions by the reaction of the acyclic bis-silylated phosphazene ligand, [HN(PPh₂NSiMe₃)₂], or the bis-phenylated phosphazene ligand, [HN(PPh₂NPh)₂], with Zn, Cd and Hg acetate in 1:1 and 2:1 molar ratios. These complexes are highly soluble in common organic solvents, but unstable hydrolytically as well as thermally, even under reduced pressure. Molecular weight determinations in benzene indicated the monomeric nature of these complexes. Further, they have been characterized on the basis of elemental analysis and spectral studies: i.r. and n.m.r. (¹H, ¹³C and ³¹P) that plausibly reveal a trigonal planar and tetrahedral geometry around the metal atom in the complexes.     

Rhodanine complexes of zinc(II), cadmium(II), mercury(II) and mercury(I)

The following rhodanine (HRd) complexes of zinc(II), cadmium(II), mercury(II) and mercury(I) have been prepared and studied by i.r. spectra: M(Rd)₂(NH₃)₂ (MZn, Cd) with a 4N,2S-six-coordination; Zn₃(Rd)₄(CH₃COO)(OH), Cd₂(Rd)₃(HRd)₃(CH₃COO)(H₂O) in which the acetato anion is bicoordinated; Hg(Rd)₂, Hg₂(HRd)₃(BF₄)₂·0.5(HAc or EtOH), Hg(HRd)(CF₃COO)₂·H₂O in which both the ligands HRd and Rd⁻ are S,N-bonded to the metal; Hg(HRd)₂Cl₂, Hg(HRd)₄(ClO₄)₂ in which the ligand HRd is S-bonded; Hg₃(Rd)₃ · NH₃ with S,N-bonded Rd⁻ ligand.     

Sulfadrug complexes of zinc(II), cadmium(II) and mercury(II)

Summary Zn^II, Cd^II and Hg^II complexes of sulfadrugs,viz., sulfathiazole, sulfadiazine, sulfamerazine and sulfamethazine were prepared and characterized by analytical and spectroscopic data. The complexes are insoluble and melt with decomposition. The drugs act as bidentate ligands yielding polymeric complexes except for the Zn^II(sulfamethazine) complex in which the drug is monodentate.     

Zinc (II), cadmium (II) and mercury (II) complexes of 2-methyl-benzothiazole

The following zinc (II), cadmium (II) and mercury (II) complexes of 2-methyl-benzothiazole (2Mebt=L) have been prepared and studied by conductometric methods, i.r. and Raman spectra: ML₂ (M = Zn, X = Cl, I, NO₃; M = Cd, X = NO₃, ClO₄; M = Hg, X = NO₃), ML_1.5X₂ (M = Zn, X = ClO₄ (H₂O); M = Hg, X = ClO₄) and MLX₂ (M = Cd and Hg, X = Cl, Br, I). The ligand is N-bonded when acting as monodentate and N,S-bonded as bridging ligand. The halide, nitrate and perchlorate ions are coordinated.     

Zinc (II), cadmium (II) and mercury (II) complexes of 2-methyl-benzoxazole

The following zinc (II), cadmium (II) and mercury (II) complexes of 2-methyl-benzoxazole (L) have been prepared and studied by conductometric and i.r. methods: MLX₂ (MCd, XCl, Br; MHg, XCl), HgL_1.5X₂ (XBr, ClO₄), ML₂X₂ (MZn, XCl, Br, I, NO₃; MCd, Hg, XI, NO₃), ZnL₃(ClO₄)₂·2H₂O, CdL₃(ClO₄)₂·3H₂O. The frequency decrease of the ligand bands at 1614 and 1573 cm⁻¹ having a ν(CN) and the increase of the ligand band at 918 cm⁻¹ having a ν(CO) contribution indicate that in the complexes the ligand is N-bonded to the metal.     

Zinc(II), cadmium(II) and mercury(II) complexes of 2-aminobenzothiazole

Zinc, cadmium and mercury(II) complexes of 2-aminobenzothiazole (HL) have been prepared and studied by conductometric, i.r. and Raman methods: MX₂·2HL (M  Zn, X  Cl, Br, I, NO₃; M  Cd, X  I), MX₂·HL (M  Cd, X  Cl, Br, NO₃(3H₂O); M  Hg, X  Cl, Br, I), M(ClO₄)₂; 1.5 HL (M  Zn(4H₂O), Hg), Cd(ClO₄)₂·3HL·4H₂O, HgNO₃·L. A comparison of the i.r. spectra of the complexes with those of the ligand, its deuterated DL and HL · HBr derivatives excludes a coordination of the ligand through the amino nitrogen atom and supports its coordination through the ring nitrogen atom. The zinc halide complexes have a tetrahedral coordination. The nitrate and perchlorate anions are coordinated.     

Zinc(II), cadmium(II) and mercury(II) complexes of 4-amino-benzophenone

The following zinc(II), cadmium(II) and mercury(II) complexes of 4-amino-benzophenone (L) have been prepared and studied by i.r. and electronic spectra: 2MX₂·3L (M=Zn, Cd; X=Cl, Br), 3ZnI₂·2L, 2ZnI₂·L, MX₂·L (M=Cd, X=I; M=Hg, X=Cl, Br). Infrared spectra show that in the zinc complexes the ligand is principally bonded through the aminic nitrogen atom and in the cadmium and mercury(II) complexes through the carboxylic oxygen atom.     

Complexometric determination of mercury(II) using Congo Red as indicator

Congo Red is suggested as an indicator for the direct titration of mercury(II) ions with EDTA or with potassium thiocyanate. An interference study of a number of cations has been made. The titration with thiocyanate is more advantageous than that with EDTA.     

Complexes of zinc(II), cadmium(II) and mercury(II) halides with ethylenselenourea

Summary Reaction of zinc(II), cadmium(II) and mercury(II) halides with ethylenselenourea yields complexes of general formula ML₂X₂ where X = Cl, Br, I. On the basis of an i.r. comparison of these complexes and their ethylenthiourea analogues in the 4000-200 cm^–1 range, it appears that the ethylenselenourea complexes are monomeric, tetrahedral and Se-bonded to the metals. The metal-halogen and metal-ligand vibrations above 200 cm^–1 are identified.This work was supported by the National Research Council (C.N.R.) of Italy.     

Thermal decomposition of complexes of cadmium(II) and mercury(II) with triphenylphosphanes

A series of substituted triphenylphosphane complexes of the type CdL₂X₂ (L= triorthotolylphosphane or trimetatolylphosphane; X=Cl⁻, Br⁻ or I⁻) and HgL₂X₂ (L=triphenylphosphane or triorthotolylphosphane) was prepared fresh. The thermal decomposition was carried out in air with heating rate programmed at 10°C min⁻¹ and it revealed that the complexes with ortho derivative were less stable and the triphenylphosphane moiety leaves along with halogen in the first step. All the complexes were stable up to 210°C. However, the stability order of the tetrahedral complexes was X=Cl>Br. Values of n, E, lnA and ΔS ^# have been approximated and compared. Complexes having Br have higher E _a, lnA and ΔS ^# values than that having Cl.     

Zinc(II), cadmium(II) and mercury(II) halide pyrrolidine-2-selone complexes

Summary Reaction of zinc(II), cadmium(II) and mercury(II) halides with Pyrrolidine-2-selone yields complexes of general formula ML₂X₂ (X = Cl, Br or I) which are monomeric, tetrahedral and Se-bonded to the metals. The comparison of their i.r. spectra with the spectrum of the free ligand confirms that the band at 1005 cm^–1 in Pyrrolidine-2-selone arises predominantly from the C=Se stretching vibration. The metalhalogen absorptions above 200 cm^–1 are identified.This work was supported by the National Research Council (C.N.R.) of Italy.     

Zinc(II), cadmium(II) and mercury(II) halide pyrrolidine-2-thione complexes

Summary White crystalline complexes of general formula ML₂X₂, where M = Zn, Cd, Hg; X = Cl, 13r, I and L = pyrrolidine-2-thione, were prepared and studied by i.r. spectroscopy in the 4000-200 cm^–1 range. Evidence for coordination of the ligand to the metal through sulphur was found in each case. The previous assignment of the band present in the ligand at 1110 cm^–1 to the(CS) fundamental is discussed.This work was supported by the National Research Council (C.N.R.) of Italy.     

Extraction spectrophotometric determination of mercury(II) using thiacrown ethers and Bromocresol Green

A reasonably sensitive and highly selective spectrophotometric method for the determination of mercury(II) is proposed. The method is based on the extraction of the ion-associate formed by a mercury(II) thiacrown ether cationic complex with Bromocresol Green as the anionic counter-ion using chloroform as the extracting solvent. The effect of thiacrown ethers of different cavity sizes, namely 1,4,7,10,13-pentathiacyclopentadecane (PTP) and 1,4,7,10,13,16-hexathiacyclooctadecane (HTO), the thiacrown ether concentration, the extracting solvent, the bromocresol green concentration and the aqueous phase pH on the extraction were investigated. Measurement of the absorbance at the lambda(max) (420 nm) of the extracted ion-associate reveals that Beer's law is obeyed over 0.5-12.0 ppm mercury(II) for both ligands. Slight interference from copper(II) and cadmium(II) is exhibited by the PTP ligand, while HTO is negligibly affected by these metal ions. Strong interference from silver(I) is evident for both ligands while alkali, alkaline earth and other transition metals tested posed negligible interference. Analysis of mercury in synthetic complex mixtures was satisfactory.     

Synthesis and characterization of ciprofloxacin compounds with cadmium(II) and mercury(II) chlorides

Five new compounds of ciprofloxacin (CfH = C₁₇H₁₈FN₃O₃) with cadmium(II) and mercury(II) chlorides were synthesized. The compounds were characterized by chemical analysis, powder X-ray diffraction, pH-metric titration, UV spectroscopy, and thermal analysis.     

Fluorometric determination of dopamine by using a terbium (III) inorganic-organic network

Microchimica Acta - A hybrid organic-inorganic optical probe was developed by using silylated precursors (including tetraethoxy silane and aminopropyltriethoxysilane), ferroferric oxide (Fe3O4) and...     

Separation of zinc(II), cadmium(II) and mercury by solvent extraction using thiocarbohydrazide and the complexing agent

The extraction behaviour is reported of zinc(II), cadmium(II) and mercury(II) complexes of thiocarbohydrazide in benzene, chloroform, carbon tetrachloride, di-isopropyl ether, ethyl acetate, amyl acetate, and amyl alcohol. The separation of the three elements has been achieved by the use of various masking agents, as well as by making use of the effect ofpH on their extractability. This work was carried out under CSIR (India) Scheme No. 1 (450/69 GAU. II.