Selective lanthanum ions optical sensor based on covalent immobilization of 4-hydroxysalophen on a hydrolyzed triacetylcellulose membrane

An optical sensor membrane is described for the determination of lanthanum(III) ions based on the immobilization of 4-hydroxysalophen on a hydrolyzed triacetylcellulose membrane. 4-Hydroxysalophen is covalently bonded to a transparent hydrolyzed triacetylcellulose film. The sensing membrane in contact with lanthanum ions at pH 4.0 changes color from white-yellow to orange (323 to 433 nm). Under the optimum conditions, the proposed membrane displayed a linear range from 1.0 × 10⁻⁶ to 1.0 × 10⁻² M La(III) with a limit of detection of 1 × 10⁻⁷ M. The response time of the membrane was within 5–6 min depending on the concentration of La(III) ions. The selectivity of the probe towards lanthanum ions was found to be excellent. The sensor was successfully applied to the determination of La(III) in water, industrial waste water, and in NIST-615 (glass matrix) and NIST-3127a (lanthanum solution) samples with satisfactory results.     

A silver optical sensor based on 5(p-dimethylaminobenzylidene)rhodanine immobilized on a triacetylcellulose membrane

An optical sensor has been proposed for the determination of silver by spectrophotometry. The sensor was prepared by immobilizing 5(p-dimethylaminobenzylidene)rhodanine on a transparent triacetylcellulose membrane. The effect of different variables on the response of the sensor was studied and the optimum conditions were established. The sensor responded linearly in the range 1.8–55.6 μM of silver with a limit of detection of 0.8 μM and a response time range of 8–10 min depending on the concentration of the silver ions. The presented optode is reversible and stable if stored in water for more than one month without reagent leaching. The relative standard deviation for seven replicated measurement of 4.6 and 37 μM silver was 3.15 and 2.76%, respectively. The sensor was successfully applied to the determination of silver in a silver sulphadiazine cream, an ore sample, and a radiology film. The text was submitted by the authors in English.     

Kinetic methods for the determination of cadmium(II) based on a flow-through bulk optode

Three kinetic methods based on flow injection, flow, and stopped-flow injection were applied for the determination of Cd(II) using a flow-through bulk optode membrane that incorporates 1-(2-pyridylazo)-2-naphtol (PAN) in a plasticized poly(vinyl) chloride membrane entrapped in a cellulose support. The calibration graphs plotting the reflectance at 560 nm versus [Cd(II)](1/2) for the first two methods and versus [Cd(II)] for the third were linear up to 56.2 mg l(-1). The detection limits of the methods were 0.01, 0.06 and 0.8 mg l(-1), respectively. The FI method was selected for application purposes. The variation coefficient of the sensor response for 11.2 mg l(-1) of Cd(II) was +/-0.31 and +/-0.65% between different membranes. The sensor can be readily regenerated with a carrier (acetic-acetate) buffer of pH 4. The FI method was applied to the determination of cadmium in an alloy and in water.     

Development of a new fluorimetric bulk optode membrane based on 2,5-thiophenylbis(5-tert-butyl-1,3-benzexazole) for nickel(II) ions

A highly sensitive and selective fluorimetric optode membrane for the determination of ultra trace amounts of Ni²⁺ ions was prepared. The plasticized PVC-membrane incorporating potassium tetrakis(p-chlorophenyl)borate (KTpClPB) and 2,5-thiophenylbis(5-tert-butyl-1,3-benzexazole) (TTBB), as a highly fluorescent chromoionophore, displays a calibration response for Ni²⁺ ions over a wide concentration range of 1.0×10⁻³ to 1.0×10⁻⁸ M. It has a relatively fast response of <40 s. In addition to high stability and reproducibility, and relatively long working lifetime, the sensor possesses good selectivity for nickel ions over several common diverse ions. The fluorescence signal of the optode membrane can be easily recovered by immersion in EDTA solution. The optode was applied successfully to the determination of traces of Ni²⁺ ion in edible oil and a wastewater sample from nickel electroplating industries.     

Design and evaluation of a thorium (IV) selective optode

A novel optical sensor has been proposed for sensitive determination of thorium (IV) ion in aqueous solutions. The thorium sensing membrane was prepared by incorporating 4-(p-nitrophenyl azo)-pyrocatechol (NAP) as ionophore in the plasticized PVC membrane containing tributyl phosphate (TBP) as plasticizer. The membrane responds to thorium ion by changing color reversibly from yellow to red-brown in glycine buffer solution at pH 3.5. The proposed sensor displays a linear range of 8.66 × 10⁻⁶-2.00 × 10⁻⁴ M with a limit of detection of 6 × 10⁻⁶ M. The response time of the optode was about 8.8-12.5 min, depending on the concentration of Th (IV) ions. The selectivity of optode to Th (IV) ions in glycine buffer is good. The sensor can readily be regenerated by exposure to a solution mixture of sodium fluoride and 5-sulfosalicylic acid (dihydrate) (0.01 M each). The optode is fully reversible. The proposed optode was applied to the determination of thorium (IV) in environmental water samples.     

Copper(II)-selective fluorimetric bulk optode membrane based on a 1-hydroxy-9,10-anthraquinone derivative having two propenyl arms as a neutral fluorogenic ionophore

A new optical chemical sensor has been developed for the selective determination of copper(II) ions in aqueous solutions. The reversible sensing system was prepared by incorporating 1-hydrpxy-2-(prop-2'-enyl)-4-(prop-2'-enyloxy)-9,10-anthraquinone (AQ) as a neutral Cu2+-selective fluoroionophore in the plasticized PVC membrane with potassium tetrakis(p-chlorophenyl borate) as an anionic additive. The response of the sensor is based on the fluorescence quenching of AQ by Cu2+ ions. At a pH 5.5, the proposed sensor displays a calibration response for Cu2+ over a wide concentration rang of 1.0 x 10(-2) to 1.0 x 10(-6) M, with a relatively fast response of less than 40 s. In addition to high stability and reproducibility, the sensor shows a unique selectivity towards Cu2+ ion with respect to common co-existing cations. The proposed fluorescence optode was applied successfully to the determination of copper(II) in black tea samples.     

Complexometric determination of mercury(II) in waters by spectrophotometry of its dithizone complex

This paper presents a new method for the determination of Hg(II) in waters, using indirect spectrophotometric measurements of the Hg(II) dithizone complex. The reagent is a mixture of dithizone, CDTA (1,2-cyclohexylene-dinitrilo-tetraacetic acid), thiourea, ethylic alcohol and glycine. Sensitivity and working range are 0.4 g · l^–1 and 2–100 g · l^–1, respectively. A comparison of the results with those of the cold-vapor atomic absorption spectrometry shows a good correlation for different samples revealing only small interferences. The new method is well suited for on-line measurements, easy to run and has low cost equipment.     

Development of an ethanol-selective optode membrane based on a reversible chemical recognition process

Lipophilic trifluoroacetophenone derivatives incorporated in plasticized PVC membranes are able to selectively extract water and alcohols from the sample solution into the organic membrane phase, reversibly forming hydrates and hemi-acetals, respectively. Since this is accompanied by a change in the absorption spectrum of the acetophenone isologue, the chemical recognition process can directly be translated into an optical signal. With N-acetyl-N-dodecyl-4-trifluoroacetylaniline (ETH 6022) as the electrically neutral, lipophilized carrier ethanol can be determined from 0.5 to 35% (v/v) in aqueous solutions. The calibration curve for different ethanol-water mixtures shows a good correlation with the mathematically derived formalism and thus confirms the theoretically expected behavior. Besides high reproducibility of the optical signals, very short response times of less than 30 s were realized. The optode membrane presented exhibits a preference for ethanol compared to water by a factor greater than 11. The selectivities for several primary alcohols, such as methanol, ethanol, 1-propanol and 1-n-butanol, are comparable, but isopropanol and tert.-butanol are rejected by a factor of about 10. The alcohol concentration in different beverages was determined to evaluate the reliability of the system. The values obtained for wine, beer and different spirits show an excellent correlation with those obtained by a conventional approach involving distillation and density measurements. A residual standard deviation of ± 0.27% (v/v) over the 0.7–40% (v/v) range was found.     

Underpotential deposition of tin(II) on a gold disc electrode and determination of tin in a tin plate sample

This work describes a study of the underpotential deposition (UPD) of Sn²⁺ on a polycrystalline gold disc electrode using cyclic voltammetry (CV) and chronocoulometry (CC). Sn²⁺ ions showed well-defined peaks from UPD and UPD stripping (UPD-S) in 1 mol/L HCl solutions, while bulk deposition (BD) and BD stripping (BD-S) of the ions were also observed. The measured UPD shifts, E_UPD, between the UPD-S and the BD-S peaks were more than 200 mV. The UPD charge and the surface coverage of tin were measured by CC. A new method for determining Sn²⁺ was therefore developed, based on the excellent electrochemical properties of the Au/Sn UPD system. A plot of the UPD-DPASV (differential pulse anodic stripping voltammetry) signal versus the Sn(II) concentration was obtained for [Sn(II)] of 1.98×10^–7 to 3.64×10^–5 M. The method developed here has been applied to determine the tin in a tin plate sample.     

The structure of nitratotriphenylstannyltin(II): A compound with a tin(IV)tin(II) bond

A compound of formula [Sn^II(NO₃) [(C₆H₅)₃ Sn^IV], containing a tin(IV)tin(II) bond, has been prepared, and its crystal structure is determined.     

Simultaneous derivative spectrophotometric determination of cobalt(II) and nickel(II) by dithizone without extraction

Dithizone (Dz), a common extractive-photometric ligand for Co(II) and Ni(II), has been dissolved in the water-miscible solvent tetrahydrofurane (THF) so as to constitute a reagent for both metals in aqueous phase without extraction. Complex formation was complete for both metals at pH 12.0 (adjusted by aqueous NH(3)) within 30 min, and the complexes were stable for at least 2 h. First-derivative spectra of the metal dithizonates (singly or as binary mixtures) were preferred to ordinary spectra, because working wavelength determination was more precise and spectral overlap was less. Two wavelengths at which the spectral overlap was minimum were selected as analytical wavelengths, i.e. 620 nm for Co and 740 nm for Ni, and the calibration curves drawn with zero-to-peak values as a function of concentration were linear for these wavelengths. Thus, the total (1)D values at 620 and 740 nm of the mixtures were used to determine Co and Ni concentrations. The relative standard deviation (R.S.D.) for the analysis of Co (3.0 mg l(-1)) individually was 3.5%, and for its admixture with Ni (3.5 mg l(-1)) was 2.5%. The R.S.D. for the analysis of Ni (5.9 mg l(-1)) individually and for its admixture with Co (1.8 mg l(-1)) were 5.5 and 5.8%, respectively. The linear range in (1)D evaluation was between 5.0x10(-6) and 1.0x10(-4) M for Co and 2.0x10(-5)-2.0x10(-4) M for Ni. Interference analysis was performed for individual metal (Co or Ni) determinations. Finally, the method has been applied to a Ni-Cr-based dental alloy (Wiron 99) successfully.     

Development of a new flow-through bulk optode for the determination of manganese(II)

A flow-through bulk optode based on the use of 1-(2-pyridylazo)-2-naphthol (PAN) immobilized in a plasticized poly(vinyl chloride) membrane entrapped in a cellulose support, in conjuntion with the flow injection analysis technique, is proposed for the determination of manganese(II). The calibration graph obtained at 570 nm was linear in the range 0.27–27.5 mg L^–1 (5 × 10^–6– 5 × 10^–4 M) Mn(II) with a detection limit of 0.18 mg L^–1. The coefficients of variation of the sensor response for 5.5 mg L^–1 of Mn(II) were ±0.22% for consecutive measurements (n = 10), ±0.48% between days (n = 5) and ±0.38% between different membranes (n = 6). The sensor was readily regenerated with the carrier acetic acid/acetate buffer of pH 4.5. The method was applied to the determination of manganese in steels, waters and lemon tree leaves. Received: 13 December 2000 / Revised: 25 January 2001 / Accepted: 26 January 2001     

Preparation of a solid membrane lead(II) diethyldithiocarbamate electrode and its application for direct and indirect anion determination

A lead(II) selective electrode has been developed. This electrode is essentially formed by a lead wire, one end of which is coated with lead(II) diethyldithiocarbamate. The response is Nernstian for lead ions in a 10⁻¹ to 10⁻⁵M concentration range. The direct determination of this element and the indirect determination of several anions are possible.     

Formation constants of Cd(II) complexes with dithizone and related compounds

The stability constants of cadmium complexes of compounds related to dithizone are reported. Substitution in the ortho position lowers the stability constant. It is probable that this is a consequence of deviation from coplanarity of the phenyl and chelate rings.     

Lead-selective fluorescent optode membrane based on 3,3′,5,5′-tetramethyl-N-(9-anthrylmethyl)benzidine

A new proton-selective fluorescing indicator, 3,3′,5,5′-tetramethyl-N-(9-anthrylmethyl)benzidine (TMANB) has been synthesized and applied in an optode membrane for the determination of lead ion that works on the basis of a cation-exchange mechanism. When embedded in a plasticized poly(vinyl chloride) (PVC) membrane containing lead ionophore (tert-butylcalix[4]arene-tetrakis(N,N-dimethylthioacetamide)) and a lipophilic anionic site [potassium tetrakis(4-chlorophenyl)borate], TMANB shows a significant fluorescence signal change on exposure to aqueous HCl solution containing lead ion, which exhibits the theoretically expected fluorescence response to lead ion concentration. The selectivity, response time, reproducibility and reversibility, and lifetime of the optode membrane were discussed.     

Complexation and thermogravimetric investigation on tin(II) and tin(IV) with norfloxacin as antibacterial agent

The interaction of tin(II) and tin(IV) chlorides with norfloxacin (NOR) has been investigated. Elemental analysis, infrared, mass spectra and thermal analysis have been used to characterize the isolated solid complexes. The results support the formation of complexes with the formula [Sn(NOR)₂]Cl₂·4H₂O and [Sn(NOR)₃]Cl₄. The infrared spectra of the isolated solid complexes suggested that NOR act as bidentate ligand through the carbonyl oxygen atom and one oxygen atom of the carboxylic group forming six-membered rings with the tin ions. The interpretation, mathematical analysis and evaluation of kinetic parameters of thermogravimetric (TGA) and its differential (DTG), such as entropy of activation, pre-exponential factors, activation energy evaluated by using Coats–Redfern and Horowitz–Metzger equations are carried out for two complexes. The data obtained indicate that the two complexes decompose in one stage and general mechanisms describing the decomposition are suggested. Furthermore, the electronic, and ¹H?NMR spectra have been studied.     

Spin-state dynamics of a photochromic iron(II) complex and its immobilization on oxide surfaces via phenol anchors

This work presents a detailed study of the photo-induced spin-state dynamics of the photochromic iron(II) complex 1, where the metal ion is in the field of a tripodal hexa-imine ligand with protolysable phenol groups. The nature of the complex’s ground state has been identified as a spin singlet by ¹H NMR and steady-state UV/vis spectroscopies, and its distorted octahedral structure was analyzed via crystal structure determination. Sub-picosecond and nanosecond time-resolved laser flash photolysis experiments identify the long-lived quintet state of 1 as the selective product of photoexcitation in the UV/vis spectral region. Thermal barriers of spin-state interconversion as a function of solvent and added base are derived from temperature-dependent rates of transient decay. Ground-state recovery is found to be significantly affected by the solvent and is strongly enhanced, in particular, by base-driven solvolysis of the ligand’s phenol groups. Partial spontaneous deprotonation of the phenolic hydroxyl groups of 1 seems to prevail on metal oxide surfaces, i.e. on alumina. Composite materials, like 1 at Al₂O₃, that retain the characteristic spectral features of the parent iron(II) complex can be readily obtained by wet impregnation of hydrous alumina with solutions of 1.     

Methylation of tin(II) and lead(II) in sediment by carbanion donors

A factorial experimental design determined separate and combined effects of MeCoB₁₂ (methylcobalamin) and Me₂Co(N₄)⁺ (a methylcobalamin model) on methylation of Sn(II) and Pb(II) in sediment matrices. Total methyltin yields ranged from 1.4% to 3.2%, and total methyllead yields varied from 0.037% to 0.11%. No methylmetal products occurred in the absence of Me₂Co(N₄)⁺.     

Variation dynamics of palladium(II) and tin(II) concentrations in activating solution

A study of the possibility of optimizing the efficiency of a catalytic palladium layer demonstrated that the minimum palladium adsorption providing a sufficient catalytic activity of the surface is Γ_min = 3.178 × 10^–6 mol m^–2, which can be reached at a palladium dichloride concentration of 0.035 g L^–1. It was shown that palladium(II) activates the surface of the insulator (is sorbed) from a true, rather than a colloid solution.