Palladium metal electrode and its analytical application to precipitation and acid–base analysis in aqueous and non-aqueous media

Electrochemical characterization of palladium electrode has been reported. The investigated electrode showed a linear dynamic response for p-toluensulfonic acid and iodide ions in the concentrations range between 5?×?10^?1 and 1?×?10^?5 mol L^?1 with a Nernstian slope of 55 mV for p-toluensulfonic acid and 63 mV per decade for iodide ions in water, as well as 53 mV for p-toluensulfonic acid and 51 mV per decade for iodide ions in dioxane. The response time of the electrodes was less than 10 s in the used solvents. Some potential analytical applications of the sensors have been pointed. Palladium electrode for the potentiometric titrations of acids (citric, barbituric, and p-toluensulfonic acid), bases (N,N’-diphenylguanidine, tributylamine, and 2,2'–bipyridine), halides, and some real samples in aqueous and non-aqueous solutions were studied. Тetrabutylammonium hydroxide, perchloric acid, and silver nitrate proved to be very suitable titrating agents for these titrations. The standard deviation of the determination of the investigated compounds was less than 0.9 % from those obtained with a glass electrode, i.e., silver electrode.     

Propylene sorption and coordinative interactions for poly(N‐vinyl pyrrolidone‐co‐vinyl acetate)/silver salt complex membranes

When poly(N‐vinyl pyrrolidone‐co‐vinyl acetate) (PVP‐co‐PVAc) containing amide and ester groups were complexed with silver salts to form silver polymer electrolyte membranes, their separation performance of propylene/propane mixtures showed the high selectivity of propylene over propane of 55 and the high mixed gas permeance of 12 GPU (1 GPU = 1.0 × 10^?6 cm³(STP) cm^?2 s^?1 cmHg^?1). The separation performance strongly depends on the composition of the copolymer: the higher concentration of PVP in the copolymer, the better separation performance was achieved. These results suggest that the amide group is more effective in facilitated propylene transport than the ester group, primarily due to the stronger interaction of the silver ions with the amide than the ester oxygens, as demonstrated by FT‐IR and FT‐Raman spectroscopies. In‐situ FT‐IR spectra upon propylene sorption also demonstrate that the interaction strength of the silver ions with the ligands is arranged: amide > C?C > ester. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2263–2269, 2007     

Kalman filter applied to setpoint control in continuous titrations

A state-space model is described for continuous titrations based on first-order dynamics. The Kalman filter allows on-line monitoring of an empirically established setpoint in the titration curve. The algorithm advocated is examined for potentiometric titrations of ca. 10^?3 M solutins of acids, silver(I) and copper(II). Only gross indications of the essential parameters such as the time constant and noise covariances are required. The computer-controlled titration system is compared with a conventional setpoint titrator. Especially in cases of slow response times and steep inflections, there are advantages in both accuracy and speed when the Kalman filter is applied.     

A potentiometric sensor of silver ions based on the Schiff base of diphenol

A potentiometric sensor based on the Schiff base 2,2′-(1E,1′E)-(1,1′-binaphthyl-2,2′-diylbis(azan-1-yl-1-ylidene))bis(methan-1-yl-1-ylidene)diphenol was synthesized and tested as an ionophore PVC-based membrane sensor selective towards silver ions (Ag⁺). Potentiometric testing demonstrated the high affinity of this receptor to silver ions. Seven membranes were fabricated with different compositions, with best performance shown by that with an ionophore composition (w/w) of 1.0?mg, PVC 33.0?mg, 2-nitrophenyl octyl ether 66?mg, and potassium tetrakis(p-chlorophenyl)borate 50?mol% in 1.0?mL tetrahydrofuran. The sensor worked well over a wide range of concentrations (1.0?×?10^?2 to 1.0?×?10^?6?M Ag⁺) at pH?6, showing a slope of 60.99?mV/dec with rapid response times of less than 3?s. The sensor also showed good selectivity towards Ag⁺ in the presence of interfering cations, with the highest selectivity coefficient observed for Hg²⁺ (2.7). A low detection limit of 3.4?×?10^?7?M Ag⁺ was established.     

Gaseous catalysts for end-point indication in titrimetric analysis in the microgram range

The method of end-point detection described is very sensitive. In titrations with sodium sulphide, the first drop of titrant in excess cause evolution of hydrogen sulphide which acts as a catalyst for the indicating iodine—azide reaction. The gas formed at the end-point is transferred by a nitrogen stream to the indicator vessel. Microgram amounts of metal ions (Sb, Ni, Fe, Hg⁺ Cd, Pb⁺ Cu, Ag⁺ Cu) and permanganate can be titrated in acidic solution with standard sulphide solution. In a variation of this method, acid-base titrations are possible.     

Time‐Dependent Surface Plasmon Resonance Spectroscopy of Silver Nanoprisms in the Presence of Halide Ions

Herein, we find that the surface plasmon resonance (SPR) spectra of silver nanoprisms in the presence of halide ions change gradually with reaction time. The changes in the spectra correspond to the shape transformation of silver nanoprisms. There are threshold concentrations of halide ions that initiate the shape‐transformation reaction. The threshold concentrations for Cl^?, Br^?, and I^? are about 3×10^?4 M , 1×10^?6 M , and 1.5×10^?6 M , respectively. Any concentrations of the added halide ions above these thresholds can eventually etch the silver nanoprisms into nanodisks if the reaction time is long enough. The higher the concentration of the halide ions, the higher the etching rate will be. The kinetics of the shape transformation of the silver nanoprisms can be studied by recording their time‐dependent surface plasmon resonance (SPR) spectra on a commercial UV/Vis–NIR spectrometer. The peak positions of in‐plane dipole SPR bands of silver colloids in the presence of chloride and bromide ions can be fitted very well with the biexponential functions. We propose that the fast components of the biexponential behaviors should correlate to the truncating effect on the corners of silver nanoprisms, and the slow component should correlate to the redeposition of the truncated residues onto the basal plane of the nanoplates.     

Sequential injection system for simultaneous determination of chloride and iodide by a Gran’s plot method

This paper describes an automated set-up based on the sequential injection analysis (SIA) concept with potentiometric detection for the determination of chloride and iodide at low concentrations. The assessment of both ion concentrations is accomplished by titration with silver ions using the Gran’s plot approach. The proposed procedure enables chloride and iodide to be determined simultaneously in the range 6.0×10⁻⁶ to 1.0×10⁻⁴ mol l⁻¹ if a minimum silver concentration in the volumetric solution is chosen (5×10⁻⁵ mol l⁻¹). Conventional titrations based on the first derivative evaluation of the equivalence points applied to the same solutions fail, especially for chloride determinations. Although, a comparison of results obtained for higher analyte concentrations shows that they have similar accuracy and precision.     

Electrochemical studies of iodine in an aluminium chloride-butylpyridinium chloride ionic liquid part II. Neutral and basic solvent composition

The electrochemical behavior of iodine in an ambient temperature molten salt system, aluminum chloride-N-(1-butyl)pyridinium chloride (BuPyCl), have been studied in basic (excess BuPyCl) and neutral (1.0:1.0 AlCl₃: BuPyCI mole ratio) melt compositions. Acid-base interactions of iodine in different oxidation states with the ionic solvent are observed. High stability of triiodide ion in neutral butylpyridinium tetrachloroaluminate indicates relatively weak intermolecular interactions in this solvent. In basic solutions polyhalogen equilibria involving iodine in different oxidation states and chloride ions are established. In iodine and tetraethylammonium triiodide solutions a mixture of ICI₂^?, I₂Cl^?, I₃^? and I^? ions forms. The formation constants of I₂Cl^? and I₃^? and the equilibrium constant for I₂Cl^? disproportionation are estimated.     

Determination of picomolar concentrations of bromide with a piezoelectric detector by catalysis of the permanganate/iodide reaction

The piezoelectric quartz crystal has been utilized to detect iodine produced by the bromide- catalyzed oxidation of iodine to iodate by permanganate in acidic solution. After extraction of iodine into toluene, the resulting frequency change caused by iodine adsorption on the crystal electrode is proportional to bromide concentration over the range 0.5–5 × 10^?12 M. Only silver (I), mercury(II) and large concentrations of chloride interfere significantly. The crystal detector is also used to indicate the end-point of a chloride titration with silver.     

Structure of iodide ion arrays in iodinated nylon 6 and the chain orientation induced by iodine in nylon 6 films

Two species of iodide ions (I₃^? and I₅^?) are found in iodine—nylon 6 complexes. Orientation of I₅^? arrays (most likely I₂/I₃^? complex) along the polymer chain and I₃^? ions perpendicular to the chain axis in uniaxially drawn films and in films with planar orientation suggests that there is and intrinsic relation between the direction of iodide ion arrays and nylon 6 chains. When an unoriented film of nylon 6 in the amorphous or the α crystalline form is treated with an aqueous solution of iodine—potassium iodide, the I₃^? species in the resulting iodine—nylon complex lie in planes parallel to the surface of the film, and I₂/I₃^? units are oriented normal to the surface of the film. The γ form obtained by desorbing the iodine from this complex shows considerable uniaxial rientation with the nylon chains oriented perpendicular to the plane of the film; this orientation is maintained during the γ to α transition. It is proposed that the iodine-induced orientation of the nylon 6 chains is due to the nucleating effects of the iodide ion species as the iodine diffuses unidirectionally into the film.     

A highly selective chemosensor derived from benzamide hydrazones for the detection of cyanide ion in organic and organic-aqueous media: design,synthesis, sensing and computational studies

ABSTRACT

A new, highly sensitive and selective chemosensing method has been developed for the detection of cyanide ion using benzamide hydrazone receptors (R1-R4). The sensing ability of these compounds towards CN^? in the presence of Br ^?, HSO₄ ^?, Cl^?, OH^?, I^?, F^?, AcO^?, NO₂ ^? and NO₃ ^? in DMF and DMF-Aqueous mixture (DMF:H₂O, 9:1 v/v) was investigated. The binding characteristics of the probe with cyanide ions carried out by ¹ H NMR titrations indicated the deprotonation of N-H group through H-bond interactions between benzamide hydrazones and cyanide ions; it has been theoretically supported by DFT. The binding constant (Ka) and stoichiometry of the host–guest complex formed was calculated by the Benesi–Hildebrand (B–H) plot, and strong interaction of the probe with CN^- ions forming a 1:2 binding stoichiometry has been noted in this study. In a DMF and aqueous medium for CN^? ion, the lower limit of detection (LOD in ppm) is compared to the limit of quantification (LOQ in ppm), which is quite better in terms of sensitivity.     

Extraction of trace amounts of silver on various amino-functionalized nanoporous silicas in real samples

Aminopropyl-functionalized mesoporous silicas, NH₂-MCM-41 and NH₂-SBA-15, as absorbents were utilized for rapid extraction, preconcentration and determination of trace amounts of silver. Flow rates of sample and eluent, pH, eluent solution, type, concentration and the least amount of eluent for desorption of silver ions were optimized; moreover, break through volume and the effect of various cationic interferences on the sorption of silver were evaluated. The extraction efficiency of silver ions was greater than 95% for MCM-41-NH₂ and 85% for SBA-15-NH₂ and the limit of detection (LOD) was less than 4 ng mL^?1 for both functionalized mesoporous silicas. The preconcentration factor was greater than 210 and the relative standard deviation (RSD) was <2%. The adsorption capacity of the mesoporous silicas is higher than 143 mg g^?1 for NH₂-MCM-41 and 137 mg g^?1 for NH₂-SBA-15. Under similar experimental conditions the results for these solid phases were compared with each other. NH₂-SBA-15, in spite of larger pore size diameter and adsorption of silver ions in higher flow rates has lower recovery and a higher RSD compared to MCM-41. This method has been applied to determine silver in photographic emulsions and real samples.     

Selective determination of silver in solution by adsorption on a piezoelectric quartz crystal

Electrodeposition of metal ions on the crystal is eliminated by using a specially constructed transistorized oscillator. When tartrate, citrate, EDTA or their mixtures are present, silver adsorption occurs. The frequency change is proportional to the silver concentration in the range 2 × 10^?7?1 × 10^?5 M after adsorption for 10 min from a 1 mM EDTA/3 mM tartrate solution. No significant interferences are caused by other metal ions. On the basis of cyclic voltammetric studies, it is suggested that silver is adsorbed as a silver (I) complex.     

Effect of silver and copper ions on the decomposition of ozone in water

Features of the kinetics of ozone decomposition in water at pH 2 are studied depending on the concentration of silver and copper ions that are present. The existence of a critical concentration of metal ions (??3?6 × 10^?6 M) is established, below which ions slow the rate of ozone decomposition and above which the accelerate the process. It is concluded that the first region is due to the capture of hydroxyl and other radicals by metal ions, inhibiting the chain of ozone decomposition in water. A further increase in the concentration of ions leads to dominance of their direct interaction with molecules of ozone. A mechanism for the process is proposed and the rate constants of reaction of ozone with silver ions and copper are calculated (0.033 and 0.06 M^?1 s^?1, respectively).     

Measurements of electrical conductivity in solid bromine and iodine

Measurements of the electrical conductivity were performed with bromine and iodine in the liquid and the solid states, both containing low concentrations of the corresponding halide ions. In bromine the specific conductivity increases dramatically upon solidification and in iodine it changes only slightly. In both systems the conductivity in the solid is rather high, with remarkably low temperature coefficients, pointing to an unusual mechanism of conduction (of the Grotthuss type) requiring very little movement of the heavy nuclei while the charge is transferred. In mixtures of bromine with a small amount of nitrobenzene (NB) an equivalent conductivity as high as 12 cm² mol^?1 Ω^?1 was observed at ?25°C. In iodine the specific conductivity reached a value of about 0.01 Ω^?1 cm^?1 at 100°C. The energy of activation for conduction in bromine down to ?40°C was found to be about 23 kJ mol^?1, increasing sharply below this temperature. In iodine, values of about 21–27 kJ mol^?1 were observed over the whole temperature range measured.     

Controlled Preparation and Reactive Silver‐Ion Sorption of Electrically Conductive Poly(N‐butylaniline)–Lignosulfonate Composite Nanospheres

Electroconductive poly(N‐butylaniline)–lignosulfonate (PBA–LS) composite nanospheres were prepared in a facile way by in situ, unstirred polymerization of N‐butylaniline with lignosulfonate (LS) as a dispersant and dopant. The LS content was used to optimize the size, structure, electroconductivity, solubility, and silver ion adsorptive capacity of the PBA–LS nanospheres. Uniform PBA–LS10 nanospheres with a minimal mean diameter of 375 nm and high stability were obtained when the LS content was 10 wt %. The PBA–LS10 nanospheres possess an increased electroconductivity of 0.109 S cm^?1 compared with that of poly(N‐butylaniline) (0.0751 S cm^?1). Furthermore, the PBA–LS10 nanospheres have a maximal silver‐ion sorption capacity of 815.0 mg g^?1 at an initial silver ion concentration of 50 mmol L ^?1 (25 °C for 48 h), an enhancement of 70.4 % compared with PBA. Moreover, a sorption mechanism of silver ions on the PBA–LS10 nanospheres is proposed. TEM and wide‐angle X‐ray diffraction results showed that silver nanoparticles with a diameter size range of 6.8–55 nm was achieved after sorption, indicating that the PBA–LS10 nanospheres had high reductibility for silver ions.     

Liquid-state mercury(II) ion-selective electrode based on N-(O,O-diisopropylthiophosphoryl)thiobenzamide

A liquid ion-exchange electrode containing a complex of mercury(II) with N-(O,O-diisopropylthiophosphoryl)thiobenzamide in carbon tetrachloride is described. The electrode shows excellent sensitivity and good selectivity. The slope of the calibration graph is 29.0 mV/pHg²⁺ in the pHg²⁺ in the pHg²⁺ range 2–15.2 in mercury(II) ion buffers. The electrode can be used for determination of 5 × 10^?5–10^?2 M Hg(II) in the presence of 10^?2 M Cu(II), Ni(II), Co(II), Zn(II), Pb(II), Cd(II), Mn(II), Fe(III), Cr(III), Bi(III) or Al(III) ions and in the presence of 10^?3 M Ag(I) ions. It can bealso used for end-point detection in titrations with EDTA of 10^?3–10^?4 M mercury(II) at pH 2.     

Physico-chemical studies in non-aqueous solvents: Part XII. Thermochemical studies of some 1:1 electrolytes in N,N-dimethylacetamide

Heats of solution of alkali metal, silver, ammonium and substituted ammonium perchlorates, lithium chloride and potassium thiocyanate have been measured in the concentration range 1.26–112.8×10^?3 mol l^?1 in N,N-dimethylacetamide (DMA) at 26.9°C. Slopes of the linear plots of heat of solution vs. square root of concentration are two to three times higher than the Debye-Hückel limiting slope indicating thereby complete dissociation of the electrolytes. Standard heats of solution of the electrolytes in DMA are higher than those in formamide and N-methylformamide and are comparable to those in N,N-dimethylformamide. Buckingham's model has been used to determine the solvation enthalpies of various ions in this solvent. The results indicate that ion solvation enthalpies decrease with increase in size of the ions and that the anion solvation enthalpies are higher than cation solvation enthalpies which is consistent with the findings in various solvents.     

Study on the chemisorption kinetics of Methylene Blue using SERS technique

SERS technique was used to study the chemisorption kinetics of Methylene Blue (MB) on the HNO3-etched silver surface. The adsorption kinetic parameters were deduced from different vibrational modes at a low concentration of 3.5×10-6 mol/L, and it showed that MB adsorbed uniformly (monolayerly) on silver surface. However, the adsorptive behavior turned anomalous at relatively higher concentrations and a possible explanation was suggested. In addition, the influence of Cl- ions on the adsorption states of MB was investigated, and it was shown that MB molecules, adsorbed on the silver surface, tended to transform from the "lying-down" state to the "end- on"4 state after Cl- ions were added.     

Isomeric Transformation Of 4-Aminobiphenyl by U.V. Radiation and its Influence on the Determination by Flow Injection Analysis with Amperometric and Spectrophotometric Detection.

Abstract

Two flow-injection methods for the determination of 4-aminobiphenyl by amperometry (glassy carbon electrode) and spectrophotometry are proposed. A sample volume of 200 or 400 μl containing an analyte concentration of 0.1–1.0 μg ml^?1 or 0.8–24.0 μg ml^?1 for amperometric or spectrophotometric detection, respectively, is injected into a carrier stream containing 0.04 or 0.02 M Britton-Robinson buffer at pH 10.0 or 8.0, respectively.

The throughput thus achieved is 200 (amperometry) and 240 samples/h (spectrophotometry) and the relative standard deviation less than 2.5% and 4.2% respectively.

Both methods were applied to the determination of 4-aminobiphenyl in commercially available, legally permitted food colouring additive.