Electrochemical Determination of Citalopram by Adsorptive Stripping Voltammetry–Determination in Pharmaceutical Products

Abstract

The electrochemical behavior of citalopram was studied by square‐wave and square‐wave adsorptive‐stripping voltammetry (SWAdSV). Citalopram can be reduced and accumulated at a mercury drop electrode, with a maximum peak current intensity being obtained at a potential of approximately ?1.25 V vs. AgCl/Ag, in an aqueous electrolyte solution of pH 12. A SWAdSV method has been developed for the determination of citalopram in pharmaceutical preparations. The method shows a linear range between 1.0×10^?7 and 2.0×10^?6 mol L^?1 with a limit of detection of 5×10^?8 mol L^?1 for an accumulation time of 30 s. The precision of the method was evaluated by assessing the repeatability and intermediate precision, achieving good relative standard deviations in all cases (≤2.3%). The proposed method was applied to the determination of citalopram in five pharmaceutical products and the results obtained are in good agreement with the labeled values.     

Hydrolysis of Tetraglycine by a Zr(IV)-Substituted Wells–Dawson Polyoxotungstate Studied by Diffusion Ordered NMR Spectroscopy

The use of diffusion ordered NMR spectroscopy (DOSY) for the analysis of complex reaction mixtures involving polyoxometalates (POMs) was demonstrated for the hydrolysis of the peptide tetraglycine by the K₁₅H[Zr(α₂-P₂W₁₇O₆₁)₂]·25H₂O Wells–Dawson type cluster. ¹H DOSY NMR studies have shown that severe signal overlap observed in the one-dimensional ¹H NMR spectrum of reaction mixtures containing a POM and peptides could be overcome by the two-dimensional character of a DOSY NMR measurement. A clear distinction between the ¹H NMR signals of the products formed during the hydrolysis of 5.0 mM of tetraglycine catalyzed by 1.0 mM of K₁₅H[Zr(α₂-P₂W₁₇O₆₁)₂]·25H₂O was observed based on the extra dimension containing information about diffusion coefficients that distinguishes a typical DOSY measurement from conventionally used 1D ¹H NMR. The spectrum clearly shows the presence of 5 species with diffusion coefficients of 3.71 × 10^?10 m²/s (3.91; 3.84; 3.82 and 3.62 ppm), 4.39 × 10^?10 m²/s (3.87; 3.76 and 3.61 ppm), 5.26 × 10^?10 m²/s (3.67 and 3.63 ppm), and 7.46 × 10^?10 m²/s (3.37 ppm) that are assigned to the non-hydrolyzed tetraglycine, the hydrolysis intermediate products triglycine and glycylglycine, and the end product of hydrolysis glycine, respectively. In addition, a signal assigned to cyclic glycylglycine, with a diffusion coefficient practically identical to the diffusion coefficient of glycylglycine was observed at 3.86 ppm. In addition, ¹H and ³¹P NMR spectroscopy were further used to study the binding of tetraglycine to K₁₅H[Zr(α₂-P₂W₁₇O₆₁)₂]·25H₂O and the solution speciation of K₁₅H[Zr(α₂-P₂W₁₇O₆₁)₂]·25H₂O.     

Application of Double Deposition and Stripping Steps System for Minimization of Interferences of Peaks’ Overlapping in Anodic Stripping Voltammetry

An anodic stripping voltammetric procedure for the determination of bismuth in the presence of excess of Cu²⁺ ions at two ex situ plated gold film electrodes was described. The procedure is based on utilization of two deposition and two stripping steps system. The presented procedure ensures increasing the sensitivity of Bi³⁺ determination and minimization of interferences related to peaks’ overlapping. The calibration graph for bismuth determination was linear from 2.5×10⁻⁹ to 2×10⁻⁸ mol L⁻¹ for deposition time of 300 s at both working electrodes while detection limit was 7.7×10⁻¹⁰ mol L⁻¹.     

Application of Adsorptive Stripping Voltammetry for the Nano‐Level Detection of Tramadol in Biological Fluids and Tablets Using Fast Fourier Transform Continuous Cyclic Voltammetry at an Au Microelectrode in a Flowing System

Abstract

A novel adsorptive fast Fourier transform cyclic voltammetry (AFFTCV) technique for the fast determination of tramadol in flow‐injection systems has been introduced in this work. The potential waveform, consisting of the potential steps for cleaning, stripping, and potential ramp, was continuously applied on an Au disk microelectrode (with a 12.5 µm in radius). The proposed detection method has some advantages, the greatest of which are as follows: first, it is no more necessary to remove oxygen from the analyte solution and second, it is a very fast and appropriate technique for determination of the drug compound in a wide variety of chromatographic analysis methods. The influences of pH of eluent, accumulation potential, sweep rate, and accumulation time on the determination of the tramadol were considered. The method was linear over the concentration range of 1.5–900,000 pg/ml (r=0.9968) with a limit of detection and quantitation 0.32 and 1.5 pg/ml, respectively. The method has the requisite accuracy, sensitivity, precision, and selectivity to assay tramadol in tablets and in biological fluids.     

Oxidative Deamination and Decarboxylation of L-Asparagine by the Aqueous Alkaline Diperiodatonickelate(IV) Complex

The kinetics of the oxidation of L-asparagine, (L-asp) by diperiodatonickelate(IV), (DPN) in aqueous alkaline medium at a constant ionic strength of 0.5 mol⋅dm⁻³, was studied spectrophotometrically. The reaction is first order in [DPN] and of fractional order in both [L-asp] and [alkali]. Addition of the products has no significant effect on the reaction rate. However, increasing the ionic strength or decreasing the dielectric constant of the medium increases the reaction rate. The oxidation process in alkaline medium is shown to proceed via two paths, one involving the interaction of L-asparagine with diperiodatonickelate(IV) ion in a slow step to yield the products, and the other path involving the interaction of alkali with the diperiodatonickelate(IV) ion to give nickel(II). Some reaction constants involved in the mechanism were determined, and calculated and observed rate constants are in excellent agreement. The activation parameters were computed for the slow step of the mechanism.     

Spectral and Mechanistic Investigation of the Osmium(VIII) Catalyzed Oxidation of Diclofenac Sodium by the Copper(III) Periodate Complex in Aqueous Alkaline Medium

The kinetics of the osmium(VIII) (Os(VIII)) catalyzed oxidation of diclofenac sodium (DFS) by diperiodatocuprate(III) (DPC) in aqueous alkaline medium has been studied spectrophotometrically at a constant ionic strength of 1.0 mol⋅dm⁻³. The reaction showed first order kinetics in [Os(VIII)] and [DPC] and less than unit order with respect to [DFS] and [alkali]. The rate decreased with increase in [periodate]. The reaction between DFS and DPC in alkaline medium exhibits 1:2 [DFS]:[DPC] stoichiometry. However, the order in [DFS] and [OH⁻] changes from first order to zero order as their concentration increases. Changes in the ionic strength and dielectric constant did not affect the rate of reaction. The oxidation products were identified by LC-ESI-MS, NMR, and IR spectroscopic studies. A possible mechanism is proposed. The reaction constants involved in the different steps of the mechanism were calculated. The catalytic constant (K _C) was also calculated for Os(VIII) catalysis at the studied temperatures. From plots of log ₁₀ K _C versus 1/T, values of activation parameters have been evaluated with respect to the catalytic reaction. The activation parameters with respect to the slow step of the mechanism were computed and discussed, and thermodynamic quantities were also determined. The active osmium(VIII) and copper(III) periodate species have been identified.     

Solubility and Solubility Product at 22°C of UO2(c) Precipitated from Aqueous U(IV) Solutions

Solubility studies on UO₂(c), precipitated at 90^°C from low-pH U(IV) solutions, were conducted under rigidly controlled redox conditions maintained by EuCl₂ as a function of pH and from the oversaturation direction. Samples were equilibrated for 24 days at 90^°C and then for 1 day at 22^°C. X-ray diffraction (XRD) analyses of the solid phases, along with the observed solubility behavior, identified UO₂(c) as the dominant phase at pH1.2 and UO₂(am) as the dominant phase at pH1.2. The UV-Vis-NIR spectra of the aqueous phases showed that aqueous uranium was present in the tetravalent state. Our ability to effectively maintain uranium in the tetravalent state during experiments and the recent availability of reliable values of Pitzer ion-interactionparameters for this system have helped to set reliable upper limits for the log K ^o value of –60.2 + 0.24 for the UO₂(c) solubility [UO₂(c) + 2H₂O U⁴⁺ + 4OH^–] and of >–11.6 for the formation of U(OH)₄(aq) [U⁴⁺+ 4H₂O U(OH)₄(aq) + 4H⁺]     

Determination of Chlorfenvinphos in Soils by Microwave‐Assisted Extraction and Stripping Voltammetry with an Ultramicroelectrode

Abstract

A methodology for the determination of the pesticide chlorfenvinphos by microwave‐assisted solvent extraction and square‐wave cathodic stripping voltammetry at a mercury film ultramicroelectrode in soil samples is proposed. Optimization of microwave solvent extraction performed with two soils, selected for having significantly different properties, indicated that the optimum solvent for extracting chlorfenvinphos is hexane‐acetone (1∶1, v/v). The voltammetric procedure is based on controlled adsorptive accumulation of the insecticide at the potential of?0.60 V (vs. Ag/AgCl) in the presence of Britton‐Robinson buffer (pH 6.2). The detection limit obtained for a 10 s collection time was 3.0×10^?8 mol l^?1. The validity of the developed methodology was assessed by recovery experiments at the 0.100 µg g^?1 level. The average recoveries and standard deviations for the global procedure reached by MASE‐square‐wave voltammetry were 90.2±2.8% and 92.1±3.4% for type I (soil rich in organic matter) and type II (sandy soil) samples, respectively. These results are in accordance to the expected values which show that the method has a good accuracy.     

Sequence-specific Hydrolysis of Single-stranded DNA by PNA-Cerium (IV) Adduct

Sequence-specific recognition and site-specific cleavage of DNA are studied and applied in various fields, such as DNA sequence determinations, chromosome analysis, gene therapeutics, and recombinant DNA manipulation1. Many sequence-specific cleavage reagents, which consist of transitional metals or polynuclear metal complex as “scissors” moiety and DNA as sequence-recognizing moiety, are developed. However, most of these “scissors”, such as Fe2+, Cu2+ and dinuclear iron (III) comple…     

Simultaneous Determination of Gold(Ⅲ) and Copper(Ⅱ) with Two-Way Stripping Voltammetry

The simultaneous determination of Au(Ⅲ) and Cu(Ⅱ) by atomic absorption spectrometry^[1,2], X-ray fluorescence^[3] and differential-pulse polarography^[4] have been reported. The apparatus used in spectrochemical analysis are complex and expensive. The method reported in reference^[4] involves a poisonous electrode-DME(dropping-mercury electrode) and unsatisfied performance with the detection limit. We had reported the determination of trace Au(Ⅲ) or Cu(Ⅱ) by a sensitive tripping voltammetry with solid electrode^[5], but there is no report about the simultaneous determination of trace Au(Ⅲ) and Cu(Ⅱ) by stripping voltammetry ever since.     

Adsorptive Stripping Voltammetric Study of the Enhancement of Copper(Ⅱ) by Poly(vinyl alcohol), Starch and Polyallylamine

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Adsorptive Stripping Voltammetric Study of the Enhancement of Copper(Ⅱ) in Phosphate and Carbonate media and in the Presence of Silicate

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Determination of the Hydrolysis Constants and Solubility Product of Chromium(III) from Reduction of Dichromate Solutions by ICP-OES and UV–Visible Spectroscopy

The determination of equilibrium constants is difficult when several chemical species are simultaneously present in solution. In this investigation, optical emission spectroscopic determinations of chromium(III) concentration in a 10⁻⁴ mol⋅dm⁻³ solution, prepared from K₂Cr₂O₇ reduced in HNO₃ or HCl media, were used to construct the pCr_(aq)–pC _H diagram. This diagram was used to calculate the pC _H borderline of precipitation, to estimate the solubility product (log₁₀K_sp,Cr(OH)3^*)(\log_{10}K_{\mathrm{sp,Cr(OH)}_{3}}^{*}), and the hydrolysis constants (log₁₀b_Cr,H^*,log₁₀b_Cr,2H^*(\log_{10}\beta_{\mathrm{Cr,H}}^{*},\log_{10}\beta_{\mathrm{Cr,2H}}^{*}, and log₁₀b_Cr,3H^*)\log_{10}\beta_{\mathrm{Cr,3H}}^{*}) of Cr(III). The hydrolysis constants were also calculated using the SQUAD and SUPERQUAD software, along with the average ligand number method. UV-Vis absorption data and associated variables were used in SQUAD, SUPERQUAD, and the average ligand calculations. Results are: 9.00±0.04 for the pC _H at the onset of precipitation, 12.40 for log₁₀K_sp,Cr(OH)3^*\log_{10}K_{\mathrm{sp,Cr(OH)}_{3}}^{*}, −3.52±0.02 for log₁₀b_Cr,H^*\log_{10}\beta_{\mathrm{Cr,H}}^{*}, −9.30±0.87 for log₁₀b_Cr,2H^*\log_{10}\beta_{\mathrm{Cr,2H}}^{*} and −17.18±0.16 for log₁₀b_Cr,3H^*\log_{10}\beta_{\mathrm{Cr,3H}}^{*}, respectively. All methods produced essentially the same values for the hydrolysis constants of Cr(III).     

Oxidation of Fursemide by Diperiodatocuprate(III) in Aqueous Alkaline Medium—a Kinetic Study

Fursemide is the chemical compound 4-chloro-2-(furan-2-ylmethylamino)-5-(aminosulfonyl) benzoic acid. It was oxidized by diperiodatocuprate(III) in alkali solutions, and the oxidation products were identified as furfuraldehyde and 2-amino-4-chloro-5-(aminosulfonyl) benzoic acid. The reaction kinetics were studied spectrophotometrically. The reaction was observed to be first order in [oxidant] and fractional order each in [fursemide] and [periodate], whereas added alkali retarded the rate of reaction. The reactive form of the oxidant was inferred to be [Cu(H₃IO₆)₂]⁻. A mechanism consistent with the experimental results was proposed, in which oxidant interacts with the substrate to give a complex as a pre-equilibrium state. This complex decomposed in a slow step to give a free radical that was further oxidized by reaction with another molecule of DPC to yield 2-amino-4-chloro-5-(aminosulfonyl) benzoic acid and furfuraldehyde in a fast step. This reaction was studied at 25, 30, 35, 40 and 45 °C, and the activation parameters E _a,ΔH ^#,ΔS ^# and ΔG ^# were determined to be 51 kJ⋅mol⁻¹,48.5 kJ⋅mol⁻¹,−63.5 J⋅K⁻¹⋅mol⁻¹ and 67 kJ⋅mol⁻¹, respectively. The value of log ₁₀ A was calculated to be 6.8.     

Solubility of Argon and Nitrogen in Aqueous Solutions of Dodecyltrimethylammonium Bromide (DTAB) from 283.15 to 298.15 K and 101325 Pa Partial Pressure of Gas

The solubility of nitrogen and argon in aqueous solutions of dodecyltrimethylammonium bromide (DTAB) were measured, using the drop pressure method, at temperatures between (283.15 and 298.15) K and partial pressure of 101325 Pa of gas in an instrument specially developed for this purpose. The gas solubility was calculated as Henry’s constant. The solubilities of argon and of nitrogen increase linearly with DTAB concentration and decrease as the temperature increases. Experimental results show that the increase in the solubility of argon and nitrogen in the DTAB micelles is between 59.0 and 83.5 higher than the solubility in pure water, reflecting the ability of DTAB micelles to increase the solubility of non-polar gases in water.     

Study of the Structure and Reactions of Bis(μ-Oxalato)tetramminediplatinum(II) in Aqueous Chloride Solutions

A comparison study of the bis(-oxalato)tetramminediplatinum(II) dimer [Pt₂(NH₃)₄(-C₂O₄)₂] and the oxalatodiammineplatinum(II) chelate [Pt(NH₃)₂C₂O₄] is performed. The kinetics and mechanism of substitution of C₂O^2– ₄ for Cl^– in aqueous chloride solutions are studied by photoelectronic spectroscopy, gravimetry, and chemical phase analysis within the 1.0–6.7 pH range at 75°C. The rate constants of substitution and the equilibrium constants for a two-step protonation for the dimeric and chelate complexes are calculated. Their solubility in 1 M KCl at 75°C; is determined. The unit cell parameters for [Pt₂(NH₃)₄(-C₂O₄)₂] are determined: a = 3.858 Å, b = 10.704 Å, c = 6.795 Å, = 94.35°. The IR spectra of [Pt(NH₃)₂C₂O₄], [Pt₂(NH₃)₄(-C₂O₄)₂], and their deuterated analogs are studied.     

Oxidation of Chloride and Subsequent Chlorination of Organic Compounds by Oxoiron(IV) Porphyrin π-Cation Radicals

Ironing it out: Oxoiron(IV) porphyrin π-cation radical complexes serve as models for the oxidation of Cl(-) into an active chlorinating reagent that chlorinates various organic compounds. Evidence suggests that Cl(-) is oxidized to Cl(2) via Cl(.) . The mechanism involving either direct electron transfer or iron(III) hypochlorite formation, and then homolysis of the Cl?O bond is discussed.     

Aggregation of Sodium Dodecyl Sulfonate in Poly—ethylene Glycol Aqueous Solutions Studied by Two—dimensional Nuclear Overhauser Enhancement Spectroscopy

Two-dimensional nuclear overhauser enhancement (2D NOESY) measurements show that sodium dodecyl sulfonate SDSN molecules co-aggregate with poly-ethylene glycol PEG in their aqueous solution at a concentration range of SDSN between the so-called co-aggregation concentration (cac) and the normal critical micellar concentration (cmc). SDSN micelles are formed when the cmc of SDSN is reached with PEG uniformly distributed in the interior.