Electrochemical behaviors and determination of melamine in neutral and acid aqueous media

The electrochemical behaviors of melamine (MEL) were studied at paraffin-impregnated graphite electrode in PBS (pH?7.0) and 0.5?M H₂SO₄. Various methods including UV?Cvis thin-layer spectroelectrochemistry, infrared spectra (IR) and electrochemicatry have been performed to investigate the characteristics. In 0.1?M PBS (pH?7.0), MEL loses two electrons to form a dication, which couples head-to-head with a neutral molecule of MEL to form a dimer accompanying the production of azocompound, the dimer plays a role of a monomer in the following polymerization. In 0.5?M H₂SO₄, unstable MEL mostly hydrolyzes to form ammeline, ammelide, s-triazine-2,4,6-trion, and tricyanic acid, respectively; The hydrolysis could be accelerated by electrochemical method; Meanwhile, MEL associates tricyanic acid to give a plane molecule cake by hydrogen bonding. The spectra responses of MEL at 205 and 234?nm are linearly increasing in a same concentration range of 1.0?×?10^?7?C1.0?×?10^?5?M in 0.5?M H₂SO₄ (determination limit, 1?×?10^?8 and 3?×?10^?8 (3??)). The proposed method was successfully applied to the determination of MEL in real sample.     

Titanium dioxide nanorod-based amperometric sensor for highly sensitive enzymatic detection of hydrogen peroxide

Titanium dioxide nanorods (TNR) were grown on a titanium electrode by a hydrothermal route and further employed as a supporting matrix for the immobilization of nafion-coated horseradish peroxidase (HRP). The strong electrostatic interaction between HRP and TNR favors the adsorption of HRP and facilitates direct electron transfer on the electrode. The electrocatalytic activity towards hydrogen peroxide (H₂O₂) was investigated via cyclic voltammetry and amperometry. The biosensor exhibits fast response, a high sensitivity (416.9 μA·mM⁻¹), a wide linear response range (2.5 nM to 0.46 mM), a detection limit as low as 12 nM, and a small apparent Michaelis-Menten constant (33.6 μM). The results indicate that this method is a promising technique for enzyme immobilization and for the fabrication of electrochemical biosensors.

A TiO₂ nanorod film was directly grown on Ti substrate by a hydrothermal route, and was further employed for a supporting matrix to immobilize horseradish peroxidase as a biosensor electrode. The as-prepared hydrogen peroxide biosensor based on Nafion/HRP/TNR/Ti electrode exhibited fast response and excellent electrocatalytic activity toward H₂O₂, i.e., a high sensitivity (416.9 μA mM⁻¹), a wide linear range (2.5 × 10⁻⁸ to 4.6 × 10⁻⁴ M) with a low detection limit (0.012 μM) and a small apparent Michaelis-Menten constant (33.6 μM).

     

Influence of pyridazine derivative on corrosion inhibition of mild steel in acidic media

The inhibition behavior of 6-methyl-4,5-dihydropyridazin-3(2H)-one (MDP) on corrosion of mild steel in 1 M HCl and 0.5 M H₂SO₄ was investigated using weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) measurements. The results indicated that the corrosion inhibition efficiency depends on concentration, immersion time, solution temperature, and the nature of the acidic solutions. It is also noted that MDP is at its the most efficient in 1 M HCl and least in 0.5 M H₂SO₄. The effect is more pronounced with MDP concentration. It is found that the inhibition efficiency attains 98 % at 5 × 10^?3 M in 1 M HCl and 75 % at 5 × 10^?2 in 0.5 M H₂SO₄. Polarization measurements showed that the MDP acts as a mixed inhibitor. EIS diagrams showed that the adsorption of MDP increases the transfer resistance and decreases the capacitance of the interface metal/solution. From the temperature studies, the activation energies in the presence of MDP were found to be superior to those in uninhibited medium. Finally, a mechanism for the adsorption of MDP was proposed and discussed.     

Ionic conductivity and thermal expansion of anion-deficient Sr11Mo4O23 perovskite

Transport properties of perovskite-type Sr₁₁Mo₄O₂₃ and composite Sr₁₁Mo₄O₂₃ - 1 wt% Al₂O₃ were studied at 400–1300 K in the oxygen partial pressure range from 0.21 down to 10⁻¹⁹ atm. The electromotive force and faradaic efficiency measurements, in combination with the energy-dispersive spectroscopy of the fractured electrochemical cells, unambiguously showed prevailing role of the oxygen ionic conductivity under oxidizing conditions. At temperatures above 600 K, protonic and cationic transport can be neglected. The oxygen ion transference numbers vary in the range of 0.95–1.00 at 973–1223 K. At temperatures lower than 550 K, the total conductivity of Sr₁₁Mo₄O₂₃ - 1 wt% Al₂O₃ composite measured by impedance spectroscopy tends to increase in wet atmospheres, thus indicating that hydration and protonic transport become significant. Reducing oxygen partial pressure below 10⁻¹⁰–10⁻⁹ atm leads to a significant increase in the n-type electronic conduction. The average thermal expansion coefficients in oxidizing atmospheres are (14.3–15.0) × 10⁻⁶ K⁻¹ at 340–740 K and (18.3–19.2) × 10⁻⁶ K⁻¹ at 870–1370 K.

     

Simple and sensitive determination of hydroxyl radical in atmosphere based on an electrochemically activated glassy carbon electrode

The hydroxyl radical (?OH) plays important roles in environment and health problems. However, the short life time and low concentrations of ?OH limited its detection. In this work, a simple method has been successfully performed for the sensitive detection of hydroxyl radical based on an activated glassy carbon electrode (AGCE).4-hydroxybenzoic acid (4-HBA) was used as a trapping agent for ?OH radicals, leading to the production of electroactive 3,4-dihydroxybenzoic acid (3,4-DHBA). Different procedures including polarisation and cyclic voltammetry in acid or base solutions have been used to activate the glassy carbon electrodes. The electrochemical behaviours of 3,4-DHBA on these activated electrodes were studied and compared. Experimental results showed that the glassy carbon electrode polarised in H₂SO₄ (AGCE-P/H₂SO₄) has the greatest sensitivity and reproducibility to 3,4-DHBA. 3,4-DHBA performed a linear relationship from 1.0 × 10^?7 to 1.0 × 10^?4 M on the AGCE-P/H₂SO₄. The detection limit was down to 6.2 × 10^?8 M. This method has been successfully applied for the detection of hydroxyl radical levels in atmosphere without separation and purification process.     

pH-controlled morphological structure and electrochemical performances of polyaniline/nickel hexacyanoferrate nanogranules during electrochemical deposition

To explore the dependences of morphology and electrochemical performance of polyaniline/nickel hexacyanoferrate (PANI/NiHCF) nanogranules on pH value of the reaction system, electrodeposition of PANI/NiHCF nanogranules was performed across a pH range from 0 to 7 on carbon nanotubes (CNTs)-modified platinum substrate by cyclic voltammetry in a mixture of 0.002 mol L^?1 NiSO₄, 0.25 mol L^?1 Na₂SO₄, 0.002 mol L^?1 K₃Fe(CN)₆, and 0.01 mol L^?1 aniline solutions. The morphology and structure of PANI/NiHCF nanogranules were characterized by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy, respectively. The supercapacitive performances of the nanogranules were investigated with cyclic voltammetry (CV), charge/discharge tests, and electrochemical impedance spectroscopy (EIS). The results showed that the nanogranules with different morphology and sizes were obtained with the change of pH values from 0 to 7, which could control the mechanism of homogeneous or heterogeneous nucleation directly. The nanogranules were dispersed in matrix uniformly at pH 0 and pH 1, while the size of which decreased with the increase of pH values. The smooth cross-linking network structure was found from pH 2 to 7. The structure of PANI/NiHCF nanogranules had slightly changed from pH 0 to 7. PANI/NiHCF nanogranules had good electrochemical performance from pH 0 to 7 in a mixture of 0.5 mol L^?1 H₂SO₄ and 0.5 mol L^?1 KNO₃ solutions, and the highest specific capacitance value of 274 F g^?1 was obtained at current densities of 2 mA cm^?2 in neutral medium. PANI/NiHCF nanogranules had high stability in neutral medium after 2,000 cycles by CV.     

The Electropolymerization of 2,6‐Diaminopyridine and Its Application as Mercury Ion Selective Electrode

A composite graphite (CG) electrode modified with poly(2,6‐diaminopyridine) (PDAP) was used as solid state‐ion selective electrode for determination of mercury. The electrooxidation of monomer 2, 6 diaminopyridine (DAP) onto CG was accomplished from the 30 mM DAP in 5% H₂SO₄ and 0.5 M ZnSO₄. The electrode displayed Nernstian response with slope of 28.4±1 mV decade⁻¹ in concentration range of 1×10⁻⁶ to 1×10⁻¹ M and in solution of pH 3–5. The limit of detection for electrode was 3×10⁻⁸ M with response time of 25 s. The electrode was also suitable as an indicator electrode in the potentiometric titration of Hg²⁺ with iodide.     

A Validated HPLC Method with Fluorescence Detection for the Determination of Droperidol in Pharmaceutical Tablets,Human Serum,and Human Milk

A sensitive and simple HPLC method with fluorimetric detection has been developed for determination of droperidol in pharmaceutical tablets, human serum, and human milk. Chromatography was performed on a 100 mm × 3 mm i.d. C₁₈ column with methanol–water, 30:70 (v/v), pH 3.5, as mobile phase at a flow-rate of 0.8 mL min⁻¹. The injection volume was 5 μL and detection was by monitoring emission at 324 nm after excitation at 283 nm. Droperidol and p-hydroxybenzoic acid (internal standard) eluted after 5.3 and 6.1 min, respectively. The method was validated over the concentration range 1.14 × 10⁻⁷ to 9.12 × 10⁻⁶ M. Selectivity was good and the limits of detection and quantitation of the method were approximately 3.54 × 10⁻⁸ and 1.07 × 10⁻⁷ M, respectively, corresponding to 13 and 40 ng mL⁻¹. The applicability of the method to determination of droperidol in pharmaceuticals, human serum, and human milk was demonstrated.

     

Acetone extracted propolis as a novel membrane and its application in phenol biosensors: the case of catechol

A novel biosensor for catechol has been constructed by immobilizing polyphenol oxidase (PPO) into acetone-extracted propolis (AEP) composite modified with gold nanoparticles (GNPs) and attached to multiwalled carbon nanotube (MWCNTs) on a gold electrode surface. The propolis for AEP was obtained from honeybee colonies. Under the optimum conditions, this method could be successfully used for the amperometric determination of catechol within a concentration range of 1 × 10⁻⁶ to 5 × 10⁻⁴ M, with a detection limit of 8 × 10⁻⁷ M (S/N = 3). The effects of pH and operating potential are also explored to optimize the measurement conditions. The best response was obtained at pH 5, while an optimum ratio of signal-to-noise (S/N) was obtained at −20 mV (versus Ag/AgCl), which was selected as the applied potential for the amperometric measurements. All subsequent experiments were performed at pH 5. Cyclic voltammetry and electrochemical impedance spectroscopy was used to characterize the PPO/CNTs/GNPs/AEP/Au biosensor. The biosensor also exhibited good selectivity, stability, and reproducibility.

     

Electrochemical Determination of Anti-Hyperlipidemic Drug Ezetimibe Based on its Oxidation on Solid Electrodes

Ezetimibe is the first of a new class of drugs that selectively inhibits cholesterol absorption in the small intestine and reduces plasma LDL cholesterol. In this study, electrochemical oxidation of ezetimibe was investigated on carbon based electrodes and a single and irreversible peak at both electrodes was observed. A linear response was detected between 2 × 10^?6 and 8 × 10^?5 M with glassy carbon electrode and between 2 × 10^?6 and 2 × 10^?4 M with a boron-doped diamond electrode in 0.1 M H₂SO₄ supporting electrolyte. The proposed methods were successfully applied for the determination of ezetimibe from pharmaceutical dosage forms and human serum samples.     

Improving electrochemical performance of poly(vinyl butyral)-based electrolyte by reinforcement with network of ceramic nanofillers

This study has concerned the development of polymer composite electrolytes based on poly(vinyl butyral) (PVB) reinforced with calcinated Li/titania (CLT) for use as an electrolyte in electrochemical devices. The primary aim of this work was to verify our concept of applying CLT-based fillers in a form of nano-backbone to enhance the performance of a solid electrolyte system. To introduce the network of CLT into the PVB matrix, gelatin was used as a sacrificial polymer matrix for the implementation of in situ sol–gel reactions. The gelatin/Li/titania nanofiber films with various lithium perchlorate (LiClO₄) and titanium isopropoxide proportions were initially fabricated via electrospinning, and ionic conductivities of electrospun nanofibers were then examined at 25 °C. In this regard, the highest ionic conductivity of 2.55 × 10⁻⁶ S/cm was achieved when 10 wt% and 7.5 wt% loadings of LiClO₄ and titania precursor were used, respectively. The nanofiber film was then calcined at 400 °C to remove gelatin, and the obtained CLT film was then re-dispersed in solvated PVB-lithium bis(trifluoromethanesulfonyl)imide (PVB-LiTFSI) solution before casting to obtain reinforced composite solid electrolyte film. The reinforced composite PVB polymer electrolyte film shows high ionic conductivity of 2.22 × 10⁻⁴ S/cm with a wider electrochemical stability window in comparison to the one without nanofillers.

     

Direct electrochemical behavior of cytochrome c, and its determination on phytic acid modified electrode

Phytic acid (PA) with its unique structure was attached to a glassy carbon electrode (GCE) to form PA/GCE modified electrode which was characterized by electrochemical impedance. The electrochemical behavior of cytochrome c (Cyt c) on the PA/GCE modified electrode was explored by cyclic voltammetry and differential pulse voltammetry. The Cyt c displayed a quasi-reversible redox process on PA modified electrode pH 7.0 phosphate buffer solution with a formal potential (E ^0′) of 57 mV (versus Ag/AgCl). The peak currents were linearly related to the square root of the scan rate in the range of 20–120 mV·s^?1. The electron transfer rate constant was determined to be 12.5 s^?1. The PA/GCE modified electrode was applied to the determination of Cyt c, in the range of 5?×?10^?6 to 3?×?10^?4 M, the currents increase linearly to the Cyt c concentration with a correlation coefficient 0.9981. The detection limit was 1?×?10^?6 M (signal/noise?=?3).     

Division Electrosynthesis of Palladium Nanomaterials with Copper–Graphene as Sacrificial Templates and Its Application for Hydrazine Sensing

One‐pot electrodeposited copper‐graphene (Cu‐GE ) nanocomposite acting as sacrificial template for the division electrosynthesis of palladium nanoparticles (PdNPs ) on pyrolytic graphite electrode (PGE ) was synthesized. The designed PdNPs‐GE nanocomposite was evaluated as a new material for highly sensitive determination of hydrazine (N₂H₄ ). Scanning electron microscopy revealed that the PdNP‐GE ‐modified PGE had uniform morphology. The results of energy‐dispersive X‐ray spectrograms confirmed the ingredients of the division electrosynthesis process. Electrochemical experiments were performed to characterize the sensing properties of PdNPs‐GE toward the electrocatalytic oxidation of N₂H₄ at 0.20 V in sodium phosphate buffered saline (0.1 M pH 7.0). The sensor showed fast response (<3 s), high sensitivity [398 (1 × 10⁻⁶ A) (1 × 10⁻³ M)⁻¹], and broad linearity in the range 2.5 × 10⁻⁸–2.7 × 10⁻⁴ M with a relatively low detection limit of 1.0 × 10⁻⁸ M (S/N = 3).     

Determination of Methimazole and Carbimazole Using Polarography and Voltammetry

Abstract

Anodic waves of methimazole (I) (1-methylimidazole-2-thiol) and carbimazole (II) (1-ethoxycarbonyl-3-methyl-2-thio-4-imidazoline) on mercury electrodes correspond to mercury salt formation. Both compounds form in the thiono form a soluble complex at pH < 6, compound (I) at higher pH-values a slightly soluble salt of the thiol form. Electrode processes involving the thiol form are complicated by adsorption. Oxidation at solid electrodes occurs only at potentials more than 0.5 V more positive. For compound (I) spectrophotometry indicated pK_a=12.0 ± 0.2. By d.c. polarography in 0.1 M H₂SO₄ containing 10% ethanol the determination of both compounds is possible between 4 × 10^? and 1 × 10^?3 M, by differential pulse polarography between 1 × 10^? and 1 × 10^?4 M, by differential pulse voltammetry at HMDE between 5 × l0^?7 and 6 × 10^? M.     

Kinetic study of some reactions related to the Mn(II)-catalyzed bromate-saccharide oscillating reactions

In the stirred batch experiment, the Mn(II)-catalyzed bromate-saccharide reaction in aqueous H₂SO₄ or HClO₄ solution exhibits damped oscillations in the concentrations of bromide and Mn(II) ions. Peculiar multiple oscillations are observed in the system with arabinose or ribose. The apparent second-order rate constants of the Mn(III)-saccharide reactions at 25°C are (0.659, 1.03, 1.76, 2.32, and 6.95) M⁻¹ s⁻¹ in 1.00 M H₂SO₄ and (4.69, 7.51, 10.2, 13.5, and 36.2) M⁻¹ s⁻¹ in (2.00–4.00) M HClO₄ for (glucose, galactose, xylose, arabinose, and ribose), respectively. At 25°C, the observed pseudo-first-order rate constant of the Mn(III)-Br⁻ reaction is k_obs = (0.2 ± 0.1) [Br⁻] + (130 ± 5)[Br⁻]² + (2.6 ± 0.1) × 10³[Br⁻]³ + (1.2 ± 0.2) × 10⁴[Br⁻]⁴ s⁻¹ and the rate constant of the Br₂ Mn(II) reaction is less than 1 × 10⁻⁴ M⁻¹ s⁻¹. The second-order rate constants of the Br₂-saccharide reactions are (3.65 ± 0.15, 11.0 ± 0.5, 4.05, 12.5 ± 0.7, and 2.62) × 10⁻⁴ M⁻¹ s⁻¹ at 25°C for glucose, galactose, xylose, arabinose, and ribose, respectively.     

Irreversible electrostatic deposition of Prussian blue from colloidal solutions

Prussian blue (PB) can be deposited from colloidal solutions (5.4 × 10⁻³ mol_PB L⁻¹, 0.01 mol L⁻¹ KNO₃) on glassy carbon, either by potential cycling or potentiostatically, provided that the deposition potential is more positive than −0.2 V vs. Hg/Hg₂Cl₂. Depending on the deposition potential, the PB particles form either a single layer of Everitt’s salt, of PB, or multilayers of Berlin green. Also depending on the electrode potential, the deposition was accompanied by currents which were either only of capacitive nature, or represent the sum of capacitive and faradaic currents. The currents were always limited by the diffusion of the colloidal particles to the electrode surface, i.e., they obeyed the Cottrell equation. The PB layers were characterized by in situ atomic force microscopy.

     

Synergetic effect of Prussian blue film with gold nanoparticle graphite–wax composite electrode for the enzyme-free ultrasensitive hydrogen peroxide sensor

Enzyme-free amperometric ultrasensitive determination of hydrogen peroxide (H₂O₂) was investigated using a Prussian blue (PB) film-modified gold nanoparticles (AuNPs) graphite–wax composite electrode. A stable PB film was obtained on graphite surface through 2-aminoethanethiol (AET)-capped AuNPs by a simple approach. Field emission scanning electron microscope studies results in formation of PB nanoparticle in the size range of 60–80 nm. Surface modification of PB film on AET–AuNPs–GW composite electrode was confirmed by Fourier transform infrared attenuated total reflection (FTIR-ATR) spectroscopy studies. Highly sensitive determination of H₂O₂ at a peak potential of ?0.10 V (vs. SCE) in 0.1 M KCl PBS, pH?=?7.0) at a scan rate of 20 mVs^?1 with a sensitivity of 23.58 μA/mM was observed with the modified electrode using cyclic voltammetry. The synergetic effect of PB film with AuNPs has resulted in a linear range of 0.05 to 7,800 μM with a detection limit of 0.015 μM for H₂O₂ detection with the present electrode. Chronoamperometric studies recorded for the successive additions of H₂O₂ with the modified electrode showed an excellent linearity (R ²?=?0.9932) in the range of 4.8?×?10^?8 to 7.4?×?10^?8 M with a limit of detection of 1.4?×?10^?8 M. Selective determination of H₂O₂ in presence of various interferents was successfully demonstrated. Human urine samples and stain remover solutions were also investigated for H₂O₂ content.     

Screen-printed electrochemical sensors for label-free potentiometric and impedimetric detection of human serum albumin

Herein, two electrochemical methods based on potentiometric and impedimetric transductions were presented for albumin targeting, employing screen-printed platforms (SPEs) to make easy and cost-effective sensors with good detection merits. The SPEs incorporated ion-to-electron multi-walled carbon nanotubes (MWCNTs) transducer. Sensors were constructed using either tridodecyl methyl-ammonium chloride (TDMACl) (sensor I) or aliquate 336S (sensor II) in plasticized polymeric matrices of carboxylated poly (vinyl chloride) (PVC-COOH). Analytical performances of the sensors were evaluated using the above-mentioned electrochemical techniques. For potentiometric assay, constructed sensors responded to albumin with −81.7 ± 1.7 (r² = 0.9986) and −146.2 ± 2.3 mV/decade (r² = 0.9991) slopes over the linearity range 1.5 μM–1.5 mM with 0.8 and 1.0 μM detection limits for respective TDMAC- and aliquate-based sensors. Interference study showed apparent selectivity for both sensors. Impedimetric assays were performed at pH = 7.5 in 10 mM PBS buffer solution with a 0.02 M [Fe(CN)₆]^−3/−4 redox-active electrolyte. Sensors achieved detection limits of 4.3 × 10⁻⁸ and 1.8 × 10⁻⁷ M over the linear ranges of 5.2×10⁻⁸–1.0×10⁻⁴ M and 1.4×10⁻⁶–1.4×10⁻³ M, with 0.09 ± 0.004 and 0.168 ± 0.009 log Ω/decade slopes for sensors based on TDMAC and aliquate, respectively. These sensors are characterized with simple construction, high sensitivity and selectivity, fast response time, single-use, and cost-effectiveness. The methods were successfully applied to albumin assessment in different biological fluids.     

Rapid Determination of Trifluoromethanesulfonate and p-Toluenesulfonate by Ion-Pair Chromatography Using a Reversed-Phase Silica-Based Monolithic Column: Application to the Analysis of Ionic Liquids

A method of ion-pair chromatography was developed on a reversed-phase silica-based monolithic column for the fast and simultaneous determination of trifluoromethanesulfonate (CF₃SO₃ ⁻) and p-toluenesulfonate (C₇H₇SO₃ ⁻). The analysis was performed using a mobile phase of tetrabutylammonium hydroxide + citric acid + acetonitrile on the Chromolith Speed ROD RP-18e column with direct conductivity detection. The effects of the eluent, column temperature and flow rate on the retention of the anions were investigated. The experimental phenomenon was discussed according to hydrophobic interaction and ion-exchange mechanism in the separation. The optimized chromatographic conditions were selected. The optimized eluent for the separation consisted of 0.2 mmol L⁻¹ tetrabutylammonium hydroxide + 0.10 mmol L⁻¹ citric acid + 9% acetonitrile (pH 5.5). The flow rate was set at 6.0 mL min⁻¹. The column temperature was 25 °C. Under the optimal conditions, the better separation of CF₃SO₃ ⁻ and C₇H₇SO₃ ⁻ was achieved without any interference by other anions (Cl⁻, Br⁻, I⁻, NO₃ ⁻, SO₄ ²⁻, ClO₃ ⁻, BF₄ ⁻ and PF₆ ⁻). The detection limit (S/N = 3) was 0.28 and 0.71 mg L⁻¹ for CF₃SO₃ ⁻ and C₇H₇SO₃ ⁻, respectively. The method has been applied to the determination of CF₃SO₃ ⁻ and C₇H₇SO₃ ⁻ in ionic liquids. The spiked recoveries of CF₃SO₃ ⁻ and C₇H₇SO₃ ⁻ were 101.1 and 100.2%, respectively.

     

Hydrolysis of HNSO2: A potential route for atmospheric production of H2SO4 and NH3

The hydrolysis of sulfonylamine (HNSO₂) results in the formation of sulfuric acid along with ammonia, and is of significant interest due to their negative impact on environment and life on Earth. The formation of H₂SO₄ through the reaction of HNSO₂ with (H₂O)_2-4 has been studied using high level electronic structure calculations. This hydrolysis reaction is a step-wise process, in the first step a H-atom from H₂O is transferred to the N-atom of HNSO₂ which results in the formation of NH₂, and in the next step, H₂SO₄, NH₃ and water molecule(s) are formed. The results show that the energy barrier associated with the formation of intermediates and product complexes is reduced by 7 to 10 kcal/mol when the number of water molecules is increased from 2 to 4. The rate constant was calculated using canonical variational transition state theory with small curvature tunneling correction over the temperature range of 200 to 1000 K. At 298 K, the calculated rate constant for the formation of intermediate in the first step is 2.24 × 10⁻¹⁶, 1.03 × 10⁻¹², and 2.10 × 10⁻¹¹ cm³ mol⁻¹ s⁻¹, respectively, for the reaction with water dimer, trimer and tetramer. The calculated enthalpy and free energy show that the reaction corresponding to the formation of H₂SO₄ is highly exothermic and exoergic in nature.