Oxidation Of Theophylline Research Articles

Xin-yi-san contains potent human CYP1A2 inhibitors and its combined use with theophylline in treatment increases adverse risks in patients

BackgroundThe Xin-yi-san herbal decoction (XYS) is commonly used to treat patients with allergic rhinitis in Taiwan. Theophylline is primarily oxidized with high affinity by human cytochrome P450 (CYP)1A2, and has a narrow therapeutic index. PurposeThis study aimed to investigate the inhibition of human CYP1A2-catalyzed theophylline oxidation (THO) by XYS and its adverse effects in patients. MethodsHuman CYPs were studied in recombinant enzyme systems. The influence of concurrent XYS usage in theophylline-treated patients was retrospectively analyzed. ResultsAmong the major human hepatic and respiratory CYPs, XYS inhibitors preferentially inhibited CYP1A2 activity, which determined the elimination and side effects of theophylline. Among the herbal components of XYS decoction, Angelicae Dahuricae Radix contained potent THO inhibitors. Furanocoumarin imperatorin was abundant in XYS and Angelicae Dahuricae Radix decoctions, and non-competitively inhibited THO activity with Ki values of 77‒84 nM, higher than those (20‒52 nM) of fluvoxamine, which clinically interacted with theophylline. Compared with imperatorin, the intestinal bacterial metabolite xanthotoxol caused weaker THO inhibition. Consistent with the potency of the inhibitory effects, the docking analysis generated Gold fitness values in the order−fluvoxamine > imperatorin > xanthotoxol. During 2017‒2018, 2.6 % of 201,093 theophylline users consumed XYS. After inverse probability weighting, XYS users had a higher occurrence of undesired effects than non-XYS users; in particular, there was an approximately two-fold higher occurrence of headaches (odds ratio (OR), 2.14; 95 % confidence interval (CI), 1.99‒2.30; p < 0.001) and tachycardia (OR, 1.83; 95 % CI, 1.21‒2.77; p < 0.05). The incidence of irregular heartbeats increased (OR, 1.36; 95 % CI, 1.07‒1.72; p < 0.05) only in the theophylline users who took a high cumulative dose (≥ 24 g) of XYS. However, the mortality in theophylline users concurrently taking XYS was lower than that in non-XYS users (OR, 0.24; 95 % CI, 0.14‒0.40; p < 0.001). ConclusionXYS contains human CYP1A2 inhibitors, and undesirable effects were observed in patients receiving both theophylline and XYS. Further human studies are essential to reduce mortality and to adjust the dosage of theophylline in XYS users.

Electrochemical determination of theophylline using a nickel ferrite/activated carbon-modified electrode

In this work, a nanocomposite based on nickel ferrite/activated carbon (NiF/AC) was used to modify a highly sensitive electrochemical sensor for the quantification of theophylline (TPL) in pharmaceutical tablets. The synthesized materials were characterized using x-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive x-ray spectroscopy-elemental mapping and surface area analysis via the Brunauer–Emmett–Teller method. Cyclic voltammetry was employed to study the electrocatalytic properties of the NiF/AC-GCE toward the oxidation of TPL. The dependence of the electrochemical response on the scan rate and pH was also investigated, and the working parameters were optimized. The linear range of the established electrochemical biosensor was from 0.5 to 5 μM (R2 = 0.997), with a detection limit of 0.21 μM. The present method was tested using three pharmaceutical formulation standard samples with good accuracy and acceptable recovery. Thus, it is a promising candidate for the determination of TPL in pharmaceutical formulations.

Identification of the perpetrator imperatorin in Xin-yi-san-theophylline interaction: observed and predicted herb-drug interaction in rats.

Theophylline is a bronchodilator with a narrow therapeutic index and primarily metabolised by cytochrome P450 (CYP) 1A2. Xin-yi-san (XYS) is a herbal formula frequently used to ameliorate nasal inflammation. This study aimed to investigate the effects of XYS and its ingredient, imperatorin, on theophylline pharmacokinetics in rats. The kinetics of XYS- and imperatorin-mediated inhibition of theophylline oxidation were determined. Pharmacokinetics of theophylline were analysed. Comparisons were made with the CYP1A2 inhibitor, fluvoxamine. XYS extract and its ingredient, imperatorin, non-competitively inhibited theophylline oxidation. Fluvoxamine (50 and 100 mg/kg) and XYS (0.5 and 0.9 g/kg) significantly prolonged the time to reach the maximum plasma concentration (tmax) of theophylline by 3-10 fold. In a dose-dependent manner, XYS and imperatorin (0.1-10 mg/kg) treatments significantly decreased theophylline clearance by 27-33% and 19-56%, respectively. XYS (0.9 g/kg) and imperatorin (10 mg/kg) significantly prolonged theophylline elimination half-life by 29% and 142%, respectively. Compared with the increase (51-112%) in the area under curve (AUC) of theophylline by fluvoxamine, the increase (27-57%) by XYS was moderate. XYS decreased theophylline clearance primarily through imperatorin-suppressed theophylline oxidation. Further human studies are essential for the dose adjustment in the co-medication regimen.

EDTA salt modified carbon paste electrode for square wave voltammetric determination of theophylline in pharmaceutical tablet formulation.

In this study, a square wave voltammetric method for determination of theophylline in tablet formulation based on EDTA salt modified carbon paste electrode is presented. CV, FT-IR, and EIS results confirmed modification of the carbon paste with EDTA salt. In contrast to the unmodified carbon paste electrode, the modified carbon paste electrode showed irreversible oxidation of theophylline with considerable current enhancement. Investigation of the effect of scan rate on the Ip and Ep response of the modified electrode for theophylline revealed predominantly diffusion controlled oxidation kinetics. Under the optimized conditions, square wave oxidative peak current of theophylline in pH 7.0 PBS showed linear dependence on concentration in the range 10–200 μM with determination coefficient (R2), limit of detection, and limit of quantification of 0.99782, 0.0257 μM, and 0.0857 μM, respectively. Detection of an amount of theophylline in the analyzed tablet formulation with 1.85% error from its nominal content (120 mg/tablet) confirmed the accuracy of the developed method. Spike and interference recovery results of 98.59%, and 95.7–100%, respectively validated the applicability of the developed method for determination of theophylline content in tablet samples.

Poly(aquachlorobis(1,10–phenanthroline)copper(II)iodidemonohydrate)/GCE for simultaneous determination of caffeine and theophylline in human serum, tea, and tablet samples

This paper presents metal complex based polymer film modified electrode for simultaneous determination of caffeine, and theophylline. Potentiodynamic fabrication of poly(aquachlorobis(1,10– phenanthroline)copper(II)iodidemonohydrate) modified glassy carbon electrode (poly(ACP 2 CuIH)/GCE) was verified using cyclic voltammetric and electrochemical impedance spectroscopic techniques. In contrast to the unmodified glassy carbon electrode, the poly(ACP 2 CuIH)/GCE in equi-molar mixture of theophylline and caffeine revealed sufficiently separated oxidative peaks with much enhanced peak current showing electrocatalytic property of the polymer film towards the oxidation of theophylline and caffeine. Under optimized solution pH and square wave voltammetric parameters, oxidative peak current response of poly(ACP 2 CuIH)/GCE showed linear dependence on the concentration of caffeine and theophylline in the concentration range 1.0–200.0 µM with limit of detection 8.92 × 10 -3 µM for theophylline, and 1.02 × 10 -2 µ M for caffeine. Spike recovery in the range 97.0-102.4% for theophylline, and 95.4-100.0% for caffeine, interference recovery in the range 96.0–101.0% for theophylline, and 95.7–104.3% for caffeine, agreement of the detected amounts of theophylline and caffeine in tablet samples with the nominal values, and stability of the modified electrode all validated the developed method for simultaneous determination of theophylline and caffeine in wide range of real samples. The method was applied for simultaneous determination of both theophylline and caffeine in three tea brands (Black lion, Addis, and Wush wush), pharmaceutical tablet brands (Panadol extra, and Theodrine), and human blood serum samples making the method an excellent candidate.

Electrocatalytic Oxidation Study of Theophylline on a Copper Nanoparticles-Modified, Carbon Paste Electrode Based on Cyclic Voltammetry

In this study, the Cu nanoparticles were prepared by reducing CuSO4. These particles were used in making copper nanoparticles modified carbon paste electrode (nano-CPE). The electrochemical characteristics of this electrode (nano-CPE) were investigated. The results of the electrocatalytic oxidation of theophylline (TP) on nano-CPE, using the cyclic voltammetry technique showed that nano-CPE, has more reactivity and more effective surface area, as compared to the unmodified carbon paste electrode (un-CPE). The investigation of voltammograms obtained from oxidation of TP at different scan rates on the nano-CPE confirmed a cyclic mediated redox mechanism followed by reducing Cu(III) which is a chemical reaction (EC mechanism). These species formed in more positive potentials and act as a redox intermediate for TP oxidation. There was a linear relationship between the oxidation peak current and the square root of the scan rate, showing that the oxidation reaction of TP at nano-CPE might be due to the diffusion-controlled process.

A novel electrochemical sensor for selective determination of theophylline in pharmaceutical formulations

Theophylline (TPN) is a medication commonly used in treatment of chronic asthma disorder. However, it is associated with a number of known troublesome side effects, hence, the need to monitor its concentration levels in pharmaceutical formulations. In this work, a nanocomposite based on ZnONPs – MWCNTs – Cyt c (zinc oxide nanoparticles – multiwalled carbon nanotubes – Cytochrome c) were used in the modification of a highly sensitive electrochemical sensor for quantification of TPN in pharmaceutical formulations. The synthesized ZnONPs, ZnONPs-MWCNTs and ZnONPs-MWCNTs-Cyt c were characterized using Thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Transmission electron microscopy (TEM), surface area analysis by Brunauer–Emmett–Teller (BET) and electrochemical impedance spectroscopy (EIS). Cyclic voltammetry was employed to study electro-catalytic properties of ZnONPs-MWCNTs-Cyt c-GCE towards oxidation of TPN. The dependence of peak currents and potentials on scan rates and pH were also investigated and the working parameters were optimized. Remarkably, ZnONPs-MWCNTs-Cyt c-GCE exhibited improved anodic peak currents as compared to ZnONPs-MWCNTs-GCE, MWCNTs-GCE and bare GCE for 0.1 M TPN at 1.0 V vs. Ag/AgCl. The linear range of the established electrochemical biosensor was from 0.4 to 15 µM (R2 = 0.9903) with detection limit of 0.0012 µM, thus making it a better candidate for the detection of TPN in pharmaceutical formulation.

Eco-friendly synthesis of aloe vera plant extract decorated iron tungstate nanorods immobilized Nafion for selective and sensitive determination of theophylline in blood serum, black tea and urine samples

Abstract This paper describes a selective and sensitive detection of bronchodilators drug (theophylline) using aloe vera plant extract decorated iron tungstate nanorods (AFW) immobilized Nafion (Nf) modified glassy carbon electrode (GCE) (AFW/Nf/GCE). The AFW was synthesized by the co-precipitation method and characterized by UV-visible spectroscopy, x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), elemental analysis (EDX) and electrochemical studies. Interestingly, the oxidation of theophylline with AFW/Nf/GCE displayed, a superior electrocatalytic activity, when compared with bare GCE and iron tungstate (FW) modified GCE. Besides, oxidation of theophylline in electrochemical sensor revealed that the tremendous current response linear ranges from 0.1-160μM and low detection limit (LOD) 0.0028μM. The electrochemical sensor studies showed a tremendous selectivity in biological and food samples. Besides, it showed manifested stability and reproducibility. The proposed method has been applied for the selective determination of theophylline in real samples such as human serum, black tea, and urine samples.

Electrochemical Oxidation of Theophylline in Organic Solvents: HPLC‐PDA‐ESI‐MS/MS Analysis of the Oxidation Products

AbstractThe electrochemical oxidation of theophylline was investigated by controlled potential electrolysis in two different organic solvents and in water for comparison. The anodic oxidation was monitored by cyclic voltammetry in situ and UV‐Vis spectrophotometry ex situ and the final electrolyzed solutions were analyzed by tandem mass spectrometry after chromatographic separation with an HPLC‐PDA‐ESI‐MS/MS system. The main oxidation products evidenced as the main diode array chromatographic peaks were tentatively assigned to dimeric forms of theophylline, two of which have never been reported before, on the base of retention time, UV‐Vis spectrum, m/z ratio in both positive and negative ESI modes and fragmentation pattern. Two chemical paths following the primary mono‐electronic anodic oxidation of theophylline to the final evidenced oxidation products have been proposed.

Oxidation of theophylline by Ferrate (VI) and formation of disinfection byproducts during subsequent chlorination

Abstract This work investigated the degradation of theophylline (TPL) of environmental concerns by ferrate (Fe(VI)) and the effect of Fe(VI) pre-oxidation on formation of disinfection by-products (DBPs) from TPL during subsequent chlorination. TPL exhibited an appreciable reactivity toward Fe(VI) with apparent second-order rate constants (kapp) ranging from 5.7 to 2480 M−1 s−1 in the pH range from 6 to10. The pH-dependence of kapp could be well simulated by a proposed kinetic model including the generation of an intermediate between Fe(VI) and TPL. A tentative transformation pathway was proposed including the hydroxylation of the imidazole ring as well as the cleavage of C N and C N bonds. The presence of humic acid (HA) apparently reduced the degradation rates of TPL with Fe(VI) even considering the competitive consumption for Fe(VI) by HA. A two channel model successfully explained the effect of HA on the TPL degradation by Fe(VI), where oxidation intermediate of TPL was either reduced back to parent by HA or irreversibly transformed to final products. Compared to direct chlorination of TPL, Fe(VI) pre-oxidation at low dosage enhanced the formation of carbonaceous disinfection by-products (C-DBPs, e.g., 1,1-dichloro-2-propanone, 1,1,1-trichloro-2-propanone, and dichloroacetic acid) during subsequent chlorination. However, a high dosage of Fe(VI) pre-oxidation could decrease the formation of C-DBPs and nitrogenous disinfection by-products (N-DBPs, e.g., dichloroacetonitrile, trichloronitromethane). The effectiveness of Fe(VI) for elimination of TPL in natural water was confirmed, and Fe(VI) pre-oxidation at high doses reduced the formation of DBPs in natural water during subsequent chlorination.

Electrochemical behavior of theophylline at methylene blue dye modified electrode and its analytical application

Electrochemical oxidation of theophylline was investigated at the surface of carbon paste electrode with methylene blue dye as an electron mediator. The electrode surface was characterized by atomic force microscopy (AFM) and XRD. Methylene blue a cationic dye is an excellent redox mediator. Cyclic voltammetric technique was used to investigate the electrochemical behaviour of modified electrode. There was enormous increase in the peak current as compared with bare electrode. The effect of pH on oxidation behaviour of theophylline in the pH range of 3.0-11.2 was carried out. Electrochemical oxidation of theophylline was predominant in pH 3.0. In addition, the effect of scan rate variation was used to calculate the number of electrons transferred and heterogeneous rate constant. Further, a possible electrode reaction mechanism was proposed. Differential pulse voltammetric method in the linear range 0.2 -10 µM was performed and limit of detection and quantification were calculated 2.25 nM and 7.52 nM respectively. The developed electrode was further successfully employed for the determination of theophylline in pharmaceutical and human urine samples.

Nitrogen-doped carbon nanotubes decorated poly (L-Cysteine) as a novel, ultrasensitive electrochemical sensor for simultaneous determination of theophylline and caffeine

In present study, a novel and facile electrochemical sensor based on glassy carbon electrode (GCE) modified with nitrogen-doped carbon nanotubes (N-CNT) decorated with poly (L-Cysteine) (PLCY) were fabricated and applied for the simultaneous voltammetric determination of theophylline (THEO) and caffeine (CAF). The morphology and structure of multilayer film modified on the surface of glassy carbon electrode were investigated successfully by Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and Raman Spectroscopy. And the properties of the modified electrode were investigated by Chronocoulometry (CC), Cyclic Voltammetry (CV) and Differential Pulse Voltammetry (DPV) were utilized to investigate the electrochemical behavior of THEO and CAF on the composite film modified electrode. The results showed that the determination towards THEO and CAF can be operated at the same potential window with the oxidation current peak separated and non-interfering respectively. Compared to the bare GCE, the PLCY/N-CNT/GCE can signally meliorate the electrocatalytic activity towards the oxidation of THEO and CAF with a remarkably increase in the anodic peak currents of 495.94% and 465.48%. Under the optimal conditions, the fabrication multilayer film sensor had excellent performances in determination towards THEO and CAF with a wide linear dynamic range from 0.10 to 70.0μM and 0.40–140.0μM, low detection limit (S/N = 3) of 0.033μM and 0.20μM, respectively. The PLCY/N-CNT/GCE sensor also had advantages as easy-made, high-sensitivity, stability and reproducibility. Moreover, it was successfully used to analyze the THEO and CAF in green tee, oral theophylline sustained release tablets and energy drink sample with a satisfactory result.

Anodic Oxidation of Caffeine and Theophylline in Glacial Acetic Acid

AbstractThe anodic oxidation of caffeine and theophylline has been carried out at a controlled potential in a one compartment cell using glassy‐carbon as the anode, platinum as the cathode and glacial acetic acid/sodium acetate as solvent‐supporting‐electrolyte (SSE). The oxidation of caffeine yields 1,3,8‐trimethyl‐1,3,6,8‐tetrazaspiro[4.4]nonane‐2,4,7,9‐tetrone and (4‐acetoxy‐1,3,7‐trimethyl‐2,6,8‐trioxo‐9H‐purin‐5‐yl) acetate. Despite of the different structure, the oxidation of theophylline leads only to the same spiro compound 1,3,8‐trimethyl‐1,3,6,8‐tetrazaspiro[4.4]nonane‐2,4,7,9‐tetrone as in the case of caffeine. The structure of both compounds is described and the reaction mechanism is discussed.

Tungsten Disulfide Nano-Flowers/Silver Nanoparticles Composites Based Electrochemical Sensor for Theophylline Determination

Tungsten disulfide (WS2) nano-flowers/silver nanoparticles (Ag NPs) composites modified glassy carbon electrode (GCE) was prepared by a simple procedure and then successfully used to determine theophylline (TP). In this synthesis process, Ag NPs were directly synthesized on the surface of WS2 nano-flowers. The composites were characterized by scanning electron microscopy (SEM) images, transmission electron microscopy (TEM) and X-ray diffraction (XRD). The electrochemical oxidation of theophylline was studied by using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Compared with the bare GCE and WS2/GCE, the WS2 nano-flowers/Ag NPs composites/GCE could effectively improve the oxidation of theophylline, due to its high surface area and excellent electric conductivity property. Under the optimized experimental conditions, the electrochemical sensor exhibited wide linear range of 0.05 to 150 μM with detection limit of 3 nM (S/N = 3). Furthermore, the sensor showed high sensitivity, good selectivity, good reproducibility and long-term stability to theophylline detection. At the same time, the fabricated electrode was successfully applied for the determination of theophylline in tea samples and pharmaceutical tablets with satisfying results. These results demonstrated that WS2 nano-flowers/Ag NPs composites were promising substrate for the development of high-performance electrochemical biosensor.

Selective electrochemical sensor for theophylline based on an electrode modified with imprinted sol–gel film immobilized on carbon nanoparticle layer

A novel electrochemical sensor based on an imprinted hybrid sol–gel film for selective and sensitive determination of theophylline was developed. The imprinted hybrid sol–gel film was prepared by using a new organosilane synthesized as a functional precursor, theophylline as a template and tetraethoxysilane as a matrix forming precursor. The mixture was allowed to hydrolyze, and then spin coated on glassy carbon electrode covered by carbon nanoparticles with sulfonic acid groups that were introduced for immobilization of imprinted sol–gel film and for enhancement of electronic transmission. The morphology and performance of the imprinted film were investigated in detail by scanning electron microscopy, FTIR Spectroscopy, cyclic voltammetry and differential pulse anodic stripping voltammetry. Molecularly imprinted sol–gel was employed to achieve a suitable conformation for electrochemical oxidation of theophylline and also to improve the selectivity of the sensor. The results showed that the imprinted film exhibited selectivity toward theophylline compared to the random sol–gel film prepared in the absence of the template. The imprinted sensor was also successfully employed to detect theophylline in a drug sample.

Detection of theophylline utilising portable electrochemical sensors

The electrochemical oxidation of theophylline (TP) is investigated utilising screen-printed electrodes. Through thorough investigation of pH, we propose a reaction mechanism, finding that the oxidation of TP is stable over a wide pH range, in particular under acidic conditions. Conversely under alkaline conditions, theophylline fouls the electrode surface. The screen-printed carbon sensors are applied towards the electroanalytical sensing of TP with a remarkable amount of success in aqueous solution at physiological pH. The screen-printed sensors have been shown to be applicable to the detection of TP at unharmful, medicinally relevant (55-110 μM), and toxic concentrations in aqueous media at physiological pH. Thus this work presents a proof-of-concept approach towards TP detection utilising sensors commonly implemented in point-of-care applications.

Hydroxyl radical induced oxidation of theophylline in water: a kinetic and mechanistic study.

Oxidative destruction and mineralization of emerging organic pollutants by hydroxyl radicals (˙OH) is a well established area of research. The possibility of generating hazardous by-products in the case of ˙OH reaction demands extensive investigations on the degradation mechanism. A combination of pulse radiolysis and steady state photolysis (H2O2/UV photolysis) followed by high resolution mass spectrometric (HRMS) analysis have been employed to explicate the kinetic and mechanistic features of the destruction of theophylline, a model pharmaceutical compound and an identified pollutant, by ˙OH in the present study. The oxidative destruction of this molecule, for intermediate product studies, was initially achieved by H2O2/UV photolysis. The transient absorption spectrum corresponding to the reaction of ˙OH with theophylline at pH 6, primarily caused by the generation of (T8-OH)˙, was characterised by an absorption band at 330 nm (k2 = (8.22 ± 0.03) × 10(9) dm(3) mol(-1) s(-1)). A significantly different spectrum (λmax: 340 nm) was observed at highly alkaline pH (10.2) due to the deprotonation of this radical (pKa∼ 10.0). Specific one electron oxidants such as sulphate radical anions (SO4˙(-)) and azide radicals (N3˙) produce the deprotonated form (T(-H)˙) of the radical cation (T˙(+)) of theophylline (pKa 3.1) with k2 values of (7.51 ± 0.04) × 10(9) dm(3) mol(-1) s(-1) and (7.61 ± 0.02) × 10(9) dm(3) mol(-1) s(-1) respectively. Conversely, oxide radicals (O˙(-)) react with theophylline via a hydrogen abstraction protocol with a rather slow k2 value of (1.95 ± 0.02) × 10(9) dm(3) mol(-1) s(-1). The transient spectral studies were complemented by the end product profile acquired by HRMS analysis. Various transformation products of theophylline induced by ˙OH were identified by this technique which include derivatives of uric acids (i, iv & v) and xanthines (ii, iii & vi). Further breakdown of the early formed product due to ˙OH attack leads to ring opened compounds (ix-xiv). The kinetic and mechanistic data furnished in the present study serve as a basic frame work for the construction of ˙OH induced water treatment systems as well as to understand the biological implications of compounds of this kind.

Voltammetric determination of theophylline in pharmaceutical formulations using aligned carbon nanotubes (ACNTs) film modified electrode

A novel rapid, convenient and sensitive electrochemical method has been described for the determination of theophylline in pharmaceutical formulations, based on the extraordinary properties of an aligned carbon nanotubes (ACNTs) thin film. The voltammetric results suggest that the ACNTs-coated glass carbon electrode can exhibit excellent electrochemical activity for direct electrochemical oxidation of theophylline. Various experimental parameters such as solution pH value, amount of ACNTs suspension, accumulation conditions and scan rate were optimized for the determination of theophylline. Furthermore, it was found that the peak current increased linearly with the concentration of theophylline in the range of 8.0 × 10−8−1.0 × 10−5 M and the detection limit was 1.6 × 10−8 M using differential pulse voltammetry. This newly proposed method has been applied successfully to the determination of theophylline in drugs.

High sensitive determination of theophylline based on gold nanoparticles/l-cysteine/Graphene/Nafion modified electrode

In the work described on this paper, a gold nanoparticles (GNP)/l-cysteine (l-cys)/Graphene (Gr)/Nafion composite film modified glass carbon electrode (GCE) was fabricated and characterized. The modified electrode showed excellent electrocatalytic activity towards the oxidation of theophylline (TP) in 0.1molL−1 H2SO4 medium. Differential pulse voltammetry (DPV) was used for the determination of TP. Under the optimum conditions, the peak current of TP was proportional to its concentration at the range of 4.0×10−9 to 6.0×10−5molL−1 with a detection limit 4.0×10−10molL−1. The newly developed method was successfully applied for the determination of TP in tea samples and pharmaceutical tablets with good percentage of recoveries.

Voltammetric behavior of theophylline and its determination at multi-wall carbon nanotube paste electrode

The voltammetric behavior of theophylline was investigated using cyclic and differential-pulse voltammetric techniques. The cyclic voltammetric results indicate that multi-wall carbon nanotube paste electrode can remarkably enhance electrocatalytic activity toward the oxidation of theophylline in pH 3.0 phosphate buffer solution than the carbon paste electrode. The oxidation of theophylline was observed to be a two-electron process, irreversible with diffusion character. Effects of anodic peak potential (Ep), anodic peak current (Ip) and heterogeneous rate constant (ko) have been discussed. Under optimal conditions, the anodic peak current was proportional to theophylline concentration in the range of 2.0×10−6 to 1.5×10−4M with a detection limit of 1.97×10−8M using differential pulse voltammetry. The proposed method was employed to determine theophylline in pharmaceutical formulations and urine as a real sample.