Effect of surfactants on the voltammetric response and determination of an antihypertensive drug

The effect of adding surface-active agents to electrolytes containing terazosin, an antihypertensive drug, on the voltammetric response of glassy carbon electrode was studied. The current signal due to the oxidation process was a function of the amount of terazosin, pH of the medium, type of surfactant, and accumulation time at the electrode surface. Two surfactants were used, an anionic type, sodium dodecyl sulfate (SDS) and a cationic type, cetyl trimethyl ammonium bromide (CTAB). Addition of SDS to the terazosin-containing electrolyte was found to enhance the oxidation current signal while CTAB showed an opposite effect. Beside the interfacial interaction of the surfactant with the electrode surface in reference to the bias applied potential and the charge of surfactant, terazosin-surfactant interaction in the electrolytic solution was found to be critical to the magnitude of current signal. Addition of SDS to terazosin-containing buffer solution resulted in a decrease in the drug absorption spectrum both in the ultra-violet and visible (UV-vis) regions. Moreover, NMR measurements showed considerable chemical shifts for the aromatic protons of the quinazolinyl moiety of the terazosin in presence of SDS. The affected aromatic protons are positioned next to the interacting protonated amino-group of the terazosin with the charged sulfonate-group of SDS. On the other hand, addition of CTAB did not cause noticeable changes both to the UV-vis and NMR spectra of the drug. The use of SDS in the electrochemical determination of terazosin using linear sweep voltammetry and differential pulse voltammetry at solid glassy carbon electrode enhanced the detection limit from 6.00 × 10⁻⁷ mol L⁻¹ in absence of surfactant to 4.58 × 10⁻⁹ mol L⁻¹ when present. The validity of using this method in the determination of drug active ingredient in urine samples and tablet formulations was also demonstrated.     

Determination of terazosin by cloud point extraction-fluorimetric combined methodology

A new sensitive and selective preconcentration-fluorimetric method for determination of terazosin based on its native fluorescence was developed. The analyte, initially present in aqueous matrix, was treated with an extractive non-ionic surfactant solution and separated by the clouding phenomenon. The optimum analytical conditions for terazosin assay were established. Under these conditions, linear calibration curves were obtained over the range of 1 × 10⁻⁵ to 7.0 μg mL⁻¹ with detection and quantification limits of 1.11 × 10⁻⁵ and 3.7 × 10⁻⁵ μg mL⁻¹, respectively. Additionally, the binding constant (K_B) for the terazosin-PONPE 7.5 system was determined given a value of 1028 L mol⁻¹. The developed coupled methodology, which thoroughly satisfies the typical requirements for pharmaceutical control processes, was proved to be appropriate for monitoring terazosin in actual pharmaceutical formulations and biological fluid sample. The results were validated by recovery test and by comparison with other reported methods, being highly satisfactory.     

A Facile Synthesis of [Tetrahydrofuran‐3H] Terazosin

Abstract

An efficient synthesis of [³H] terazosin at high specific activity from prazosin is described.     

Chiral Separation of Esmolol and Terazosin by Cyclodextrinmodified Capillary Zone Electrophoresis

IntroductionTheincreasingnecessity0fpharmacologicalresearchforchiraldrugshasrenderedchiralseparationanactiveareaincaPillaryelectroph0resis(CE)today.Variousmodes0fCE,includingcaPillaryzoneelectroph0resis(CZE),micellarelectrokineticchromatography(MEKC),caPillarygelelectrophoresis(CGE)andcapillaryisotachophoresis(CITP),havebeenappliedforthispurp0se',amongwhichCZEisthemostpopularoneforitshighefficiency,lowexpenseandeaseofoperation.Forsuccessfulchiralseparati0ninCZE,theselectortypeisofcr…     

Direct high-performance liquid chromatography enantioseparation of terazosin on an immobilised polysaccharide-based chiral stationary phase under polar organic and reversed-phase conditions

High-performance liquid chromatography (HPLC) enantioseparation of terazosin (TER) was accomplished on the immobilised-type Chiralpak IC chiral stationary phase (CSP) under both polar organic and reversed-phase modes. A simple analytical method was validated using a mixture of methanol–water–DEA 95:5:0.1 (v/v/v) as a mobile phase. Under reversed-phase conditions good linearities were obtained over the concentration range 8.76–26.28 μg mL⁻¹ for both enantiomers. The limits of detection and quantification were 10 and 30 ng mL⁻¹, respectively. The intra- and inter-day assay precision was less than 1.66% (RSD%). The optimised conditions also allowed to resolve chiral and achiral impurities from the enantiomers of TER. The proposed HPLC method supports pharmacological studies on the biological effects of the both forms of TER and analytical investigations of potential drug formulations based on a single enantiomer. At the semipreparative scale, 5.3 mg of racemic sample were resolved with elution times less than 12 min using a mobile phase consisting of methanol–DEA 100:0.1 (v/v) and both enantiomers were isolated with a purity of ≥99% enantiomeric excess (ee). The absolute configuration of TER enantiomers was assigned by comparison of the measured specific rotations with those reported in the literature.     

A validated stripping voltammetric procedure for quantification of the anti-hypertensive and benign prostatic hyperplasia drug terazosin in tablets and human serum

The electrochemical behavior of terazosin at the hanging mercury drop electrode was studied in Britton-Robinson buffer (pH 2-11), acetate buffer (4.5-5.5), and in 0.1 M solution of each of sodium sulfate, sodium nitrate, sodium perchlorate and potassium chloride as supporting electrolytes. The square-wave adsorptive cathodic stripping voltammogram of terazosin exhibited a single well-defined two-electron irreversible cathodic peak which may be attributed to the reduction of CO double bond of the drug molecule. A fully validated, simple, high sensitive, precise and inexpensive square-wave adsorptive cathodic stripping voltammetric procedure was described for determination of terazosin in bulk form, tablets and human serum. A mean recovery for 1×10⁻⁸ M terazosin in bulk form, following preconcentration onto the hanging mercury drop electrode for 60 s at a −1.0 V (versus Ag/AgCl/KCl_s), of 99±0.7% (n=5) was obtained. Limits of detection (LOD) and quantitation (LOQ) of 1.5×10⁻¹¹ and 5×10⁻¹¹ M bulk terazosin were achieved, respectively. The proposed procedure was successfully applied to determination of the drug in its Itrin^® tablets and human serum samples. The achieved LOD and LOQ of the drug in human serum samples were 5.3×10⁻¹¹ and 1.8×10⁻¹⁰ M THD, respectively. The pharmacokinetic parameters of the drug in human plasma were estimated as: C_max=77.5 ng ml⁻¹, t_max=1.75 h, AUC_0-t=602.3 ng h ml⁻¹, K_e=0.088 h⁻¹ and t_1/2=11.32 h) which are favorably compared with those reported in literature.     

Spectrophotometric and Spectrofluorimetric Methods for the Determination of Terazosin in Dosage Forms

Five simple and accurate methods are presented for the determination of terazosin (TZ) in tablets. These methods are based on: the direct measurements of the first and second derivative spectra of samples (A), the reaction of TZ with chloranil (CH) in aqueous solution of pH 9 to give an intense yellow color measured at 340 nm (B), the reaction of the drug with mercurochrome (MER) in aqueous alkaline medium to give an intense red color measured at 543 nm (C), the formation of an ion-pair salt between the drug and bromocresol purple (BCP) with subsequent absorbance measurements at 412 nm (D), and a sensitive fluorimetric method (E). The latter method was extended to determine TZ in presence of its degradation products.     

Fabrication of Electrochemical Sensor Based on Layered Double Hydroxide/Polypyrrole/Carbon Paste for Determination of an Alpha‐adrenergic Blocking Agent Terazosin

New insights into the design of highly sensitive, carbon‐based electrochemical sensors are presented in this work. This was achieved by exploring the interesting properties of conductive (Mg/Al) layered double hydroxide‐dodecyl sulphate/polypyrrole nanocomposites which were synthesized by in‐situ polymerization of pyrrole during the assembly of (Mg/Al) layered double hydroxide, and by employing the anionic surfactant dodecyl sulphate as a modifier. Changes in morphology and surface area of the nanocomposites occured as a result of change in pyrrole percentage. Under optimal conditions, the modified carbon paste electrode successfully achieved detection limits of 0.057 and 0.134 nmol L⁻¹ of Terazosin hydrochloride in pharmaceutical formulation and spiked human serum fluid, respectively. Moreover, the sensors are highly stable, reusable and free of interference by other commonly present excipients in drug formulations.     

Fluorescent quantification of terazosin hydrochloride content in human plasma and tablets using second-order calibration based on both parallel factor analysis and alternating penalty trilinear decomposition

Two second-order calibration methods based on the parallel factor analysis (PARAFAC) and the alternating penalty trilinear decomposition (APTLD) method, have been utilized for the direct determination of terazosin hydrochloride (THD) in human plasma samples, coupled with the excitation-emission matrix fluorescence spectroscopy. Meanwhile, the two algorithms combing with the standard addition procedures have been applied for the determination of terazosin hydrochloride in tablets and the results were validated by the high-performance liquid chromatography with fluorescence detection. These second-order calibrations all adequately exploited the second-order advantages. For human plasma samples, the average recoveries by the PARAFAC and APTLD algorithms with the factor number of 2 (N = 2) were 100.4 ± 2.7% and 99.2 ± 2.4%, respectively. The accuracy of two algorithms was also evaluated through elliptical joint confidence region (EJCR) tests and t-test. It was found that both algorithms could give accurate results, and only the performance of APTLD was slightly better than that of PARAFAC. Figures of merit, such as sensitivity (SEN), selectivity (SEL) and limit of detection (LOD) were also calculated to compare the performances of the two strategies. For tablets, the average concentrations of THD in tablet were 63.5 and 63.2 ng mL⁻¹ by using the PARAFAC and APTLD algorithms, respectively. The accuracy was evaluated by t-test and both algorithms could give accurate results, too.     

Study of the interaction between terazosin and serum albumin: Synchronous fluorescence determination of terazosin

The interactions between terazosin and bovine serum albumin (BSA) were studied by spectrofluorimetry. The binding constants of terazosin with BSA were measured at different temperatures. The effects of various metal ions on the binding constants of terazosin with BSA were also studied. The optimum conditions of synchronous fluorometric determination of terazosin were studied and the method was successfully applied to the determination of terazosin added to serum and urine samples (3σ detection limit 0.21 mg l⁻¹).