The electrochemistry and determination of Ligustrazine hydrochloride

Ligustrazine is one of the active ingredients contained in Ligusticum chuanxiong Hort. (Umbelliferae), which is widely used in traditional Chinese medicine for the treatment of cardiovascular problems. In this work, the electrochemistry of Ligustrazine hydrochloride (LZC) and its determination are investigated. The detection limit is estimated to be 8.0×10^–8 M, with three linear ranges from 1.0×10^–6 to 1.0×10^–4 M, 1.0×10^–4 to 5.0×10^–4 M, and 6.5×10^–4 to 1.6×10^–3 M. The method has been proved to be highly sensitive, selective, and stable, and has been successfully applied to determining LZC in LZC injections.     

Electrogenerated Chemiluminescence (ECL) Determination of Ephedrine with a Self-Assembly Multilayer Ni(II)-Polyluminol Modified Electrode

By combining the layer-by-layer (LBL) self-assembly technique with the electrochemical polymerization method, multilayer Ni(II)-polyluminol films were modified on the surface of a vaseline-impregnated graphite electrode. It was found that, compared with an electrode modified by direct electrochemical polymerization, this modified electrode offered a suitable ECL reaction micro-environment created by the special multilayer films, which was beneficial to the ephedrine hydrochloride enhancing effect for luminol ECL intensity. The ECL enhancing effect of ephedrine hydrochloride on the electro-oxidation luminol was improved on this modified electrode. Based on this finding, a new sensitive ECL method was developed for ephedrine hydrochloride determination under the optimal conditions. At the same time, a new idea is proposed for improving the analytical performance of the luminol ECL system by modifying the ECL reaction micro-environment with the layer-by-layer self- assembly method. Under the optimum experimental conditions, the ephedrine hydrochloride concentration in the range of 2.0 × 10⁻⁸–7.0 × 10⁻⁶ mol L⁻¹ was proportional to the enhanced ECL signal, and it offered an 8.0 × 10⁻⁹ mol L⁻¹ detection limit for ephedrine hydrochloride.     

Electrochemical and Spectroelectrochemical Studies on Pyridoxine Hydrochloride Using a Poly(methylene blue) Modified Electrode

The electrochemical redox processes of pyridoxine hydrochloride (VB₆) at a poly(methylene blue) film modified glass carbon electrode (PMBE) in a phosphate buffer solution (PBS, pH 8.0) were studied by cyclic voltammetry. The VB₆ electrode reaction with quasi‐reversible characteristics was diffusion‐controlled at low scan rates and adsorption‐controlled at high scan rates. The anodic peak current positive to 0.6 V (vs. SCE) was found to be proportional to the concentration of VB₆ in the range of 0.010 to 1.03 mg?mL^?1 with a detection limit of 1.34 μg mL^?1. Fluorescence and UV‐vis absorption spectroelectrochemical measurements suggest that the pyridine ring was not destroyed over the potential range from ?0.8 to 1 V (vs. SCE), and the electrocatalytic generation of pyridoxal was anodically started at 0.57 V.     

Non-equilibrium determination of metoclopramide and tetracaine hydrochloride by sequential injection spectrophotometry

A new sequential injection spectrophotometric method was proposed for the determination of metoclopramide and tetracaine hydrochloride. The method was based on the detection of an unstable red intermediate compound resulting from the reaction of metoclopramide or tetracaine hydrochloride with potassium dichromate, in the presence of sodium oxalate, in sulfuric acid solution. The related reaction mechanisms of this new method have been studied. The experimental conditions were optimized for the stopped-flow and continuous-flow sequential injection models. For continuous flow, the linear range for determination of metoclopramide, the detection limit and the sampling frequency were 13-130 μg ml⁻¹, 9.4 μg ml⁻¹ and 40 samples per hour, respectively. For stopped flow, they were 3-42 μg ml⁻¹, 1.0 μg ml⁻¹ and 18 h⁻¹, respectively. Adopting the continuous-flow model for tetracaine hydrochloride, the linear range was 25-300 μg ml⁻¹, and the detection limit was 18.0 μg ml⁻¹ with sampling frequency of 40 h⁻¹. This method has been used to determine metoclopramide and tetracaine hydrochloride in pharmaceutical preparations, and the results are compared with those determined by the pharmacopoeia method. Statistical analysis reveals that there was no evidence of significant difference between the methods.     

Infrared and Raman Study of Benzocaine Hydrochloride

The infrared and laser Raman spectra (100-4000 cm¹) of benzocaine hydrochloride were recorded and its vibrations analysed. A theoretical spectrum with the AM1 semiempirical method was calculated. An infrared study with the temperature was also made. From the experimental data, the torsion and inversion barriers of amine group were calculated.     

Determination of antazoline hydrochloride in rat plasma and excreta by reversed‐phase ion‐pair chromatography and its application to pharmacokinetics

A reversed‐phase ion pair chromatography method with liquid–liquid extraction analytical method was developed and validated for the determination of antazoline hydrochloride in plasma and excreta of rat. The aim of our study was to characterize the preclinical pharmacokinetics and excretion profiles of antazoline hydrochloride in rats after intravenous injection at the dose of 10 mg/kg. Plasma and excreta samples were extracted with ethyl acetate, and phenacetin was used as the internal standard. The result showed that the method is suitable for the quantification of antazoline hydrochloride in plasma and excreta samples. Analysis of accuracy (90.89–112.33%), imprecision (<7.1%) and recovery (>82.5%) showed adequate values. After a single intravenous administration at 10 mg/kg to rats, plasma concentration profile showed a relative fast elimination proceeding with a terminal elimination half‐life of 3.53 h. Approximately 61.8 and 14.2% of the administered dose were recovered in urine and bile after 72 and 24 h post‐dosing respectively; 5.9% of the administered dose was recovered in feces after 72 h post‐dosing. The above results show that the major elimination route is urinary excretion. Copyright © 2013 John Wiley & Sons, Ltd.     

Flow Injection Chemiluminescence Method for Nalbuphine Hydrochloride in Pharmaceutical Formulations Using Tris(2,2'-bipyridyl)ruthenium(II) Chloride-diperiodatocuprate(III) Reaction

Asensitive and selective method employing chemiluminescence(CL) coupled with flow injection(FI) is reported for nalbuphine hydrochloride(NAL) assay in pharmaceutical formulations. The enhancement effect of NAL on the CL reaction between tris(2,2'-bipyridyl)ruthenium(II) chloride-diperiodatocuprate(III) {Ru[(bpy)₃]²⁺-Cu(III) complex} in acidic medium is used as analytical measurement. The optimal conditions of the CL reaction were sulfuric acid 1.0×10^-3 mol/L, Ru[(bpy)₃]²⁺ 7.5×10^-5 mol/L, Cu(III)/Ag(III) complexes 4.0×10^-4/5.0×10^-4 mol/L, sample loop volume of 120 μL and flow rate of 2.5 mL/min. The sensitivities of the method in terms of detection(S/N=3) and quantification(S/N=10) limits are 5×10^-4 and 0.001 ppm(1 ppm=1 mg/L), respectively. The linear response of the instrument in the form of CL intensity with respect to NAL concentration is over the range 0.001-15.0 ppm(R²=0.9999) with relative standard deviation from 0.8% to 3.2% and injection throughput of 120 injection/h. The applications of the method include the quantitative analysis of NAL in pharmaceutical injection samples. Variations and the average results of the proposed method are not signi-ficantly different from the results of a reported method by applying F- and paired student t-test. The most likely CL reaction mechanism is written in accordance with spectrophotometric and CL studies.     

Permanent antimicrobial silicone rubber based on bonding guanidine polymers

Recently, silicone rubber (VMQ) was extensively used in household articles and medical devices. To develop a kind of safe and long‐term antimicrobial VMQ was of great significance. In this work, a kind of vinyl‐contained polyhexamethylene guanidine hydrochloride (VPHMG) was synthesized and used as antimicrobial additive for VMQ. With the increasing of VPHMG addition, the mechanical properties and antimicrobial properties of VMQ‐VPHMG were significantly improved. In particular, the antimicrobial rates against Escherichia coli and Staphylococcus aureus were higher than 99.99% as for 4 wt% of VPHMG addition. Moreover, the surface concentration of VPHMG as well as the antimicrobial rates revealed almost unchanged after being extracted by water and methanol. All the results indicated the vinyl‐contained VPHMG vulcanization and therefore provided the permanent antimicrobial performance for VMQ.     

A simple and high‐resolution HPLC‐PDA method for simultaneous quantification of local anesthetics in in vitro buccal permeation enhancement studies

A simple, isocratic, high‐resolution and prompt HPLC‐PDA method was developed and validated for the simultaneous quantification of prilocaine (PCL) and lidocaine (LCL) hydrochlorides in in vitro buccal iontophoresis‐driven permeation studies. A reversed‐phase C₁₈ column (250 mm x 4.6 mm, 3μm, 110Å) was used for the chromatographic separation. The mobile phase contained acetonitrile: 0.1M sodium phosphate buffer, pH 7.0 (1:1, v/v), plus 0.05% (v/v) diethylamine. The isocratic flow rate was set at 1 mL/min and the detection wavelength was 203 nm. PCL and LCL eluted in 8.9 min and 13 min, respectively, and the system suitability parameters varied within an acceptable range. The method was selective, sensitive, precise, accurate and robust, producing a linear plot at the concentration range of 0.25 to 10 µg/mL. The application of this method was demonstrated by a significant enhancement of the permeation of PCL and LCL with the application of iontophoresis (1 mA/cm² per 1 h) through isolated porcine esophageal epithelium. The amount of the drug retained in the epithelium also increased with the application of an electrical current. Copyright © 2015 John Wiley & Sons, Ltd.     

Bioactive Penta-Coordinated Diorganotin(Iv) Complexes of Pyridoxalimine Schiff Bases

Abstract

Diorganotin(IV) complexes of an extended system derived from the condensation of pyridoxal hydrochloride with 2-amino phenol (H₂L¹), 2-amino-4-methyl phenol (H₂L²), 2-amino-4-chloro phenol (H₂L³), 2-amino-4-nitro phenol (H₂L⁴), 1-amino-2-naphthol hydrochloride (H₂L⁵) have been synthesized by the reaction of dichlorodiorganotin(IV) in a 1:1 molar ratio with these ligands. Spectral studies (IR, ¹H, ¹³C, ¹¹⁹Sn NMR) along with physical data evidenced the formation of penta-coordinated species with the ligands acting as tridentate (ONO) with oxygen occupying the axial positions, and nitrogen at one of the equatorial positions. The ligands and their organotin complexes have been evaluated for antimicrobial activity against phytopathogenic fungi Candida albicans and Aspergillus niger at 25 ± 1 °C and bacteria Bacillus subtilis, Escherichia coli, and Staphylococcus aureus at 37 ± 1 °C. The activities of the ligands have been enhanced on complexation and the results indicate that they exhibit significant antimicrobial properties.

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