Britton-Robinson Buffer pH Research Articles

Adsorptive stripping voltammetric determination of ofloxacin

The fluoroquinolone antibacterial agent ofloxacin was studied by adsorptive stripping voltammetry. Controlled interfecial accumulation of ofloxacin on a static mercury drop electrode in the hanging mercury drop mode provides high sensitivity. The linear concentration range was 0.079–197.5 μg ml−1 when using a 60-s preconcentration at −1 V vs. Ag/AgCl in Britton-Robinson buffer of pH 6.00. The detection limit of ofloxacin was 1 ng ml−1. The precision is excellent with a relative standard deviation of ca. 0.75% at a concentration of 0.848 μg ml−1.

Adsorptive stripping voltammetric determination of midazolam as a method for quality control

Controlled interfacial accumulation of the benzodiazepine midazolam at a hanging mercury drop electrode provides the basis for a highly sensitive and accurate adsorptive stripping voltammetric procedure. The response was linear in the range 1.9 × 10 −6− × 10 −9 M when using a 120-s preconcentration at −0.45 V vs. Ag/AgCl in Britton-Robinson buffer of pH 5.00. In this range the relative standard deviation was between 1.21 and 1.62%. The applicability of the method to pharmaceutical preparations is discussed.

Cyclic voltammetry of Tifluadom at a C18-modified carbon-paste electrode

Tifluadom, N-[5-(2-fluorophenyl)-2,3-dihydro-methyl-1H-1,4-benzodiazepine]-2-4-methyl-3-thiophene carboxamide, was determined by using a carbon-paste electrode modified with C18 μBondapak. Adsorption on the electrode served as a preconcentration step which improved the limit of detection. Preconcentration for 5 min (open circuit) gave a linear range of 2.2×10−7 M−4.5×10−6 M with a detection limit of 1.3×10−7 M (%C18=25, w/w) for Tifluadom in Britton-Robinson buffer pH 6. The determination of Tifluadom added to urine required no preliminary treatment; the detection limit was 1.3×10−6 M.

Oxidation of β-blocking agents—VII. Periodate oxidation of labetalol

The oxidation of labetalol with sodium metaperiodate is described. In spite of the bulky substituent on the amino group of labetalol, glycol cleavage of the molecule occurred. Spectrometric methods verified that the aromatic aldehyde formed was 2-hydroxy-5-formylbenzamide and that the amine was 1-methyl-3-phenylpropylamine. The polarographic behaviour of the aldehyde was examined as well. The half-wave potential in Britton—Robinson buffer pH 5.68 was −1.24 V. Direct linearity ( r = 0.9999) was observed between the diffusion current and the concentration of the aldehyde. Quantitation of labetalol was carried out polarographically by measuring the concentration of 2-hydroxy-5-formylbenzamide formed in the oxidation.

Differential-pulse polarographic determination of isonicotinic acid hydrazide, and analogous hydrazides in admixture

The differential pulse polarographic behaviour of isonicotinic, nicotinic and picolinic acid hydrazides in Britton-Robinson buffers of pH 2–11 is described. The isonicotinic compound (isoniazid) is best determined at pH 5–6 at a peak potential at ca. −1.0 V (vs. Ag/AgCl). This method was applied to analysis of tablets. At pH 9, the peak potentials are −1.22, −1.34 and −1.6 V, respectively, for the three hydrazides mentioned. Calibration graphs are linear in the range 10 −6−5×10 −4 M with relative standard deviations of 1.4–2.5%.

Direct determination of lead in blood by differential pulse stripping voltammetry

A simple and rapid method for determination of lead in blood by differential pulse stripping voltammetry (DPS) without preliminary mineralization of the sample, is described. Lead determination was performed in native samples of blood in the electrolyte of Britton-Robinson buffer (pH 5–5.5). The proposed method is shown to be reproducible and in good agreement with the reference technique AAS used on mineralized blood samples. Our results indicate that differential pulse stripping voltammetry is a reliable, rapid and highly sensitive method for blood lead analysis.

Coulometric microdetermination of nitrite via diazotization of 1-amino-4-naphthalenesulfonic acid

A controlled-potential coulometric method for the trace determination of nitrite is described. It is based on the formation of a diazonium salt with 1-amino-4-naphthalenesulfonic acid in a Britton-Robinson buffer (pH 1.5). The method is characterized by a high degree of accuracy and by an experimental detection limit of 0.1 ppm (2.17 × 10 −6 M) of nitrite.

A study of the electrochemical oxidation of some 1,4-benzodiazepines

The electrochemical oxidation of the 1,4-benzodiazepines flurazepam, chlordiazepoxide, oxazepam, lorazepam, potassium chlorazepate, nitrazepam, flunitrazepam, prazepam, diazepam and medazepam and some of their metabolites has been investigated at a glassy carbon electrode in Britton-Robinson buffers (pH 2–10) and in 0.01 M sodium hydroxide solution, each containing 10% of methanol. Oxidation mechanisms are proposed and analytical applications for use in assays of formulations and biological fluids are recommended.

Quantitative analysis of tertiary and quaternary alkaloids in Corydalis Tuber by ion-pair high-performance liquid chromatography and its application to an oriental pharmaceutical preparation.

A new, simple and precise method using ion-pair high-performance liquid chromatography was developed for the determination of alkaloids in Corydalis Tuber and Anchusan-to dry extract, i.e., tetrahydrocolumbamine, glaucine, tetrahydropalmatine, corydaline, columbamine, coptisine, palmatine, berberine and dehydrocorydaline. Reversed-phase systems with an octadecylsilane chemically bonded silica gel column using a mixture of sodium dodecyl sulfate, 0.05M tartaric acid and acetonitrile (0.5 : 62 : 38) and a mixture of sodium dodecyl sulfate, Britton-Robinson buffer (pH 3.0) and acetonitrile (0.5 : 56 : 34) as the mobile phases were suitable for the separation of tertiary alkaloids and quaternary alkaloids, respectively, in Corydalis Tuber.

Electrochemical reduction of ketoprofen and its determination in pharmaceutical dosage forms by differential-pulse polarography.

A simple differential-pulse polarographic method has been developed for the determination of ketoprofen in dosage forms. Methanol was employed as the solvent for extracting the drug from the formulations, and Britton-Robinson buffer (pH 6.0) containing 5%V/V methanol was used as the supporting electrolyte. The EP occurs at – 1.15 V. Results obtained by the proposed method are in excellent agreement with those provided by the manufacturer's laboratory. Commonly used tablet excipients and suppository bases were found not to interfere. A mechanism for the electrochemical reduction of ketoprofen at – 1.25 V is proposed that involves the transfer of two electrons.

ChemInform Abstract: REACTIVITY STUDIES OF S‐METHYLTHIOPHENIUM TETRAFLUOROBORATES

AbstractFür die S‐Methylthiophenium‐tetrafluoroborate (I)‐(IV) werden polarographische Untersuchungen diskutiert und die Demethylierung bestimmt.

Polarographic Behavior of Arsenite at a Rotating Platinum Electrode and Amperometric Determination of Arsenite with N-Bromosuccinimide

The polarographic behavior of arsenite at a rotating platinum electrode and the amperometric determination of arsenite with N-bromosuccinimide were investigated. Arsenite gave a peak-shaped oxidation wave, having the half-peak potential at +0.50 V vs. SCE, in an electrolyte solution cotaining 0.1 M KNO3 and Britton-Robinson buffer of pH 5.0. Arsenite did not show any remarkable reduction wave except a cathodic peak at about -0.5 V vs. SCE. The diffusion current of the oxidation wave, measured at +0.60 V, was found to be proportional to the concentration of arsenite from 10-3 to 2×10-5 N within the deviations of ±2.0%. Its temperature coefficient was determined to be 1.9 per cent deg-1 at 25±0.5°C. Arsenite in the low concentration over the range from 10-3 to 8×10-5 N could be determined within an error of ±2.0% by the short-circuit amperometric titration with N-bromosuccinimide by use of a rotating platinum electrode.

The use of solubilizing agents in chromatography and electrophoresis : IV. Study of solubilization of isoquinoline alkaloids

The solubilizing effects of 7-(2-hydroxyethyl)-theophylline, tetramethyluric acid and theophylline-7-acetic acid on papaverine, papaverinol, papaveraldine, 3,4-dihydropapaverine, 3,4-dihydropapaveraldine and narcotine were studied by paper chromatography and electrophoresis. The formation of molecular complexes of the purine derivatives with the isoquinoline alkaloids, with the exception of narcotine, has been anticipated. Systems containing Britton-Robinson's buffer pH 3.5–4 in the mobile phase and o-xylene in the stationary phase were suitable for the separation of isoquinoline alkaloids.