Adsorptive stripping voltammetry as a method of analysis of some pharmaceutical and other purine derivatives

Adsorptive stripping voltammetry (AdSV) is a recent technique (initially named by Lam, Kalvoda and Kopanica in 1983) in which there is generally a nonelectrolytic accumulation (adsorption) of the determinand followed by a cathodic reductive or anodic oxidative scan. In this work, a hanging mercury drop electrode (HMDE) was used to accumulate several purine derivatives with and without the addition of Cu(lI) in a suitable buffer (usually Britton-Robinson, pH 7.5). In the presence of copper(lI) the copper(l) purine complex was usually accumulated at about -0.1 V. Some of the compounds studied (i.e dimenhydrinate, theophylline, guanine and azathioprine) can be determined as free compounds (i.e with no Cu(lI) added) after accumulation at potentials ranging from 0 to -0.2 V versus Ag/AgCI reference electrode. The determination of these compounds was made after optimising pH, buffer constituents, accumulation potential and accumulation time. The addition of Cu(lI) to these purines makes possible accumulation at shorter accumulation times , and improves the detection limits. For example, the detection limit of azathioprine in the presence of Cu(lI) is as low as 2x10-10 M. Both differential-pulse polarography (DPP) and DP-AdCSV (differential pulse adsorptive cathodic stripping voltammetry) were used in the determination of theophylline and azathioprine in their dosage forms (tablets). The relative standard deviations for the determination of the pharmaceutical purines in their tablets were 3.0%. 4.2% and 1.3% for the measured concentrations of dimenhydrinate(1.5x10-7 M) , theophylline(2x10-7 M) by AdSV ; and azathioprine(2x10-6 M) by DPP, respectively . Other purines (eg xanthine,1,3-dimethyluric acid and some methylguanines) did not give peak currents useful for their determination. The addition of Cu(lI) was necessary to obtain satisfactory peak currents for these purines. At low copper(lI) concentrations (Le.< 10-6 M), it is suggested that the purines form Cu(l) complexes which are adsorbed at the HMDE surface: Cu(lI) + Cu(O) + 2 L ~ 2 Cu(I)-L adsorbe

Ion-pair Spectrophotometric Determination of Dibucaine

A simple and sensitive spectrophotometric determination of dibucain has been established. It is based on the formation of colored ion-pair complexes between Dibucaine and each of Orange II, Orange G, Bromothymol blue and Bromocresol green. The extract with each of the previous dyes in chloroform exhibited a specific wavelength of maximum absorbance, and all these wavelengths lied in the range 416 to 500 nm. The linear range extended from 1.5 to 60 ppm. The optimum conditions were selected after studying many variables such as pH, shaking time, temperature and dye concentrations. The method was also selective for the analyte and the drug excipients did not interfere

Successful embolization of an anterior chest wall arteriovenous malformation using combined transfemoral and transradial approaches with onyx

We present a case of successful embolization of an anterior chest wall arteriovenous malformation (AVM) in a 24-year-old male patient. This report aims to highlight the efficacy and safety of using the liquid embolic agent (onyx) as well as the combined approaches (trans-femoral and trans-radial) in managing rare complex chest wall AVMs

The electrochemical behavior of nitrazepam at a screen-printed carbon electrode and its determination in beverages by adsorptive stripping voltammetry

The cyclic voltammetric behavior of nitrazepam was investigated at screen-printed carbon electrodes over the range1.5 V to {thorn}1.5 V. Two reduction peaks were observable on the negative scan, at 0.7 V, and 1.2 V using pH 6 buffer. On the return scan a single oxidation peak was obtained at 0.05 V. For quantitative analysis of beverages, we developed an anodic adsorptive stripping voltammetric method which required only dilution with buffer. The identification of nitrazepam and flunitrazepam could be achieved using cyclic voltammetry.© 2009 Wiley-VCH Verlag GmbH& Co. KGaA, Weinheim

Voltammetric Behaviour of 7-Methylguanine Using Screen-printed Graphite Electrodes: towards a Guanine Methylation Electrochemical Sensor

The determination of 7-methylguanine (7mG) is an interesting analytical target since its quantification can be correlated with the methylation of cytosine which is one of the most relevant epigenetic modification of DNA. In this work, screen-printed graphite electrodes were used to study the electrochemical characterization of 7mG by cyclic and square wave voltammetry. 7mG concentration and pH were examined, as well as the repeatability of the measurements. The electrochemical response of 7mG in the presence of guanine and adenine was also investigated. Results aim to the future development of an electrochemical sensor for the methylation degree in DNA.Authors would like to acknowledge funding obtained through the Spanish Ministry of Science and Innovation (MICINN) CTQ2013–48280-C3–3-R project