Miguel F. Silva

Screening of pharmacologic adulterant classes in herbal formulations using voltammetry of microparticles

A solid state electrochemical method for screening different families of adulterant chemicals illegally added to commercial phytotherapuetic formulations is described. The proposed method, based on the voltammetry of microparticles approach, permits a fast and sensitive way to distinguish between anorexics (amfepramone, fenproporex, sibutramine), benzozodiazepinic anxiolytics (clonazepam, flurazepam, alprazolam, midazolam, medazepam, chlordiazepoxide, diazepam), antidepressants (bupropione, fluoxetine, sertraline, paroxetine), diuretics (hydrochlorothiazide, furosemide, chlortalidone, amiloride, spironolactone), and hypoglycemics (glimepiride, chlorpropamide, glibenclamide) based on characteristic voltammetric signals recorded on solid micro- or nanosamples attached to graphite electrodes immersed into aqueous electrolytes.

Study of behaviour on simulated daylight ageing of artists’ acrylic and poly(vinyl acetate) paint films

AbstractThis work proposes a multi-method approach that combines advanced microscopy (SEM/EDX, AFM) and spectroscopy (UV-vis and FTIR) techniques. This approach not only characterises the behaviour of the additives of two commercial poly(vinyl acetate) (PVAc) and acrylic emulsion paints but also simultaneously characterises the changes in chemical composition and morphology observed in the paint films as a result of ageing due to the paints being exposed to an intense source of simulated daylight. In parallel, a series of mechanical tests were performed that correlate the chemical changes in composition and the changes observed in the films’ mechanical properties. This work was a comparative study between both types of acrylic and PVAc paints. The results obtained are of great interest for the modern paint conservation field as they provide valuable information on the mid- and long-term behaviours of these synthetic paints. FigureTensile test of phthalocianyne blue Liquitex® paint film

Study of ageing of ketone resins used as picture varnishes by FTIR spectroscopy, UV-Vis spectrophotometry, atomic force microscopy and scanning electron microscopy X-ray microanalysis.

This paper presents a study of thin films of the commercial ketone resins Laropal K80, Keton N and MS2A, attempting to reproduce the pictorial layers and protective finishes commonly present in contemporary paintings. Chemical and morphological changes due to the degradation effect of environmental agents have been specially considered. For this purpose, three different accelerated ageing processes were applied to a series of specimens prepared from the studied commercial products: thermal, UV light and ageing in an SO2-polluted chamber. Spectroscopic techniques such as FTIR spectroscopy and UV–Vis spectrophotometry were applied in combination with microscopic examination techniques, namely, AFM and scanning electron microscopy energy dispersive X-ray microanalysis (SEM-EDX). Chemical changes due to UV light and thermal ageing are in good agreement with those previously reported in the literature. Bleaching exhibited by the three commercial products after exposure to a SO2-saturated atmosphere has been related to the diffusion of SO2-rich water vapour into the film. This effect was particularly strong in the MS2A resin due to the higher content of hydroxyl groups in this product.

Identification of additives in poly(vinylacetate) artist’s paints using PY-GC-MS

AbstractCommercial poly(vinyl acetate) (PVAc) paint formulations for artists include a number of compounds in addition to the PVAc polymer and pigments to improve the physical and chemical properties of the resulting product. Among the most common additives are surfactants, coalescing agents, defoamers, freeze–thaw agents and thickeners. These products significantly influence the behaviour of the dried film. Nevertheless, they are usually difficult to detect with conventional analytical methods given their low concentration. In order to identify these additives, present in the dried film as minor components, an analytical method based on in situ thermally assisted pyrolysis–silylation gas chromatography–mass spectrometry (GC-MS) using hexamethyldisilazane as a derivatisation reagent is proposed. This method improves the conventional GC-MS analysis performed by direct pyrolysis and enables the simultaneous identification of the PVAc binding medium and the additives included by the manufacturer in the commercial paint. Five different commercial PVAc paints have been analysed, namely, armour green, burnt umber, oriental red, raw umber and white from Flashe®. Internal plasticiser VeoVa consisting of C10 fatty acids with highly branched chains has been recognised from the MS spectra. On the other hand, the differences found in the additive content of the studied paints, in particular the poly(ethylene glycol)-type surfactant, are in good agreement with their mechanical properties. FigurePicture of armour green Flashe® paint sample breaking in the mechanical tester’s gauge. The photo evidences the type of break these samples experience. Rather than a clean break, the sample experiences several simultaneous fractures with a saw-tooth-like pattern

Standard additions-dilution method for absolute quantification in voltammetry of microparticles. Application for determining psychoactive 1,4-benzodiazepine and antidepressants drugs as adulterants in phytotherapeutic formulations

A standard additions-dilution solid-state electrochemical method for the determination of psychoactive 1,4-benzodiazepine and antidepressants drugs used as adulterants in commercial slimming herbal formulations is described and compared with conventional standard addition method. The proposed method, based on the voltammetry of microparticles approach, permits quantify, via standard additions methodology, 1,4-benzodiazepine and antidepressants drugs in phytotherapeutic formulations with no need of sample dissolution using dilution with a reference electroactive compound. The method was used to measure 1,4-benzobenzodiazepines (clonazepam, flurazepam, alprazolam, midazolam, bromazepam, chlordiazepoxide, lorazepam and diazepam) and antidepressants (bupropion, sertraline, paroxetine and fluoxetine) in slimming formulations that have been commercialized in Brazil.