Gabriella Favaro

Determination of pharmaceutical thiols by liquid chromatography with electrochemical detection: Use of an electrode with a conductive carbon cement matrix, chemically modified with cobalt phthalocyanine

Abstract An electrode made with a conductive carbon cement (CCC) matrix and modified with cobalt phthalocyanine was utilized for the detection of some thiols of pharmaceutical interest: captopril, thiopronine, penicillamine. The performance of the electrode and the influence of pH were examined by hydrodynamic voltammograms and compared with those of unmodified CCC and glassy carbon electrodes. Calibration curves were performed in aqueous solutions at acidic pH in the range 5 × 10−6 to 1 × 10−4 M. Stability experiments showed that electrode response in flowing solutions decreased about 1% for hour. Satisfactory liquid chromatographic (LC) separation by reverse phase was obtained for the three compounds. Limits of detection reached with LC were in the range of pmoles. The modified electrode showed quite satisfactory performance: good sensitivity, good stability and detection of low concentration of the examined thiols.

Effect of eluent composition and pH and chemiluminescent reagent pH on ion chromatographic selectivity and luminol-based chemiluminescence detection of Co2+, Mn2+ and Fe2+ at trace levels

The alkaline-luminol/H(2)O(2)-based chemiluminescent (CL) detection of Fe(2+), Co(2+), and Mn(2+), separated with a Dionex CS5A ion chromatographic phase was studied by means of a multi-pump flow system allowing the variation of the post-column solution composition. A perchlorate gradient at pH 1.9 (with HCl) was used to separate cations partially complexed with 5.6mM oxalate present in the eluent and necessary for the chosen separation phase. A 0.91mM luminol, 3.3mM H(2)O(2) in 0.25M carbonate buffer at pH 10.5 composition was chosen as CL reagent solution. The chosen pH value warrants signal repeatability and wider linearity range although absolute signal is not maximum. The CL signal was related to the pH of the two post-column mixing solutions. Calibration plots of Co(2+) and Fe(2+) were linear in the chosen concentration range whilst a parabolic model was the best fit for Mn(2+). Detection limits were 0.24, 0.50 and 375nM for Co(2+), Fe(2+) and Mn(2+), respectively. The method was used to determine Co(2+) at trace level in commercial copper chelates used for animal feeding. A comparison with a chromatographic method with spectrophotometric detection was made giving results comparable both in absolute values and accuracy.

Helicobacter pylori acidic stress response factor HP1286 is a YceI homolog with new binding specificity.

HP1286 from Helicobacter pylori is among the proteins that play a relevant role in bacterial colonization and persistence in the stomach. Indeed, it was demonstrated to be overexpressed under acidic stress conditions, together with other essential virulence factors. Here we describe its crystal structure, determined at 2.1 Å resolution. The molecular model, a dimer characterized by two‐fold symmetry, shows that HP1286 structurally belongs to the YceI‐like protein family, which in turn is characterized by the lipocalin fold. The latter characterizes proteins possessing an internal cavity with the function of binding and/or transport of amphiphilic molecules. Surprisingly, a molecule of erucamide was found bound in the internal cavity of each monomer of recombinant HP1286, cloned and expressed in an Escherichia coli heterologous system. The shape and length of the cavity indicate that, at variance with other members of the family, HP‐YceI has a binding specificity for amphiphilic compounds with a linear chain of about 22 carbon atoms. These features, along with the fact that the protein is secreted by the bacterium and is involved in adaptation to an acidic environment, suggest that its function could be that of sequestering specific fatty acids or amides from the environment, either to supply the bacterium with the fatty acids necessary for its metabolism, or to protect and detoxify it from the detergent‐like antimicrobial activity of fatty acids that are eventually present in the external milieu.

Application of LC‐MS and LC‐MS‐MS to the analysis of photo‐decomposed crystal violet in the investigation of cultural heritage materials aging

In this work, the accurate liquid chromatography-ultraviolet-visible (LC-UV-Vis), LC-mass spectrometry (MS) and LC-MS-MS analysis of the photo-degradation products of crystal violet (CV) is reported. CV is a light fugitive early synthetic dye which had a widespread diffusion into the market starting from the end of the XIX century and was used among others by V. Van Gogh and P. Gauguin in their writings, drawings or paintings. On-line photodiode array detector enabled simultaneous UV-Vis spectra acquisition. Many degradation compounds were identified through their exact mass (2 ppm accuracy) and MS-MS technique. In particular, all CV demethylated products, demethylated Michlers ketone and particularly some compounds that most likely contain oxygen, such as N-oxides, were found. Fragmentation products are all justified by the proposed fragmentation scheme, in term of precursor exact mass and isotopic profile, characteristic losses in fragmentation and rebuilt structure formula. In particular, we hypothesized the presence of N-imido oxides and hydroxylamine derivates, never reported before, together with the demethylated derivatives of the studied dyes. All these compounds, although at trace level in our samples, contribute to the discoloration and fading of works of arts made with CV. In particular, demethylation of CV by UV light leads to formation of compounds absorbing at shorter wavelengths than CV (blue shift) or no-absorbing in visible range (yellow-colourless) with an overall effect that may appear reddish-brown. This phenomenon justifies drawings appearing grey or brown on aged yellowed paper, when CV-based inks or paints were used. The final aim was to better characterize the photo-degradation of early synthetic dyes (in particular of CV) and to gain a better insight into the discoloration and fading of purple ink strokes made of CV.

Evidence of Cr(VI) formation during analysis of leather Proposal of an alternative method of analysis through the ion-chromatographic approach and post-column reaction.

The formation of Cr(VI) in Cr(III) tanned leather, in neutral and alkaline solution, has been demonstrated by means of crossed experiments using different pH buffers, ethylenediaminetetraacetic acid as Cr(III) complexing agent and NaCl solutions. According to the found results the composition of the extracting solution suitable to extract Cr(VI) amount present in leather was pH 4.4 (which is also the tanned leather natural pH) and 5% NaCl (w/v). Interferences coming from coloured compounds have been eliminated with suitable SPE cartridges. A new protocol for the analysis of Cr(VI) based on ion chromatography and a diphenylcarbazide post-column reaction has been implemented. The use of a large volume injection loop (500mul) allowed to obtain a very low quantification limit (0.15mgkg(-1)) despite the low amount of leather extracted (0.2g with respect to 2.0g used by the IUC 18 official method). Evidence of the transient nature of Cr(VI) in leather requires using the external calibration procedure for the correct quantification of the species.

Identification of wine aroma precursors in Moscato Giallo grape juice: a nuclear magnetic resonance and liquid chromatography-mass spectrometry tandem study.

In this work, several aroma precursors present in Moscato Giallo grape juice were identified and characterized using LC-MS and NMR techniques. A preliminary separation of various fractions was obtained using adsorption on Amberlite(®) XAD resin and HPLC chromatography on a reverse phase column. Subsequently, U-HPLC with mass spectrometry allowed the identification of some compounds corresponding to mono- and disaccharides linked to terpenes. The MS-MS fragmentation step indicated which kind of glycosides, the moiety sequence and sometimes which kind of terpene were present. NMR enabled the correct identification of glycosides and terpene when the fraction analyzed was sufficiently concentrated and with few components. Twelve glycosidically bound terpenes were characterized: (E) and (Z)-furanosyl-linalooloxide-7-O-[α-D-apiofuranosyl-(1→6)-1-β-D-glucopyranoside], (E)-furanosyl-linalooloxide-7-O-[1-β-D-glucopyranoside], (Z)-8-hydroxylinalool-8-O-[1-β-D-glucopyranoside], 1,2-dihydroxylinalool-1-O-[1-β-D-glucopyranoside], linalool-3-O-[α-L-arabinofuranosyl-(1→6)-1-β-D-glucopyranoside], linalool-3-O-[α-L-apiofuranosyl-(1→6)-1-β-D-glucopyranoside], linalool-3-O-[α-L-rhamnopyranosyl-(1→6)-1-β-D-glucopyranoside], nerol-1-O-α-D-apiofuranosyl-(1→6)-1-β-D-glucopyranoside, geraniol-1-O-[α-L-arabinofuranosyl-(1→6)-1-β-D-glucopyranoside], geraniol-1-O-[α-L-rhamnopyranosyl-(1→6)-1-β-D-glucopyranoside], and a geranic acid disaccharide derivative. It is the first time that this kind of compounds are directly detected and identified in a mixture with these two techniques.

A pH-stat study of the reaction of some transition metal cations with disodium ethylenedinitrilotetraacetate (EDTA) and its analytical application

The pH-stat titration technique is an autonomous and very powerful tool for performing and monitoring chelatometric titrations of metal cations with great accuracy, poorly known, however, and seldom exploited. Based on measurement of the amount of strong base required to keep the pH of the test solution at a selected value during stepwise known additions of ethylenedinitrilotetraacetate (EDTA), it requires a glass electrode as the only sensor and is easily implemented on potentiometric titrators. It was introduced a quarter of century ago on an empirical basis for a very peculiar purpose (determination of calcium in diary products), but only very recently it was generalised and its fundamentals were thoroughly examined. In this work, pH-static titrations of some transition metal cations of analytical relevance (Co(2+), Cu(2+), Mn(2+), Zn(2+)) were thoroughly investigated in the acid pH range between 2.3 and 5 or 7 (the highest pH depending on the metal hydroxide or carbonate solubility). The results at higher acidity showed unsuspected properties of such chelation reactions. At moderately acid pH (generally >/=4), indeed, pH-static titrations yield results of high precision and accuracy. On decreasing pH, however, the reaction stoichiomety deviates more and more from the 1:1 ratio between chelating agent and cation, seemingly because of formation of binuclear complexes, an occurrence very seldom mentioned in the current literature. The optimal titration conditions for each metal are defined, and directions for establishing a laboratory protocol for quantitative determinations are given.

Degradation Products from Naturally Aged Paper Leaves of a 16th-Century-Printed Book: A Spectrochemical Study

In this work, we present a wide-range spectrochemical analysis of the degradation products from naturally aged paper. The samples obtained from wash waters used during the de-acidification treatment of leaves from a 16th-century-printed book were analysed through NMR, IR, Raman UV/Vis, EPR and X-ray fluorescence (XRF) spectroscopy and HPLC-MS and inductively coupled plasma (ICP) analysis. By these methods we also studied some of the previous samples treated by acidification (sample AP) and catalytic hydrogenation (sample HP). Crossing all the data, we obtained precise indications about the main functional groups occurring on the degraded, water-soluble cellulose oligomers. These results point out that the chromophores responsible for browning are conjugated carbonyl and carboxyl compounds. As a whole, we show that the analysis of wash waters, used in the usual conservation treatments of paper de-acidification, gives much valuable information about both the conservation state of the book and the degradation reactions occurring on the leaves, due to the huge amount of cellulose by-products contained in the samples. We propose therefore this procedure as a new very convenient general method to obtain precious and normally unavailable information on the cellulose degradation by-products from naturally aged paper.

Liquid chromatographic determination of non-volatile nitrosamines by post-column redox reactions and voltammetric detection at solid electrodes. Behaviour of the Ce(IV)-Ce(III) couple at gold, platinum and glassy carbon electrodes and suitability of the Ce(IV) reagent

Abstract The suitability of Ce(IV) in acidic medium as post-column reagent in the liquid chromatographic (LC) amperometric determination of non-volatile nitrosamines was investigated by studying the Ce(IV)-Ce(III) couple with a rotating disk electrode, whose behavior approaches the operational conditions of a “channel-thin-layer” cell with solid electrodes as frequently used for liquid chromatographic detectors. The conditional kinetic parameters k 0 ′ and α were evaluated at platinum, glassy carbon and gold electrodes. Gold was found to be the most suitable material. The reaction between Ce(IV) and NO − 2 (which is the product of the decomposition of the nitrosamines in warm acidic solution) was considered. The biamperometric behavior of the system was studied by varying the concentration of Ce(III) in presence of excess of Ce(IV) and also by producing Ce(III) by reaction between Ce(IV) and nitrite.

The mystery of the discolored flints. New molecules turn prehistoric lithic artifacts blue

Prehistoric artifacts turning blue in the store rooms of the Natural History Museum in Verona, Italy recently raised serious issues for heritage materials conservation. Our analytical investigation showed that the unusual discoloration process of the flint tools is caused by the surface presence of at least three previously unknown pigmenting molecules of the triphenylmetane dyes class: 6-(bis(2,2,4-trimethyl-1,2-dihydroquinolin-6-yl)methylene)-2,2,4-trimethyl-2,6-dihydroquinolinium and its hydrogenated derivatives 2,2,4-trimethyl-6-((2,2,4-trimethyl-1,2,3,4-tetrahydroquinolin-6-yl)(2,2,4-trimethyl-1,2-dihydroquinolin-6-yl)methylene)-2,6-dihydroquinolinium and 6-(bis(2,2,4-trimethyl-1,2,3,4-tetrahydroquinolin-6-yl)methylene)-2,2,4-trimethyl-2,6-dihydroquinolinium. The peculiar formation of the molecules is possibly catalyzed within the silica pore surface starting from a well-known rubber stabilizer 2,2,4-trimethyl-1,2-dihydroquinoline released by the plastic pads flooring the storing cabinets. The investigated reaction and its surprising blue product represent a case study of the application of modern materials science to conservation and a serious warning towards the unpredictable challenges faced in the preservation of our cultural heritage.