Giovanni Mori

Comparative investigation of UV, electrochemical and particle beam mass spectrometric detection for the high-performance liquid chromatographic determination of benzoic and cinnamic acids and of their corresponding phenolic acids

Abstract The capabilities of different detection techniques, UV, controlled-potential coulometry and particle-beam electron-impact mass spectrometry (PB-EI-MS) for the HPLC analysis of phenolic acids were studied; fifteen benzoic and cinnamic acid derivatives were considered. For the electrochemical detector (ED) a reversed-phase LC method was set up, whereas normal-phase partition chromatography, on a CN column, was used for UV and MS. Library-searchable EI mass spectra were obtained using the PB-MS technique with flow-injection analysis. UV detection was performed at 280 nm, whereas measurements with the LC-coulometric system were carried out using a porous graphite electrode. The detector responses were compared in terms of linearity, precision and limits of detection; for this purpose, the mass spectrometer was operated under selected-ion monitoring conditions. A linear dynamic range of at least 10 3 was found for the HPLC method with electrochemical detection, with detection limits ranging from 1 to 5 pg injected; the relative standard deviation (R.S.D.) was typically 0.6–3.0% at the 0.1 ng level ( n =4). Using UV or PB-EI-MS detection, minimum amounts in the 5–50 and 2–5 ng ranges, respectively, could be detected. Calibration curves were linear from the limit of detection to at least 15 μg for most of the analytes detected by UV; the R.S.D. of the peak areas obtained in UV mode ranged from 1.2 to 3.1% at the 500 ng level ( n =4). Non-linear behaviour over the entire amount range studied (from 10 ng to 10 μg) was observed using the LC-PB-MS technique, so that two different calibration fittings at low and high levels were calculated. Precision of the LC-PB-MS system was generally good (R.S.D. between 0.5 and 1.8% at the 100 ng level, n =4) except for caffeic acid (R.S.D. 7.5% at the 50 μg level, n =4).

A voltammetric immunosensor based on nanobiocomposite materials for the determination of alpha-fetoprotein in serum.

The development of a voltammetric immunosensor for determination of alpha-fetoprotein (AFP) in serum is presented. ELISA assays with voltammetric reading were carried out exploiting the peculiar properties of nanobiocomposite materials based on gold nanoparticles for the immobilization of Antibody (Ab)/Antigen/Antibody-HRP (Horseradish Peroxidase) sandwich on the glassy carbon (GC) electrode surface. The electrochemical transduction was mediated by thionin, which was used in its monomeric form dissolved in the reading solution, so avoiding critical immobilization procedures. The study was aimed at the development and validation of an immunosensor able to provide results in short time, simple to use, rugged and cost-effective for AFP monitoring purposes. A crucial aspect of the study was the development of an experimental protocol leading to highly standardized and consequently reproducible sensors. Two-way analysis of variance (ANOVA) was applied to study the effect of the concentration of the solutions used for the incubation of the antibodies. The sensor was validated in serum assessing stability of the immunocomplex, linearity of response, limit of detection (3.7 ng/ml) and limit of quantitation (11 ng/ml), precision (intra- and inter-sensor repeatability) and recovery rate (103%). The stability of the GC/Ab functionalized substrate was demonstrated over one month, showing variation coefficients below 5%. Experiments carried out with real samples of clinical interest evidenced that the developed immunosensor can be considered as powerful tool in cancer screening programmes.

Electropolymerization of Tetrakis(o-aminophenyl)porphyrin and Relevant Transition Metal Complexes from Aqueous Solution. The Resulting Modified Electrodes as Potentiometric Sensors

The mechanism of electrogeneration of polyporphyrin from ortho-substituted phenylporphyrins, either free or complexing transition metals, is different when performed in aqueous solution from that operative in organic solvents, that has been reported in the literature. Polymerization occurs through the amino phenyl substituents, leading to a three dimensional ‘cage’ structure. The polymer is sensitive to morphology and nature of the surface it grows on. The mass deposited on a gold electrode was about 2 × 10–4 g/cm2. If the polymerization is performed under potentiodynamic conditions, the polymer forms essentially during the first scan, while no significant further growth is observed in subsequent potential cycles, from both free and metallated porphyrins. All polyporphyrin films, except the one obtained from CoTAPP, exhibit poor electrical conductivity, due to the three dimensional growth of the polymer chain that does not allow the necessary conjugation of π orbitals inside the macromolecules. On the other hand, interesting properties are shown by the unmetallated as well as by metallated polymer films as possible coverages for ‘coated wire’ ion selective electrodes. The results obtained with respect to different ions and, in particular, a selectivity study carried out on iodide ions are reported.

Development of latent fingerprints on metallic surfaces using electropolymerization processes.

We propose a new process for developing latent fingerprints on metal items, applicable to unfired weapons made of Ergal in particular. The method is based on the presence of fatty acids that are contained in fingerprints and act as an insulator on the surface where fingerprints are to be developed. The process of polymerization occurs on the metal portions left untouched by finger contact. Hence, the developing process results as a negative pattern of the original fingerprint. The reaction consists in the electropolymerization of pyrrole and substituted porphyrins, i.e., tetra (o-aminophenyl) porphyrine: radical-cations are generated on superficial nucleation sites by oxidation of monomer, close to the electrode surface; subsequently, the radical species react with the neutral monomer, which begins to diffuse to the electrode. We have also studied the polymers morphology by means of SEM and AFM, in order to find a correlation between the reagent to be used and the quality of the enhancement process. These are only preliminary results; however, they show that the suggested method is a new way to increase the rate of success in developing latent fingerprints on metal surfaces. In this regard, it may be considered complementary to other conventional procedures, due to the low costs of the instruments and reagents, and the rapidity and simplicity of the treatment.

In-flow speciation of copper, zinc, lead and cadmium in fresh waters by square wave anodic stripping voltammetry Part II. Optimization of measurement step

Abstract The measurement unit of an automatic system for in situ determination of dissolved Zn2+, Cd2+, Pb2+ and Cu2+ in fresh waters with square wave anodic stripping voltammetry (SWASV), is described. The effect of supporting electrolyte solution concentration, pre-electrolysis potential, metal deposition time and thickness of the Hg-film was studied by means of a full factorial experimental design and the significativity levels were determined by a multifactorial ANOVA. Subsequently, the parameters were optimized by using a sequential modified simplex method. Under the so found experimental conditions, the effects of foreign ions and of dissolved oxygen have been investigated, the stability of calibration curves have been studied and the detection limits determined.

HPLC analysis of fat-soluble vitamins on standard and narrow bore columns with UV, electrochemical and particle beam MS detection

SummaryThe application of different detection techniques; UV, electrochemical (ED) and particle beam-mass spectrometry (PB-MS) for the high-performance liquid chromatography analysis of fat-soluble vitamins were studied. Separation of all compounds examined was performed using both C8 standard-bore and narrow-bore columns for UV and MS detection, whereas in the case of HPLC-ED, a C8 standard-bore column only was used. Detector responses were studied in terms of linear range, detection limit and precision. The HPLC methods with UV, PB-MS and electrochemical detection were applied to the assay of vitamins A and E in an infantformula, powdered-milk sample. Recovery studies showed good results both for vitamins A and E, within-run precision being 2–4% for LC-UV and LC-ED techniques. In addition, excellent aggrement between the results obtained with the detection systems explored was found.

Discrimination between Butylammonium Isomers by Calix[5]arene-Based ISEs.

Penta-O-alkylated p-tert-butylcalix[5]arenes 1-5 (R = benzyl, isohexyl, isopropoxyethyl, isopropoxycarbonylmethyl, and tert-butoxycarbonylmethyl, respectively) in a fixed C(5)(v) cone conformation have been studied as ionophores in liquid membrane ion-selective electrodes (ISEs) for n-butylammonium against the other branched butylammonium isomers, alkali metals, and ammonium ions, in terms of detection limits, sensitivity, and selectivity. The highest levels of potentiometric selectivity and detection limits up to 3 × 10(-)(6) M are observed with ISEs based on ionophore 2, where selectivity follows the order n-BuNH(3)(+) ≫ i-BuNH(3)(+) > s-BuNH(3)(+) > t-BuNH(3)(+). The lower potentiometric selectivity displayed by ISEs based on ionophores 3-5 is ascribed to their affinity for the Na(+) ion of the lipophilic salt present in the membrane, as evidenced by appropriate (1)H NMR competition experiments with Na(+) and n-BuNH(3)(+) ions. Further investigation on the selectivity mechanism of ionophore 2 by means of frequency response analysis shows that the interaction of the linear butylammonium ion with membranes containing 2 involves a lower resistance process than that occurring with the other branched isomers, thus suggesting the presence of a favorable kinetic-controlled mechanism.

The chemical and electrochemical oxidation of pyridonate-bridged ruthenium(I) dimers. X-Ray structure of [Ru2(μ-pyO)2(CO)4(pyOH)2] (pyOH = 2-pyridone)

Abstract Chemical and electrochemical studies have shown that the pyridonate-bridged ruthenium(I) dimers [Ru 2 (μ-pyO) 2 (CO) 4 (L) 2 ] ( 1 ) (L = PPh 3 , 1a ; P i Pr 3 , 1b ; or pyOH, 1c ; pyOH = 2-pyridone) can be oxidized to the cationic paramagnetic species [Ru 2 (μ-pyO) 2 (CO) 4 (L) 2 ] + ( 2 ). The species 2 are very unstable at room temperature, decomposing into a mixture of 1 and the ruthenium(II) cations [Ru(pyO)(CO) 2 (L)] + ( 3 ). The latter can be obtained quantitatively by reaction of 1 with two equivalents of oxidant. The structure of complex 1c , which has an oxidant peak in its cyclic voltammogram at an unexpectedly high potential (1.11 versus 0.47 V for 1a and 0.33 V for 1b ), has been determined by X-ray crystallography, revealing the presence of two intramolecular hydrogen bonds between the oxygen. atoms of the bridging and the terminal pyO fragments.

Analysis of variance applied to determinations of equilibrium constants.

The statistical analysis of variance has been applied to the values of the equilibrium constants of the glycinate-proton and glycinate-nickel systems, determined in different laboratories by pH-titration in aqueous solution. The analysis shows how the main part of the error derives from the variability from one titration to another even in the same laboratory. Therefore the data for a single titration (k) must be processed separately, thus yielding a mean value for the equilibrium constant logbeta (pqr)(k) of the species M(p)H(q)L(r); from these mean values for different titrations in each laboratory l, a within-laboratory grand average, logbeta (pqr)(l), can be calculated; the variance of this grand average measures the experimental error. A further analysis of the data from the different participating laboratories shows that there were no significant differences between laboratories for the constants reported. From these results it can be inferred that all the values of the mean constants logbeta (pqr)(k) for one species, as determined separately for each titration in four laboratories, belong to the same population. A chi(2) analysis of these populations demonstrates that the stability constants of the species HL, H(2)L(+), NiL(+), NiL(2) (with L(-) = glycinate) are normally distributed, but not that for NiL(-)(3). Therefore, general mean values of the first four constants can be calculated and proposed as reliable standard values at 25 degrees and I = 1.0M Na(Cl): protonation of glycinate, log beta(011) = 9.651(12), log beta(021) = 12.071(26); nickel-glycinate complexes, log beta(101) = 5.615(35), log beta(102) = 10.363(62). These values indicate that the standard deviations are rather higher than those often reported in the literature.

A new multivariate approach for the optimisation of the simultaneous distillation–extraction technique for free fatty acids using a face centred cube experimental design: application to Parmigiano–Reggiano cheese

Abstract A face centred cube (FCC) experimental design was used to investigate effects of extraction time, solvent temperature and sample temperature on the simultaneous distillation–extraction (SDE) extraction yields of 13 fatty acids from Parmigiano–Reggiano cheese, and to find the best extraction conditions for these compounds. Each factor was tested at three levels; 20 experiments were carried out, each producing 13 responses. In order to create a mathematical model representing the relationships between factors and responses and to determine the best conditions for the SDE procedure, GC peak areas were processed by using the multiple regression analysis. The backward stepwise selection of the regression coefficients led to the identification of seven groups of compounds having similar behaviour with respect to the three variables investigated. The same set of models was found by performing principal component analysis (PCA) on the t -values of the regression coefficients of the unrefined polynomials and cluster analysis on the scores of the 13 acids obtained by PCA. The best experimental conditions were evaluated for each compound. The use of the FCC experimental design allowed to evaluate not only the main effects of the variables analysed, but also curvature effects and interaction effects among them.