Publications

Abstract A three-way analytical methodology experimentally based on fluorescence excitation emission matrix (EEM) and in PARAFAC and TLD chemometric analysis was assessed for the quantification of verapamil drug in a tablet formulation. A standard addition procedure generates experimental information compatible with the chemometric data analysis model allowing the estimation of verapamil with a detection limit of about 0.04 mg/l using methanol as solvent. The structure of the verapamil EEM follows a trilinear model, but background signals (first- and second-order scatter bands) did not-a trilinear three-factor model is necessary to describe experimental datasets. The comparison of a three-factor PARAFAC model with a United States Pharmacopoeia (USP) standard chromatographic method showed similar results.

Abstract The effect of the pH (in the range between 3 to 6) on the stability of the complexes formed between the stronger fluorescent binding sites of a soil fulvic acid (FA) and Cu(II), Ni(II) and Fe(III) ions, at a concentration of 25 mg L-1 in KNO3 0.1 M, was studied The analytical methodology consisted on monitoring the synchronous fluorescence spectra of FA as function of the metal ion concentration. Spectral data were preprocessed by SIMPLISMA, a self-modeling mixture analysis method, to obtain improved quenching profiles to be used in the estimation of equilibrium parameters. Two methods were used in the interpretation of the quenching profiles: (i) graphical procedures based in Stern-Volmer analysis; and (ii) a non-linear least-squares procedure. Both two methods allowed estimation of the conditional stability constants (Kc). However, the Stern-Volmer analysis originated useful results only when the logarithm of Kc is relatively small (Log Kc < 5). Besides the calculation of Kc, the two methods allowed the estimation of the percentage of fluorescent structures not accessible for the complexation of the three metal ions. The Log Kc were: Cu(II) ion, 3.42 +/- 0.04, 4.12 +/- 0.07, 4.63 +/- 0.07 and 5.1 +/- 0.3 respectively for pH = 3, 4, 5 and 6; Ni(II) ion, 3.1 +/- 0.1, 3.48 +/- 0.06, and 4.03 +/- 0.07 respectively for pH = 4, 5 and 6; Fe(III) ion, 5.7 +/- 0.2 and 5.86 +/- 0.09 respectively for pH = 3 and 4.

Abstract Butyltin compounds are widespread contaminants which have also been found in some wines, determined by Liquid-liquid extraction followed by alkylation with a Grignard reagent and gas chromatography-mass spectrometric (GC-MS) analysis. A promising alternative to this extraction/derivatization method is the one-step tetraethylborate in situ ethylation/solid-phase micro-extraction (SPME) method. In this work, a SPME-GC-MS method for the determination of butyltin compounds in wine was optimised. The optimised parameters concerned the pre-treatment with tetramethylammonium. hydroxide, matrix modification with sodium chloride, tetraethylborate concentration, extraction time and temperature, and the GC separation program. The analytical figures of merit of the optimised method (range, limit of detection (LOD) and reproducibility) were evaluated. The sensitivity (range 20-1421 kcounts mug(-1) 1(-1) as Sn) and LOD (range, 0.01-0.2 mug 1(-1) as Sn) depended greatly on the butyltin species to be measured and on the type of wine. For the tested species (monobutyltin, dibutyltin and tributyltin) the highest sensitivities were achieved for Port wine samples, followed by red wine > white wine > white Verde wine. The method allowed acceptable repeatability (relative standard deviation (R.S.D.), 6-8%; n = 4) and reproducibility (R.S.D., 8-9%; n = 3).

Abstract Butyltin compounds are widespread contaminants that have also been found in some wines. The purpose of the present work was to make a survey of butyltin compounds in Portuguese wines. Forty-three table wines and 14 Port wines were analyzed for butyltin contents by using solid-phase microextraction gas chromatography mass spectrometry (SPME-GC-MS). In 14% of the analyzed wine samples, measurable dibutyltin (DBT) was found at concentrations ranging between 0.05 and 0.15,mug/L as Sn. Monobutyltin (MBT) was also observed (0.05 mug/L as Sn) in just a single wine. A search for the possible sources of DBT residues found in the wines was carried out. Therefore, some plastics and oak wood used in the process of wine-making, which have been directly in contact with the musts or the wines, were studied to check their possible release of butyltins. The eventual presence of DBT was also tested directly along the vinification process, from the must to the finished product. The results suggest that high-density polyethylene containers used in the transfer of wine in an early stage of the vinification process may be the main sources of these contaminants. Therefore, it is recommendable that plastic materials to be used in wineries be previously tested for the release of butyltin compounds.

Abstract A chemiluminescent flow system for bromate detection, based on the reaction of bromate with sulphite in acid medium and using the steroid hydrocortisone as sensitiser, was studied. A factorial analysis strategy for the study of the effect on the system response of the experimental factors, flow rates of two pumps (Q(1) - acid sulphite plus hydrocortisone aqueous solution; Q(2) carrier, water), sample injection volume (V-L), reactor volume (V-R), sulphite concentration (C-S), hydrocortisone concentration (C-H) and acid concentration (C-A), was used. Screening analysis of the system performance was made using Plackett Burman designs. The system optimisation procedure was achieved by three levels three factors full factorial designs. V-L and C-H are the most significant factors - a quadratic C-H term was also observed to be significant. The optimised system responded linearly (logarithm of the detector signal as function of the logarithm of the bromate concentration) in the concentration range between 3.6 x 10(-7) and 5.0 x 10(-4) M with a limit of detection of about 8.0 x 10(-8) M (about 10 microg/l). An analysis of some interfering ions was made and it was suggested that bromide and chloride begin to quench chemiluminescence when they are in a 10-fold excess relatively to bromate concentration.

Abstract Firefly oxyluciferin (2-(6'-hydroxybenzothiazolyl)-4-hydroxythiazole) was chemically synthesized and characterized by means of C-13 and H-1 NMR, UV-vis spectrometry and RP-HPLC using different pH elution conditions. One of the chromatographic peaks observed in luciferase-catalyzed reaction mixtures was identified Lis corresponding to oxyluciferin.

Abstract The standard (p(o) = 0.1 MPa) enthalpies of formation of 2,6-di-tert-butyl-4-methylphenol and 3,5-di-tert-butylphenol in the gaseous phase, -315.5 +/- 4.4 kJ mol(-1) and -312.7 +/- 4.6 kJ mol(-1), respectively, were derived from the standard enthalpies of combustion, in oxygen, at 298.15 K, measured by static bomb combustion calorimetry, and from the standard enthalpies of sublimation, at 298.15 K, measured by Calvet microcalorimetry. The O-H bond dissociation enthalpies in those compounds were determined in benzene by photoacoustic calorimetry, leading to the standard enthalpies of formation of the gaseous phenoxy radicals: -189 +/- 8 kJ mol(-1) and -154 +/- 6 kJ mol(-1), respectively. These results were used to calculate enthalpies of substituent redistribution reactions, which are proposed as a method to estimate new data for substituted phenols.

Abstract The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following crystalline dicarboxylic acids: succinic acid, between T = 360.11 K and T = 375.14 K; methylsuccinic acid, between T = 343.12 K and T = 360.11 K; 2,2-dimethylsuccinic acid, between T = 350.11 K, and T = 365.11 K; 2-methylglutaric acid, between T = 338.38 K and T = 347.63 K; and 2,2-dimethylglutaric acid between T = 342.18 K and T = 352.66 K. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation were derived by the Clausius-Clapeyron equation and the molar entropies of sublimation at equilibrium pressures were calculated. Using estimated values for the heat capacity differences between the gas and the crystal phases of the studied compounds, the standard, p(o) = 10(5) Pa, molar enthalpies, entropies and Gibbs energies of sublimation at T = 298.15 K, were derived: (C) 2001 Academic Press