Maria Teresa Vasconcelos

Assessment of the Pb and Cu in vitro availability in wines by means of speciation procedures

The speciation of Pb and Cu in white and red table wines was investigated, in order to estimate their respective bioavailability to man. For this purpose, wines were subjected to in vitro gastrointestinal digestion, and the following properties were studied in the wines and in their gastric and intestinal digests: (1) the average conditional stability constant (Kav) of the strongest complexes (those inert to cathodic voltammetry) and of the respective ligand concentration (CCinert); (2) the distribution of the metal among the different bands of reverse phase high performance liquid chromatography (RP-HPLC) (groups of compounds of different molecular weight and/or polarity); (3) the total metal concentration and metal present in the soluble and in the dialyzable fractions of the digest. The CCinert of the red wines and the respective digests were much greater than those of the white wines and their digests. The conditional stability constants of the strongest soluble complexes after the digestion ranged between 5.9 and 6.1 for Pb. These parameters could not be determined for Cu. After the digestion the dialyzable metal fraction (a relative index of the metal potentially available for interaction with the inner biologic ligands) was only 16% of the total Pb in red wine, 62% in white Verde and 75% in white wine. For Cu the dialyzable metal fraction was 45% of the total metal in red wine, 64% in white Verde and 98% in white wine.

The influence of Cu concentration on ethanolic fermentation by Saccharomyces cerevisiae.

In the present work, the influence of Cu concentration on alcoholic fermentation by Saccharomyces cerevisiae was studied in white grape musts and in YNB medium containing glucose. In the YNB medium, the yield of ethanol, relative to the control, doubled in the presence of 0.50 and 1.0 mM Cu. As for production of ethanol from musts, only minor effects were observed at different Cu concentrations, which indicates that Cu levels do not effect changes in fermentation, and, therefore, are below any toxic level regarding the yeast performance.

Electrochemical studies of complexation of Pb in red wines

Ion-selective electrode potentiometry and cathodic voltammetric techniques were used to study the Pb complexometric properties of four monovarietal wines, ‘Touriga Nacional’ (TN), ‘Touriga Francesa’ (TF), ‘Tinta Roriz’ (TR) and ‘Tinta Barroca’ (TB). The data from titrations of the samples with a Pb solution were treated by two methods suitable for systems involving polymeric heterogeneous ligands: (1) the Scatchard plot, which provided the total complexation capacity of the sample (CCtotal) and average conditional stability constants (Kav), and (2) the differential equilibrium function (DEF), which provided values for differential conditional stability constants (KDEF) as a function of the titration point. The CCtotal of the wines ranged between 4.5 × 10−3 M (TF) and 1.0 × 10−2 M (TN). Potentiometric titrations provided values of log(|Pb|bound/CCtotal) = log θ between 0.015 and 0.45, and the respective log Kav between 5.6 (TF) (log KDEF between 4.7 and 5.5) and 3.0 (TR) (log KDEF between 2.8 and 3.7). Cathodic voltammetry, carried out only for TR and TN, provided the concentrations of only the strongest ligands of the wines (i.e. those that are operationally inert), which were 27 μM (TR) and 43 μM (TN), and two different log Kav for TN, 7.6 and 6.6, and only one, 7.2, for TR, for log θ 0.0025–0.015 (TN) and 0.0014–0.0075 (TR). Since the values of log θ in wines are lower than those embraced in the experiments, this study indicates that Pb is strongly complexed in wines. Therefore, a low bioavailability of Pb can be expected.

Study of sorptive properties of trap systems for selective enrichment of volatile organic compounds from tobacco smoke samples

Currently for compound detection the most difficult are sampling steps and sample preparation for analysis of highly volatile compounds (VOC) and their derivatives, such as ethylene, propylene, acetaldehyde and acetone. For this purpose single- and multibed sorbent tubes were prepared, filled with the following materials: Tenax TA, Carbotrap, Carbopack C, Carbosieve SIII, Carboxen 569. The linear relationship between the mass of analysed compounds and decreased recovery from carbon molecular sieve was determined. The highest desorption recovery (∼100%) for C2–C5 hydrocarbons from multibed sorption traps contained Tenax TA/Carbotrap/Carbosieve SIII. Sorbent traps were also used to determine selected VOC (acetone, acetaldehyde, 2-butanone, benzene, toluene, m,p-xylene) in gas phase of tobacco smoke from single 1R5F reference cigarette. Quantitative analysis of selected compounds was done by standard addition method with r 2 = 0.9931 for 2-butanone and 0.9773 for acetaldehyde. The best combination of sorbent materials included Tenax TA/Carbotrap/Carboxen 569 allowing for VOC determination at low level: 0.31 µg L−1 for m,p-xylene and 40.24 µg L−1 for acetaldehyde. This composition of multibed sorption trap also gave the highest recovery for acetone and 2-butanone as well as the lowest RSD (9.81%, and 9.14%, respectively).

Interferences of surfactants during determination of chlorophenols by acetylation coupled to headspace-solid phase microextraction-gas chromatography with an electron capture detector.

The micellar extraction (ME) of chlorophenols (CPs) from solid samples is rapid and avoids the use of organic solvents. The cationic surfactant cetyltrimethylammonium bromide (CTAB) is a powerful agent for ME of CPs. However, CTAB will be an important interference when the extracts are subsequently analyzed by direct solid phase microextraction (SPME) without a previous derivatization step. Therefore, CTAB is usually replaced by the nonionic surfactant polyoxyethylene-10-lauryl ether (POLE), which causes less interference but is less efficient in extracting CPs. In order to assess to what extent the derivatization of CPs with headspace (HS) sampling would be able to reduce surfactant interferences, CPs were measured in the presence of CTAB or POLE using acetylation and HS-SPME coupled to GC with an electron capture detector. Experiments were carried out both in water and in a 0.1 g/mL solution of NaCl (salting out agent). Acetylation and HS-SPME strongly decreased the interference of CTAB for CP determination. Therefore, the application of CTAB followed by SPME determination for an efficient ME of CPs from solid samples should be reconsidered since using CTAB with HS-SPME after acetylation proved to be a potential tool for CP determination in those matrixes after method optimization.

Stability of chlorophenols and their acetylated derivatives in water: sample storage procedures.

The determination of chlorophenols (CPs) in water samples is a subject of increasing interest. Reduction of sample storage space and the stability of CPs when present at very low levels are still problems that deserve research. The stability of CPs at ng/L levels at different temperatures and in the presence or absence of sodium carbonate and acetic anhydride was studied for up to 39 days. Stable and reproducible CP concentrations for about a month of storage in both river and wastewater were achieved in two storage conditions as follows: at -18 degrees C with addition of 10% sodium chloride; and at 4 degrees C with addition of both 10% sodium chloride and 10 mglmL sodium carbonate. These sample treatments are good alternatives to the immobilization of CPs on SPE cartridges in terms of both analyte stability and saving of storage space.