M.L. Rodríguez-Méndez

Combination of an e-nose, an e-tongue and an e-eye for the characterisation of olive oils with different degree of bitterness.

An electronic panel has been used to characterise the organoleptic characteristics of twenty-five extra virgin olive oils from varieties Hojiblanca, Picual and Arbequina, with different degree of bitterness. The method consists in the combination of three systems: electronic nose, electronic tongue and electronic eye. The Principal Component Analysis (PCA), where PC1, PC2 and PC3 explained 59% of the total variance between the samples, has demonstrated that the capability of discrimination of the combined system is superior to that obtained with the three instruments separately. This improvement is due to the increased information extracted from each sample. Partial Least Squares-Discriminant Analysis (PLS-DA) has allowed separation of the groups in function of olive variety with a root mean square error of prediction (RMSEP) lower than 0.099. Using PLS1 and PLS2 regression models, good correlations have been found between the signals obtained from the electronic tongue and the polyphenolic content (measured by chromatographic methods) or the bitterness index (scored by a panel of experts) with correlation coefficients higher than 0.9 in calibration and validation. These preliminary results indicate that the combination of an e-nose, an e-tongue and an e-eye can be a useful tool for the analysis of olive oil bitterness.

Electronic nose based on conducting polymers for the quality control of the olive oil aroma. Discrimination of quality, variety of olive and geographic origin

An electronic nose purposely designed for the organoleptic characterisation of olive oil is reported. The instrument works using an array of electrodeposited conducting polymer-based sensors. Such an array has been able to distinguish among not only olive oils of different qualities (extra virgin, virgin, ordinary and lampante) but also among Spanish olive oils prepared from different varieties of olives and even of different geographic origins.

Array of sensors based on lanthanide bisphtahlocyanine Langmuir–Blodgett films for the detection of olive oil aroma

Abstract In this paper a sensor array based on Langmuir–Blodgett (LB) films of lanthanide bisphthalocyanines (LnPc2) aiming to discriminate among diverse virgin olive oils has been designed. For this purpose, sensors based on bisphthalocyanines including unsubstituted bisphthalocyanines with different central metal atom (PrPc2 and LuPc2) and a octatertbutyl substituted bisphthalocyanine (PrPc2t) have been prepared. The interaction of the sensors with the headspace of olive oil samples has been studied by registering the changes in the conductivity produced in the LB films. The influence in the response of parameters such as the number of monolayers or the proportion of arachidic acid used in the preparation of the LB films has been analysed. Studies on the stability and reproducibility of the LB film-based sensors have been carried out. Using the previous results, the sensors with the best performance characteristics have been selected, and an array of five sensors has been constructed. The array has been exposed to four types of Spanish olive oils with different organoleptic properties and qualities. The principal component analysis of the obtained signals has allowed the discrimination of the different types of olive oils.

Crown-ether lutetium bisphthalocyanine Langmuir-Blodgett films as gas sensors

Abstract The gas adsorption and electrochromic properties of Langmuir-Blodgett films of octa-(15-crown-5)-lutetium bisphthalocyanine (CRue5f8Pc2Lu) are reported. Films of CRue5f8Pc2Lu were sensitive to electron donor and electron acceptor gases as well as tobacco smoke. The adsorption was traced using electronic adsorption spectroscopy. The presence of crown ether groups on the phthalocyanine ring increased the sensitivity of the films to oxidizing gases. Stable red films were prepared using 0.01 M HCl as a subphase. Red films were also obtained by chemical oxidation. The use of previously oxidized LB films as the active layer highly increases the sensitivity of the proposed sensor towards electron donor gases. The possibility of discriminating between the main and the side streams of the tobacco smoke, as well as the sensitivity to increasing amounts of smoke, were studied.

DTG and DTA studies on amino acids

Abstract In this paper, the analysis techniques DTG and DTA were used to study a range of 22 amino acids, the most significant as constituents of proteins. Our research is mainly concerned with the structure-thermal behaviour relationships. In the α-amino acid molecule, the R side chain, which is responsible for specific characteristics of each particular amino acid, influences the thermal effects that occur during their heating.

Langmuir—Blodgett films of lanthanide diphthalocyanines as environmental tobacco smoke sensors

Abstract Langmuir—Blodgett (LB) films of praseodymium, gadolinium, ytterbium diphthalocyanines and octa-tert-butyl praseodymium diphthalocyanine have been prepared on various substrates. The spectroscopic characterization (UV—Vis and Raman) of the films before and after being exposed to a tobacco smoke side stream (SS) has been carried out. The chemisorption of the SS to the lanthanide diphthalocyanines LB films reversibly forms a complex that reduces the oxidation state of the material. These changes can be followed in the electronic and vibrational spectra. The potential use as a tobacco smoke sensor is discussed.

Array of lutetium bisphthalocyanine sensors for the detection of trimethylamine

Abstract An array of electronic sensors based on thin films of phthalocyanine derivatives with a controlled thickness and designed for the evaluation of vapours produced by the decomposition of fish and seafood is presented. The sensors were prepared by using the Langmuir–Blodgett technique and by vacuum sublimation. The individual sensing units undergo changes in their electrical resistivities that are proportional to the concentration of volatile amines. The combined responses of this array allow for the assessment of the freshness of these alimentary products.

A.c. conductivity of gas-sensitive Langmuir-Blodgett films of ytterbium bisphthalocyanine

Abstract The a.c. conductivity of Langmuir-Blodgett multilayers of ytterbium bisphthalocyanine has been measured in the frequency range 10–10 6 Hz and for temperatures from 20 to 60 °C. The effects of two common atmospheric pollutants, nitrogen dioxide/dinitrogen tetroxide (NOX) and tobacco smoke, on the complex impedance of the material have been analyzed in terms of the Havriliak-Negami model for conduction.

Energy transfer between Langmuir-Blodgett monolayers of Titanylphthalocyanine and Bisneopentyl(imido)perylene

Abstract In the present work, the energy transfer between Langmuir–Blodgett (LB) monolayers of a donor molecule (the Bisneopentyl(imido)perylene) and an acceptor molecule (the Titanylphthalocyanine) has been investigated. The Langmuir–Blodgett technique has also been used to study the distance dependence of the energy transfer, using spacer layers of arachidic acid between the donor and acceptor planes. The optical properties of the LB films have been characterized using absorption and emission spectroscopy. The energy transfer has been extracted from photoluminescence measurements and illustrated with fluorescence imaging. A discussion of the different physical models and a first estimation of the critical energy transfer distance is presented.

Small angle X-ray reflectivity study of langmuir-blodgett films of a peripherally substituted zinc phthalocyanine

Abstract Langmuir-Blodgett films of zinc 11,18,25-tri(tert-butyl)-4-sulfo-phthalocyanine (ZnPctSO3Na) have been deposited onto hydrophilic and hydrophobic silicon wafers. Y-type films were formed on both types of substrate, and the transfer ratio was very close to unity. The organization of the films on the molecular level was probed by X-ray specular reflectivity.