Marta I.S. Veríssimo

Detection of volatile amines using a quartz crystal with gold electrodes

Abstract A quartz crystal with gold electrodes is used to detect and quantify volatile amines. The magnitude of the observed frequency decrease is highly dependent on the roughness of the surface of the gold electrodes and sensitivity can be increased by rubbing them with alumina. Water increases the observed signal, leading to important errors in the amine quantification. However, the presence of minor amounts of water is readily detected, as the plotted frequency signal shows a marked distortion. The effect of water on the interaction between amine and gold was studied by infrared spectroscopy.

Suitability of PZT ceramics for mass sensors versus widespread used quartz crystals

Abstract Two piezoelectric materials, quartz and ceramic (PZT), were evaluated as mass sensors. Quartz crystals (polished and unpolished) and one ceramic (Nb–Mn–PZT) were used to detect and quantify fructose in aqueous solutions and s -butylamine in vapour. The frequencies at minimum impedance (fn), maximum impedance (fm), series resonance frequency (fs) and parallel resonance frequency (fp) were monitored. Sensitivities of the devices to the chemical compounds are compared and related to the observed changes of the electrical parameters of the equivalent circuit. Roughness of the surface of the discs (ceramic and quartz crystals) and electrodes were measured and their influence in the observed frequency responses discussed.

Aluminium migration into beverages : Are dented cans safe?

Aluminium (Al) migration from cans to beer and tea was studied along time. Analyses of Al in the canned drinks were performed till the sell-by date, and, in seven months, aluminium migration was found to increase 0.14 mg L(-1) in beer, and 0.6 mg L(-1) in tea. This study included dented cans from which aluminium migration into tea was found to be particularly severe. Al concentration in dented canned tea increased 9.6 mg L(-1) in seven months.

The quality of our drinking water: Aluminium determination with an acoustic wave sensor

A new methodology based on an inexpensive aluminium acoustic wave sensor is presented. Although the aluminium sensor has already been reported, and the composition of the selective membrane is known, the low detection limits required for the analysis of drinking water, demanded the inclusion of a preconcentration stage, as well as an optimization of the sensor. The necessary coating amount was established, as well as the best preconcentration protocol, in terms of oxidation of organic matter and aluminium elution from the Chelex-100. The methodology developed with the acoustic wave sensor allowed aluminium quantitation above 0.07 mg L(-1). Several water samples from Portugal were analysed using the acoustic wave sensor, as well as by UV-vis spectrophotometry. Results obtained with both methodologies were not statistically different (alpha=0.05), both in terms of accuracy and precision. This new methodology proved to be adequate for aluminium quantitation in drinking water and showed to be faster and less reagent consuming than the UV spectrophotometric methodology.

A New Method for Monitoring the Contamination of Glycerol with Diethylene Glycol

A quartz crystal microbalance has been used to check the purity of glycerol.

Determination of 5-hydroxymethylfurfural in honey, using headspace-solid-phase microextraction coupled with a polyoxometalate-coated piezoelectric quartz crystal

High concentrations of 5-hydroxymethylfurfural (HMF) in honey provide an indication of overheating under inappropriate storage conditions or aging. Conventional methods for determining HMF are cumbersome and require expensive equipment or hazardous reagents. Hence the aim of this study was to propose a new analytical tool for HMF determination in honey, using a low cost acoustic wave sensor. Volatile organic compounds (VOCs) of honey samples were extracted, using the solid phase microextraction (SPME) technique, and HMF was quantified, using a piezoelectric quartz crystal with gold electrodes coated with a layer of decamolybdodivanado phosphoric acid, sensitive to HMF. The reliability of the proposed method was confirmed after comparing the results of HMF quantification with those obtained by the conventional spectrophotometric White method, and no statistical differences were found (α=0.05).

Analytical advantages of monitoring a particular characteristic frequency in a thickness shear mode acoustic wave sensor

Abstract The oscillator or active method, where just the series resonance frequency ( f s ) can be measured, has been the method of choice for analytical applications of bulk acoustic wave sensors. However, the present work shows that an increase in the analytical signal can be obtained if the frequency at minimum impedance ( f n ) is measured. An example is given, where quantitative analysis is only possible if f n is measured instead of f s . Sensitivity of a particular analysis can be improved if a previous study is performed in order to select the most suitable characteristic frequency ( f s , f n or f p ) to be monitored.

N-Confused Porphyrin Immobilized on Solid Supports: Synthesis and Metal Ions Sensing Efficacy

In this work, the N-confused porphyrin 5,10,15,20-tetraphenyl-2-aza-21-carbaporphyrin (NCTPP) was immobilized on neutral or cationic supports based on silica and on Merrifield resin. The new materials were characterized by appropriate techniques (UV-Vis spectroscopy, SEM, and zeta potential analysis). Piezoelectric quartz crystal gold electrodes were coated with the different hybrids and their ability to interact with heavy metals was evaluated. The preliminary results obtained showed that the new materials can be explored for metal cations detection and the modification of the material surface is a key factor in tuning the metal selectivity.