Quartz Microbalance Sensors Research Articles

Structure identification of non-linear models for QMB polymer-coated sensors

This article deals with the representation of quartz-microbalance (QMB) polymer-coated sensors by block-structured models, their structural identification and their functional identification. The block-structured modelling approach is one of the techniques available for obtaining a complete description of the dynamic behaviour of a non-linear sensing device without having detailed information about its inner structure. A QMB sensor, employed for the detection of mixtures of n-octane and toluene, is studied at the high concentration range (up to 100000 ppm), where a non-linear behaviour is expected. The sensor is exposed to time-varying concentrations of toluene and n-octane having quasi-white power spectral density. It is recognized that the sensor is very likely to admit a special model structure, called the ′Wiener model′, which is a simple non-linear cascade consisting of sequential dynamic linear, static non-linear and dynamic linear processes. The model is completely identified and gives a good approximation to the response of the sensor to any time-varying concentration. Our approach has not yet been widely applied because of the complication of the structure testing procedure, but it is demonstrated that the method is well suited for the study of most chemical transducers provided certain considerations and preliminary analyses are made, as described in this paper.

Soluble polystyrene derivatives of metal bis(3,4-dicarboxybenzoyl)phthalocyaninates: Synthesis, thermal analysis, and sensitivity towards toxic gases

Polystyrene-bound metal [2,9 or 2,10 (or 2,16 or 2,17) bis(3,4-dicarboxybenzoyl)]phthalocyaninates were synthesized by Friedel-Crafts reaction of polystyrene with the corresponding metal phthalocyaninates. Co(II) and Cu(II) [2,9 or 2,10 (or 2,16 or 2,17) bis(3,4-dicarboxybenzoyl)]-phthalocyaninate (PS-CodaPc and PS-CudaPc) contained 0,13 mmol · g−1 (12,4 wt.-%) and 0,13 mmol · g−1 (12,8 wt.-%) of CodaPc and CudaPc, respectively. They were soluble in N,N'-dimethylformamide, but only partially soluble in chloroform, tetrahydrofuran (THF), dimethyl sulfoxide, N-methyl-2-pyrrolidone, and pyridine. The THF extracts contained 0,12 mmol · g−1 (11,4 wt.-%) and 0,18 mmol − g−1 (17,2 wt.-%) of PS-CodaPc and PS-CudaPc, respectively. The thermal stability of the polymers was studied using thermogravimetric and differential thermal analysis in nitrogen and synthetic air atmosphere. The contents of MdaPc(M: metal) in THF-extracted polymers calculated from the data of residue in thermogravimetric analysis are 0,12 mmol · g−1 for PS-CodaPc and 0,19 mmol · g−1 for PS-CudaPc. In addition, the sensitive properties of the polymers towards toxic gases were also investigated by quartz microbalance transducers. The results show that the quartz microbalance sensors coated with both polymers were sensitive to NO2 and chlorinated hydrocarbons, i.e. chloroform and perchloroethylene. The sensitivity to NO2 was 6,53 · 10−7 m3 · mL−1 · s−1 for PS-CodaPc and 1,90 · 10−6 m3 · mL−1 · s−1 for PS-CudaPc, and that to chloroform and perchloroethylene was 2,33 · 10−8 and 4,60 · 10−8 m3 · mL−1 · s−1, respectively, for PS-CodaPc and 4,79 · 10−8 and 9,51 · 10−7 m3 · mL−1 · s−1 for PS-CudaPc.

Reliable CO 2 sensors with silicon-based polymers on quartz microbalance transducers

Quartz microbalance sensors coated with silicon-based polymers are found to be extremely reliable for the detection of CO 2 around 70 °C. The optimization of our differently functionalized silicon-based polymers leads to excellent sensor performances with a low detection limit (<50 vpm). The response times in the order of 1 min can be optimized by adjusting optimum operation temperatures. The sensors have been used for more than nine months without significant loss in sensitivity, reversibility and reproducibility in the continuous monitoring of CO 2 in air. Small effects due to interferences from other gases are discussed finally.

Cavitands as selective materials for QMB sensors for nitrobenzene and other aromatic vapours

The sensitivity of vase-like cavitands to nitrobenzene and other organic and inorganic vapours has been investigated by using the technique of the quartz microbalance (QMB) in order to determine the variation of the mass adsorbed. Cavitands at room temperature showed a high selectivity to nitrobenzene with respect to benzene and other organic vapours like toluene, fluorobenzene and carbon tetrachloride. This material is insensitive towards other vapours, present in a concentration of 1000 ppm, like H 2, CO, SO 2, H 2S, NO and NO 2, an it is also insensitive to relative humidities up to 90%. The X-ray structure analysis of the host—guest complex with the fluorobenzene is also described.

Chemical sensors based upon polysiloxanes: comparison between optical, quartz microbalance, calorimetric, and capacitance sensors

Optical, quartz microbalance, calorimetric, and capacitance transducers to monitor changes of thicknesses Δ d, masses Δ m, temperatures Δ T, and capacitances Δ C are coated with layers of chemically sensitive polysiloxanes. They are tested comparatively as prototype sensors to monitor organic aliphatic, aromatic, and halogenated gas components in air at different temperatures and partial pressures. The results of this comparative study using the different transducer principles are explained by reversible interactions between the organic component in the gas phase and the polymeric polysiloxanes. Characteristic diffusion constants, and hence response times, occur to adjust bulk concentrations of the organic components in the polymer matrices. For a specific polysiloxane with a certain dielectric constants ∈ 2, the distribution coefficient p g describing the thermodynamic equilibrium is related to the boiling temperature T b of the detected organic component and the operation temperature T of the sensor. For different polysiloxanes with different dielectric coefficients ∈ 2, the dipole moment μ of the organic component is related to the distribution coefficient p g with a specific dependence of the sensor signals Δ d, Δ m, Δ T, and Δ C on p g . Finally, the advantages and disadvantages of these transducer principles for specific practical applications are discussed.

Quartz microbalance sensors for gas detection

Abstract We have studied different chemically sensitive coatings such as amines, siloxanes and supramolecular compounds for quartz microbalance sensors to detect polar and apolar organic and inorganic compounds such as CO 2 , CO, NO 2 , Cl 2 C CHCl, Cl 2 C CCl 2 and C 8 H 18 in the gas phase.