Test method for detecting adulterated apple juice using piezoelectric resonators

The adsorption of a mixture of volatile components comprising the aroma of apple juice was studied using piezoelectric quartz microweighing. Conventional gas-chromatographic adsorbents and specific films of different natures were used to modify the electrodes of a piezoelectric sensor. The conditions of the juice analysis were optimized using a piezoelectric sensor array in the batch mode. Different samples of apple juice and nectar were analyzed under the same conditions using the piezoelectric sensor array. The quality of the samples was estimated by comparing kinetic mass aromagrams. A method was developed for the rapid estimation and assortment identification or the detection of the adulteration of natural and reconstituted apple juice.     

Determination of formic and acetic acids in air by piezoelectric microweighing

The quantitative and kinetic parameters of sorption of formic and acetic acids on thin films of various modifiers of piezoelectric quartz resonator electrodes are determined. Parameters of film formation on the electrodes (application procedure and thickness) are optimized. Methods for joint and separate determination of formic and acetic acids in air by piezoelectric microweighing with single- and double-sensor devices are developed.     

Solvent Effect on the Sensitivity and Selectivity of Determining Aniline and Toluidines in the Air by Piezoelectric Microweighing

Batch conditions were optimized for the sorption of aniline and toluidines from the air on polystyrene, polyethyleneglycol-2000, and polyethyleneglycol succinate using piezoelectric microweighing. It was found that the analytical signal of a quartz crystal resonator depended on the mass of the modifier on the electrode surface and on the solvent. The selectivity of modifiers with respect to the compounds studied was estimated.     

Determination of Acetonitrile in Air Using a Piezoelectric Quartz Crystal Microbalance

The affinity of acetonitrile to different adsorbents used as modifiers of quartz crystal microbalance electrodes was estimated from quantitative sorption parameters. A piezoelectric quartz crystal microbalance with electrodes modified with a squalane solution in hexane was proposed for determining acetonitrile in air at a level of 0.5 MPC. The conditions of the formation of sensitive films (modifier weight and solvent) were optimized, and the interfering effect of alkyl acetates was studied.     

Gravimetric And Quantum-chemical Study of Interaction of Monoethanolamine Vapor With Silica Surface

Kinetics of the monoethanolamine vapor adsorption on the surface of silica previously deposited onto quartz plate was examined by the piezoelectric microweighing. With the assumptions which are in accord with the experimental data, the kinetic equation of the process was obtained and thus the adsorption and desorption constants were found. The structure of the possible adsorption complexes was studied in the framework of the quantum-chemical MNDO method and the conclusion was made that the two-center adsorption of the monoethanolamine on the silica surface proceeds as a two-stage process with the participation of both functional groups. The bonding is mainly effected owing to the proton-acceptor properties of amine groups. This revised version was published online in August 2006 with corrections to the Cover Date.     

Application of principal component analysis and discriminant analysis using latent structure regression to the identification of highly volatile organic compounds in gas mixtures based on piezoelectric quartz microweighing parameters

The applicability of the new parameters of piezoelectric quartz microweighing and principal component and discriminant analysis with the use of latent structure regression to the treatment of the output data of an array of piezoelectric sensors in the identification of individual highly volatile compounds in model three-component gas mixtures is discussed. The parameters proposed and the methods of chemometrics were used in the treatment of the multidimensional data of an electronic nose for detecting individual aromaforming compounds and evaluating changes in the aroma of food systems with functional additives.     

Physicochemical characteristics of the reaction of vapors of organic liquids with divinyl-styrene and isoprene polymer films of piezoelectric chemical sorption sensors

The reaction of vapors of organic liquids with films of carbon-chain polymers was studied on piezoelectric quartz resonators. Physicochemical characteristics of sorption processes in the system vapor-film sorbent were determined in the region obeying Henry’s law. It was concluded that divinyl-styrene polymer can be used in piezoelectric chemical sensors for environmental control of trace organic toxicants.     

A novel quartz crystal microbalance gas sensor based on porous film coatings. A high sensitivity porous poly(methylmethacrylate) water vapor sensor

We describe a novel and generally applicable approach for creating voids in films deposited on the surface of solid substrates. Such films are advantageous when a quartz crystal microbalance (QCM) is the basis of a sensor. We show that films with large void volumes produce more sensitive sensors than with the original film. Poly(methylmethacrylate) (PMMA) was used as the polymer layer deposited on a quartz crystal microbalance (QCM) to demonstrate our technique for the model system of water vapor analysis in flowing nitrogen gas. A film of pure PMMA on a QCM is a sensor for water vapor in a gas phase. A more sensitive sensor was created by dip coating QCM crystals into solutions containing mixtures of PMMA and poly(d,l-lactide) (PDLL) and then evaporating the solution films on the QCM crystals to form mixed polymer films of varying PDLL content. The PDLL was then removed from the mixed polymer films by exposure to a NaOH solution to form pure PMMA films having various void volumes. A leached PMMA film that originally contained 50% by weight PDLL had a 3.7 times larger QCM sensitivity for water vapor than a pure PMMA film.     

Organic vapor sensing properties and characterization of α-naphthylmethacrylate LB thin films

Determination of organic vapor sensing properties of α-Naphthylmethacrylate (α-NMA) monomer based Langmuir-Blodgett (LB) thin films was aimed in this study. LB thin film fabrication was performed on quartz glass and quartz crystal substrates in order to investigate the characterization and organic vapor properties of α-NMA materials by using UV-Visible, Atomic Force Microscopy (AFM) and Quartz Crystal Microbalance (QCM) techniques. π-A isotherm graph was taken and a suitable surface pressure value were primarily determined as 13?mN m^?1 for successful α-NMA LB thin film fabrication. Transfer ratio value was found to be ≥ 0.93 for quartz glass and quartz crystal substrates. The typical frequency shift per layer was obtained as 16.93?Hz/layer and the deposited mass onto a quartz crystal was calculated as 271.30?ng/layer (1.02?ng mm^?2). The sensing responses of α-NMA LB films against dichloromethane, chloroform, toluene and m-xylene were measured by QCM system. Dichloromethane created the maximum shift in the resonance frequency than other organic vapors used in this study. Results exhibited that α-NMA LB thin films were potential candidates for organic vapor sensing applications, especially high sensitive detection of dichloromethane at room temperature.     

Application of Planar Chromatography with the Computer Processing of Chromatograms to the Analysis of Flavoring Materials Using the Determination of 4-(4-Hydroxyphenyl)-2-Butanone (Raspberry Ketone) as an Example

The applicability of planar chromatography in combination with the computer-aided processing of thin-layer chromatograms to the determination of 4-(4-hydroxyphenyl)-2-butanone (raspberry ketone), an essential component of the raspberry aroma, was demonstrated. The procedure was tested with model solutions of raspberry ketone and with commercial samples of flavoring materials of the raspberry line. Iodine vapor, 4-(dimethylamino)benzaldehyde, and vanillin were examined as visualizing agents. The procedure gives good quantitative results comparable to the data of currently available analytical techniques (densitometry), and it can be used in the analysis of flavoring materials.     

Effect of solvent on the adsorption of benzene vapors by dicyclohexane-18-crown-6 thin films

The solvent effect on the stability of the zero signal of resonators with a dicyclohexane-18-crown-6 film was studied. The adsorption capacity and sensitivity of the film coatings to benzene vapors was estimated. The performance characteristics of the microweighing of benzene vapors were calculated. A model was proposed for benzene adsorption from the gas phase on thin films of crown ether.     

The surface energy of hydrophilic and hydrophobic adsorbents

Water vapor adsorption and heats of water wetting are studied for hydrophilic quartz, hydrophobic-hydrophilic talc, and hydrophobized Silochrom samples. Water contact angles on the materials under examination are found. The surface thermodynamic parameters of the sorbents are calculated from the data obtained. It is shown that boundary water layers on hydrophilic quartz surface are ordered to a higher extent, while those on hydrophobic basal surfaces of talc particles and hydrophobic surfaces of modified Silochrom samples are ordered to a lower extent relative to liquid water. An empirical equation relating the surface pressure of water films adsorbed on hydrophilic high-energy surfaces with the surface free energy of the latter is proposed. The values of surface free energy are estimated from this equation for a number of important hydrophilic adsorbents.     

Use of synthetic adsorbents in preparative normal-phase liquid chromatography

Normal-phase liquid chromatographic separation using polymeric synthetic adsorbents was investigated. The retention behavior of dialkyl phthalates under a hexane-isopropanol eluent system revealed that both polystyrenic and polymethacrylic adsorbents can be used for normal-phase liquid chromatography, and that the polymethacrylic adsorbent has stronger retentivity than the polystyrenic adsorbent. Applicability of these synthetic adsorbents, especially the polymethacrylic adsorbents, was verified by the separation of polyunsaturated fatty acids, schizandrin in Schisandra chinensis fruit, tocopherols and tocotrienols in vegetable oils using a 10-microm adsorbent packed into an HPLC column. Furthermore, the separation was expanded to preparative scale by using polymethacrylic adsorbents with 17- and 31-microm fine grade particle sizes. The effect of loading volume on the retention or separation was also examined, and separation was maintained up to the loading of several grams per liter adsorbent. These results demonstrate that commercially available synthetic adsorbents possess considerable performance as normal-phase chromatographic media for more precise purification of bioactive compounds. including pharmaceuticals and nutraceuticals with scale-up possibilities.     

Monitoring iodine adsorption onto zeolitic-imidazolate framework-8 film using a separated-electrode piezoelectric sensor

In this work, a separated-electrode piezoelectric sensor (SEPS), constructed by a naked quartz crystal mounted between two electrodes, is reported for applications in a corrosive gaseous phase. The response of SEPS was measured by an impedance analysis method. It was shown that SEPS has an excellent frequency stability because its quality factor is in the order of 10⁵. The SEPS can be operated even with the electrode gap in air larger than 1 cm. Compared with a conventional quartz crystal microbalance, the resonant frequency of the SEPS is independent of the mass change in the electrode. The SEPS was applied to monitor the adsorption of iodine on quartz surface and zeolitic-imidazolate framework-8 (ZIF-8) film as well as in the transfer of iodine between two ZIF-8 films. The SEPS offers the advantages of easy preparation, corrosion-resistant and convenience in combination with mass and optical measurements.     

Silane modification and characterization of activated carbon

Activated carbons have been wildly used as adsorbents for various purpose. When used in a cigarette filter activated carbon can selectively remove a number of the vapor phase compounds to varying degrees of efficiency. To improve the wet-feeling of cigarette smoke with AC in the filter, a new method is developed to chemically functionalize a coal-based activated carbon (AC) based on silanization reaction. Silanization using 3-glycidoxypropyltrimethoxy silane was performed after the oxidized AC was reduced by lithium aluminum hydride.     

A novel piezoelectric quartz crystal immnuosensor based on hyperbranched polymer films for the detection of α-Fetoprotein

This paper reports a novel piezoelectric quartz crystal immnuosensor based on hyperbranched polymer films for the detection of α-Fetoprotein. In this strategy, the sensing interfaces consist of a primary cystamine monolayer assembled onto Au electrodes associated with the piezoelectric quartz crystal. The monolayer is further modified with a new hyperbranched polymer which was synthesized through direct polycondensation of monomer 5-[3-(4-aminophenyl) propionylamino] isophthalic acid. The detection performances of resulting immunosensor were investigated by use of the antibody-antigen model system of α-Fetoprotein (AFP), an important indicator in the diagnosis of clinical cancers. The analytical technique is characterised through the investigation of different methods of assembling the monolayers used as supports, as well as by comparing two different types of supports. It was found that the developed sensing interface could perform more effectively in antibody-antigen binding and consequently increased the sensitivity of the whole piezoelectric immunosensor. Moreover, the method should also be useful for the construction of other kind of immunosensors.     

Pyrolytic carbon from an aromatic precursor and its application as a counter electrode in dye-sensitized solar cells

Pyrolytic carbon thin films were deposited on quartz plates through a chemical vapor deposition process, by using a biphenyl precursor, 4,4'-bis(chloromethyl-1,1'-biphenyl). The pyrolytic carbons were microporous and catalytic toward reduction of tri-iodide, and the films thus obtained possessed a metallic appearance with good mirror reflections, hydrophilic surfaces, and low sheet resistances. The pyrolytic carbon-coated quartz plates were used, in place of the commonly used Pt-coated fluorine-doped tin oxide glass, as the counter electrode for dye-sensitized solar cells (DSSCs). The light to electricity conversion efficiency of the cell thus obtained was reasonably high, achieving 78% of that obtained by using the conventional but much more expensive Pt counter electrode. From the electrochemical impedance spectroscopic analysis, one found that the minor reduction in the conversion efficiency came from the relatively higher resistance and lower catalytic activity of the pyrolytic carbon. This work demonstrates that the newly developed pyrolytic carbon films may be a promising alternative to Pt as the counter electrode material for DSSCs.     

Micro-phase titrations

Summary A micromethod for phase titration is described. The volume of solution used in the titration may be as little as 0.1 ml. Results for phase titrations of 141 synthetic mixtures containing ethanol and a variety of artificial flavoring and perfuming agents are presented.

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Zusammenfassung Ein Mikroverfahren zur Phasentitration wurde beschrieben. Man kann mit 0,1 ml Untersuchungslösung auskommen. Die Ergebnisse für 141 synthetische Gemische aus Äthanol und verschiedenen Geschmacks- und Geruchsstoffen (ätherischen Ölen) wurden mitgeteilt.

     

Piezoelectric Detection of Ricin and Affinity-Purified Goat Anti-ricin Antibody

Abstract

Detection of ricin, in a piezoelectric quartz crystal microbalance format, can be accomplished with the use of capture antibody techniques. These techniques allow for the specific attachment of ricin to immobilized capture antibodies on the quartz crystal transducer area. A reversed format can also be used to detect antibody in solution. In this case, the antigen is immobilized and antibody attaches specifically, thus increasing the overall mass and decreasing the resonant frequency. In this report we describe detection of both ricin and anti-ricin antibody using immunological piezoelectric quartz crystal microbalance techniques.

     

基于金属离子螯合的压电免疫传感器新型固定化方法

提出了一种基于金属离子螯合作用的压电免疫传感器新型固定化方法. 先在压电石英晶振表面沉积正丁胺等离子体聚合膜(BA-PPF), 再在BA-PPF表面修饰可与金属离子螯合的氨三乙酸基团, 用金属铜离子活化后, 修饰了二乙三胺五乙酸基团的IgG抗体蛋白质分子即可螯合固定于BA-PPF上. 将固定了抗体的压电石英传感器用于正常人免疫球蛋白IgG (NHIgG)的测定, 其频率响应与NHIgG浓度在0.36～63.8 μg/mL范围内存在良好的线性关系. 这种新型压电免疫传感器固定化方法简单快速, 具有良好的通用性.