Piezoelectric quartz crystals, measurement

Bulk-wave piezoelectric quartz crystal sensors indirecdy measure mass changes of the coating on the surface of the sensing device. This change in mass causes changes in the resonant frequency of the device, and measurements ate based on frequency differences. 

Quite a number of recent papers have concentrated on techniques which allow the gravimetric detection of only a few femtograms of an analyte [105]. In one of these, PAHs could be measured in concentration of down to a few ng ml-1 in degraded oil when a piezoelectric quartz crystal coated with Mi-polymers imprinted either with a fresh or with a degraded lubricant was immersed into the... 

Film electrodes have been essential components of quartz microbalance studies of stoichiometry of many electrodeposition and dissolution experiments as well as polymer electrode characterization [25]. In the quartz microbalance, changes in mass are detected by measurement of changes in the resonant frequency of a quartz crystal oscillator as the mass adhering to the surface changes. The oscillation is feasible because thin-film metal electrodes (typically gold) applied to opposing faces of a piezoelectric quartz crystal serve both to induce the oscillation and to provide a site for electrochemical reaction. 

Most cascade impactors do not give data in real time. The collection surfaces must be removed from the device and subjected to chemical or gravimetric analysis. However, one impactor does give data in real time. The Model PC-2 Air Particle Analyzer (California Measurements, Inc., Sierra Madre, CA) achieves a real-time measurement by using piezoelectric quartz crystal microbalance (QCM) mass sensors to electronically weigh particles at each impactor stage [62,63], The device has 10 stages and separates the aerosol into... 

The photoswitchable complexation/dissociation properties of n donor-acceptor complexes between xanthene dyes and photoisomerizable bipyrid-inium salts have been used to generate an optoelectronic interface [97] (Fig. 28). Eosin isothiocyanate (52) was covalently linked to an electrode surface via a thiourea bond (Fig. 28A). The electron acceptor 3, 3 -bis(N-methylpyridinium) azobenzene 53 was used as the photoisomerizable component. The association constants of the n donor-acceptor complexes generated between eosin and 53a or 53b in solution correspond to Ka — 8.3 x 103 M-1 and Ka — 3.4 x 103 M 1, respectively. The analysis of complexation on the functionalized surface was accomplished by quartz crystal microbalance measurements. The frequency change (Af) of a piezoelectric quartz crystal on which a mass change Am occurs is given by the Sauerbrey equation (Eqn. 1) ... 

Piezoelectric quartz crystals serve as resonator-based transducers for direct and real-time monitoring of immunoaffinity interactions. The measuring system is briefly characterized several examples for immobilization of antibodies are recommended. The piezoelectric immunoassays employing direct, competitive, and displacement-based formats are demonstrated on examples. The method for kinetic characterization of immunoaffinity interactions is presented. 

The quartz crystal microbalance device (QCM)21-24 allows one to measure the change of the mass of the films. This method is based on the ability of a piezoelectric quartz crystal to oscillate at a resonance frequency determined by the mass of the crystal. For these measurements, gold is evaporated directly onto the surface of such a quartz sensor which is then exposed to the vapour or solution of the adsorbate. What makes this method very valuable is that it can be used like SPR for monitoring molecular adsorption/desorption at the surfaces in situ. 

Two commercially available aerosol mass concentration analyzers have been described for the determination of aerosols and particulates [18], The instruments are both portable and relatively rugged and operate on ordinary commercial power. A portable system utilizing an electrostatic precipitator was described for mass concentration measurements in the range of airborne dust particles smaller than 10 /Am [19]. Chuan [20] also described a typical commercial instrument based on the piezoelectric quartz crystal microbalance for the rapid assessment of particular mass concentrations in the atmosphere. The adhesive coating used in the device is non-hygroscopic and non-reactive to the usual concentrations of pollutant gases in the atmosphere, such as CO, SO2, NOjt, and hydrocarbons. 

Piezoelectric quartz crystal oscillators function on the basis of the well-established relationship (Sauerbery equation) between the oscillation frequency of a quartz crystal and the mass of a thin film deposited on its surface [501]. QCM has been extensively used in measurements in vacuo and in the gas phase, which includes the studies on gas phase silylation for oxygen RIE development [443] (see 6.2) and on resist outgassing [439,502]. The QCM technique has been extended to measurements in the liquid phase including aqueous media and has found powerful utility in studies of dissolution kinetics of phenolic and other acidic resists in aqueous base [503]. 

This article provides some general remarks on detection requirements for FIA and related techniques and outlines the basic features of the most commonly used detection principles, including optical methods (namely, ultraviolet (UV)-visible spectrophotometry, spectrofluorimetry, chemiluminescence (CL), infrared (IR) spectroscopy, and atomic absorption/emission spectrometry) and electrochemical techniques such as potentiometry, amperometry, voltammetry, and stripping analysis methods. Very few flowing stream applications involve other detection techniques. In this respect, measurement of physical properties such as the refractive index, surface tension, and optical rotation, as well as the a-, //-, or y-emission of radionuclides, should be underlined. Piezoelectric quartz crystal detectors, thermal lens spectroscopy, photoacoustic spectroscopy, surface-enhanced Raman spectroscopy, and conductometric detection have also been coupled to flow systems, with notable advantages in terms of automation, precision, and sampling rate in comparison with the manual counterparts. 

Determination of the pressure as a function of the combustion time is now mainly performed by means of piezoelectric pressure transducers. They operate such that the measured pressure that acts on their quartz-crystal measuring element via a diaphragm is transformed into a corresponding electric charge. After the electric charge is amplified, it is recorded by suitable measuring equipment. Quartz-crystal, barium titanate, and lithium sulphide can be used as the measuring elements in piezoelectric transducers. 

Randin, J.P. and Ziilig, F. (1987). Relative humidity measurements using a coated piezoelectric quartz crystal sensor. Sensors Actuators 11 319. 

EQCM [172] significantly contributed to the elucidation of mechanisms of electrochemical reactions of fullerene films. The principle of the method is simple and based on frequency measurement of a piezoelectric quartz crystal. The frequency is sensitive to mass and viscosity changes on a thin metal film (electrode) deposited on the quartz crystal. Most commonly any contribution from shear forces is neglected and the observed fi-equency changes are regarded as being... 

The most sensitive solvent vapor sorption method is the piezoelectric sorption detector. The amount of solvent vapor absorbed by a polymer is detected by a corresponding change in frequency of a piezoelectric quartz crystal coated with a thin film of the polymer because a frequency change is the response of a mass ehange at the surface of such a crystal. The frequency of the crystal decreases as mass increases when the crystal is placed in a gas or vapor medium. The frequency decrease is fairly hnear. The polymer must be coated onto the crystal from a solution with some care to obtain a fairly uniform film. Measurements can be made at dynamic (vapor flow) or static conditions. With reasonable assumptions for the stabihty of the crystal s base frequency and the precision of the frequency counter employed, the piezoelectric method allows the detection of as little as 10... 

The measurement of mass using a quartz crystal microbalance is based on the piezoelectric effect.When a piezoelectric material, such as a quartz crystal, experiences a mechanical stress, it generates an electrical potential whose magnitude is proportional to the applied stress. Gonversely, when an alternating electrical field is... 

The quartz crystal microbalance (QCM) is a piezoelectric device consisting of a thin (e.g.) quartz wafer sandwiched between two electrodes. A potential applied across the electrodes results in an oscillation of the quartz. The frequency of the oscillation, which can be measured accurately, is sensitive to mass loading. The relationship between frequency and mass loading is described by the Sauerbray equation ... 

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