Yao Shouzhuo

Frequency properties of a piezoelectric quartz crystal in solutions and application to total salt determination

Abstract For an integrated circuit oscillator, the slope of the linear portion of the frequency shift/electrolyte concentration plot for a AT-cut quartz piezoelectric crystal immersed in a solution is dependent on the circuit capacitance, decreasing from positive to negative values with increasing capacitance. The slope does not vary significantly with the kind of salt. A method based on the frequency measurement is suggested for the rapid determination of the total salt content of natural waters.

On equivalent circuits of piezoelectric quartz crystals in a liquid and liquid properties: Part I. Theoretical derivation of the equivalent circuit and effects of density and viscosity of liquids

Abstract An electromechanical coupling equivalent circuit model for a piezoelectric quartz crystal in a liquid phase is suggested. The relations between the equivalent circuit parameters, series resonance frequency shift (Δ f s ) of a quartz crystal and the density ϱ, viscosity (η), specific conductance (ϰ), dielectric constant (&ϵ) of the liquid are derived as follows: Dielectric loss resistance R 0 = L / A * k , the incremental static capacitance Δ C 0 = &ϵ A * /4π L , the incremental motional resistance Δ R q = 2(π f s ϱη) 1 2 A / k 2 , Δ f s = f s 3 2 (ϱη/πϱ q μ) 1 2 . Here ϱ q , μ, f s , A , k are the density, elastic modulus, series resonance frequency, electrode area and coefficient of electromechanical coupling of the quartz crystal, respectively; A * , L are constants relating to the crystal electrodes, electrode leads and their construction. From the detailed studies on the admittance/impedance behavior of a crystal in sucrose solutions, the effects of ϱ, η are verified experimentally. The factors influencing the slopes d Δ f s /d(ϱη) 1 2 , d R q /d(ϱη) 1 2 and the effects of spurious modes in the crystal are also discussed.

Bulk acoustic wave sensor for investigating hemorheological characteristics of plasma and its coagulation

A method of using a bulk acoustic wave (BAW) device to study the hemorheological phenomena is proposed. By measuring the resonant resistance of a BAW device, the dependence of the plasma viscosity on its composition is investigated. It has been found that during the process of the plasma coagulation, the frequency response of a BAW device is dominated by the change in plasma viscoelasticity, and useful information such as the coagulation time and the viscoelasticity of coagulated plasma can be obtained from the curve of frequency response. Based on the BAW quartz detection system, effects of fibrinogen, thrombin and some drugs on the plasma coagulation are investigated. The results show that the BAW device based on the oscillator method possesses some advantages, such as high sensitivity, simplicity of use, cost effectiveness and small sample volume for clinical hemorheological study.

Selective determination of silver in solution by adsorption on a piezoelectric quartz crystal

Abstract Electrodeposition of metal ions on the crystal is eliminated by using a specially constructed transistorized oscillator. When tartrate, citrate, EDTA or their mixtures are present, silver adsorption occurs. The frequency change is proportional to the silver concentration in the range 2 × 10−7−1 × 10−5 M after adsorption for 10 min from a 1 mM EDTA/3 mM tartrate solution. No significant interferences are caused by other metal ions. On the basis of cyclic voltammetric studies, it is suggested that silver is adsorbed as a silver (I) complex.

Using Piezoelectric Quartz Crystal to Study Hemorheological Phenomena: Blood Clotting and Urokinase Activated Fibrinolysis

Abstract A piezoelectric quartz crystal (PQC) was used to study hemorheological phenomena. On the basis of equivalent circuit parameters, the frequency response corresponding to the blood clotting was discussed. The results show that the response of PQC was dominated by viscosity change at the initial stage, and then by mass effect and surface stress. With PQC monitoring the change of coagulated plasma viscosity, the urokinase activated fibrinolysis was investigated.

Frequency characteristics of an electrode-separated piezoelectric crystal sensor in contact with a liquid

The equations characterizing the frequency response of an electrode-separated piezoelectric crystal (ESPC) sensor, with one side in contact with a liquid, to the properties of the liquid were derived from an electric equivalent circuit model and supported by experiments. The frequency shift of the ESPC can provide information on the permittivity, conductivity, density and viscosity of the liquid.

Determination of quinine in some pharmaceutical preparations using a ring-coated piezoelectric sensor

Quinine is a highly active blood schizontocide and is still used in the treatment of P. fulciparum malaria resistant to chloroquine or other antimalarial drugs. For its determination, most pharmacopoeias recommend non-aqueous titration [l-3] or an extractionweighing method [l]. Other methods that have been proposed include spectrophotometry [4], fluorimetry [5], liquid chromatography [6] and ion-selective electrode potentiometry [7]. The conventional extraction-weighing method which is based on neutralization, extraction, evaporation and weighing the quinine base is time-consuming and rather inconvenient; in addition a relatively large sample is required. The piezoelectric quartz crystal is very sensitive for weight determination and is widely used as a quartz crystal microbalance (QCM) in both science and technology [8]. In the present paper, a new method is proposed for the determination of quinine based on the use of a specially designed ring-coated piezoelectric crystal sensor. The method is simple and sensitive and enables submicrogram amounts of quinine to be determined.

Equivalent circuits of piezoelectric quartz crystals in a liquid and liquid properties: Part 2. A unified equivalent circuit model for piezoelectric sensors

Abstract A unified equivalent circuit model is proposed to simulate the electrical behavior of liquid or quasi-liquid piezoelectric sensors including normal, series, parallel and separated-electrode-piezoelectric crystal. The relationships of the resonance frequency and the effective quality factor of these piezoelectric sensors to the liquid properties (permittivity, conductivity, density and viscosity) are derived and verified experimentally. The frequency shift characteristics and effective quality factors of these piezoelectric sensors are compared.

An impedance analyzer method to simulate the oscillating characteristic of a series piezoelectric sensor in oscillators with zero or non-zero phases.

An impedance analyzer method is employed to simulate the oscillation frequency of a series piezoelectric quartz crystal (SPQC) in electrolyte or non-electrolyte solutions. The influence of the oscillator phase on the oscillation frequency and response sensitivity are theoretically derived and experimentally verified. In non-electrolyte liquids, the oscillator phase has little effect on both the oscillation frequency and the response to the permittivity. But in electrolyte solutions, the oscillator phase has a significant influence on the oscillation frequency and the response sensitivity to the conductivity. Depending on the oscillator phase, the oscillation frequency of the SPQC may increase, be maintained or decrease with increasing conductivity in low or high conductive solutions. The dependence of the oscillation frequency of the SPQC on the supply voltage is explained. As an example of the applications, the SPQC is applied to the determination of the critical micelle concentration of ionic surfactants in aqueous solutions.

Theory and application of analytical spectroelectrochemistry with long path length spectroelectrochemical cells: Part I. Integral equation connecting the absorbance with the concentration distribution and its use in digital simulation for long path length thin layer spectroelectrochemical cells

Abstract An integral equation connecting the absorbance with the concentration distribution for analytical spectroelectrochemistry in long path length cells was derived. On the basis of the numerical integration form of the equation a finite difference model for digital simulation of the long path length thin layer spectroelectrochemical cell with a single potential step was set up. The concentration distribution at different moments determined with the technique was confirmed by theoretical results and the variation with time of the simulated absorbance curve was in agreement with that obtained by experiment, and hence the treatment can be applied for the estimation of parameter and the study of kinetics and mechanisms of electrochemical systems.