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

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.     

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

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.     

Electrolytic determination of traces of iodide in solution with a piezoelectric quartz crystal

The frequency of a piezoelectric quartz crystal is decreased when iodide is electrodeposited on the silver electrode of the crystal at—0.05 V vs. Ag/AgCl. From 3 × lO^-7 M to 1 × 10^-5 M iodide can be determined with few interferences, and a procedure for removal of interfering species is given. Iodide is removed from the electrode by electrolysis at —0.4 V after each determination.     

Single-drop method for determination of cyanide in solution with a piezoelectric quartz crystal

The change in frequency of a horizontal quartz crystal in contact with a single drop of solution is measured. When the gold electrode of the crystal is dissolved by reaction with cyanide in alkaline solution, the further change of frequency is linearly related to cyanide concentration in the range 10^-3–10^-4 M at pH 10.4. Only silver(I) and mercury(II) interfere if EDTA is added.     

Electrolytic determination of nanomolar concentrations of silver in solution with a piezoelectric quartz crystal

Silver in solution is determined in situ by the frequency change of a piezoelectric quartz crystal on electrodeposition on the electrode of the crystal. The electrolyte solution flows through a cell containing the platinum-plated electrode (cathode) of the quartz crystal, a coiled platinum-wire anode and a silver—silver(I) chloride reference electrode, and is electrolyzed at —0.2 V vs. $\text{Ag}\text{AgCl}$. The frequency change is proportional to the silver concentration in the range 10^-5–5 × 10^-7 M after electrodeposition for 5 min, and in the range 10^-8–10^-9 M by recycling 20 ml of the solution over the electrodes for 3 h.     

Real-time monitoring of formaldehyde-induced DNA-lysozyme cross-linking with piezoelectric quartz crystal impedance analysis

A novel method for monitoring, in real time, the formaldehyde (FA)-induced DNA-protein cross-linking process with the piezoelectric quartz crystal impedance (PQCI) technique is proposed. The method was used to monitor FA-induced DNA-lysozyme cross-link formation. Lysozyme was directly immobilized on the silver electrode surface of a piezoelectric quartz crystal by adsorption. The lysozyme-coated piezoelectric sensor was in contact with FA and DNA solutions. The time courses of the resonant frequency and equivalent circuit parameters of the sensor during the cross-linking were simultaneously obtained and are discussed in detail. On the basis of the feature of the multi-dimensional information provided by the PQCI technique, it was concluded that the observed frequency decrease could be mainly ascribed to the mass increase resulting from the cross-linking. According to the frequency decrease with time, the kinetics of the cross-linking process were quantitatively studied. A piezoelectric response model for the cross-linking was theoretically derived. Fitting the experimental data to the model, the kinetic parameters, such as the binding and dissociation rate constants (k(1) and k(-1)) and the cross-linking equilibrium constant (Ka), were determined. At 37 degrees C, the k(1), k(-1) and Ka values obtained were 7.0 (+/-0.1) x 10(-5) (microg ml(-1))(-1) s(-1), 6.6 (+/-0.1) x 10(-3) s(-1) and 1.06 (+/-0.02) x 10(-2) (microg ml(-1))(-1), respectively.     

Electrolytic determination of mercury(II) in water with a piezoelectric quartz crystal

Mercury(II) is deposited on the gold electrodes of a piezoelectric quartz crystal and the change in weight causes a frequency change proportional to the mercury (II) concentration in the range 2–30 μM. Of the cations tested in 10-fold molar amounts, only silver(I) interfered.     

Electrodeless piezoelectric quartz crystal and its behaviour in solutions

An electrodeless piezoelectric quartz crystal system was constructed with a quartz crystal plate, electrolyte solutions and platinum plates or rods immersed in the solutions for connecting to an oscillator, instead of the electrodes. The crystal without electrodes oscillates in the solutions. The frequency varies with temperature, specific conductance of the solutions and the mass change of the plate caused by the adsorption of material from the solution in, the same way as a normal piezoelectric quartz crystal with electrodes.     

Calibration method for determination of acids and bases with piezoelectric quartz crystal sensors

Based on the linear relation between the frequency response of the piezoelectric quartz crystal sensor and the conductivity of the solution to be measured, calibration models for quantitative analysis of acid and base systems are derived and are verified both theoretically and experimentally. Then quantitative determinations of aspirin and penicilline were done with the calibration technique. The quantitative analysis results of the two true pharmaceutical systems indicate that the models, combining linear regression, can give precise and accurate concentration estimates, which can reduce the influence of the presence of interferences.     

Rapid detection of Escherichia coliform with a bulk acoustic wave sensor based on the gelation of Tachypleus amebocyte lysate

A new sensing method (BAW-TAL technique), which combined the bulk acoustic wave (BAW) technique with the gelation reaction of Tachypleus amebocyte lysate (TAL), was used for viscosity and density measurement and applied to the detection of Escherichia coliform (E. coli). This method depended on the fact that the viscosity and density of the mixture increased, and as a result, the resonance frequency decreased correspondingly after TAL was mixed with the heated E. coli solution that contained endotoxin. Results showed that the frequency shift was linearly related to the logarithm of E. coli concentration in the range of 2.7x10(4)-2.7x10(8) cells/ml. The correlation coefficient was 0.996. This BAW-TAL method was compared with the standard pour plate counts (PPC) method. The proposed method was much more rapid and simpler for detection of E. coli than the traditional methods.     

Behaviour of piezoelectric quartz crystals in solutions with application to the determination of iodide

The frequency of oscillation of a piezoelectric quartz crystal immersed in solution changes with the temperature of the solution and with the ambient temperature of the oscillator, especially where the latter is transistorized. The frequency is also affected by the specific gravity, viscosity and specific conductivity of the solution. When all the properties are maintained constant, iodide present in the solution electrodeposits on the silver electrodes of a crystal to produce a reproducible change in frequency which allows iodide to be determined in the range 0.5–7 μM. Thiosulphate, cyanide, sulphide, Fe(III), Hg(II) and Ag interfere, but procedures for preventing their interference are given.     

Frequency response to liquid density of a piezoelectric quartz crystal sensor with longitudinal wave

Elimination of longitudinal wave effect is an important aspect in the detection cell design, although such consideration is ignored in most of references. Three detection cells were designed to investigate the influence of longitudinal wave effect on the frequency response of a piezoelectric quartz crystal (PQC) to liquid density. In the cell with horizontally mounted quartz crystal, the air/liquid interface acts the reflection surface for the longitudinal wave. The variation in liquid height by regent addition or solvent evaporation can result in fluctuation in the oscillating frequency of the PQC. The influence of the longitudinal wave is more obvious in a test liquid of lower density. In the cell with perpendicularly mounted quartz crystal, the longitudinal wave is mainly reflected back by the inner wall body. The fine structure of plotting of frequency shift (Δf) versus (ρη)^1/2 shows a wave shape, which is different from the well-known linear relationship between of Δf and (ρη)^1/2, where ρ and η are the density and viscosity of the liquid, respectively. And wave-shaped frequency-temperature curves were observed. The longitudinal wave was a kind of potential error source in the PQC measurements. The longitudinal wave effect can be efficiently eliminated by using a rough reflection surface. After eliminating the influence of reflected longitudinal wave, the stability of the sensor PQC was much improved.     

Discrimination between endotoxin and (1----3)-beta-D-glucan using turbidimetric kinetic assay with Limulus amebocyte lysate

A procedure for the Limulus amebocyte lysate (LAL) test discriminating between endotoxin and (1----3)-beta-D-glucan based on the turbidimetric kinetic method was proposed. Endotoxin and (1----3)-beta-D-glucan, which are elicitors of the activation of LAL, showed different reaction courses with this lysate. To analyze the difference in the reactions, two parameters, the maximum differential coefficient of the reaction (Dmax) and the reaction time required to obtain Dmax (Tp) were defined. The logarithmic plottings of Tp versus Dmax (Tp-Dmax plot) discriminated between endotoxin and (1----3)-beta-D-glucan. Endotoxin was measured with a standard curve plotting logarithmic endotoxin concentration versus Dmax (ET-Dmax plot). The endotoxin calculated from Dmax was less influenced by (1----3)-beta-D-glucan than that calculated from the usual gelation time. A small amount of endotoxin in a sample could be concealed by the addition of polymyxin B, which inhibited the activation of LAL by endotoxin. (1----3)-beta-D-glucan was measured without being affected by the presence of a small amount of endotoxin using LAL with polymyxin B. The following procedure is proposed as a LAL test to discriminate between endotoxin and (1----3)-beta-D-glucan. (1) Identify the main substance (endotoxin or (1----3)-beta-D-glucan) triggering the activation of LAL using the Tp-Dmax plot. (2) Use the appropriate method to measure the main substance: the ET-Dmax plot for endotoxin or the LAL with polymyxin B for (1----3)-beta-D-glucan.     

Monitoring of DNA oxidative damage with piezoelectric quartz crystal method

The piezoelectric quartz crystal (PQC) sensor was used to detect the whole process of DNA damage oxidized by H(2)O(2) system containing Cu(2+) or Zn(2+) based on the density-viscosity change of the detected solution. The PQC impedance method has been applied to further investigate the damage process of DNA oxidized by H(2)O(2) system containing Cu(2+). It was found that the ratio of DeltaR(1) to Deltaf(0) or DeltaL(1) coincided well with that calculated from Martin's equations reflecting the solution density-viscosity effect, suggesting that the continuing change in liquid loading on to the PQC surface caused the significant variation of Deltaf(0), DeltaR(1) and DeltaL(1). It has also been found that the H(2)O(2) system containing Cu(2+) could oxidize DNA more completely than that containing Zn(2+), and a trace Cu(2+) in the system could cause DNA damage. However, no significant breakage in the DNA backbone was observed if the system contained only H(2)O(2). The DNA concentration was linearly related to Deltaf(0s), which is the different between the initial frequency and the frequency after a reaction time of 45 min, in the range of 50-1000 mug ml(-1). The effect of H(2)O(2) or Cu(2+) concentration of was also investigated. The above-mentioned results that the H(2)O(2) system containing Cu(2+) or Zn(2+) could break the DNA backbone were also supported by the agarose gel electrophoresis technique.     

Kinetic determination of organic vapor mixtures with single piezoelectric quartz crystal sensor using artificial neural networks

A single piezoelectric quartz crystal coated with one kind of crown ether was applied to the simultaneous determination of binary acid and amine vapor mixtures. From the adsorption and desorption curves of analytes, which were somewhat different in shape, frequency shifts from ten time windows were taken as inputs for artificial neural networks (ANN). Prediction results were satisfactory for ANN in both sample sets. The average relative errors, for formic acid and acrylic acid were 5%, for n-butylamine and aniline, they were 3% with ANN respectively. The effects of number of neurons in the hidden layer of ANN on the performance of the network are also discussed.     

Monitoring of mutagenic process with piezoelectric quartz crystal impedance analysis

A novel method for monitoring of mutagenic process of dimethyl sulfate to Salmonella typhimurium strain (TA100) was proposed by using piezoelectric quartz crystal impedance (PQCI) analysis technique. The time courses of responses piezoelectric impedance parameters for a quartz crystal in a culture system were simultaneously obtained and discussed. It was found that the motional resistance variation (DeltaR(m)) increases and frequency shift (Deltaf) of PQC sensor decreases correspondingly during the mutagenic process of the bacteria. These parameters could reflect the variations of viscosity and density of culture system. By fitting DeltaR(m) versus time curves toward Gompertz bacterial growth model, we obtained and discussed the bacterial growth parameters for both normal growth and mutagenic process. The experiments showed that the proposed method could provide real time and multidimensional impedance information to the monitoring of mutagenic process.     

Determination of lead in solution with a piezoelectric quartz crystal coated with copper oleate

Copper(II) oleate was coated on a piezoelectric quartz crystal, and the copper removed by passing EDTA solution. The remaining coating reacted with aluminium, copper(II), iron(III) and lead ions in a flowing acidic solution, to form absorbed compounds which changed the frequency of the crystal. Lead (3–40 μM) could be determined at pH 5.5–5.8 with good reproducibility. Interfering metal ions (Al³⁺, Cu²⁺, Fe³⁺) were masked with acetylacetone.     

Crystallization monitoring in supersaturated solution with a quartz crystal sensor

The degree of supersaturation is an important measure for the operation of crystallization processes, because it is directly related to the control of crystal size distribution and shape. A conventional technique utilizing solution composition and temperature has a variety of problems caused from the measurement error and the handling of analyzing samples.A monitoring system of the supersaturation using a quartz crystal sensor is proposed here, and its performance is examined applying different manipulations of coolant temperature. The experimental outcome and photographic examination indicate that the measurements of resonant frequency and resistance of the sensor can be used for the prediction of the formation and growth of solid crystal from the crystallization process. The monitoring system eliminates the intrinsic error source of the conventional system to give the improved measurement and on-line application availability.     

Piezoelectric transmission spectroelectrochemistry with a normal piezoelectric quartz crystal as an optically-transparent electrode

Piezoelectric transmission spectroelectrochemistry (PTSEC), i.e., the combination of electrochemistry and spectroelectrochemistry (SEC) with electrochemical quartz crystal microbalance (EQCM) technique is reported by using a normal piezoelectric quartz crystal (PQC) as an optically-transparent electrode (OTE). A theoretical relationship between the PQC response and the spectroelectrochemical response is derived and used to estimate the apparent molar absorptivity of the absorbing species deposited on the OTE on the PQC surface. The complex of copper with aspartic acid is used to test this new PQC-SEC technique. Results show that the combination of three such diverse techniques provides a very useful methodology for studying electrode processes and electrode surface characteristics in situ.     

Adsorption of metal ions from solution onto a piezoelectric quartz crystal

Many metal ions are spontaneously adsorbed onto a piezoelectric quartz crystal and change the oscillation frequency. The pH ranges in which the metal ions adsorbed were just below that of precipitate formation as the ‘hydroxides’; frequency changes caused by adsorption were not observed in these pH ranges where the ‘hydroxides’ formed. Cationic organic reagents, such as crystal violet and methylene blue, were also adsorbed on the piezoelectric quartz crystal but non-ionic and anionic organic compounds were not. These results showed that the crystal was negatively charged on the surface.