Piezoelectric Crystal Detector Research Articles

Rapid screening of poly(ethylene glycol) polymers by C18 column-flow injection with piezoelectric detection system

A rapid and low cost analytical method for the screening and determination of poly(ethylene glycol)s polymers has been developed. Several initial studies were carried out in order to demonstrate the utility of a piezoelectric quartz crystal as a detection system for the quantification of poly(ethylene glycol)s. The method involves the use of a simple flow injection device connected to a piezoelectric quartz crystal detector. Several parameters associated with the simple flow injection manifold were optimized. Subsequently, this detector was coupled to a C18 column and the best experimental conditions were investigated in order to perform the screening and determination of poly(ethylene glycol)s. The applicability of this method, as an analytical screening tool, was demonstrated by the characterization of samples with different molecular mass polymers without using HPLC and CE techniques to carry out oligomer separations. A standard curve to determine the polymer content was obtained by relating the resonance frequency shift and polymer concentration, which showed good linearity and good regression coefficients. The working range, repeatability, limit of detection and recovery were all acceptable for the analysis of the poly(ethylene glycol)s. Finally, the proposed method was applied to determine these polymers in several samples, such as pharmaceutical products, washing powder, detergents and a body spray.

Polyethylene Maleate Copolyesters as Coating Materials for Piezoelectric Quartz Crystal-based Chemical Sensors

Polyethylene maleate (PEM) was synthesised by direct polycondensation of maleic anhydride and ethylene glycol in toluene under reflux usingp-toluene sulphonic acid as a catalyst. Structure of PEM was further modified by varying nature of diols and acid components, chain length of glycols, incorporation of aromatic and fluorine groups in the chain. Formation of PEM was monitored by gas chromatography. The parameters like degree of polymerisation, number average molecular weight (Mn), and weight average molecular weight (Mw) were calculated from the extent of reaction and stoichiometric ratio of the reactants. The number average molecular weight was also determined using Knauer vapour pressure osmometer. Cohesive energy, volume, and solubility parameters of PEM-based copolyesters were calculated by group contribution method. These PEM-based copolyesters’ have been evaluated as sorbent-coating materials for the detection of organ0 phosphorus(OP)compo using dimethylmethylphosphonate (DMMP) as model compound and piezoelectric crystal detector. PEMbisphenol A is found to be the most sensitive and potential coating material for the detection of OP compounds using piezoelectric crystal detector. Potential PEM-based copolyesters have been characterised by viscosity, infrared spectroscopy, NMR spectroscopy, Mn and thermal stability.

Piezoelectric Crystal Liquid Flow Detection Systems Based on Alkyl (C18)-Benzo-15-Crown 5 for Organic Compounds and Metal Ions

A water in soluble long-chain crown ether alkyl (C18)-benzo-15-crown-5 was synthesized and applied as a coating material on quartz crystal membranes of a liquid flow piezo electric crystal sensor. The oscillating crown ether-coated piezo electric (PZ) crystal with a home-made computer inter face was prepared as a liquid chromato graphic (LC) detector for organic species and metal ions in aqueous solutions. The oscillating frequency of the quartz crystal decreased due to the adsorption of organic molecules or metal ions on crown ether molecules. Effects of functional group, molar mass, steric hindrance, and polarity of organic molecules on frequency responses of the crown ether coated PZ crystal detector were investigated. The frequency responses of the crown ether coated PZ crystal detector for various molecules were in the order: amines > carboxylic acids > alcohols > ketones. The crown ether PZ detector also exhibited good sensitivity for some heavy metal ions and the frequency shifts were in the order: Cr3+ » Pb2+ > Co2+ > Cd2+ > Ni2+ > Cu2+. The crown ether coated piezo electric crystal LC detector demonstrated low detection limits for various polar organic molecules, e.g., 6.0 × 10−5 M for propylamine, and metal ions, e.g., 2.9 × 10−5 M (1.8 ppm) for Cu2+; the crown ether PZ detector also gave good reproducibility when re used. A quite sensitive electrochemical quartz crystal microbalance (EQCM) detection system was also set-up for detecting trace heavy metal ions in solutions. The variation in frequency of the PZ crystal and the diffusion current were observed simultaneously after the reduction in heavy metal ions such as Cu2+ and Ni2+. The EQCM detection system exhibited fairly good sensitivity, e.g., 112 Hz/ppm for Cu2+ and a good detection limit, e.g., 0.13 ppm for Cu2+ ions. Comparison between EQCM and PZ detection systems was made and discussed.

Fluorinated Epoxy Resins-based Sorbent Coating Materials for Quartz Piezoelectric Crystal Detector

Fluorinated epoxy resins were synthesised and evaluated as sorbent coating materials for the detection of organophosphorus compounds using quartz piezoelectric crystal detector. These resins were prepared by reacting excess of epichlorohydrin with each of or in combination of fluorinated diols, ie, a, a, a', a' tetrakis (trifluoromethyl) 1,3 benzene dimethanol (TTFMBD), 4,4'bis-2-hydroxy hexafluoro isopropyl) biphenyl (BHHFIBP), 4,4'dihydroxyocta fluorodiphenyl (DHOFDP) and 2,2,3,3,4,4 hexafluoro 1,5 pentanediol (HFPD) in the presence of sodium hydroxide at reflux temperature. These polymers were extracted in organic solvents and dried. Each of these fluoroepoxy resins were coated over quartz piezoelectric crystal by solution-casting method and tested using dimethylmethyl phosphonate (DMMP) as model compound. Change in the frequency (AF) of quartz piezoelectric crystal oscillator was recorded. Sensitive and potential fluorinated epoxy resins, ie, diglycidylethers (DGE) of HFPD-TTFMBD (in the molar ratio 6:4) and DGE (HFPD-BHHFIBP in the molar ratio 4:6) were characterised by viscosity, number average molecular weight (Mn), epoxy equivalent, infrared spectroscopy, and thermal stability.

Polymer Coated Piezoelectric Quartz Crystal Protein Bio‐Sensors

AbstractA polymer coated piezoelectric crystal detection system with a home‐made computer interface for signal acquisition and data processing was prepared as a liquid chromatographic detector for various proteins. Various polymers, e.g., polyvinyl aldehhyde (polyacrolein) (PVA), polyacrylamide/glutaldehyde (PAA/GA) and bio‐gel A, were used as coating materials on quartz crystals for adsorption of various protein molecules, e.g., catalase (CA), hemoglobin (Hb), α‐chymotrypsin (Ch), albumin (Ab). The frequency responses of the polyacrlein coated piezoelectric detector for various proteins were in the order: catalase> hemoglobin> α‐chymotrypsin > albumin. In contrast, the order of the frequency responses of bio‐gel A and polyacrylamide/glutaldehyde coated piezoelectric crystals for these proteins were: hemoglobin> catalase > α‐chymotrypsin ≥ albumin and hemoglobin > albumin > catalase. The polyacrolein coated piezoelectric crystal protein detector exhibited a good linear frequency response with a high sensitivity of about 2.5×103 Hz/(mg/mL) for catalase. In addition, bio‐gel A and polyacrylamide/glutaraldehyde coated crystals were sensitive to hemoglobin with sensitivities of about 4.5×103 Hz/(mg/mL) and 3.0×103 Hz/(mg/mL), respectively. Study of the interference of various organic molecules, e.g., alcohols, amines, ketones and carboxylic acids, in the detection of proteins with theses polymer coated crystals was also made. The polyacrolein coated crystal for proteins under went less interference from various organic molecules than bio‐gel A or polyacrylamide/glutaraldehyde coated crystals. Effects of coating load, concentration of proteins and flow rate of liquid chromatographic eluent were also investigated and discussed.

Monitoring of Lactobacillus fermentation process by using ion chromatography with a series piezoelectric quartz crystal detector

A new method monitoring Lactobacillus fermentation process, which combines ion chromatography (IC) with a series piezoelectric quartz crystal (SPQC) technique, is presented in this paper. Monitoring of the fermentation process was realized by examining the rate of production of lactic acid. An automatic membrane dialyser was used for the pretreatment of the sample in on-line monitoring. A mixture of p-hydroxybenzoic acid and N, N-diethylethanolamine was adopted as mobile phase and its flow rate was 0.8 ml/min. The effects of some fermentation conditions were also discussed in detail. Accordingly, the optimal fermentation conditions were obtained. This method is simple and convenient while the results obtained are accurate and reliable.

Fullerene‐Crown Ether Coated Piezoelectric Crystal Liquid Chromatographic Detector for Metal Ions and Polar/Nonpolar Organic Molecules

AbstractFullerene(C60)‐dibenzo‐16‐crown‐5‐oxyacetic acid (DBI6C5‐OCH2‐COOC60) was prepared and applied as the coating material on piezoelectric quartz crystals for detection of various metal ions and polar/nonpolar organic molecules. The C60‐crown ether‐coated piezoelectric crystal sensor with a home‐made computer interface for signal acquisition and data processing was applied as an ion chromatographic (IC) detector for various metal ions, e.g., alkali metal, alkaline earth metal and transition‐metal ions. The piezoelectric detector exhibited quite good sensitivity of 104 ∼ 106 Hz/M and good detection limit of 10−3 ∼ 10−4 M for these metal ions. The C60‐crown ether piezoelectric detector compared well with the commercial conductivity detector conventionally used for metal ions. The ionic size and ionic charge seemed to have significant effect on the frequency response of the piezoelectric detector. The C60‐crown ether coated piezoelectric crystal sensor was also employed as a high performance liquid chromatographic (HPLC) detector for various polar organic molecules with frequency responses in the order: amines > carboxylic acids > alcohols > ketones. Furthermore, nonpolar organic molecules, e.g., n‐hexane, 1‐hexene and 1‐hexyne, were also detected with this piezoelectric crystal detector. The frequency responses of the piezoelectric crystal detector for these nonpolar organic molecules were in the following order: alkynes > alkenes > alkanes. The effects of solvents and flow rate on the frequency responses of the piezoelectric crystal detector were investigated. The C60‐crown ether coated piezoelectric crystal detector also showed short response time (< 1 min.) and good reproducibility.

Piezoelectric cryptand-coated quartz crystal liquid chromatographic detector for cations/anions and polar organic molecules in solutions

A reusable and sensitive multifunctional piezoelectric quartz crystal liquid chromatographic detector was developed for the detection of cations, anions and organic molecules in solutions. The quartz crystal coated with dioctadecanoyl-cryptand-22 could adsorb cations or anions depending on whether the cryptand was protonated or not. The cryptand molecule which can be protonated in an acid solution with pH <6.0 can absorb the anion in the solution. The adsorption of catons such as alkali, alkali earth, Cu 2+, Cd 2+, Zn 2+, Pb 2+ and Cr 3+ metal ions or anions such as halides, NO 3 −, SO 4 2− and CrO 4 2−, resulted in a decrease of the oscillating frequency of the cryptand-coated quartz crystal. The cryptand-coated crystal detector can also be applied to detect organic molecules, e.g., benzoic acid, in solutions. The cryptand-coated crystal detector behaved like a commercial conductivity detector in detecting cations or anions and with a UV-Visible spectrometric detector in detecting organic molecules. The detection limits of the cryptand-coated piezoelectric detector for ions and organic molecules were estimated at about 10 −5 M and 10 −4 M, respectively.

Rapid Analysis of Preservatives in Beverages by Ion Chromatography with Series Piezoelectric Quartz Crystal as Detector

A rapid ion chromatography method employing a series piezoelectric quartz crystal (SPQC) detector was used to analyze sorbic and benzoic acids in wine, syrups, cola, and Wahaha drink. The analytical procedure was performed using a Shimpack IC-A1 anion-exchange column and 3.0 mM sodium carbonate with sodium hydroxide to adjust the pH to 9.5 as the mobile phase. The high resolution of chromatography combined with the good sensitivity of the SPQC (detection limit = 0.5 ppm) resulted in good recovery and reproducibility. The obvious advantages of this technology are the elimination of the need for sample derivation or extraction and the simplicity of the analytical procedure.

Preparation and application of cryptand-coated piezoelectric crystal gas-chromatographic detector

A re-usable and sensitive cryptand-22-coated quartz-crystal membrane piezoelectric sensor with a homemade computer interface for signal acquisition and data processing was prepared and applied as a gas-chromatographic (GC) detector for various organic molecules. The oscillating frequency of the quartz crystal decreased due to the adsorption of organic molecules on cryptand-22. Effects of functional group, molar mass, steric hindrance and polarity of organic molecules on frequency responses of the cryptand-coated piezoelectric crystal detector were investigated. The cryptand-coated piezoelectric crystal GC detector had demonstrated high sensitivity for various polar organic molecules and good reproducibility when re-used. The frequency responses of the cryptand-coated crystal for various molecules were in the following order: carboxylic acids (RCOOH)≫primary amines (R-NH 2)>alcohols (ROH)>secondary amines (R 2NH)>tertiary amines (R 3N)>ketones. More polar molecules exhibited better frequency responses. The effect of temperature and amount of coating on the frequency responses of cryptand-coated crystal GC detector were also investigated. The cryptand-coated piezoelectric crystal GC detector compared well with the commercial thermal conductivity detector (TCD).

Detection of olefin vapours with silver(I)/cryptand-coated piezoelectric crystal sensors

A piezoelectric quartz crystal detector based on Ag +/cryptand-22/ethylenediamine/NH 3/PVC coating with a computer interface for signal processing was prepared for olefin vapours, e.g. alkenes and alkynes. The silver(I)/cryptand-coated detector exhibited a high sensitivity with a frequency shift range of 10–350 Hz/(mg 1 −1) for olefin vapours, a short response time with < 2 min, good selectivity and good reproducibility for reusage. The cryptand-22/Ag + coating was sensitive for olefin vapours, but not for conventional alkyl polar organic molecules such as alkyl alcohols. Alkenes with a higher carbon number showed a better sensitivity than smaller alkenes and cis-alkenes exhibited a better response than trans-alkenes. Effects of temperature and interferences of water and alkyl sulfides were also investigated and discussed.

Development of a Portable Organic Vapour Analyser Using Quartz Crystal Piezoelectric Sorption Detector for Monitoring of Total Organic Compounds in Air.

To solve the problem of high humidity interfering with the monitoring of organic vapours commonly found in workplace air using the piezoelectric crystal detector, a battery operated fan dryer was incorporated with the P/Z detector to provide a light, sensitive and portable monitor for analysing organic vapours in air. The organic vapour monitor developed is sensitive to analyse organic vapours at ppm levels below the control limits of these vapours. To select a suitable coating for the P/Z crystal detector to be used for diumal monitoring of organic compounds in indoor air and in factories, eight gas-liquid chromatography coatings was chosen for study. Based on their sensitivity, selectivity, bleeding rate and long term stability towards commonly encountered organic vapours such as 1,1,1-trichloroethane, chloroform, benzene and toluene, Apeizon grease L was selected as the coating of the P/Z crystal. The optimised analytical parameters are : temperature 22°C - 43°C, relative humidity 40% -100%, response time 2 - 30 minutes and linear working ranges 88.8ppm - 1880ppm.

Determination of lactic acid and pyruvic acid in serum and cerebrospinal fluid by ion-exclusion chromatography with a bulk acoustic wave detector

A chromatographic method based on a combination of ion-exclusion chromatography separation and bulk acoustic wave series piezoelectric quartz crystal detector quantification for the determination of pyruvic acid and lactic acid in serum and cerebrospinal fluid (CSF) was developed. The separation was carried out using a Shim-pak SCR-102H ion-exclusion column with phosphoric acid solution as eluent. The method shows an acceptable detection limit and anti-interference ability. Serum and CSF from healthy individuals and patients were analysed successfully.

Application of pattern recognition and piezoelectric sensor array for the detection of organic compounds

Organic vapours were measured by an array of piezoelectric crystal detectors. Quartz crystals were coated by different GC stationary phases. Four coated crystals were placed in an array and pattern recognition was used for identification of the compounds including acetone, benzene, chloroform and pentane. A computer program was developed for the measurement of the frequency changes and data processing. Pattern recognition method using feature extraction was applied for identification of analytes.

Application of crown ether coated piezoelectric crystal as a detector for ion chromatography

A reusable and sensitive piezoelectric quartz crystal detector was developed for the detection of either cations or anions in ion chromatography. The quartz crystal electrode coated with crown ether (sym-dibenzo-16-crown-5-oxydodecanic acid) was prepared and was found to give the best results in terms of stability, sensitivity and reproducibility. Linear frequency (voltage) responses on a 10 MHz AT-cut crystal for ions were found on the range 0.1–5 × 10–5 mol l–1. Variations of the crystal frequencies were converted to voltage using a TC 9400 chip. Polystyrene–poly(divinyl benzene) with cryptand [2,2] as an anchoring group was synthesized and applied as a bifunctional ion chromatographic packing material for the separation of both cations and anions. The crown ether coated piezoelectric crystal detector with detection limits of 2 × 10–5(1 × 10–10 mol)–5 × 10–5 mol l–1(2.5 × 10–10 mol) for various ions showed a similar detection limit to that of a commercial conductivity detector in ion chromatography. The effects of solvents, reproducibility of responses and competitiveness with respect to a commercial conductivity detector were also investigated.

A Piezoelectric crystal detector for continuous monitoring of water evolved during thermal decomposition reactions

A method for the continuous monitoring of water vapour evolved during thermal decomposition reactions is developed based on the reversible adsorption of water on a bare piezoelectric crystal with nickel electrodes. Gaseous decomposition products formed in the furnace chamber of the thermoanalytical equipment are collected and transported to the detector cell by the carrier gas. A linear relationship exists between the decrease in vibrational frequency of the crystal and the concentration of water in the carrier gas up to 900 μg/l. H 2O [1200 ppm (v/v)]. The signal curve of the piezoelectric water monitor can be recorded simultaneously along with the TG, DTG and DTA curves and used to identify the decomposition step(s) in which water was formed. CO, CO 2 and low molecular weight hydrocarbons do not interfere. Condensable organic crack products can be removed by a suitable pretrap.

Regression analysis of piezoelectric titration data to estimate system parameters

A non-linear model connecting the frequency response of the piezoelectric quartz crystal detector in acid-base titration with the added quantity of titrants has been derived in detail. It has been verified theoretically and used for the regression analysis of response curves of acid-base titrations for four acid solutions with different dissociation constants to estimate the original acid concentrations of the solutions to be titrated, dissociation constants of the acid, the equivalent ionic conductivities and the other two crystal response parameters, viz., the response sensitivity for conductivity and the basic frequency when the conductance contribution of the reacting substances equals zero. the experiments and computations indicate that the technique possesses good estimation precision and accuracy.

Flow-injection analysis of inorganic pollutants in gaseous phase with piezoelectric detection Part 1. Verification of principal experimental parameters affecting the detector response

Piezoelectric quartz crystal detectors with several coating materials sensitive to sulphur dioxide and ammonia are used as model sensors for the optimization of a flow-injection measuring system with a gaseous carrier. As factors affecting the quality of detector response, the amount of coating material and its distribution on the quartz oscillator surface, the composition, flow rate and purity of the gaseous carrier, the design of the flow-through detector, the temperature and the injection volume are considered. The experimental data obtained illustrate the significance of careful optimization of these parameters for the detectability, stability and reproducibility of flow-injection analysis in the gaseous phase with piezoelectric detection.

Titrations with piezoelectric monitoring : Part 1. Fundamental theory and titration of acids and bases

The use of a piezoelectric quartz crystal detector is proposed for monitoring the course of a titration reaction by observation of the frequency shift of the oscillating crystal. Satisfactory titrations can often be obtained using the acid-base technique, which is much more sensitive than the classical conductimetric titration and oscillometric titrration, with a lowest titratable concentration that is much lower but which can still be applied in the presence of a large amount of unreacting electrolyte.

A coated piezoelectric crystal detector system with high stability

A coated piezoelectric crystal (CPC) detector system with high stability designed for the detection of pollutants in ambient air is described. The system is based on the use of two crystals, which are exposed to the air to be analysed. The incoming air flow is divided into two paths; one is led directly to one of the CPCs and the other flow is connected to a molecular sieve filter that absorbs the pollutants before the flow is led to the other CPC. The flows are controlled by magnetic valves in such a way that one crystal is exposed to either clean air from the molecular sieve filter or to polluted air. The other crystal is exposed in the same way, but in counter phase. By careful design and control of the air flows, a high stability is reached and virtually no thermal drift is present. A long-term stability of ±0.002 Hz is demonstrated. The noise sources are analysed and methods to reduce their impact are demonstrated.