The quantification of sodium in mineral waters using a quartz crystal microbalance

A sensor for sodium based on a piezoelectric quartz crystal is proposed. The quartz crystal was coated with 5% of bis[(12-crown-4)methyl] dodecylmethylmalonate, 33% of PVC and 62% of NPOE to which KTpClPB in a 22% molar proportion to the ionophore was added. Coating amounts producing a frequency decrease around 18 kHz show optimum linear calibration ranges for the analysis of sodium in commercial mineral waters. Besides sensitivity, coating stability and selectivity of the sensor over other cations were adequate for those analyses. The results obtained analysing commercial mineral waters by the proposed method are not significantly different (α=0.05) from the ones obtained by atomic spectrometry.     

Development of a sensor for calcium based on quartz crystal microbalance

A new sensor for calcium based on a piezoelectric quartz crystal is presented. The selectivity depends on the ratio lipophilic salt/ionophore of the composition of the coating of the quartz crystal. A crystal coated with a THF solution of PVC (34.5% w/w), DOS (62.1% w/w) and 10,19-bis[(octadecylcarbamoyl) methoxyacetyl]-1,4,7,13,16-pentaoxa-10,19-diaza cycloheneicosane (3.4% w/w) and a salt/ionophore molar proportion of 60%, corresponding to a frequency decrease of the dry crystal of 6.0 kHz, showed a detection limit to calcium of 2.2 mg/L. Both a standard calcium chloride solution and a commercially balanced salt solution for tissue culture were analyzed subsequent to ion chromatographic separation. The results obtained with the sensor developed were compared with those obtained with a conductivity detector. Although the results from both detectors agreed for the standard solution, only the quartz crystal sensor was able to give reliable results for the tissue culture solution.     

Development of a sensor for calcium based on quartz crystal microbalance

A new sensor for calcium based on a piezoelectric quartz crystal is presented. The selectivity depends on the ratio lipophilic salt/ionophore of the composition of the coating of the quartz crystal. A crystal coated with a THF solution of PVC (34.5% w/w), DOS (62.1% w/w) and 10,19-bis[(octadecylcarbamoyl) methoxyacetyl]-1,4,7,13,16-pentaoxa-10,19-diaza cycloheneicosane (3.4% w/w) and a salt/ionophore molar proportion of 60%, corresponding to a frequency decrease of the dry crystal of 6.0 kHz, showed a detection limit to calcium of 2.2 mg/L. Both a standard calcium chloride solution and a commercially balanced salt solution for tissue culture were analyzed subsequent to ion chromatographic separation. The results obtained with the sensor developed were compared with those obtained with a conductivity detector. Although the results from both detectors agreed for the standard solution, only the quartz crystal sensor was able to give reliable results for the tissue culture solution.     

Determination of carboxylic acid vapour by a thickness-sheer-mode acoustic wave sensor coated with crown ethers

The frequency response sensitivities for 39 organic vapours by thickness-sheer-mode (TSM) acoustic wave sensors coated with monobenzo-15-crown-5 (B15C5), monobenzo-18-crown-6 (B18C6) and dibenzo-30-crown-10 (DB30C10) have been reported. It shows that crown ethers are the most efficient adsorptively active material for sensing carboxylic acid vapour, particularly B15C5 can be used for sensing formic acid vapour. The B15C5 based sensor possesses good reproducibility, high stability and short response time with wide linear detection range and a low detection limit down to 0.0201 mg l(-1) (about 5.70 ppm, V/V) of formic acid vapour while coating with 12 mug of B15C5. There is no significant interference from other organic vapours except for some nitrogen containing compounds such as diethylamine, pyridine and N,N-dimethylformamide, and carboxylic acid homologues such as acetic and propionic acids. The effect of humidity is easily controllable. Compared with acid-base titration method, the sensor can be used for the determination of HCOOH vapour with recovery rate of 98.4 approximately 103.8%, the analytical results are in good agreement with those obtained by the more time consuming acid-base titration method.     

Preparation and Application of Fullerene C60‐Polymers in Piezoelectric Quartz Crystal Sensors for Hemoglobin and Olefins

The C60—polycinnamaldehyde (C₆₀—PCA) and C60—polyphenylacetylene (C60—PPA) polymers were synthesized by the Friedel—Craft reaction and applied as piezoelectric (PZ) quartz crystal coating materials. A C60—polycinnamaldehyde (PCA) coated piezoelectric quartz crystal liquid sensor with a homemade computer interface was prepared and applied as a PZ hemoglobin sensor. The adsorption of hemoglobin onto the C60—PCA coated crystal resulted in a decreased oscillating frequency. The variations in crystal frequency were converted to voltage with a frequency to voltage converter, followed by amplification with OPA and data acquisition with an analog to digital converter. The PZ hemoglobin sensor exhibited good sensitivity of 6530 Hz/(mg/mL) with a detection limit at the ppm level for hemoglobin. Further, a C60—polyphenylacetylene (C60—PPA) coated piezoelectric quartz crystal gas sensor with an Intell‐8255 data processing system for various olefin vapors was also made. The aromatic hydrocarbons such as toluene seem to have greater adsorption onto C60—PPA membrane than alkynes, alkenes, and alkanes. The adsorption of polycyclic aromatic hydrocarbons (PAHs) onto the C60—PPA membrane was also examined. The C₆₀—PPA coated PZ crystal gas sensor showed much better sensitivity for PAHs than for other olefins such as toluene, 1‐hexyne and 1‐hexene, and a much larger frequency shift for naphthalene than other PAHs was also found.     

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-NH₂)>alcohols (ROH)>secondary amines (R₂NH)>tertiary amines (R₃N)>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).     

Critical assessment of the parameters that affect the selection of coating compounds for piezoelectric quartz crystal microbalances

The selection of the compound to be used as a coating for a piezoelectric quartz crystal is of utmost importance in the development of a chemical sensor. The relevant parameters to be evaluated (stability, sensitivity, reversibility, response time, reproducibility, and selectivity), and the main variables affecting the results and influencing the choice of coatings are discussed and illustrated with experiments performed during the evaluation of coatings to detect carbon dioxide.     

含嘧啶环的双冠醚（Ⅱ）

由4，6－二氯－5－硝基嘧啶、2，4－二氯－5－硝基－6－甲基嘧啶分别与4′-氨基苯并冠醚反应合成了6种以嘧啶环为桥链的新双冠醚，其中分别含有苯并－12－冠－4（Al,Bl)、苯并－15－冠－5（A2，B2）和苯并－18－冠－6（A3，B3）单元。用这些双冠 氯仿溶液绎碱金属苦味酸盐水溶液进行了萃取，计算了萃取平衡常数Kc。结果表明双冠醚（A1，B1）、（A2，B2）和（A3，B3）分别对钠、钾和铯具有较高的萃取能力，其选择性显著优于相应的单冠醚。     

Investigations on growth, thermal, electrical, and etching studies of KCl-doped triglycine sulfate single crystals

Single crystals of pure triglycine sulfate (TGS) and potassium chloride (KCl)-doped TGS with different concentrations (0.2, 0.4, 0.6, and 1?mol%) were grown from aqueous solutions by natural evaporation process at room temperature. Thermal stability of the grown crystals was investigated by differential thermal analysis (DTA) and thermogravimetric (TG) studies. DTA curve shows a lower decomposition temperature for KCl-doped TGS crystal than that of pure TGS crystal. The dielectric properties of pure TGS and KCl-doped TGS crystals were performed in the frequency range of 1?C500?kHz at 30?°C and this study showed that the dielectric constant was increased due to KCl concentration. DC electrical conductivity measurements were made in the temperature range from 35 to 100?°C and showed that the DC conductivity was increased with the increase of temperature as well as doping concentrations of KCl. The etching feature of the surface of the grown crystals was studied in water etchant.     

Cu2+‐doped ITO as a Novel Efficient,Transparent, and Fast‐Response Transducer for Ammonia Sensing

As a novel approach, the effect of Cu²⁺‐doped indium tin oxide (ITO) on a flexible polycarbonate substrate is considered as an ammonia sensor. The sensor was fabricated using spin‐coating and subsequent annealing at 160°C for 60 min. The constructed sensor morphology accomplished by surface composition was explored using scanning electron microscopy (SEM) and energy dispersiveX‐ray (EDX) spectroscopy. Using the new strategy, a flexible sensor for ammonia determination with a fast response time of less than 7 s and a recovery time of 8 s was achieved. Sensor characteristics, such as sensitivity, recyclability, response/recovery time, selectivity, stability, flexibility, and transmittance of the layers, were examined. The impedance results showed high sensitivity when the constructed sensor was exposed to NH₃ concentrations in the range 5–1000 ppm. The results showed that doping ITO with Cu²⁺ imparted higher electronic charge density to the sensor surface and enhanced the sensitivity of the sensor by a factor of 352% in comparison with that of pure ITO. The sensitivity, fast response, and recovery time with low‐cost materials and deposition procedure suggest an effective and disposable ammonia sensor at room temperature (23°C).     

Recognition of alkyl ketone molecules based on thickness-shear-mode acoustic sensors with calixarene derivatives

The frequency response characteristics for twenty-two organic vapours by piezoelectric thickness-shear-mode (TSM) acoustic wave sensors coated with four supramolecule compounds—calixarenes have been investigated. Among them, 2,8,14,20-tetraethyl-4,6,10,12,16,18,22,24-octahydroxylcalix[4]arene (I) was the most efficient actively adsorptive material for host-guest recognizing alkyl ketone molecules such as 2-butanone and acetone. The supramolecule recognition mechanism has been discussed, that is based on the formation of C-H?π bond interaction between the methyl group of ketone molecule and the phenyl ring of the calixarene compound. The linear range of the TSM sensor upon exposure to 2-butanone vapour was 0-940.5 ppm with a detection limit of 2.67 ppm when the coating mass of the compound I was selected as 19 μg. The kinetics behaviours in the adsorption and desorption processes have been examined with polynomial curve fitting procedure. Furthermore, the proposed TSM sensor possessed good selectivity, reversibility, reproducibility and high stability. Compared with gas chromatography (GC) method, the proposed sensor can be used for on-line determination of 2-butanone vapour in air with a recovery of 94.8-106.5%, which was in consistent with those obtained by GC method.     

Experimental and theoretical study of the coordination of 1,2,4-triazolato, tetrazolato, and pentazolato ligands to the [K(18-crown-6)]+ fragment

Treatment of 3,5-diisopropyltriazole, 3,5-diphenyltriazole, 3,5-di-3-pyridyltriazole, phenyltetrazole, pyrrolidinyltetrazole, or tert-butyltetrazole with equimolar quantities of potassium hydride and 18-crown-6 in tetrahydrofuran at ambient temperature led to slow hydrogen evolution and formation of (3,5-diisopropyl-1,2,4-triazolato)(18-crown-6)potassium (88%), (3,5-diphenyl-1,2,4-triazolato)(tetrahydrofuran)(18-crown-6)potassium (87%), (3,5-di-3-pyridyl-1,2,4-triazolato)(18-crown-6)potassium (81%), (phenyltetrazolato)(18-crown-6)potassium (94%), (pyrrolidinyltetrazolato)(18-crown-6)potassium (90%), and (tert-butyltetrazolato)(18-crown-6)potassium (94%) as colorless crystalline solids. (1,2,4-Triazolato)(18-crown-6)potassium was isolated as a hemi-hydrate in 81% yield upon treatment of 1,2,4-triazole with potassium metal in tetrahydrofuran. The X-ray crystal structures of these new complexes were determined, and the solid-state structures consist of the nitrogen heterocycles bonded to the (18-crown-6)potassium cationic fragments with eta2-bonding interactions. In addition, (3,5-diphenyl-1,2,4-triazolato)(tetrahydrofuran)(18-crown-6)potassium has one coordinated tetrahydrofuran ligand on the same face as the 3,5-diphenyl-1,2,4-triazolato ligand, while (3,5-di-3-pyridyl-1,2,4-triazolato)(18-crown-6)potassium forms a polymeric solid through coordination of the distal 3-pyridyl nitrogen atoms to the potassium ion on the face opposite the 1,2,4-triazolato ligand. The solid-state structures of the new complexes show variable asymmetry in the potassium-nitrogen distances within the eta2-interactions and also show variable bending of the heterocyclic C2N3 and CN4 cores toward the best plane of the 18-crown-6 ligand oxygen atoms. Molecular orbital and natural bond order calculations were carried out at the B3LYP/6-311G(d,p) level of theory on the model complex, (phenyltetrazolato)(18-crown-6)potassium, and demonstrate that the asymmetric potassium-nitrogen distances and bending of the CN4 core toward the 18-crown-6 ligand are due to hydrogen bond-like interactions between filled nitrogen-based orbitals and carbon-hydrogen sigma orbitals on the 18-crown-6 ligands. Calculations carried out on the model pentazolato complex (pentazolato)(18-crown-6)potassium predict a structure in which the pentazolato ligand N5 core is bent by 45 degrees toward the best plane of the 18-crown-6 oxygen atoms. Such bending is induced by the formation of intramolecular nitrogen-hydrogen-carbon hydrogen bonds. Examination of the solid-state structures of the new complexes reveals many intramolecular and intermolecular nitrogen-hydrogen distances of < or =3.0 A which support the presence of nitrogen-hydrogen-carbon hydrogen bonds.     

The X-ray structure of the trichlorocuprate of naphtho-15-crown-5 complexed potassium

The structure of the trichlorocuprate of naphtho-15-crown-5 complexed potassium has been determined by X-ray analysis. The crystal contains the complex cations [K(naphtho-15-crown-5)₂]⁺, the anion [Cu₂Cl₆]^2– and water molecules. The full composition of the compound in the solid state is represented by the formula [K(naphtho-15-crown-5)₂]₂[Cu₂Cl₆]·nH₂O), wheren3. The sandwich type cations are similar to those found previously for potassium complexes with benzo-15-crown-5. The coordination number of potassium is equal to 10; the coordination polyhedron is a 15-crown-5. The coordination number of potassium is equal to 10; the coordination polyhedron is a pentagonal antiprism. The water molecules are disordered and occupy six symmetrically independent positions with a probability of 0.5 in the crystal. The lack of close contacts between water molecules and the remaining components enabled the treatment of the complex as a clathrate. Supplementary Data relating to this article has been deposited with the British Library as Supplementary Publication No. 82154 (20 pages).     

Substituent effects on complexation and extraction of alkali metals with chromogenic crown ethers

The placing of chromogenic tags on crown ethers makes it possible to incorporate the natural selectivities of crown ethers into extractions with detection by visible spectrophotometry. The structures of these reagents include a monobasic amine linkage which, upon dissociation and complexation, gives a color change. The parent compound, 2″,4″,6″-trinitrophenyl-4'-aminobenzo-15-crown-5, provides a linear range for 10–800 ppm potassium ion in the presence of > 2000 ppm sodium ion. Changes in substituents on the chromophore (e.g., nitrile or trifluoromethyl for nitro) and the effects of these substituents on the visible spectra, extraction constants, equilibrium constants, the wavelength of maximum absorption, and the molar absorptivity are presented. Application of a compound to the determination of potassium ion in blood serum is reported.     

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.     

4'-picrylamino-5'-nitrobenzo-18-crown-6 as a sensing reagent in potassium ion-selective electrode membranes

Five crown ethers, namely, 4'-picrylamino-5'-nitrobenzo-18-crown-6 (I), dibenzo-18-crown-6 (III), dibenzo-30-crown-10 (IV), dicyclohexano-18-crown-6 (V) and bis-[(benzo-15-crown-5)-15-ylmethyl pimelate] (VI) have been compared with valinomycin (II) for their role as potassium ion-sensors in PVC matrix membrane ion-selective electrodes (ISEs). Sensor I was found to be the best, but fell short of the high quality of the well established sensor II (valinomycin) in terms of selectivity towards potassium over sodium and ammonium. Nevertheless, electrodes made from membranes containing sensor I, 2-nitrophenyl octyl ether (NPOE) or 2-nitrophenyl phenyl ether and potassium tetra-p-chloro-phenylborate (anion excluder) in PVC were of long lifetimes. The loss of slope of the ISEs is linked to small falls in the electrical resistance of the ISE membranes; this being associated with leaching of sensor and solvent mediator from the membranes into test or storage solutions. No chromatographic evidence was found of anion excluder being leached.     

Applications of Macrocyclic Polyethers in Analytical Sensors and Ion Separation

Artificial macrocyclic polyethers were synthesized and applied as neutral carriers for ion-selective PVC membrane electrodes, ion-chromatographic packing materials, extractants and adsorbents for ion separation, coating materials for piezoeletrical membrane sensors for organic species, and ion-transport carriers through liquid membranes. Ion-selective electrodes such as those for K⁺ Na⁺, UO₂²⁺, Cs⁺, Pb²⁺, Fe³⁺, Hg²⁺ and Ag⁺ ions based on crown ether-phosphotungstic acid (PW) precipitates and dithio crown ethers respectively were prepared and showed good sensitivity and selectivity. Crown ether-PW precipitates were applied as adsorbents of rare-earth ions and some common heavy-metal ions. Some rare-earth ions were easily extracted with crown ethers, especially 15-crown-5. Poly(stytene/divinyl benzene) cryptand-22 resin was synthesized and applied as a bifunctional stationary phase of ion chromatography to separate bom cations and anions, even some organic carboxylate geometric isomers. Crown ethers such as mono-benzo-15-crown-5 was successfully applied as a coating material on piezoelectric quartz membrane sensors for some organic species. The oscillation frequency of the crown-ether quartz-membrane sensor was sensitive to organic vapours such as amines and alcohols. Upon adsorption of organic species on the crown-ether quartz membrane, the oscillation frequency of the sensor decreased obviously. Special crown ether such as dibenzo-16-crown-5-oxyacetic acid, decyl-cryptand-22 and 1, 4-dihydro-pyridine-18-crown-5 were synthesized and successfully applied as ion-transport carriers (ionophores) for transport of Na⁺ K⁺ and Mg²⁺ ions through liquid membranes.     

Extraction of tetrafluoroborate with crown ethers and its application to silicate rock analysis

Summary The extraction behaviour of tetrafluoroborate with crown ethers was studied. A high distribution ratio of tetrafluoroborate is obtained by extraction with dicyclohexano-18-crown-6 (DC18C6) in an organic solvent of high dielectric constant from potassium fluoride solution. The molar ratios of crown ether to KBF₄ in the extracted species are probably 1:1 for DC18C6, dibenzo-18-crown-6 and 18-crown-6, and 2:1 for benzo-15-crown-5 and 15-crown-5. The flow-injection extraction-spectrophotometric determination of tetrafluoroborate with Brilliant Green was worked out. Many rock reference samples were analyzed for boron (1–150 ppm).     

A comparative study of different extraction systems for the spectrophotometric determination of potassium with 18-crown-6

A comparative study on the extractive-spectrophotometric determination of potassium with 18-crown-6 employing different colored counterions and organic extraction solvents is described.Extraction systems using methyl orange/chloroform, bromcresol purple/chloroform and bromcresol green/benzene demonstrated good preliminar features for such purpose and are studied in detail. Analytical performance characteristics including: sensitivity, selectivity, precision, linearity, etc. are given for each method. The main disadvantage of this type of determinations is the lack of reproducibility. Some explanations to this fact are discussed.A new method for the determination of trace amounts of potassium based on its extraction into chloroform with 18-crown-6 and methyl orange is proposed. The linear working range goes from 0.5 to 7 ppm of potassium, the apparent molar absorptivity being 8.8 × 10³ liters mol^?1 · cm^?1, and the precision, expressed in terms of relative standard deviation, of ±4.6%.     

Comparison of fluorescence and QCM technologies: Example of explosives detection with a π-conjugated thin film

A π-conjugated compound was synthesized as a sensitive material for explosives detection. The detection of vapors of 2,4-dinitrotoluene was demonstrated with quartz crystal microbalance (QCM) and fluorescence transduction methods. The fluorescence intensity monitoring shows a higher sensitivity and selectivity than the monitoring of the QCM frequency. Both methods appear to be synergic when used simultaneously as the sensor helps to discriminate interferent vapors from nitroaromatics.