Detecting solution pH changes using poly (N-isopropylacrylamide)-co-acrylic acid microgel-based etalon modified quartz crystal microbalances

Poly (N-isopropylacrylamide)-co-acrylic acid (pNIPAm-co-AAc) microgel-based etalons have been shown to have visible color and unique spectral properties, which both depend on solution temperature and pH. In this investigation, pNIPAm-co-AAc microgel-based etalons were fabricated on the Au electrode of a quartz crystal microbalance (QCM), and the resonant frequency of the QCM monitored as a function of temperature, at pH 3.0. Furthermore, the resonant frequency at either pH 3.0 or 7.0 was monitored while keeping the solution temperature constant at various temperatures. In all cases, when the solution temperature was below the collapse transition for the microgels (∼32 °C), the resonant frequency at pH 3.0 was lower than at pH 7.0, which we attribute to the film transitioning from a deswollen to swollen state, respectively. It was observed that the magnitude of the resonant frequency change increased as the solution temperature approached the collapse temperature for the microgels. The overall sensitivity to pH was determined to be 1.3 × 10⁻⁸ M [H⁺] Hz⁻¹ and a theoretical detection limit of 390 nM was obtained. This sensitivity will be exploited further for future biosensing applications.     

Different experimental results for the influence of immersion angle on the resonant frequency of a quartz crystal microbalance in a liquid phase: with a comment

This paper presents different experimental results of the influence of an immersion angle (θ, the angle between the surface of a quartz crystal resonator and the horizon) on the resonant frequency of a quartz crystal microbalance (QCM) sensor exposed one side of its sensing surfaces to liquid. The experimental results show that the immersion angle is an added factor that may influence the frequency of the QCM sensor. This type of influence is caused by variation of the reflection conditions of the longitudinal wave between the QCM sensor and the walls of the detection cell. The frequency shifts, measured by varying θ, are related to the QCM sensor used. When a QCM sensor with a weak longitudinal wave is used, its resonant frequency is nearly independent of θ. But, if a QCM sensor with a strong longitudinal wave is employed, the immersion angle is a potential error source for the measurements performed on the QCM sensor. When the reflection conditions of the longitudinal wave are reduced, the influence of θ on the resonant frequency of the QCM sensor is negligible. The slope of the plot of frequency shifts (ΔF) versus (ρη)^1/2, the square root of the product of solution density (ρ) and viscosity (η), may be influenced by θ in a single experiment for the QCM sensor with a strong longitudinal wave in low viscous liquids, which can however, be effectively weakened by using the averaged values of reduplicated experiments. In solutions with a large (ρη)^1/2 region (0-55 wt% sucrose solution as an example, with ρ value from 1.00 to 1.26 g cm⁻³ and η value from 0.01 to 0.22 g cm⁻¹ s⁻¹, respectively), the slope of the plot of ΔF versus (ρη)^1/2 is independent of θ even for the QCM sensor with a strong longitudinal wave in a single experiment. The influence of θ on the resonant frequency of the QCM sensor should be taken into consideration in its applications in liquid phase.     

A 13C and 1H NMR analysis of perfumes

Composition of a series of formulations used in Russia for production of various perfumes, among them car air fresheners, was studied by ¹³C and ¹H NMR. The main components were identified, approximate compositions of several perfumes were determined, and spectral data are given. These spectral data can be used for prompt analysis for composition of commercial odorants with the aim of monitoring their quality and hygienic characteristics.     

Electrophotographic and microwave photodielectric studies on titanium dioxide pigments in the solid state

In this paper, we report some novel preliminary findings on the photoactivity of titanium dioxide pigments using photoconductive and microwave dielectric techniques. A variety of pigment types were investigated by both methods, including the two crystalline forms of titanium dioxide, anatase and rutile, and a variety of coated pigments. Analysis of the data obtained indicates that there are possible relationships between the photoconductive and photodielectric results, and that these may be used to characterize the pigment types rapidly. Photoconductive measurements were carried out on pigmented films of poly(N-vinylcarbazole) (PVK). Uncoated pigments were found to be more photoconductive than coated pigments with the anatase modification being the more active. It is believed that the pigments act as “trapping” sites to the holes produced by PVK, and that the more photoactive the pigment, the easier it is to regenerate the holes. Various factors influence the band gap of the pigment and these have a significant effect on the photoactivity and photoconductivity of the pigment samples. These include the presence of traps and recombination centres (present as coatings on the surface of the pigment particle) and impurities which can act as acceptors or donors.

Microwave dielectric measurements were carried out on the different anatase and rutile pigments, each exhibiting a different microwave resonant frequency loss depending on the nature of the crystalline modification and the coating. However, on illumination on the pigments with polychromatic light in the microwave cavity, the resonant frequency losses exhibit shifts, the nature of which depend on the pigment type and the coating. Thus the anatase pigments exhibit greater responses than the rutile pigments, particularly with regard to the shift in the resonant frequency values and the change in the Q factor of the resonant peak. The resonant frequency values of the anatase samples are also higher than those obtained for the rutile samples. Furthermore, the frequency shifts are in opposite directions, with the anatase modification exhibiting a more rapid shift to lower frequencies and rutile a slower shift to higher frequencies. It appears that, when the anatase samples are irradiated, their dielectric properties change from those characteristic of a conductor-like material to those of an insulator-like material. However, these changes are reversible once the illumination is terminated. With the rutile samples, irradiation increases the resonant frequency values and hence their dielectric constants. Thus the pigments appear to become more like conductors.     

Piezoelectric Crystal Biosensor System for Detection of Escherichia Coli

Abstract

A piezoelectric crystal biosensor system was applied to the detection of Escherichia coli. the system consists of an oscillator, a frequency counter, a flow cell and a modified piezoelectric crystal. Anti-E. coli antibody is immobilized on the surface of the crystal. It is used as an E. coli detection by measuring its resonant frequency shift due to a mass change caused by specific binding of the micro organisms to the surface. the frequency shift correlates with an E. coli concentration in the range of 10⁶?10⁸ cells·cm^?3. the resonant frequency shift is increased by further treatment to bind micro-particles modified with anti-E. coli antibody. This method allows us to improve the determination limit to 10⁵ cells · cm^?3.     

The response of some organic microsensor coatings to a variety of vapors

Six organic compounds were spray-coated onto surface acoustic wave devices which were then exposed to vapors of acetone, diethyl ether, dichloromethane, chlorobenzene, benzene, and acetonitrile. Changes in the resonant frequency of the device or in the resistance of the coating were collected by computer-controlled data acquisition. Different patterns of response to the six vapors were observed for each of the coatings.     

Enzyme‐Mediated Preparation of Chiral 1,3‐Dioxane Odorants

The enantiomerically enriched diastereoisomers of the chiral 1,3‐dioxane odorants Floropal^® ( 1 ) and Magnolan^® ( 2 ) were prepared by an enzyme‐mediated approach. Their olfactory properties were evaluated to investigate differences in the odor perception for the stereoisomers.     

Role of counteranions in polymeric ionic liquid-based solid-phase microextraction coatings for the selective extraction of polar compounds

A polymeric ionic liquid (PIL) poly(1-vinyl-3-hexylimidazolium chloride) (poly(ViHIm⁺Cl⁻)) was designed as a coating material for solid phase microextraction (SPME) to extract polar compounds including volatile fatty acids (VFAs) and alcohols. The extracted analytes were analyzed by using gas chromatography (GC) coupled with flame ionization detection (FID). Extraction parameters of the HS–SPME–GC–FID method, such as ionic strength, extraction temperature, pH and extraction time were optimized. Calibration studies were carried out under the optimized conditions to further evaluate the performance of the PIL-based SPME coating. For comparison purposes, the PIL poly(1-vinyl-3-hexylimidazolium bis[(trifluoromethyl)sulfonyl]imide) (poly(ViHIm⁺NTf₂⁻)) was also used as the SPME coating to extract the same analytes. The results showed that the poly(ViHIm⁺Cl⁻) PIL coating had higher selectivity towards more polar analytes due to the presence of the Cl⁻ anion which provides higher hydrogen bond basicity than the NTf₂⁻ anion. The limits of detection (LODs) determined by the designed poly(ViHIm⁺Cl⁻) PIL coating ranged from 0.02 μg L⁻¹ for octanoic acid and decanoic acid and 7.5 μg L⁻¹ for 2-nitrophenol, with precision values (as relative standard deviation) lower than 14%. The observed performance of the poly(ViHIm⁺Cl⁻) PIL coating was comparable to previously reported work in which commercial or novel materials were used as SPME coatings. The selectivity of the developed PIL coatings was also evaluated using heptane as the matrix solvent. This work demonstrates that the selectivity of PIL-based SPME coatings can be simply tuned by incorporating different counteranions to the sorbent coating.     

Characterization of Controlled Release Fertilizer by Infrared Microspectroscopy

The feasibility and potential of infrared microspectroscopy for quantitatively characterizing the dynamic changes in the coating of controlled release fertilizer granules are discussed to better characterize the release of nutrients. Two polymer-coated compound fertilizers were selected as typical samples. A frozen section technique was used for sample pretreatment, where freeze-dried controlled release fertilizer granules were cut into 20-µm-thick sections. Optimal parameters for the spectral range, spectral resolution, and pixel dimensions in the transmission spectra were determined to be 4000–750?cm^?1, 16?cm^?1, and 6.25?×?6.25?µm, respectively. A mean spectrum of four scans was used in data processing for second-derivative analysis with nine smoothing points. This work is aimed to quantitatively distinguish between the coating and fertilizer core according to radial variations in second-derivative spectra using characteristic wavelengths that represent the coating and fertilizer core. During nutrient release, the fertilizer core gathered gradually and adhered in uniform distribution around the coating, while some nutrients were trapped in micropores. The coating thickness of the controlled release fertilizers fluctuated within 37.5––55 and 15–55?µm, respectively. Although measurement results based on infrared microspectroscopy were in accordance with the scanning electron microscopy observations, they were shown to be more accurate and were not influenced by the coating mixed with the fertilizer core. Furthermore, infrared microspectroscopy was effectively used to quantify the dynamic thickness of the coating of controlled release fertilizer granules and visually characterize fertilizer penetration through the coating.     

Resonance raman spectra of würster's cation dimers: p-phenylenediamine and 2,3,5,6-tetramethyl-p-phenylenediamine

Resonance Raman spectra have been observed for the dimers of p-phenylenediamine cation (PPD⁺) and of 2,3,5,6-tetramethyl-p-phenylenediamine cation (TMPD⁺). When the exciting light frequency approached the absorption bands characteristic of the dimers, new polarized Raman lines appeared at 161 cm^?1 for (PPD⁺)₂ and at 117 cm^?1 for (TMPD⁺)₂ with a striking resonance enhancement. The resonant behaviour as well as the frequency values indicate that they are reasonably assigned to the interradical stretching vibrations of the parallel D_2h dimer molecules.     

Selective piezoelectric odor sensors using molecularly imprinted polymers

Molecular imprinting technique has been used to create sensors with a predetermined selectivity for molecules in the gas phase. Piezoelectric quartz crystals coated with a 2-methylisoborneol (MIB) imprinted polymer gave responses which were consistently 5–10 Hz (1.1–1.3 times) higher than those of sensors coated with a non-imprinted polymer. Geosmin, another tertiary alcohol odorant with an earthy odor resembling, and often accompanying MIB, produced almost equal responses on either imprinted- or non-imprinted sensors. A number of other odorants were examined and their responses to the non-imprinted sensors were found to be similar to or greater than their responses to the imprinted sensors. The responses of MIB to the imprinted sensors were always the highest, while other odorants produced equal or higher responses using the non-imprinted sensor. The sensor has a detection limit of ca. 5 mg l⁻¹ and a dynamic range of at least 1000 mg l^−l. When the time taken for the sensor to stabilize is used as the response, instead of the frequency change, the detection limit is lowered to ca. 200 μg l^−l.     

High sensitive piezoelectric quartz crystal liquid density sensor

<正>We report for the first time a cleavage phenomenon in the resonant peak of a piezoelectric quartz crystal(PQC) in liquid phase.In the presence of a strong longitudinal wave effect,an additional resonant peak appears in the conductance-frequency curve.With gradually increasing liquid density,the additional peak moves from low to high frequency region then disappears.The frequency of the additional resonant peak is sensitive to the change in liquid density.The frequency shift of the additional peak is linear with the liquid density in a given range.For a 5 MHz PQC with a reflection distance of 16 mm for longitudinal wave,the sensitivity to liquid density is 2.61×10~6 Hz g~(-1) cm~3.The overlap between the primary resonant peak and the additional resonant peak causes a decrease in the intensity of the former and an increase in the intensity of the latter.In a combined impedance analysis method,the changes in surface mass loading,density and viscosity of the liquid were monitored simultaneously by a PQC sensor.     

Characterisation of flavour compounds formed by γ-irradiation of polypropylene

Sterilisation of plastic packaging materials for food, pharmaceutical or cosmetic products with ⁶⁰Co γ-irradiation in the presence of oxygen can result in the formation of volatile substances. These may subsequently induce off-odours in these materials that might be regarded as negative by the consumers. Trace volatiles and odorous substances of polypropylene, irradiated with ⁶⁰Co γ rays at 10 and 20 kGy, respectively, were collected and analysed by gas chromatography–olfactometry (GC–O), GC–MS and GC–GC–MS. The methodology was successfully applied for identification of 29 characteristic odorants in a non-irradiated control sample and 38 odorants in γ-irradiated polypropylene samples. Selected odour-active compounds were quantified using GC–GC–MS in combination with stable isotope dilution assays. The quantitative data mirrors the compositional changes in volatile odorous substances from polypropylene during treatment with ionising γ rays in a ⁶⁰Co-irradiation plant.     

The relationship between the times of spin-lattice relaxation and 35Cl NQR frequencies for three EtSiCl3 phases

A coupling equation that relates ³⁵Cl NQR frequencies to reciprocal times of spin-lattice relaxation, which allowed us to isolate the contributions to the NQR frequency with respect to short- and longrange orders of the neighborhood of a resonant chlorine atom, was found for three (C₂H₅)SiCl₃ crystalline phases. The value of ³⁵Cl NQR frequency for an isolated molecule was estimated. The changes in the intensity of local electric fields stipulated by the crystal field were determined.     

Development of a Sol-Gel Procedure for Preparation of a Diglycidyloxycalix[4]arene Solid-Phase Microextraction Fiber with Enhanced Extraction Efficiency

5,11,17,23-Tetra-tert-butyl-25,27-dihydroxy-26,28-diglycidyloxycalix[4]arene (diglycidyloxy-C[4]) has been synthesized and used for preparation of a sol-gel solid-phase microextraction fiber with enhanced extraction efficiency. The sol-gel procedure was developed using a sol solution containing diglycidyloxy-C[4] as organic component and both tetraethoxysilane and 3-aminopropyltriethoxysilane (KH-550) as precursors. No additional catalysts were used and no centrifugation was performed. Diglycidyloxy-C[4] was highly chemically reactive toward KH-550 even at room temperature, which increased the calixarene content of the coating, simplified the sol-gel procedure, reduced the sol-gel reaction time, enhanced the polarity of the coating, and improved extraction performance. The sol-gel mixture also had very good coating properties and was highly uniformly distributed on the surface of the fiber; because of these characteristics several fibers could be prepared from one sol-gel solution. Efficient extraction of trace analytes (µg L^?1 levels) from aqueous samples was accomplished using this kind of new fiber. Very low detection limits (ng L^?1 level) were achieved for most polar (aromatic amines and phenols) and nonpolar (polycyclic aromatic hydrocarbons) aromatic compounds by SPME followed by gas chromatography with flame ionization detection. The new coating had excellent solvent and thermal (350 °C) stability. Lifespan was also good—a fiber could be used more than 300 times in headspace SPME without substantial changes in the properties of the coating.     

Plasma source ion trap mass spectrometry: Enhanced abundance sensitivity by resonant ejection of atomic ions

An experimental study of resonant ion excitation in an rf quadrupole ion trap is reported. Atomic ions are generated in an inductively coupled plasma and injected into the ion trap where, after collisional cooling, they are irradiated by a low-voltage, dipole coupled waveform. Single frequency, narrowband, and broadband excitation pulses have been used. Absorption lineshapes (plots of observed ion signal versus excitation frequency) are shown for variations in buffer gas pressure and the amplitude and duration of the single frequency pulses. The absorption lineshapes are usually asymmetric and tail toward lower frequencies. At sufficiently low buffer gas pressure or potential well depth, the lineshapes broaden and become more asymmetric to the point that absorption by ions with adjacent mass-to-charge ratios overlaps. This overlapping absorption reduces the selectivity with which a single mass-to-charge ratio ion can be excited and ejected relative to nearby mass-to-charge ratio ions. The rate of ion ejection is different on the low versus high frequency edges of the absorption lines. This difference in ejection rates provides an important key to understanding the shape of the absorption lines. All of these observations are explained in terms of the known kinematic behavior of ions in real traps, that is, traps with substantial higher order symmetry components in the trapping field (“nonlinear” fields). The importance of the nonlinearity of the trapping field in understanding the observed lineshapes and their time dependencies is discussed. We also report resonant ejection results obtained using multiple frequency (narrow or broad bandwidth) excitation. Multiple frequency excitation allows ions with different mass-to-charge ratio values to be ejected from the trap using one excitation waveform. The finite ion storage capacity of the ion trap is thereby reserved for the ion(s) of interest. We show that ejection of ⁸⁹Y ions can be ～ 10⁵ times more efficient than ejection of ions at either m/z 88 or 90.     

Fluorescence spectra and intramolecular vibrational redistribution in jet-cooled perylene

The jet-cooled fluorescence spectra of perylene excited to the S₁ state with E_vib = 0–1600 cm^?1 are recorded and analyzed. For E_vib <800 cm^?1 only the resonant fluorescence was detected. Ground- and excited-state frequencies of 14 low-frequency normal modes are determined. A drastic change in frequency of the “butterfly” modes upon electronic excitation shows that perylene slightly deviates from planarity in its ground state and is more rigid in the excited singlet state. For a number of levels in the E_vib = 800–1600 cm^?1 range, the fluorescence is composed of the resonant emission and of non-resonant (“‘relaxed’”) bands. It is shown that apparently single bands in the fluorescence-excitation spectrum correspond to ovelapping bands pumping different molecular eigenstates resulting from the intrastate coupling. The relative role of the anharmonicity and of the Coriolis interaction are discussed. The data are treated in terms of a selective coupling between doorway and hallway states with the coupling constant rapidly decreasing with the difference in the overall vibrational quantum number between initial and final state.     

Polymer Coated Piezoelectric Quartz Crystal Protein Bio‐Sensors

A 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.     

Monitor adsorption of acetone vapor to a room temperature ionic liquid 1-octyl-3-methylimidazolium bromide by a langasite crystal resonator

In this work, the responses of a Y-cut langasite crystal resonator (LCR) in liquid phases were investigated by an impedance analysis method. The resonant frequency (f_S) of the LCR decreases with increasing mass loading on the active surface of the resonator. The LCR can be operated at the resonant frequency that is down to about 60% of the fundamental frequency (f₀) under foreign mass loading. The frequency-mass coefficient of the Y-cut LCR is theoretically derived to be −1.282 × 10⁻⁶, which is supported by the experimental results. The resonant frequency of the LCR decreases linearly while its motional resistance (R_m) increases linearly with increasing (ρη)^1/2, where η and ρ are the viscosity and density of the liquid phase, respectively. The slopes of the plots of f_S versus (ρη)^1/2 and R_m versus (ρη)^1/2 are related to the region of (ρη)^1/2 because of the influence of surface roughness of the LCR. The changes in viscodensity of a room temperature ionic liquid (RTIL), 1-octyl-3-methylimidazolium bromide ([C₈MIM][Br]), were investigated in acetone vapor adsorption and ascending temperature processes by the LCR. The adsorption of acetone into [C₈MIM][Br] causes a significantly drop in viscosity of the [C₈MIM][Br] film, which induces an increase in f_S and a decrease in R_m for the RTIL modified LCR. When the thickness of [C₈MIM][Br] film is less than the decay distance of the thickness-shear wave, a mass effect model is observed in the early adsorption process. Based on the responses of the LCR, the viscodensity of the [C₈MIM][Br] film as well as the adsorbed amounts of acetone into film were monitored in real time during the adsorption or desorption processes.