The investigation of coating materials for the detection of nitrobenzene with coated quartz piezoelectric crystals

Powdered activated charcoal, quadrol tetrabase and polyethylene glycol (PEG)-400 and -750 are used as coatings on 15-MHz quartz piezoelectric crystals for the detection of nitrobenzene in air. The response to nitrobenzene over the range 2–10 ppm (2–10 × 10^?6 mol mol^?1)_was almost linear for all the coatings except charcoal which exhibited marked non-linearity, as well as greater sensitivity than the other coatings. The charcoal response was linear over the range 0.7–7.6 ppm nitrobenzene. For the other coatings, sensitivity increased in the order tetrabase < quadrol < PEG-400 < PEG-750.     

Detection of toluene diisocyanate with a coated quartz piezoelectric crystal: Part 4. A portable automatic detector with humidity correction

Microcomputer-controlled measurement of the frequency of two differently-coated quartz piezoelectric crystals and subsequent data processing permits the immediate correction of instrumental response for fluctuations in water vapour concentration and the display of the corrected toluene diisocyanate concentration in air. Crystal pairs with coatings of polyethylene glycol 400 or 1540 or tri-n-octylphosphine oxide and cobalt(II) chloride were used to illustrate the performance of the instrument. Toluene diisocyanate can be detected over the range 0.1—15 ppm in atmospheres with relative humidities ranging from 30 to 60% without significant interference from changes in water concentration.     

Study on Chemiluminescence Assay of Surfactant PEG-400 Using Luminol–Hydrogen Peroxide System

Abstract

Based on the fact that nonionic surfactant polyethylene glycol-400 (PEG-400) catalyzed the chemiluminescence of luminol-H₂O₂ system, a novel and simple chemiluminescence method has been developed for the determination of PEG-400. Under the optimal conditions, the standard curve was Y = 198835X–2091.8, where the correlation coefficient (R) was 0.9999. The detection limit was 4 × 10^?5 g·ml^?1 PEG-400 and the linear range was 1.0 × 10^?4–4.0 × 10^?2g·ml^?1. The relative standard deviation was 3.2% at 2.0 × 10^?3 g·ml^?1 PEG-400 (n = 7). This method has been applied to the determination of PEG-400 in cosmetic samples with satisfactory results. Furthermore, the dynamics characteristic curve of PEG-400 in luminol-H₂O₂ system was compared to typical metallic ion and other surfactants. Moreover, the mechanism of the luminol-H₂O₂-PEG-400 chemiluminescence system was studied, assisted by fluorescence spectra and UV spectra.     

A Spectrophotometric Study on Complex Formation of Nickel (II) and Cobalt (II) with Bromopyrogallol Red

Nickel (II) and Cobalt (II) form in 50% ethanolic medium, a bluish violet complex with Bromopyrogallol Red (BPR) in the mole ratio of 1:1 (Ni(II)) and 1:2 (Co(II)), both having at 620 nm, stable in the pH ranges 6.0-7.5 and 5.5-7.0, respectively. The thermodynamic stability constants and overall changes in the free energy of formation, enthalpy and entropy have been determined in both the cases. Beer's law is obeyed over the concentration range 0.5-5.0 ppm of Nickel and 0.2-3.0 ppm of Cobalt at 620 nm. The net molar absorptivities are 1.6 × 10⁴ and 2.9 × 10⁴ and the sensitivities are 0.00367 and 0.00219 μg of Nickel and Cobalt per cm,/². The effect of diverse ions on the metal ions determination is also reported.     

Ionic Liquid‐based Microchannels for Highly Sensitive and Fast Amperometric Detection of Toxic Gases

Ionic liquid (IL)‐based microchannels sensors have been fabricated and employed for the detection of toxic ammonia (NH₃) and hydrogen chloride (HCl) gases, with enhanced sensitivity and response times compared to conventional electrodes. Electrochemical techniques were employed to understand the behaviour of these highly toxic gases in two ionic liquids, [C₄mpyrr][NTf₂] and [C₂mim][NTf₂], on a gold modified microchannels electrode. The limits of detection (LODs) obtained in [C₄mpyrr][NTf₂] for NH₃ (3.7 ppm) and in [C₂mim][NTf₂] for HCl (3.6 ppm) were lower than the current Occupational Safety and Health Administration Permissible Exposure Limit (OSHA PEL) for the two gases (25 ppm for NH₃ and 5 ppm for HCl). The response time of the sensor is 15 s with a sensitivity of 143 nA ppm^?1 and 14 nA ppm^?1 for HCl and NH₃, respectively. These results demonstrate the superiority of IL‐based microchannels sensors for detecting toxic gases, when compared to commercially available sensors or traditional IL‐based sensor designs, where high sensitivity or fast response time is still a challenge.     

Characterization of N-cyclohexylmethacrylamide LB thin films for room temperature vapor sensor application

This study reports the synthesis, characterization and gas sensing applications of N-cyclohexylmethacrylamide (NCMA) monomer material using FT-IR, ¹H and ¹³C NMR, UV-visible spectroscopy, Quartz Crystal Microbalance (QCM) and Langmuir-Blodgett (LB) thin film deposition techniques. The thin film deposition conditions of NCMA monomer material, which are prepared by LB film technique, are characterized by UV-visible spectroscopy and QCM system. The sensing behaviors of the LB film with respect to volatile organic compounds (VOCs) at room temperature are investigated. Surface pressure change as a function of surface area of NCMA molecule at the water surface shows a well-organized and stable monolayer at 18 mN m^?1 surface pressure value for LB film deposition. Transfer ratio values are found to be ≥ 0.94 for quartz glass and ≥ 0.93 for quartz crystal substrate. The typical frequency shift per layer is obtained 20.10 Hz/layer and the deposited mass onto a quartz crystal is calculated as 824.62 ng/layer. The sensing responses of the LB films against chloroform, dichloromethane, acetone, toluene, benzene and ethanol are measured by QCM system. The sensitivities of the NCMA LB film sensor are determined between 0.085 and 0.029 Hz ppm^?1. Sensitivities with detection limits are between 35.29 and 100.33 ppm against organic vapors. These results can be concluded that the monomer LB film sample is found to be significantly more sensitive to chloroform and dichloromethane vapors than others organic vapors used in this work. This material may find potential applications in the development of room temperature organic vapor sensing.     

Synthesis of New Reagent 2,6‐Diacetylpyridine Bis‐4‐Phenyl‐3‐Thiosemicarbazone (2,6‐DAPBPTSC): Selective,Sensitive and Extractive Spectrophotometric Determination of Co(II) in Vegetable,Soil, Pharmaceutical and Alloy Samples

New synthesized reagent 2,6‐diacetylpyridine bis‐4‐phenyl‐3‐thiosemicarbazone (2,6‐DAPBPTSC) is proposed as a sensitive and selective analytical reagent for the extractive spectrophotometric determination of cobalt(II). Cobalt(II) forms a reddish brown colored complex with 2,6‐DAPBPTSC, which is extracted into isoamylalcohol, under optimum conditions. The maximum absorption of the isoamylalcohol extract is measured at 400 nm. Beer's law is applied in the range 0.6‐6.0 ppm of cobalt(II). The molar absorptivity and Sandell's sensitivity of the complex is calculated as 2.2 × 10⁴ L mol^?1 cm^?1 and 2.68 × 10^?3 μg cm^?2, respectively. An adequate linearity with a correlation coefficient value of 0.969 is obtained for the Co(II)‐2,6‐DAPBPTSC complex. The instability constant of the complex, calculated from Asmus' method is 3.75 × 10^?4 The precision and accuracy of the method is checked with calculation of relative standard deviation (n = 5), 0.388 and the detection limit a value is 0.0028 μg mL^?1. The method is successfully employed for the determination of cobalt(II) in real samples, such as vegetables, soil, water samples, standard alloy samples, and the performance of the present method was evaluated in terms of Student ‘t’ test and Variance ‘f’ test, which indicates the significance of the present method is an inter comparison of the experimental values, using atomic absorption spectrometer (AAS).     

Novel low humidity sensor made of TiO(2) nanowires/poly(2-acrylamido-2-methylpropane sulfonate) composite material film combined with quartz crystal microbalance

A novel ceramic nanowires of TiO₂ and poly(2-acrylamido-2-methylpropane sulfonate) (TiO₂ NWs/PAMPS) composite material films coated on quartz crystal microbalance (QCM) was prepared as a low humidity sensor. The 50 wt.% of TiO₂ NWs/PAMPS composite material films showed excellent sensitivity (2.63 −ΔHz/Δppm_v) at 31.5 ppm_v), linearity (R² = 0.9959) and acceptable response time (64 s at 34.6 ppm_v). The low humidity sensing mechanism was discussed in terms of surface texture and nanostructured morphology of the composite materials. Moreover, the adsorption dynamic analysis, molecular mechanics calculation (association constant), was used to elucidate the effect of adding 50 wt.% TiO₂ NWs into PAMPS in the increased sensitivity of low humidity sensing.     

Effect of Biochemical Stimulants on Biomass Productivity and Metabolite Content of the Microalga, Chlorella sorokiniana

The influence of 12 biochemical stimulants, namely 2-phenylacetic acid (PAA; 30 ppm), indole-3 butyric acid (IBA; 10 ppm), 1-naphthaleneacetic acid (NAA; 2.5, 5 and 10 ppm ), gibberellic acid (GA3, 10 ppm), zeatin (ZT; 0.002 ppm), thidiazuron (0.22 ppm), humic acid (20 ppm), kelp extract (250 ppm), methanol (500 ppm), ferric chloride (3.2 ppm ), putrescine (0.09 ppm), spermidine (1.5 ppm) were prescreened for their impact on growth and chlorophyll for the green alga—Chlorella sorokiniana. C. sorokiniana responded best to phytohormones in the auxin family, particularly NAA. Thereafter, two studies were conducted on combinations of phytohormones to compare blends from within the auxin family as well as against other families. These treatments were NAA_{5 ppm}+PAA_{30 ppm}, NAA_{2.5 ppm}+PAA_15 ppm, NAA_5 ppm+IBA_10 ppm, NAA_5 ppm+GA3_10 ppm, NAA_5 ppm+ZT_1 ppm, and NAA_5 ppm+GA3_10 ppm+ZT_1 ppm. Combinations of NAA with other auxins did not have synergistic or antagonistic effects on the growth. However, combinations of compounds from different phytohormone families, such as NAA_5 ppm+GA3_10 ppm+ZT_1 ppm, dramatically increased the biomass productivity by 170% over the control followed by the treatments: NAA _5 ppm+GA3_10 ppm (138%), NAA _5 ppm+ZT_1 ppm (136%), and NAA _5 ppm ( 133%). The effect of biochemical stimulants were also measured on metabolites such as chlorophyll, protein, and lipids in C. sorokiniana. Renewed interest in microalgae for biotechnology and biofuel applications may warrant the use of biochemical stimulants for cost reduction in large-scale cultivation through increased biomass productivity.     

1,3-Cyclopentanedione bis(4-methylthiosemicarbazone) monohydrochloride as a spectrophotometric reagent for the determination of lodate in acetic and perchloric acid media

1,3-Cyclopentanedione bis(4-methylthiosemicarbazone) monohydrochloride produces colored solutions with iodate ions in acid medium. The yellow color obtained has been used to proposed Spectrophotometric methods for determination of IO₃^? in the concentration range 1.0–11.0 ppm in acetic acid medium (molar absorptivity 1.08 × 10⁴ liters mol^?1 cm^?1 at a wavelength of 415 nm) and 0.5–8.0 ppm in perchloric acid medium (molar absorptivity 2.05 × 10⁴ liters mol^?1 cm^?1 at a wavelength of 400 nm).     

Ozone reduction at Nafion modified Au electrode and the measurement of ozone concentration in highly resistive solutions

The mass transport and charge transfer kinetics of ozone reduction at Nafion coated Au electrodes were studied in 0.5 mol/L H2SO4 and highly resistive solutions such as distilled water and tap water. The diffusion coefficient and partition coefficient of ozone in Nafion coating are 1.78×10-6 cm2·s-1 and 2.75 at 25℃ (based on dry state thickness), respectively. The heterogeneous rate constants and Tafel slopes for ozone reduction at bare Au are 4.1×10-6 cm·s-1, 1.0×10-6 cm·s-1 and 181 mV, 207 mV in 0.5 mol/L H2SO4 and distilled water respectively and the corresponding values for Nafion coated Au are 5.5×10-6 cm·s-1, 1.1×10-6 cm·s-1 and 182 mV, 168 mV respectively. The Au microelectrode with 3 μm Nafion coating shows good linearity over the range 0-10 mmol/L ozone in distilled water with sensitivity 61 μA·ppm-1 ·cm-2, detection limit 10 ppb and 95% response time below 5 s at 25℃. The temperature coefficient in range of 11-30℃ is 1.3%.     

A kinetic study of the decomposition of HNO3 and its reaction with NO

The rate of reaction between NO and HNO₃ and the rate of thermal decomposition of HNO₃ have been measured by FTIR spectroscopy. The measurements were made in a teflon lined batch reactor having a surface to volume ratio of 14 m^?1. During the experiments, with initial HNO₃ concentrations between 2 and 12 ppm and NO concentrations between 2 and 30 ppm, a reactant stoichiometry of unity and a first order NO and HNO₃ dependence were confirmed. The observed rate constant for the reaction at 22°C and atmospheric pressure was determined to 1.1 (±0.3) 10^?5 ppm^?1 min^?1. At atmospheric pressure, HNO₃ decomposes into NO₂ and other products with a first order HNO₃ dependence and with a rate constant of 2.0 (±0.2) 10^?3 min^?1. The apparent activation energy for the decomposition is 13 (±4) kJ mol^?1.     

Effects of humidity,imidization history,and thickness on water sorption behavior of poly(p-phenylene biphenyltetracarboximide) films

Poly(p-phenylene biphenyltetracarboximide) films with various thicknesses were prepared from the poly(amic acid) precursor by thermal imidization at 230–400°C for 1–10 h under a nitrogen atmosphere. The water sorption in the films was measured at 25°C over 22–100% relative humidity using a Cahn microbalance as a function of film thickness and thermal imidization history. The water diffusion in all the films followed nearly Fickian process despite the morphological heterogeneity due to the ordered and less ordered phases. The diffusion coefficient and water uptake varied in 0.85 × 10^?10 ? 7.50 × 10^?10 cm²/s and 0.12–2.4 wt %, respectively, depending upon humidity, film thickness, and imidization history. Both diffusion coefficient and water uptake increased with increasing humidity, but decreased as imidization temperature and time increased. With increasing film thickness, the diffusion coefficient increased whereas the water uptake decreased. The water sorption behavior was interpreted with the consideration of morphological variations, such as polymer chain order, in-plane orientation, and intermolecular packing order due to the film thickness and imidization history. © 1995 John Wiley & Sons, Inc.     

Synthesis,crystal structure and properties of a quaternary oxide with a new structure type,BiGaTi4O11

A new quaternary oxide, BiGaTi₄O₁₁ (bismuth gallium tetratitanium undecaoxide), was prepared by heating a mixture of the binary oxides at 1373 K in air. BiGaTi₄O₁₁ melts at 1487 K and prismatic single crystals were obtained from a sample melted at 1523 K and solidified by furnace cooling. The structure of BiGaTi₄O₁₁ was analyzed using single‐crystal X‐ray diffraction to be of a new type that crystallized in the space group Cmcm. A Bi³⁺ site is coordinated by nine O^2? anions, and three oxygen‐coordinated octahedral sites are statistically occupied by Ga³⁺ and Ti⁴⁺ cations. A relative dielectric constant of 46 with a temperature coefficient of 57 ppm K^?1 in the temperature range 297–448 K was measured for a polycrystalline ceramic sample at 150 Hz–1 MHz with a dielectric loss tan δ of less than 0.01. Electrical resistivities measured at 1073 K by alternating‐current impedance spectroscopic and direct‐current methods were 1.16 × 10^?4 and 1.14 × 10^?4 S cm^?1, respectively, which indicates that electrons and/or holes were conduction carriers at high temperature. The optical band gap estimated by the results of diffuse reflectance analysis was 2.9–3.0 eV, while the band gap obtained from the activation energy for electrical conduction was 3.5 eV.     

Galvanostatic Studies on Reduction of Oxygen at Silver Electrode

Galvanostatic studies with low current density in 0.1 N KNO₃ medium reveal that reduction of oxygen at silver electrode is totally irreversible and in the range of oxygen concentration studied, 2.2-306.3×10^?9 mole/cm³, the E-log [0₂] plot consists of two straight lines, one has a slope of 0.12 volts/decade (C>1 ppm up to air-saturated) and the other, 0.72 volts/decade (0.1<C<0.8 ppm). The transfer coefficient, α, the heterogeneous rate constants, k^o_fh and k^o_gh were evaluated to be 0.12, 2.8×10^?4, 1.6×10^?7 for the higher concentration range, and 0.02, 4.4×10^?4 for the lower concentration region respectively. A possible analytical method for tenths ppm level of oxygen is suggested.     

Development of a Piezoelectric Crystal Sorption Detector for Monitoring of Total Organic Compounds in Air

Abstract

A light and portable organic vapours monitor has been developed using piezoelectric (P/Z) quartz crystal to determine Volatile Organic Compounds (VOCs) commonly found in workplace air. Out of the eight coating material studied, High Vacuum Grease (HVG) was found to be the best for determining commonly encountered organic vapours such as 1,1,1-Trichloroethane, Chloroform, Benzene and Toluene in room air. The optimised coating weight was 23 μg HVG at a flow rate of 200 mL/min. Moisture was found to interfere and the use of a Nafion gas dryer was found to reduce the relative humidity to a constant 37 % for room air with 43–81 % relative humidity. Under optimised conditions, a mean sensitivity of 1.9 × 1^?2 Hz/ppm was obtained for total VOCs with 17.2% RSD variation towards different VOCs. Excellent linear working ranges were obtained from 40 to 2400 ppm (v/v), with response time and recovery time within one minute up to 500 ppm (v/v) of analyte. High and relatively constant response factors were obtained for different VOCs. The reliability of the mcthod has been established by parallel method comparison using established GC-FID method. The P/Z detector developed could also be used to monitor individual VOCs.     

Organic vapor sensing properties of copolymer Langmuir-Blodgett thin film sensors

In this study, a novel poly[Styrene (ST)-co-Glycidyl Methacrylate (GMA)] copolymer material is used to fabricate Langmuir-Blodgett (LB) thin films and investigate organic vapor sensing properties. Quartz Crystal Microbalance (QCM) system is used to investigate gas sensing performance of copolymer LB films during exposure to Volatile Organic Compounds (VOCs). The poly[Styrene (ST)-co-Glycidyl Methacrylate (GMA)] LB thin film sensor sensitivities are determined to be between 0.12 and 0.25 Hz ppm^?1. Detection limits of the copolymer LB thin film are found to be between 23 and 49 ppm against organic vapors. The copolymer LB thin films are more sensitive to chloroform than other vapors used in this study. The results demonstrated that the poly[Styrene (ST)-co-Glycidyl Methacrylate (GMA)] copolymer material is promising as a organic vapor sensing device at room temperature.     

Studies on the adsorption of nitrogen dioxide onto manganese dioxide-coated quartz piezoelectric crystals

A technique for obtaining thin; evenly distributed manganese dioxide coatings by melting manganese nitrate is outlined. Responses of an AT-cut quartz piezoelectric crystal coated with manganese dioxide to nitrogen dioxide (12.5-10 000 μl 1^?1) over a range of humidities (400–4,800 μ1 l^?1 water) and temperatures (20–35 °C) are given. The response of the simulated product manganese nitrate, over the same range of humidities, is evaluated in relationship to real product formation. The approach may be applicable to other metal salt/metal oxide systems. The detection limit is 7 μl^?1 nitrogen dioxide.     

Flow Injection Determination of Chloride Ions with Spectrophotometric Detection

Abstract

A single-line FIA system with a stream-sample splitting device for chloride determination is presented. The analytical method is based on the Fe^3+/Hg(SCN)₂/Cl^? system and the absorbance of the red Fe(SCN)²⁺ species monitored spectrophotometrically at 480 nm. Using a stream-sample splitting device, the recorded signal is composed of two merged peaks. Three calibration curves were obtained, once injecting the standard solution series, two using the maximum heights of P₁ and P₂ peaks and one using the height of T trough. The FIA system showed three linear responses to the concentration of chloride in the ranges 10-100 ppm (P₁); 10-500 ppm (P₂) and 20-1000 ppm (T), respectively. Also, it was capable of detecting chloride ions in different types of water with a throughput of 15 samples h^?1 and the RSD for 240 ppm of Cl^? (n=10) were 1.67% (P₁); 2.38% (P₂) and 1.23% (T), respectively. The interference of several ions (commonly found in water) on the FIA outputs was investigated.     

Ozone–isoprene reactions: Product formation and aerosol potential

Dark-phase experiments between isoprene and O₃ are discussed. UNC outdoor chamber experiments have shown that in high-concentration systems of isoprene and O₃ (5 ppm C and 1 ppm) approximately 75% of the reacted carbon can be observed in the product formation of HCHO, CO, methacrolein, methylvinylketone, methylglyoxal, acetaldehyde, and propylene. Mechanisms were developed which gave reasonable fits to dark-phase chamber experiments of MACR, MVK, isoprene, and O₃. Experimental data and modeling results were used to generate O₃ rates of attack on MVK and MACR. An isoprene–O₃ rate of 1.67 × 10^?2 ppm^?1·min^?1 was used and is consistent with other rates reported in the literature. Dark isoprene–O₃ systems appear to form homogeneously nucleated aerosol. Most of these particles appear and remain at diameters well below the optical cutoff region (0.3–0.5 μm), as opposed to the particles from similar α-pinene–O₃ systems, which also form at smaller sizes but then grow into the optical size range (0.5 μm). Lower concentrations of α-pinene and O₃ (0.2 ppm C and 0.12 ppm) still generated substantial aerosol, but by comparison, rapid CN nucleation was not observed during a similar side-by-side system of isoprene and O₃.