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1.
Sulfur dioxide (SO2) trace gas detection based on quartz-enhanced photoacoustic spectroscopy (QEPAS) using a continuous wave, distributed feedback quantum cascade laser operating at 7.24 μm was performed. Influence of water vapor addition on monitored QEPAS SO2 signal was also investigated. A normalized noise equivalent absorption coefficient of NNEA (1σ) = 1.21 × 10?8 cm?1 W Hz?1/2 was obtained for the ν 3 SO2 line centered at 1,380.93 cm?1 when the gas sample was moisturized with 2.3 % H2O. This corresponds to a minimum detection limit (1σ) of 63 parts per billion by volume for a 1 s lock-in time constant.  相似文献   

2.
A resonant photoacoustic cell capable of detecting the traces of gases at an amplitude-modulation regime is represented. The cell is designed so as to minimize the window background for the cell operation at a selected acoustic resonance. A compact prototype cell (the volume of acoustic cavity of ~0.2 cm3, total cell weight of 3.5 g) adapted to the narrow diffraction-limited beam of near-infrared laser is produced and examined experimentally. The noise-associated measurement error and laser-initiated signals are studied as functions of modulation frequency. The background signal and useful response to light absorption by the gas are analyzed in measurements of absorption for ammonia traces in nitrogen flow with the help of a pigtailed DFB laser diode operated near a wavelength of 1.53 µm. The performance of absorption detection and gas-leak sensing for the prototype operated at the second longitudinal acoustic resonance (the resonance frequency of ~4.38 kHz, Q-factor of ~13.9) is estimated. The noise-equivalent absorption normalized to laser-beam power, and detection bandwidth is ~1.44 × 10?9 cm?1 W Hz?1/2. The amplitude of the window-background signal is equivalent to an absorption coefficient of ~2.82 × 10?7 cm?1.  相似文献   

3.
A compact two-gas sensor based on quartz-enhanced photoacoustic spectroscopy (QEPAS) was developed for trace methane and ammonia quantification in impure hydrogen. The sensor is equipped with a micro-resonator to confine the sound wave and enhance QEPAS signal. The normalized noise-equivalent absorption coefficients (1σ) of 2.45×10?8 cm?1?W/ $\sqrt{}$ Hz and 9.1×10?9 cm?1?W/ $\sqrt{}$ Hz for CH4 detection at 200 Torr and NH3 detection at 50 Torr were demonstrated with the QEPAS sensor configuration, respectively. The influence of water vapor on the CH4 channel was also investigated.  相似文献   

4.
Quartz-enhanced photoacoustic spectroscopy (QEPAS) is demonstrated for acetylene detection at atmospheric pressure and room temperature with a fiber-coupled distributed feedback (DFB) diode laser operating at ~1.53 μm. An efficient approach for gas concentration calibration is demonstrated. The effect of residual amplitude modulation on the performance of wavelength modulated QEPAS is investigated theoretically and experimentally. With optimized spectrophone parameters and modulation depth, a minimum detectable limit (1σ) of ~2 part-per-million volume (ppmv) was achieved with an 8.44-mW diode laser, which corresponds to a normalized noise equivalent coefficient (1σ) of 6.16 × 10?8 cm?1 W/Hz1/2.  相似文献   

5.
Electron paramagnetic resonance spectra of Cu2+ impurities in cytosine hydrochloride single crystals are observed at liquid nitrogen temperature. Two magnetically equivalent sites for Cu2+ have been observed. The parameters of 63Cu obtained with the fitting of spectra to rhombic symmetry spin Hamiltonian are: g x  = 2.047 ± 0.002, g y  = 2.187 ± 0.002, g z  = 2.390 ± 0.002, A x  = (86 ± 3) × 10?4 cm?1, A y  = (87 ± 3) × 10?4 cm?1, and A z  = (138 ± 3) × 10?4 cm?1. The observed bands in optical spectra of the single crystal recorded at room temperature are assigned to various d–d and charge-transfer transitions. Using both EPR and optical data, the nature of bonding of metal ion with different ligands is discussed.  相似文献   

6.
X-band electron paramagnetic resonance (EPR) studies are carried out on Fe3+ ions doped in ammonium dihydrogen phosphate (ADP) single crystals at room temperature. The crystal field and spin Hamiltonian parameters are evaluated from the resonance lines obtained at different angular rotations. The obtained values of spin Hamiltonian and zero-field parameters of the Fe3+ ion in ADP are: g = 1.994 ± 0.002, |D| = (220 ± 5) × 10?4 cm?1 and a = (640 ± 5) × 10?4 cm?1. On the basis of EPR data, the site symmetry of the Fe3+ ion in the crystal is discussed. The Fe3+ ion enters the lattice substitutionally replacing the NH4 + sites. The optical absorption of the crystal is also studied at room temperature in the wavelength range of 195–925 nm. The energy values of different orbital levels are calculated. The observed bands are assigned as transitions from the 6 A 1g (S) ground state to various excited quartet levels of the Fe3+ ion in a cubic crystalline field. From the observed band positions, Racah interelectronic repulsion parameters (B and C), cubic crystal field splitting parameter (D q ) and Trees correction are calculated. There values are: B = 970, C = 1,923, D q  = 1,380 cm?1 and α = 90 cm?1, respectively. On the basis of EPR and optical data, the nature of bonding in the crystal is discussed. The zero-field splitting (ZFS) parameters are also determined theoretically using B kq parameters estimated from the superposition model. The values of ZFS parameters thus obtained are |D| = (213 ± 5) × 10?4 cm?1 and |E| = (21 ± 5) × 10?4 cm?1.  相似文献   

7.
X-band electron paramagnetic resonance (EPR) study of Cr3+-doped dipotassium tetrachloropalladate single crystal is done at liquid nitrogen temperature. EPR spectrum shows two sites. The spin-Hamiltonian parameters have been evaluated by employing hyperfine resonance lines observed in EPR spectra for different orientations of crystal in externally applied magnetic field. The values of spin-Hamiltonian and zero-field splitting (ZFS) parameters of Cr3+ ion-doped DTP for site I are: g x  = 2.096 ± 0.002, g y  = 2.167 ± 0.002, g z  = 2.220 ± 0.002, D = (89 ± 2) × 10?4 cm?1, E = (16 ± 2) × 10?4 cm?1. EPR study indicates that Cr3+ ion enters the host lattice substitutionally replacing K+ ion and local site symmetry reduces to orthorhombic. Optical absorption spectra are recorded at room temperature. From the optical absorption study, the Racah parameters (B = 521 cm?1, C = 2,861 cm?1), cubic crystal field splitting parameter (Dq = 1,851 cm?1) and nephelauxetic parameters (h = 2.06, k = 0.21) are determined. These parameters together with EPR data are used to discuss the nature of bonding in the crystal.  相似文献   

8.
ABSTRACT

Single-crystal and powder EPR studies of VO2+-doped lithium hydroxylammonium sulphate (LiNH3OHSO4) were carried out at room temperature. The results indicate the presence of two magnetically inequivalent VO2+ sites. The VO2+ ion takes up a substitutional position in the host lattice. The angular variation of EPR spectra in three mutually perpendicular planes were used to determine the spin Hamiltonian parameters, and the values obtained were the following: For Site 1, gx = 2.0249 ± 0.0002, gy = 1.9698 ± 0.0002, gz = 1.9552 ± 0.0002, Ax = (51 ± 2) × 10?4 cm?1, Ay = (93 ± 2) × 10?4 cm?1, and Az = (165 ± 2) × 10?4 cm?1; and for Site 2, gx = 2.0267 ± 0.0002, gy = 1.9743 ± 0.0002, gz = 1.9213 ± 0.0002, Ax = (40 ± 2) × 10?4 cm?1, Ay = (80 ± 2) × 10?4 cm?1, and Az = (155 ± 2) × 10?4 cm?1. The optical absorption spectrum recorded at room temperature shows four bands. From the optical and EPR data, various molecular coefficients are evaluated, and the nature of bonding in the crystal is discussed.  相似文献   

9.
A new bis(diphenylphosphate)diimine ligand (BP1) was prepared and evaluated for its ability for selective detection of deoxycytidine 5??-monophosphate (dCMP). BP1 exhibited off-type fluorescence in the presence of dCMP. The fluorescence of BP1 was significantly quenched upon the addition of 2.5?×?10?4 M dCMP and the detection limit was 1.25?×?10?5 M in MeCN-H2O (1:1, v/v). The binding ratio between BP1 and dCMP was determined to be 1:1 with the binding constant of 3.98?±?0.60?×?10?3 M?1.  相似文献   

10.
We report what we believe to be a novel demonstration of simultaneous detection of multiple trace gases by near-IR tunable diode laser photoacoustic spectroscopy using a cell containing a cantilever microphone. Simultaneous detection of carbon monoxide (CO), ethyne (C2H2), methane (CH4) and combined carbon monoxide/carbon dioxide (CO+CO2) in nitrogen-based gas mixtures was achieved by modulation frequency division multiplexing the outputs of four near-IR tunable diode lasers. Normalized noise-equivalent absorption coefficients of 3.4×10?9, 3.6×10?9 and 1.4×10?9 cm?1?W?Hz?1/2 were obtained for the simultaneous detection of CO, C2H2 and CH4 at atmospheric pressure. These corresponded to noise-equivalent detection limits of 249.6 ppmv (CO), 1.5 ppmv (C2H2) and 293.7 ppmv (CH4) respectively over a measurement period of 2.6 s at the relevant laser power. The performance of the system was not influenced by the number of lasers deployed, the main source of noise arising from ambient acoustic effects. The results confirm that small-volume photoacoustic cells can be used with low optical power tunable diode lasers for rapid simultaneous detection of trace gases with high sensitivity and specificity.  相似文献   

11.
The sensitization of the excited triplet state of a novel symmetrical Bis(dialkylamino)phenoxazinium salt was developed in the presence of Hg2+. This effect was used to determine the concentration of Hg2+ in different water samples. The phenoxazinium salt sensor was characterized by different spectroscopic tools such as: UV, FTIR, NMR and fluorescence spectra. The sensor has an emission band at 347 nm in DMSO. Hg2+ in DMSO at pH 5.6 can remarkably quench the fluorescence intensity of the sensor at 347 nm and a new band was appeared at 436 nm due to the strong complex formation between Hg2+ and sensor. The quenching of the band intensity at 347 and the enhancement of the intensity of the new band at 436 were used to determine the Hg2+ in different waste water samples. The dynamic range found for the determination of Hg2+ concentration is 8.7?×?10-10 – 1.4?×?10-6 mol L?1 with a detection limit of 5.8?×?10?10 mol L?1 and quantification detection limit of 1.8?×?10-9 mol L-1.  相似文献   

12.
Jing Li  Huaqing Xie 《Ionics》2013,19(1):105-112
A sensitive hydroxylamine sensor is developed by electrodeposition of Pt nanoparticles on pre-synthesized polypyrrole nanoparticles modified glassy carbon electrode. The modified electrode presents distinctly electrocatalytic activity toward hydroxylamine oxidation. The kinetic parameters such as the overall numbers of electrons involved in hydroxylamine oxidation, the electron transfer coefficient, standard heterogeneous rate constant, and diffusion coefficient are evaluated. The current response increases linearly with increasing hydroxylamine concentrations and exhibits two wide linear ranges of 5.0?×?10?7–1.1?×?10?3 and 1.1?×?10?3–18.8?×?10?3 M with a detection limit of 0.08 μM (s/n?=?3). The proposed electrode presents excellent operational and storage ability for determining hydroxylamine. Moreover, the sensor shows good sensitivity, selectivity, and reproducibility properties.  相似文献   

13.
The electrooxidation of hydrochlorothiazide (HCT) at the surface of a benzoylferrocene modified multi-walled carbon nanotube paste electrode was studied using electrochemical approaches. Under the optimized conditions (pH 7.0), the square wave voltammetric peak current of HCT increased linearly with HCT concentration in the ranges of 6.0?×?10?7 to 3.0?×?10?4 M. The detection limit was 9.0?×?10?8 M HCT. The diffusion coefficient (D?=?1.75?×?10?5 cm2/s) and electron transfer coefficient (α?=?0.45) for HCT oxidation were also determined. The proposed sensor was successfully applied for the determination of HCT in human urine and tablet samples.  相似文献   

14.
A quantum cascade laser (QCL)-based absorption sensor for the simultaneous dual-species monitoring of CH4 and N2O was developed using a novel compact multipass gas cell (MGC). This sensor uses a thermoelectrically cooled, continuous wave, distributed feedback QCL operating at ~7.8 µm. The QCL wavelength was scanned over two neighboring CH4 (1275.04 cm?1) and N2O (1274.61 cm?1) lines at a 1 Hz repetition rate. Wavelength modulation spectroscopy (f = 10 kHz) with second harmonic (2f) detection was performed to enhance the signal-to-noise ratio. An ultra-compact MGC (16.9 cm long and a 225 ml sampling volume) was utilized to achieve an effective optical path length of 57.6 m. With such a sensor configuration, a detection limit of 5.9 ppb for CH4 and 2.6 ppb for N2O was achieved, respectively, at 1-s averaging time.  相似文献   

15.
Measurements of carbon monoxide (CO) mixing ratios in Houston, Texas, during the period from May 16, 2013 to May 28, 2013 were performed using a sensitive, selective, compact, and portable quartz-enhanced photoacoustic spectroscopy (QEPAS)-based CO sensor employing a high-power continuous wave (CW) distributed feedback quantum cascade laser (DFB-QCL). The minimum detectable CO concentration was 3 ppbv for the strong, interference-free R(6) absorption line at 2,169.2 cm?1 and a 5 s data acquisition time. The average CO concentration during the measurement period was 299.1 ± 81.4 ppb with observed minimum and maximum values of 210.5 and 4,307.9 ppb, respectively. A commercially available electrochemical sensor was employed in-line for simultaneous measurements to confirm the response of the CW DFB-QCL-based QEPAS sensor to variations of the CO mixing ratios. Moderate agreement (R 2 = 0.7) was found between both sets of CO measurements.  相似文献   

16.
We report on optical and structural properties of α-Fe2O3 and Co3O4 thin films, grown by direct oxidation of pure metal films deposited on soda-lime glass. Structural characteristics and morphology of the films were investigated by X-ray diffraction, atomic force microscopy, and scanning electron microscopy. Linear optical absorption, and linear refraction as well as nonlinear optical properties were investigated. The third-order optical susceptibilities were measured applying the Thermally managed Z-scan technique using a Ti: sapphire laser (150 fs; 800 nm). The results obtained for the Co3O4 film were \( \text{Re} \chi^{\left( 3 \right)} \) = ?(5.7 ± 2.4) ×10?9 esu and \( \text{Im} \chi^{(3)} \) = ?(1.8 ± 0.2) ×10?8 esu while for the α-Fe2O3 film we determined \( \text{Re} \chi^{(3)} \) = +(6.6 ± 2.4) ×10?10 esu and \( \text{Im} \chi^{(3)} \) = +(2.2 ± 0.4) ×10?10 esu.  相似文献   

17.
In this study, poly (vinyl chloride)(PVC) membrane electrodes with/without multi-walled carbon nanotubes (MWCNTs) based on a calix[4]arene derivative for perchlorate ion were described. The influence of membrane composition, pH, conditioning solution on the potentiometric response of the electrodes was investigated. Perchlorate-selective PVC membrane electrode exhibited a slope of 47.8 ± 0.6 mV/pClO4 in the range of 1.0 × 10?7–1.0 × 10?1 mol L?1at pH 4.0 while the coated Pt electrodes with MWCNT-OH, MWCNT-COOH and MWCNT displayed slopes of 46.1 ± 0.7 mV/pClO4 (5.0 × 10?6–1.0 × 10?1 mol L?1), 50.4 ± 1.9 mV/pClO4 (1.0 × 10?6–1.0 × 10?1 mol L?1) and 44.4 ± 0.3 mV/pClO4 (1.0 × 10?5–1.0 × 10?1 mol L?1), respectively. Other response characteristics of these electrodes such as response time, lifetime and detection limit were identified, and the selectivity coefficients towards various anions were calculated by separate solution method. Moreover, the perchlorate-selective electrodes described here were successfully used as an indicator electrode for the determination of perchlorate in real samples such as tap water, river water and human urine by direct calibration method.  相似文献   

18.
An effective potentiometric sensor had been fabricated for the rapid determination of Pb2+ based on carbon paste electrode consisting of room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6), multiwalled carbon nanotubes (MWCNTs), nanosilica, synthesized Schiff base, as an ionophore, and graphite powder. The constructed nanocomposite electrode showed better sensitivity, selectivity, response time, response stability, and lifetime in comparison with typical Pb2+ carbon paste electrode for the successfully determination of Pb2+ ions in water and in waste water samples. The best response for nanocomposite electrode was obtained with electrode composition of 18% ionophore, 20% BMIM-PF6, 49% graphite powder, 10% MWCNT, and 3% nanosilica. The new electrode exhibited a Nernstian response (29.76?±?0.10 mV decade?1) toward Pb2+ ions in the range of 5?×?10?9?C1.0?×?10?1 mol L?1 with a detection limit of 2.51?×?10?9 mol L?1. The potentiometric response of prepared sensor is independent of the pH of test solution in the pH range of 4.5?C8.0. It has quick response with response time of about 6 s. The proposed electrode show fairly good selectivity over some alkali, alkaline earth, transition, and heavy metal ions.  相似文献   

19.
Co2+ binding to the nicotinamide adenine dinucleotide (NAD+) molecule in water solution was studied by electron paramagnetic resonance (EPR) and electron spin echo at low temperatures. Cobalt is coordinated by NAD+ when the metal is in excess only, but even in such conditions, the Co/NAD+ complexes coexist with Co(H2O)6 complexes. EPR spin-Hamiltonian parameters of the Co/NAD+ complex at 6 K are g z  = 2.01, g x  = 2.38, g y  = 3.06, A z  = 94 × 10?4 cm?1, A x  = 33 × 10?4 cm?1 and A y  = 71 × 10?4 cm?1. They indicate the low-spin Co2+ configuration with S = 1/2. Electron spin echo envelope modulation spectroscopy with Fourier transform of the modulated spin echo decay shows a strong coordination by nitrogen atoms and excludes the coordination by phosphate and/or amide groups. Thus, Co2+ ion is coordinated in pseudo-tetrahedral geometry by four nitrogen atoms of adenine rings of two NAD+ molecules.  相似文献   

20.
A very sensitive and reversible optical chemical sensor based on a novel tetradentate Schiff base namely N.N/bis(2-aminothiophenol)benzene-1,2-dicarboxaldehyde (ATBD) immobilized within a plasticized PVC film for Hg2+ determination is described. At optimum conditions (i.e. pH 6.0), the proposed sensor displayed a linear response to Hg2+ over 1.0?×?10?10 ? 1.0?×?10?2 mol L?1 with a limit of detection of 7.23?×?10?11 mol L?1 (0.0145 μgL?1). Moreover, the results revealed that, under batch condition, the sensor is fully reversible within a response time?~?35 s. In addition to its high stability and reproducibility, the sensor showed good selectivity towards Hg2+ ion with respect to common metal cations. The sensor was successfully applied for determination of Hg2+ ion in some real samples, including hair, urine and well water samples. The results were in good correlation with the data obtained using cold vapor atomic absorption spectrometry.  相似文献   

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