Simultaneous measurement of CO and CO2 at elevated temperatures by diode laser wavelength modulated spectroscopy

One single semiconductor distributed-feedback (DFB) laser is used to demonstrate the possibility of simultaneous measurements of CO and CO₂ at elevated temperatures. Wavelength modulation spectroscopy with second-harmonic detection is used to improve the detection sensitivity and accuracy. The concentrations of CO and CO₂ are determined from the WMS-1-normalized absorption-based WMS-2f signal peak heights of a proper line pair of CO and CO₂ near 6357.814 cm⁻¹ and 6357.312 cm⁻¹, which are selected using some line-selection criterions for the target temperature range of 300–1000 K. The CO and CO₂ concentrations measurements are within 2.86% and 2.69% of the expected values over the tested temperature range 300–1000 K. The minimum detectable concentrations of CO and CO₂ at 1000 K are 250 ppm m and 280 ppm m respectively.     

MEASUREMENT OF RADIATION INDUCED LOCALIZED ABSORPTION IN CHROMATOGRAPHIC ELUENTS BY MEANS OF THE CO LASER AND THE PZT PYROELECTRIC DETECTOR

Abstract

Combined use of the CO laser and PZT piezoelectric detector is proposed as a sensitive and specific detector for gas chromatography. The feasibility of this detection scheme is demonstrated for a model mixture containing varying proportions of acetone in water. After separation on a GC column, spectra of both constituents were recorded in the 1600 cm^?1 to 1900 cm^?1 range that encompasses the characteristic frequency of C=O bond in acetone. Reasonably high sensitivity (mass concentration limit is 1.2x10^?8 g acetone) and a good degree (factor 530) of spectral discrimination was achieved by a proper selection of analytical wavelengths.     

Spectrophotometric Determination of Silicon in Rice and Alloy Steel Samples

Abstract

In the medium of 0.128 mol/L nitric acid and 0.450 mol/L sulfuric acid, silicon(IV) and ammonium molybdate form molybdosilicate blue blue complex in the presence of ascorbic acid. The maximum absorption wavelength of the complex locates at 810 nm. The apparent molar absorptivity is ε_810 nm = 3.18 × 10⁴ L · mol^?1 · cm^?1. Beer's law is followed over the range of 0 ～ 1.0 µg/mLof silicon(IV). The present method has been successfully applied to the determination of silicon in rice and alloy steel samples.     

Near-field and confocal surface-enhanced resonance Raman spectroscopy at cryogenic temperatures

For laser spectroscopy at variable temperatures with high spatial resolution a combined scanning near‐field optical and confocal microscope was developed. Rhodamine 6G (R6G) dye molecules dispersed on silver nano‐particles or nano‐clusters were investigated. For optical excitation of the molecules, either an aperture probe or a focused laser spot in confocal arrangement were employed. Raman spectra in the wavenumber range between 300 cm^?1 and 3000 cm^?1 at room temperatures down to 8.5 K were recorded. Many of the observed Raman lines can be associated with the structure of the adsorbed molecule. Intensity fluctuations in spectral sequences were observed down to 77 K and are indicative of single molecule sensitivity.     

Automated Microscope-Absorption-Spectrophotometry Of Rock-Forming Minerals In The Range 40,000–5000 Cm−1 (250–2000 Nm)

To measure polarized absorption spectra of microcrystals of 3dⁿ-ion bearing silicate minerals, computer processed, microscope-spectrophotometric methods have been developed. Absorbance, log (I₀/I), can be measured with high relative accuracy (near u.v. and vis: ±0·002 to 0·001; n.i.r.: ±0·004 to 0·002), and relatively small spectral band widths are available. Hence, weak spin-forbidden dd-bands of 3dⁿ-ions can be recognized alongside spin-allowed dd-transitions without artificial broadening of absorption bands due to finite resolution. The smallest area from which absorption spectra can be taken is 8 μm in diameter. As one example of the many applications in mineralogy and material sciences, absorption spectra of a natural spessartine garnet, Spess_69·7Alm_30·0Gross_0·05, containing Mn²⁺, Fe²⁺, and traces of Fe³⁺ as 3dⁿ-ions, and of a pure Mn²⁺-garnet, Spess₆₇Gross₃₃, are presented. From these it is evident that bands in natural spessartines at ～ 26,900, 23,200 cm^?1 which were assigned to dd-transitions in Fe³⁺⁽⁶⁾, have to be reassigned to Mn²⁺⁽⁸⁾. Comparison of spectra obtained with the microscopic equipment described with those obtained by means of conventional macroscopic equipment prove that the methods described produce true spectra.     

Rapid and Highly Sensitive Method for Protein Determination in Biological Samples with m‐Nitrophenylfluorone‐Mo(VI) Complex as a Spectral Probe

Abstract

A simple, rapid, highly sensitive, and selective method for detecting protein in biological samples has been developed, which is based on the interaction between protein and m‐nitrophenylfluorone‐Mo(VI) complex as a spectral probe. The optimum condition for the reaction is investigated. Bovine serum albumin (BSA) obeys Beer's law up to 10 µg · mL^?1, having a molar absorption coefficient of 8.51×10⁶ L · mol^?1 · cm^?1 at 535 nm. Many amino acids and metal ions do not interfere. The results of determination for biological samples are comparable to those obtained by the Bradford method. Meanwhile, the binding number is also determined.     

Tribological Sensitivity of PTFE/Alumina Nanocomposites to a Range of Traditional Surface Finishes

Wear tests were performed with polytetrafluoroethylene (PTFE) + Al ₂ O ₃ nanocomposites on various manufactured surfaces to determine whether or not the wear resistance of these nanocomposites is a strong function of surface preparation. Four different surface finishes of grade 304 stainless steel counterfaces were used: electropolished (R _q = 88 nm), lapped (R _q = 161 nm), wet-sanded (R _q = 390 nm), and dry-sanded (R _q = 578 nm). PTFE + Al ₂ O ₃ nanocomposites made from powders of roughly 2-20 μm PTFE (matrix) and ～44 nm Al ₂ O ₃ (filler) were prepared at filler weight percentages of 0, 1, 5, and 10% and tested on each surface finish. Additionally, 5 wt% 44-nm nanocomposites were compared to identically prepared 5 wt% 80- and 500-nm Al ₂ O ₃ filled PTFE composites on each surface. Friction coefficients were between 0.12 and 0.19 and wear rates decreased from K = 810 × 10^{? 6} mm ³ /(Nm) for the 5 wt% 500-nm alumina-filled PTFE on the dry-sanded surface to K = 0.8 × 10^{? 6} mm ³ /(Nm) for the 5 wt% 80-nm filled composite on the lapped surface. It was found that the minimum wear rate occurred on the lapped counterface for every composite, and the wear rate is a strong function of the transfer film thickness and morphology.     

New inverse gas chromatographic methodology for studying mass transfer caused by the evaporation of volatile liquids

Abstract

Physico-chemical quantities related to evaporation have been simply and directly calculated by a new methodology of reversed-flow inverse gas chromatography. The only demand is a preliminary determination of quantification coefficient(s), converting the signal to solute(s) molar or volume units. Time-dependent, k_c(t) and overall mass transfer, k_c, coefficients were determined for the evaporation of methanol at temperatures from 305 to 336 K, using two diffusion column lengths (10.0 and 40.5 cm) to evaluate the effect of the mass transfer route. Mass transfer coefficients indicate the endothermic nature of evaporation, while the longer diffusion route resulted in lower k_c values. The precision in the determination of evaporation rates was high (98.3%). Time-resolved diffusion coefficients, D_g(t), were also estimated. The smaller diffusion route resulted in lower values due to the higher enrichment of the mobile phase in the solute vapors. In the case of the smaller diffusion route, the change of D_g(t) values increased from 0.1% to 0.8%, while in the longer it was less than 0.1%. The respective temperature exponent increased with the diffusion route length from 1.68 to 1.74. Removing the effect caused by the different lengths of diffusion routes, the activation energy corresponding to pure evaporation was equal to 35.2 kJ mol^?1, rather close to the literature values for methanol’s vaporization enthalpy, indicating the reliability of the new methodology. Finally, the effect of mass transfer route was estimated to be 229 MJ mol^?1 km^?1, revealing the huge amounts of heat transfer accompanying evaporation at high altitudes.     

LASER PHOTOACOUSTIC TRACE GAS DETECTION,AN EXTREMELY SENSITIVE TECHNIQUE APPLIED IN BIOLOGICAL RESEARCH

Abstract

The use of infrared laser based photo-acoustic trace gas detection equipment in biological research is discussed on the basis of two examples. A CO₂ laser based photo-acoustic trace gas detection system is employed to follow the time-dependent pattern of the nitrogen fixation process by the cyanobacteria Nodularia Spumigena on a one-minute time scale. Due to the high sensitivity of the detection system for ethylene (detection limit 6 part per trillion; 6:10¹²), the fixation process can be followed on-line in a flow-through system. Following a 50 h dark incubation period, the bacteria show nitrogen fixation only after a certain illumination period, indicating lack of carbohydrates needed to start the nitrogen fixation.

Another, CO laser based, system allowed to monitor acetaldehyde emission (detection limit 0.1 part per billion) of Docks Rumex palustris during the change from anoxic environment to O₂ levels of air. An almost immediate emission is found, indicating that acetaldehyde plays an important role for post-anoxic injury in Rumex palustris.     

Effects of Environment on Friction and Wear of Al-Si Alloy Impregnated Graphite Composite

Pin-on-disk-type wear experiments for an Al-Si alloy impregnated graphite composite (pin) in contact with a bearing steel (disk) were conducted at 100N normal load (100 Newtons) in air, argon, and deionized water to investigate the effects of environment on the tribological characteristics of the composite. The friction and wear behavior and the pin-lifting phenomenon due to wear particle ingress into the contact surfaces were continuously measured during the experiments. At low relative humidity (RH) levels, the friction coefficients in air and argon are high (0.32 to 0.39) and decrease with increasing RH to values around 0.2. The friction coefficients in air have reached a minimum of 0.15 to 0.17 between 50 and 70% RH and increased slightly at 80% RH. The friction coefficients in argon are constant at about 0.2 between 10 and 80% RH. Because of the lubricating action of a water film, the friction coefficient in deionized water is slightly lower (0.1 to 0.17) than that in air. The mean wear rate of 10^?4 to 8 × 10^?4 mm ³ /mm (specific wear rate; w _s = 10 ^?6 to 8 × 10^{? 6} mm ² /N) is very high in a severe wear regime at RH levels lower than 10% in air, decreases with increasing RH to a minimum in the middle RH range (30 to 60%), and increases slightly at RH levels higher than 70%. Although the mean contact pressure is very high (31.8 MPa), mild wear with the rates of 10^?8 to 10^?7 mm ³ /mm (w _s = 10^?10 to 10^?9 mm ² /N) occurs in the middle RH range. The same change in wear with RH as that in air is found in argon but the wear rate in argon is slightly lower than the wear rate in air. The height of the pin-lifting, having a wear reduction effect, is greater in argon than in air over almost the whole RH range. The wear rate in deionized water is nearly equal to the rate at 70% RH in air and argon.     

Comparison of some physical techniques for detection of spoilage in apple juice inoculated with Saccharomyces cerevisiae: Optical and photothermal methods

Abstract

Several physical techniques were used to study the extent of spoilage in apple juice deliberately inoculated with yeast (concentration of Saccharomyces cerevisiae ranged from 25 cells mL^?1 to 2.5 × 10⁶ cells mL^?1, respectively) and their performance compared in terms of detection limit achieved. The optical methods used in this investigation rely on the measurement of either absorption [as is the case for classical spectrophotometry (SP) and the so called optothermal window (OW), a variant of a photothermal method], or scattering [examples are turbidimetry (TB), laser scattering (SC), and laser speckle fluctuation (SF)]. It is shown that the presence of yeast increases both optical absorption and scattering. The most favorable detection limit (25 cells mL^?1) and a highest (nearly 10⁴) dynamic range, combined with a good linearity, were obtained with the experimental set‐up for SC. In addition, the extent of correlation between different methods was determined using two markedly different reference substances, i.e., (i) the mixture of apple and blackcurrant juices, representing a strongly absorbing sample, and (ii) diluted (dilution factor of 10³) milk as a strong scatterer. Finally, one has monitored the progress of a spontaneous spoilage process in the inoculated juices stored at 5°C under aerobic conditions.     

Changes in nail keratin observed by Raman spectroscopy after Nd:YAG laser treatment

Lasers and photodynamic therapy have been considered a convergence treatment for onychomycosis, which is a fungal infection on the nail bed and nail plate. Laser therapies have shown satisfactory results without significant complications for onychomycosis; however, the mechanism of clearing remains unknown. In this work, we investigated changes in the chemical structure of nail keratin induced by Nd:YAG laser using Raman spectroscopy. Toe nails with onychomycosis were treated with 1064 nm Nd:YAG laser. After laser treatment, the disulfide band (490–590 cm^?1) of nail keratin was rarely observed or was reduced in intensity. The amide I band (1500–1700 cm^?1) also showed changes induced by the laser. The α‐helical (1652 cm^?1) structures dominated the β‐sheet (1673 cm^?1) in nontreated nail, but the opposite phenomenon was observed after laser treatment.     

Hydrothermal synthesis of a lamellar zinc dimolybdate hydroxide with application as the anode for lithium-ion batteries

Abstract

A lamellar zinc dimolybdate hydroxide Zn₃Mo₂O₈(OH)₂ was prepared for the first time by a facile hydrothermal synthesis. The electrochemical properties of the lamellar Zn₃Mo₂O₈(OH)₂ as an anode material were investigated by cyclic voltammetry (CV), reversible capacity, cycling stability and rate capability for lithium ion batteries (LIB). The lamellar zinc dimolybdate hydroxide exhibits a reversible capacity of 404.6 mAh g^?1 at a current density of 100?mA g^?1 after 200 cycles. The reversible capacity of the lamellar Zn₃Mo₂O₈(OH)₂ remained at 60 mAh g^?1 even at a current density of 3000?mA g^?1. When the current density was returned to 100?mA g^?1, a discharge capacity of 380 mAh g^?1 was maintained after 200 discharge/charge cycles. The excellent electrochemical performance may be due to its unique lamellar structure, which buffers the volume change during the Li⁺ intercalation/de-intercalation and provides the electrode with convenient lithium ions and electron transport pathways. These results suggest the promising potential application of the lamellar zinc dimolybdate hydroxide in lithium-ion batteries.     

HgCdTe structures for dual-band photodetectors operating in the 3–5 and 8–12 µm spectral ranges

A bilayer cadmium-mercury-tellurium (CMT) heterostructure was designed consisting of photosensitive layers of compositions x _CdTe = 0.29–0.32 and x _CdTe = 0.220–0.230, sensitive in the spectral ranges of 3–5 and 8–12 µm, a barrier layer between them, and wide-band variable-gap layers on the heterojunction and the surface grown on a GaAs substrate with ZnTe and CdTe buffer layers. The molecular beam epitaxial (MBE) growth of the heteroepitaxial structure (HES) was controlled by real time ellipsometry. After the growth, the composition distribution throughout the thickness was measured by reflection spectra with layer-by-layer chemical etching. There is good agreement between the results of composition measurements using ellipsometry and reflection spectra. P-type conductivity of bilayer MBE CMT HESs was obtained after thermal annealing at 220–240 °C in an inert gas (helium) for 24 h. The concentration of holes in the photosensitive layers is (4–10) ·10¹⁵ cm^?3 and (8–20) · 10¹⁵ cm^?3 at 78 K.     

Tribological Characteristics of Nitrogen (N+) Implanted Iron

The effect of implantation of nitrogen ions (1.5 MeV) on the friction and wear characteristics of pure iron sliding against M-50 steel (unimplanted) was studied in a pin-on-disk sliding friction apparatus. Test conditions included room temperature (～25°C), a dry air atmosphere, a load of ½ kg (4.9 N), sliding velocities of 0.043 to 0.078 m/s (～15 to 25 rpm), a pure hydrocarbon lubricant (n-hexadecane), or a USP mineral oil and nitrogen ion implantation doses of 5 × 10¹⁵ and 5 × 10¹⁷ ions/cm².

No differences in wear rates were observed in the low-dose (5 × 10¹⁵ ions/cm²) experiments. In the high-dose experiments (5 × 10¹⁷ ions/cm²), small reductions in initial (～40 percent) and steady-state (～20 percent) wear rates were observed for nitrogen-implanted iron riders as compared with unimplanted controls. No differences in average friction coefficients were noted for either dose.

Auger electron spectroscopy combined with argon ion bombardment revealed a subsurface Gaussian nitrogen distribution with a maximum concentration of 6 atomic percent at a depth of 8 × 10^?7 m (0.8 μm). Similar analysis within the wear scar (～2.0 × 10^?5 m subsurface) of an implanted rider after 20 μm of wear yielded only background nitrogen concentration. No inward migration of nitrogen ions was observed.     

PVC Membrane Sensor for Potentiometric Determination of Atropine in Some Pharmaceutical Formulations

Abstract

The construction and general performance of a novel potentiometric membrane sensor for determination of atropine has been developed. It is based on the formation of the ion association complex of the atropinium cation with phosphotungstate counter anion as electroactive material dispersed in a PVC matrix, β‐Cyclodextrin and o‐nitrophenyl octyl ether serve as a plasticizer. The sensor shows a fast, stable, near Nernstian response for 1×10^?2 M to 1×10^?6 M atropine at 25°C over the pH range of 3–8 with a cationic slope of 51±0.5 mV/decade. The lower detection limit is 8×10^?7 M and the response time is 20–45 sec. Selectivity coefficients of atropine, relative to a number of interfering substances, were investigated. There are negligible interferences caused by most of the studied cations, anions, and pharmaceutical excipients. The direct determination of atropine shows an average recovery of 98.6% and a mean relative standard deviation (RSD) of 1.6% at 100 µg/mL. The results obtained by determination of atropine in some formulations (atropine injection and eye drops) are favorably comparable with those obtained by the British Pharmacopoeia method. The developed membrane electrode has been used as end point indicator electrode for some potentiometric titrations.     

Water loss at normal enamel histological points during air drying at room temperature

This in vitro study aimed to quantify water loss at histological points in ground sections of normal enamel during air drying at room temperature (25°C) and relative humidity of 50%. From each of 10 ground sections of erupted permanent human normal enamel, three histological points (n = 30) located at 100, 300 and 500 μm from enamel surface and along a transversal following prisms paths were characterized regarding the mineral, organic and water volumes. Water loss during air drying was from 0 to 48 h. Drying occurred with both falling and constant‐drying rates, and drying stabilization times (T_eq) ranged from 0.5 to 11 h with a mean 0.26 (±0.12)% weight loss. In some samples (n = 5; 15 points), T_eq increased as a function of the distance from the enamel surface, and drying occurred at an apparent diffusion rate of 3.47 × 10^?8 cm² s^?1. Our data provide evidence of air drying resulting in air replacing enamel's loosely bound water in prisms sheaths following a unidirectional water diffusion rate of 3.47 × 10^?8 cm² s^?1 (from the original enamel surface inward), not necessarily resulting in water evaporating directly into air, with important implications for transport processes and optical and mechanical properties.     

A microwave detector based on an MCT photodiode for subthermonuclear plasma research

A microwave detector including a single-element infrared (IR) photodiode mounted in a cooled Dewar and a preamplifier is developed. An IR photodiode of the n ⁺-p type is created on the basis of mercury-cadmium telluride (HgCdTe or MCT) heteroepitaxial structures grown by means of molecular beam epitaxy. A special profile of MCT structures throughout the MCT layer thickness ensures a low series resistance of less than 10 Ω and a high quantum efficiency at a level of 0.65 without any antireflection coating. For the spectral range of 8 to 12 μm, IR photodiodes are characterized by a low threshold power of 3.8·10^?13 W·Hz^?1/2 and 10^?19 W·Hz^?1 in the direct and heterodyne regimes, respectively. The cooled Dewar maintains the operating temperature of the IR photodiode in the interval of 77 to 80 K for 8. The preamplifier operates in a frequency range up to 1 GHz. With the use of this microwave detector, a method is developed for detection of intensity of a CO₂ laser beam on plasma fluctuations caused by heating by a relativistic electron beam (REB). At high REB intensities, dips of the turbulence signal with a duration of several nanoseconds are observed, which is interpreted as a collapse of Langmuir waves.     

Characterization of an ultraviolet irradiation chamber to monitor molecular photodegradation by Raman spectroscopy

A homemade ultraviolet chamber is reported to induce photochemical changes with characterization by Raman spectroscopy. The equipment has compartments for ultraviolet-A (UV-A) (8 lamps of 8 W) and for UV-A + ultraviolet-B (UV-B) irradiation (4 lamps of 26 W and 1 lamp of 15 W). The irradiance was measured 3, 5, and 10 cm from the light sources. The maximum irradiance was obtained at 3 cm (UV-A: 2.66 mW/cm² and UV-A + UV-B: 4.30 mW/cm²). The chamber internal temperature was stabilized at 30°C after 1 hr of operation with an internal relative humidity of approximately 45%. 10% Collagen was irradiated with UV-A at 2.0 mW/cm² for 3 hr with changes in Raman peaks at 1253, 1271, 1453, and 1660 cm^?1 indicating changes in conformation. 5% Atenolol was irradiated with UV-A + UV-B at 4.30 mW/cm² for 8 hours with changes to Raman peaks at 822, 1186, 1206, 1248, and 1618 cm^?1. A commercial insect repellent was irradiated with UV-A + UV-B at 4.30 mW/cm² for 8 hr and decreases in Raman intensity were observed at 526, 690, 1003, and 1606 cm^?1 due to degradation of N, N-diethyl-m-toluamide. The results demonstrate proper operation of the irradiation chamber with Raman spectroscopic monitoring.     

PVC Membrane Sensor for Potentiometric Determination of Fluoxetine in Some Pharmaceutical Formulations

Abstract

The construction and general performance of a novel potentiometric membrane sensor for determination of fluoxetine has been developed. It is based on the formation of the ion association complex of fluoxetine with picrolonic acid as electroactive material, dispersed in a PVC matrix and o‐nitrophenyl octyl ether as a plasticizer. The sensor shows a fast, stable, and near Nernstian response for 1×10^?2 M to 8×10^?6 M fluoxetine at 25°C over the pH range of 1–5 with a cationic slope of 51±0.5 mV/decade. The lower detection limit is 6×10^?6 M and the response time 20–35 sec. Selectivity coefficients for fluoxetine, related to number of interfering substances, were investigated. There are negligible interferences from the studied cations, anions, and pharmaceutical excipients. The determination of fluoxetine in aqueous solution shows an average recovery of 98.6% and a mean relative standard deviation (RSD) of 1.5% at 100 µg/mL. The direct determination of fluoxetine in some formulations gave results that compare favorably with those obtained by a spectrophotometric method. The developed membrane electrode has been used as an end point indicator electrode, e.g., potentiometric titration of fluoxetine with sodium tetraphenylborate as a titrant has been monitored.