Standard Wavelength Research Articles

Cavity Ring-down Spectroscopy for Detection in Liquid Chromatography: Extension to Tunable Sources and Ultraviolet Wavelengths

In earlier studies, it was demonstrated that the sensitivity of absorbance detection in liquid chromatography (LC) can be improved significantly by using cavity ring-down spectroscopy (CRDS). Thus far, CRDS experiments have been performed using visible laser light at fixed standard wavelengths, such as 532 nm. However, since by far most compounds of analytical interest absorb in the ultraviolet (UV), it is of utmost importance to develop UV-CRDS. In this study, as a first step towards the deep-UV region, LC separations with CRDS detection (using a previously described liquid-only cavity flow cell) at 457 and 355 nm are reported for standard mixtures of dyes and nitro-polyaromatic hydrocarbons (nitro-PAHs), respectively. For the measurements in the blue range a home-built optical parametric oscillator (OPO) system, tunable between 425 and 478 nm, was used, achieving a baseline noise of 2.7 x 10(-6) A.U. at 457 nm, improving upon the sensitivity of conventional absorbance detection (typically around 10(-4) A.U.). An enhancement of the sensitivity can be seen at 355 nm as well, but the improvement of the baseline noise (1.3 x 10(-5) A.U.) is much less pronounced. The sensitivity at 355 nm is limited by the quality of the UV-CRDS mirrors that are currently available: whereas the ring-down times as obtained at 457 nm are around 70-80 ns for the eluent, they are only 20-25 ns at 355 nm. Critical laser characteristics for LC-CRDS measurements, such as pulse length and mode structure, are given and prospects for going to shorter wavelengths are discussed.

Icosahedral coordination of phosphorus in the crystal structure of melliniite, a new phosphide mineral from the Northwest Africa 1054 acapulcoite

Melliniite, ideally (Ni,Fe) 4 P, is a new mineral from the Northwest Africa 1054 acapulcoite. It occurs as anhedral to subhedral grains up to 100 µm, associated with kamacite and nickelphosphide. Melliniite is opaque with a metallic luster and possesses a gray streak. It is brittle with an uneven fracture; the Vickers microhardness (VHN 500 ) is 447 kg/mm 2 (range 440-454) (calculated Mohs hardness of 8-8½). The calculated density is 7.88 g/cm 3 (on the basis of the empirical formula). In plane-polarized reflected light, melliniite is cream-yellowish. Between crossed polars it is isotropic, with no internal reflections. Reflectance percentages (R) for the four standard Com wavelengths are 60.5 (471.1 nm), 50.4 (548.3 nm), 52.5 (586.6 nm), and 55.9 (652.3 nm), respectively. Electron-microprobe analyses give the chemical formula (Ni 2.30 Fe 1.64 Co 0.01 ) Σ=3.95 P 1.05 on the basis of total atoms = 5. Melliniite is cubic, space group P2 1 3, with a = 6.025(1) Å, V = 218.71(6) Å 3 , and Z = 4. The crystal structure has been solved and refined to R = 2.72% using single-crystal X-ray diffraction data. It shows the AlAu 4 -type structure, which is an ordered form of the β-Mn structure. The metal atoms occupying the 12b site (M1) are effectively 14 coordinated whereas the metals at the 4a site (M2) are 12 coordinated by three P atoms and nine metals. The phosphorus atoms (4a site) coordinate 12 metal atoms in a somewhat distorted icosahedral arrangement. This new phosphide is the first phase with such a high coordination-number for phosphorus. The new mineral is named after Marcello Mellini, Professor of Mineralogy, who strongly developed the study of meteorites in Italy. The new mineral and mineral name have been approved by the Ima Commission on New Minerals and Mineral Names (2005-027).

SELENOJALPAITE, Ag3CuSe2, A NEW MINERAL SPECIES FROM THE SKRIKERUM Cu Ag Tl SELENIDE DEPOSIT, SMALAND, SOUTHEASTERN SWEDEN

Selenojalpaite, ideally Ag3CuSe2, is a very rare mineral newly identifi ed at the Skrikerum Cu–Ag–Tl selenide deposit, near Valdermarsvik, Smaland, southeastern Sweden. It occurs as dark grey anhedral to subhedral grains up to 200 m across, closely associated with eucairite, altaite, berzelianite and chalcopyrite. Selenojalpaite is opaque with a metallic luster; it possesses a black streak. It is brittle with an uneven fracture; the Vickers microhardness (VHN25) is 37 kg/mm 2 (range 36–40), equivalent to a Mohs hardness of 4–4½. The calculated density is 7.64 g/cm 3 (on the basis of the empirical formula). In plane-polarized refl ected light, selenojalpaite is light grey, weakly to moderately birefl ectant, and weakly pleochroic from brownish grey to a slightly darker greenish grey. Between crossed polars, it is anisotropic, without characteristic rotation-tints or internal refl ections. Values of refl ectance in the range 400–700 nm are tabulated; values of Rmin and Rmax for the four standard COM wavelengths are 33.5, 37.1 (471.1 nm), 31.8, 35.1 (548.3 nm), 30.4, 34.0 (586.6 nm), and 29.3, 32.4 (652.3 nm), respectively. Its unit-cell parameters were derived by comparison with jalpaite, Ag3CuS2, which shows strong chemical and crystallographic similarities. Selenojalpaite is tetragonal, probable space-group I41/amd, with unit-cell parameters refi ned from powder data: a 8.939(1), c 11.844(2) A, V 946.4(2) A 3 , c : a 1.3250, Z = 8. The strongest seven powder-diffraction lines [d in A(I)(hkl)] are: 4.47(60)(200),

Reconfigurable optical filter based on digital mirror arrays

We present a reconfigurable optical filter with multiple passband channels based on the combination of a diffraction grating and an array of digital micromirrors. The filter allows for adjustment of the central frequency of its individual passband channels to match standard wavelength grids with precision better than 0.033 nm. The number of channels, the channel passband width, and the channel peak profile can be dynamically reconfigured by changing the periodic pattern imposed to the digital micromirror array. Experimental results are in excellent agreement with basic design relations describing the spectral characteristics of the filter.

A high efficiency ultrahigh vacuum compatible flat field spectrometer for extreme ultraviolet wavelengths

A custom, flat field, extreme ultraviolet spectrometer built specifically for use with low power light sources that operate under ultrahigh vacuum conditions is reported. The spectral range of the spectrometer extends from 4 nm to 40 nm. The instrument optimizes the light gathering power and signal-to-noise ratio while achieving good resolution. A detailed description of the spectrometer and design considerations are presented, as well as a procedure that could be used to obtain a synthetic wavelength calibration with the aid of only a single known spectral feature. This synthetic wavelength calibration is compared to a standard wavelength calibration obtained from previously reported spectral lines of Xe, Ar, and Ne ions recorded with this spectrometer.

8×10 Gb/s transmission system over 2015 km with dispersion compensation by fiber Bragg Grating

The cascaded chirp fiber Bragg gratings (CFBGs) with ITU-T standard wavelengths and wavelength grid are applied to compensate the dispersion of 8×10 Gb/s WDM system. The ASE of the EDFA could be reduced, the OSNR of the transmitted signal can be increased and the fluctuation of the EDFA gain can be restrained in a certain scope by the CFBG employed in the system. Experiment of error-free 8×10 Gb/s 2015 km transmission without FEC and electric regeneration is demonstrated in this paper. In this system, only EDFA is used as amplifier, and no other form of dispersion compensator is adopted except CFBG. The experimental result showed that after 2015 km transmission, the consistency of the dispersion compensating for each channel is perfect.

Determination of Spectrometer-Detector Parameters from Calibration Spectra and the Use of the Parameters in Spectrometer Calibrations

The grating equation is used to generate quadratic calibration equations for multichannel detectors with perpendicular and tilted focal planes. The quadratic coefficients are not independent and contain terms that are used to solve for spectrometer-detector parameters. The parameters can be calculated from a quadratic fit at one spectrometer position, but more accurate values can be obtained from quadratic fits at two spectrometer positions. The calculations show that the detector focal plane is tilted by about two degrees. Once values for the spectrometer-detector parameters are obtained from calibrations using at least three lines at one or two spectrometer positions, only one calibration line at any spectrometer position is required to obtain accuracies on the order of 0.1 cm(-1) over a several thousand wavenumber range. The main cause of spectrometer drift is a change in the diffraction angle and/or the spectrometer included angle. This drift is almost totally compensated by the one-line calibration, which adjusts the diffraction angle. A neon pen lamp is used to generate the calibration spectra. Using standard air wavelengths compared to true wavelengths can produce calibration errors of 0.1 to 0.6 cm(-1); the magnitude depends on local conditions and how the laser wavelength is treated.

Resonant Cavity Time-Division-Multiplexed Fiber Bragg Grating Sensor Interrogator

The first resonant-cavity time-division-multiplexed (TDM) fiber Bragg grating sensor interrogation system is reported. This novel design uses a pulsed semiconductor optical amplifier in a cyclic manner to function as the optical source, amplifier, and modulator. Compatible with a range of standard wavelength detection techniques, this optically gated TDM system allows interrogation of low reflectivity "commodity" sensors spaced just 2 m apart, using a single active component. Results demonstrate an exceptional optical signal-to-noise ratio of 36 dB, a peak signal power of over +7 dBm, and no measurable crosstalk between sensors. Temperature tuning shows that the system is fully stable with a highly linear response.

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Planar concave grating demultiplexer for coarse WDM based on confocal ellipses

A novel planar concave grating demultiplexer is described in which the reflecting facets are placed on confocal ellipses. Total internal reflection is used to reduce the sensitivity to non-vertical etching of the facets. Two beam-shaping parabolic waveguide horns are used on the input waveguide to obtain flat-top passbands and high channel isolation. Scalar electromagnetic simulations show promising results for both 4- and 18-channel devices working on the standard coarse wavelength division multiplexing (CWDM) wavelength grid.

Optical fiber sensor based on lutetium bisphthalocyanine for the detection of gases using standard telecommunication wavelengths

In this work, a vapochromic material, the lutetium bisphthalocyanine (LuPc 2), whose refractive index changes in the presence of organic compound vapors such as ethanol, hexanal, n-butyl acetate, acetic acid, etc., has been used in combination with an optical fiber to fabricate an optical fiber volatile organic compound (VOC) sensor. The behavior of the sensor has been studied for the 1310 nm wavelength in the telecommunication window, with the associated advantages that this fact implies. In addition, different concentrations of volatile organic compound vapors have been tested. For instance, changes up to 10 dB in the reflected optical power have been detected for a 88 mmol/l concentration of acetic acid.

CHLORBARTONITE, K6Fe24S26(Cl,S), A NEW MINERAL SPECIES FROM A HYDROTHERMAL VEIN IN THE KHIBINA MASSIF, KOLA PENINSULA, RUSSIA: DESCRIPTION AND CRYSTAL STRUCTURE

Chlorbartonite, ideally K 6Fe24S26(Cl,S), is a new potassium iron sulfide chloride found as an accessory mineral in a microcline – pectolite – sodalite – aegirine vein within feldspathic urtite at Mount Koashva, Khibina massif, Kola Peninsula, Russia. The mineral occurs as roundish grains up to 2 cm across included in sodalite and natrolite crystals; it is associated with djerfish erite and rasvumite. Chlorbartonite is weakly magnetic, brittle, and has a conchoidal fracture. Cleavage and parting were not observe d. Macroscopically, the mineral is opaque, brown-black, with a black streak and submetallic luster. In reflected light, it appears optically isotropic, yellowish brown, and without internal reflections; interpolated values of reflectance ( R, %) at the standard wavelengths (nm) are: 10.8 (470), 13.5 (546), 15.1 (589), and 17.2 (650). The hardness VHN 40 is 203–212, average 207 kg/mm 2 ; the Mohs hardness is 4. The density is 3.70 g/cm 3 (measured) and 3.65 g/cm 3 (calculated). The electron-microprobe analysis of six grains gave, as an average composition: S 33.84, Cl 0.99, K 9.62, Fe 54.09, Co 0.04, Cu 0.57, total 99.15 wt.%. The empiric al formula calculated on the basis of a total of 57 atoms is K 6.08(Fe23.93Cu0.22Co0.01)� 24.16S26.00(Cl0.69S0.07)� 0.76, which yields an ideal formula of K6Fe24S26(Cl,S). The mineral is tetragonal, I4/mmm, a 10.3810(8), c 20.614(2) A, V 2221.5(3) A 3 , Z = 2. The strongest eight lines in the X-ray powder-diffraction pattern [ d in A (I)(hkl)] are: 9.25(33)(101), 5.97(65)(112), 3.121(45)(312), 2.986(100)(224), 2.380(38)(332), 2.374(57)(316), 1.834(51)(440), and 1.830(82)(408). The crystal structure has been refined to an R1 of 0.020 (447 unique observed reflections with Fo ≥ 4� Fo). The structure consists of a framework of the Fe 8S14 clusters of eight edge-sharing FeS4 tetrahedra. The framework has large cavities occupied by ClK 6 octahedra. As the name indicates, chlorbartonite is the Cl-dominant analogue of bartonite.

Optical fiber gas sensors based on hydrophobic alumina thin films formed by the electrostatic self-assembly monolayer process

Optical fiber gas sensors have been fabricated by deposition of Al/sub 2/O/sub 3/ and polymer ultra-thin films on the ends of optical fibers using the electrostatic self assembly monolayer process. These sensors are designed to operate at the standard transmission wavelengths with no cross sensitivity to temperature from at least 10 to 70/spl deg/C. Experimental results of the response of these sensors to organic volatile compounds such as acetone, dichloromethane, or ethanol, are presented. In addition, a thermal curing process is proposed for achieving a humidity cross sensitivity of less than 1.4% from 11% to 85% of relative humidity, this cross sensitivity was still negligible after one year of the thermal curing process.

Design, fabrication, and testing of an integrated si-based light modulator

We have fabricated and characterized a novel Si-based light modulator working at the standard communication wavelength of 1.5 μm. It consists of a three-terminal bipolar mode field effect transistor integrated with a silicon rib waveguide on epitaxial Si wafers. The modulator optical channel is embodied within its vertical electrical channel. Light modulation is achieved moving a plasma of carriers inside and outside the optical channel by properly biasing the control electrode. The carriers produce an increase of the Si absorption coefficient. The devices have been fabricated using clean-room processing. Detailed electrical characterization and device simulations confirm that strong conductivity modulation and plasma formation in the channel are achieved. The plasma distribution in the device under different bias conditions has been directly derived from emission microscopy analyses. The device performances in terms of modulation depth will be presented.

Effect of Acridine Derivatives on the Dissolution of α-Brass

Acridine derivatives as inhibitors of diffusion- and diffusion–kinetic-controlled dissolution of α-brass are studied. Inhibition coefficients of the dissolution and its steps correlate with parameters of a standard reaction series and wavelengths of the longest-wave absorption band of the electronic spectrum.

Jeans' gravitational instability and nonextensive kinetic theory

The concept of Jeans gravitational instability is rediscussed in the framework of nonextensive statistics and its associated kinetic theory. A simple analytical formula generalizing the Jeans criterion is derived by assuming that the unperturbed self- gravitating collisionless gas is kinetically described by the $q$-parameterized class of power law velocity distributions. It is found that the critical values of wavelength and mass depend explicitly on the nonextensive $q$-parameter. The standard Jeans wavelength derived for a Maxwellian distribution is recovered in the limiting case $q$=1. For power-law distributions with cutoff, the instability condition is weakened with the system becoming unstable even for wavelengths of the disturbance smaller than the standard Jeans length $\lambda_J$.

Three‐satellite comparison of polar mesospheric clouds: Evidence for long‐term change

Measurements of polar mesospheric clouds (PMCs) from three different satellite instruments are compared. These instruments are the Solar Mesospheric Explorer (SME), the Wind Imaging Interferometer (WINDII), and the Polar Ozone and Aerosol Measurement (POAM II). These measurements have been put on a common basis, correcting for differences in the wavelengths and measurement techniques used. This common basis is the probability distribution of the excess extinction ratio (EER) at a standard wavelength of 265 nm, where the EER is the ratio of the PMC extinction coefficient to the background molecular Rayleigh scattering coefficient. The results indicate that the POAM and WINDII measurements in the Southern Hemisphere had a higher probability of observing bright PMCs during the 1993–1996 time period than SME did a decade earlier in 1983–1986. Local time variations identified in WINDII data are interpreted in terms of a diurnal and semidiurnal component of average EER. These results are qualitatively similar to those found from lidar soundings of noctilucent cloud at sites in Norway and at the South Pole. Differences in interannual variability, local time of the measurements, assumed particle size distributions, and solar cycle effects are ruled out as possible explanations of the differences.

Automated molecular weight assignment of electrospray ionization mass spectra.

Process improvements in the synthesis of therapeutic agents and their intermediates are often facilitated by identification of reaction by-products. Analysis by liquid chromatography/mass spectrometry (LC/MS) with electrospray ionization is a powerful approach for obtaining molecular weight information for these compounds. Such analyses are well suited for 'open-access' mass spectrometry using generic chromatographic conditions, provided spectral interpretation for unknown compounds is facile. We have developed a software application (MassAssign) that facilitates automated data processing and molecular weight assignment for chromatographic peaks detected by any standard ultraviolet-visible wavelength detector. The program assigns [M + H](+) ions (and thus molecular weight) in the mass spectra using predetermined criteria. This evaluation process differentiates [M + H](+) ions from other signals in a complex mass spectrum such as those resulting from chromatographic coelution or the presence of multiple species (i.e., fragment ions, singly charged ions, doubly charged ions, adduct ions, proton-bound dimers, etc.). Once the program has evaluated all ions in a mass spectrum that exceed a preset abundance threshold, MassAssign reports either a numeric value-indicating the chromatographic peak consists of a single component having the displayed molecular weight, 'MC'-indicating the peak consisted of multiple components, or 'ND'-that a molecular weight could not be determined unequivocally. The performance of the program was evaluated by comparing mass assignments made by MassAssign against manual interpretation for 55 samples analyzed by positive electrospray ionization using a generic HPLC method. Correct molecular weight assignments were obtained in 90% of the cases.

Sensitive determination of cell number using the CyQUANT® cell proliferation assay

We describe here the development and characterization of the CyQUANT® cell proliferation assay, a highly sensitive, fluorescence-based microplate assay for determining numbers of cultured cells. The assay employs CyQUANT GR dye, which produces a large fluorescence enhancement upon binding to cellular nucleic acids that can be measured using standard fluorescein excitation and emission wavelengths. The fluorescence emission of the dye–nucleic acid complexes correlated linearly with cell number over a large range using a wide variety of cell types. Under the recommended assay conditions, standard curves were linear ( r 2>0.995), detecting as few as 10–50 cells and as many as 25,000–50,000 cells with a single dye concentration, depending on cell type. Increasing the dye concentration extended the linear range of the assay to 100,000–250,000 cells. Results of cell proliferation and growth inhibition studies with the assay were similar to those obtained in published studies using other standard assays. CyQUANT assay measurements of serum-stimulated cell proliferation correlated well with measurements made using [ 3H]-thymidine. Also, the assay was used to analyze cellular DNA or RNA content, with the addition of a nuclease digestion step to the protocol. The assay procedure is simple and convenient, with no wash steps, and is readily amenable to automation.

Precision and Noise in Inductively Coupled Plasma Atomic Emission Spectroscopy with Charge-Injection Device Detection

An inductively coupled plasma (ICP)-echelle optical system coupled with a charge-injection device (CID) detector was evaluated for precision and noise. Simultaneous collection of analyte wavelengths and simultaneous background correction have invalidated underlying assumptions in some traditional models. Signal flicker noise, a major limitation in single-channel detection, was eliminated by the time correlation of analyte and internal standard wavelengths. Once flicker noise was eliminated, most fluctuation was found to be caused by slight wavelength shifts along the axis of the detector, rather than by the theoretically predicted signal shot noise. This fluctuation can be corrected by increasing center subarray sizes or by employing well-matched internal standard lines. In either case, precision of 0.3 to 0.18% relative standard deviation (RSD) was achieved over a time span of 7 h. Background flicker noise was also eliminated by simultaneous background correction, demonstrating a multichannel advantage of ICP detection using charge-transfer devices. In this work, theoretical expressions were developed to incorporate major sources of noise based on the specific readout characteristics of an array detector. These expressions match experimental data extremely well for measurement of relative standard deviation in background (RSDB) and detection limits. These data have then been compared to the single-channel case, which describes photomultiplier tube (PMT) detection, as well as the theoretical limit dictated by background shot noise.