Differential Absorption Measurements Research Articles

Detection of S2 by magnetic tuning of a chromium(I) atomic emission line

A technique called tunable atomic line molecular spectroscopy (TALMS) was utilized to detect S/sub 2/ by absorption of a Cr(I) atomic emission line at 3018 A. The Cr line was split into Zeeman components, and a differential absorption measurement was obtained as a function of magnetic field strength. Several closely spaced lines belonging to different branches which result from the triplet splitting in the (7,2) band of the B/sup 3/..sigma../sub u//sup -/-X/sup 3/..sigma../sub g//sup -/ system of S/sub 2/ were resolved. A resolution greater than 6 x 10/sup 4/ was demonstrated.

Fluorescence and differential light absorption recordings with calcium probes and potential-sensitive dyes in skinned cardiac cells.

This report describes an optical system for microspectrophotometry in a single cardiac cell from which the sarcolemma has been removed by microdissection (skinned cardiac cell). This system is attached to the high power inverted microscope used for the microdissection and includes (a) a single variable wavelength microspectrophotometer used to define the spectrum of a given dye or Ca2+ probe; and (b) a dual wavelength, differential microspectrophotometer used to record differentially between the optimum wavelength and a wavelength separated by 25--30 nm. Results are presented using the following optical methods: (a) fluorescence measurements with chlorotetracycline to monitor the amount of Ca2+ bound to the inner face of the sarcoplasmic reticulum (SR) membrane; (b) differential absorption measurements with arsenazo III to measure changes of myoplasmic [Ca2+]free resulting from Ca2+ release from the SR; (c)fluorescence and (or) differential absorption measurements with the potential-sensitive dyes merocyanine 540, NK 2367, and di-S-C3(5) to monitor changes of charge distribution on the SR membrane during Ca2+ accumulation in the SR, as well as before and during Ca2+-induced release of Ca2+ from the SR. A small and rapid signal is observed which precedes the Ca2+-induced release of Ca2+ from the SR. It is detected as an increase of CA2+ binding inside the SR with chlorotetracycline and as a "hyperpolarization" with potential-sensitive dyes, while no transient change of myoplasmic [Ca2+]free is detected with arsenazo III. This small and rapid signal preceding the Ca2+ release may be a first hint to an understanding of the mechanism whereby a small increase of [Ca2+]free outside the SR triggers Ca2+ release from the SR.

Optically active hydrocarbon polymers with aromatic side chains, 10. Synthesis and properties of homopolymers and copolymers of 6‐vinylchrysene

AbstractThe synthesis of 6‐vinylchrysene (1) starting from chrysene is described. The study of the polymerizability of 1 by conventional radical, cationic, and Ziegler‐Natta procedures indicates the tendency of 1 of give head‐to‐tail polymeric products with a similar degree of polymerization independent of the catalytic system. Copolymers of 1 with optically active (−)‐menthyl acrylate (2), (−)‐menthyl methacrylate (3), and (S)‐4‐methyl‐1‐hexene (4), were also prepared. No apparent copolymerization of 1 with optically active alkyl vinyl ethers occurred by cationic initiation. Spectroscopic and chiroptical properties are presented to support the formation of copolymer macromolecules. Finally, the differential dichroic absorption measurements allow one to stress that in optically active vinylaromatic copolymers the extent of preferential asymmetry, induced by the dissymmetric field of units derived from the optically active nonaromatic comonomer, increases with increasing bulkiness and polarizability of the vinylaromatic comonomer.

A two-wavelength oscillation CO2 laser for differential absorption measurements of atmospheric trace molecules

A two-wavelength oscillation C02 laser was constructed for the differential absorption measurement of low concentrations of atmospheric trace molecules and pollution molecules. A diffraction grating was alternately angle-modulated for the two-branch oscillation using a single C02 laser. The output power of the two wavelengths was balanced to be equal. With these characteristics, the phase-sensitive detection technique can be applied to give highly sensitive detection of the received power difference, which is proportional to the absorption in the optical path of the transmitted beams. A differential absorption spectrometer was used to demonstrate the usefulness of this two-wavelength laser oscillation method incorporating the output power balancing technique. The concentration of ethylene molecules was detected in a calibration cell and was also measured in real time in the exhaust of a combustion engine. From these results it has been shown that this differential absorption scheme offers a minimum detectable absorption of approximately 0.8%.

Solution chemistry of lanthanide complexes—III: Spectroscopic studies of lanthanide complexes of glycine and polyglycines

The lanthanide complexes of glycine, diglycine and triglycine have been studied by a variety of physical means. Measurements of differential absorption of Ho(III) complexes, luminescence intensities of Tb(III) complexes, and intermolecular energy transfer from Tb(III) to Eu(III) complexes were all used to characterize the nature of the solution chemistry. The complexes tend to remain mononuclear at low pH, but associate through hydroxide linkages above neutral pH. The degree of association is much less for complexes of diglycine relative to those of glycine, suggesting that the steric nature of the amino acid ligand plays a dominant role in determining the degree of association.

Stereoselectivity in lanthanide complexes of malic acid

A variety of spectroscopic and potentiometric studies have been carried out detailing the nature of the complex formation between lanthanide ions and malic acid. Formation constants calculated below pH 7 (where the complexes are mononuclear) demonstrate that both Gd 3+ and Dy 3+ complexes of DL-malic are more stable than corresponding complexes of either D- or l-malic acid. Studies of intermolecular energy transfer, on the other hand, indicate that above pH 7 (where the complexes are found to self-associate) complexes of resolved ligand associate to a greater extent than complexes prepared from racemic ligand. Supporting evidence is obtained from measurements of differential absorption. It appears that the weaker D- or L-MAL complexes are more prone to hydrolysis than the DL-MAL complexes, and evidence is presented from measurements of luminescent titrations that dimeric complex units are apparently bridged by either one or two -OH bridges. No evidence was found at 1:5 metal-to-ligand ratios for the existence of 1:3 lanthanide.malic acid complexes and no experimental effects could be detected which pointed toward participation of the malic acid hydroxyl group in the complex bonding.

Molecular Air Pollution Monitoring by Pulsed CO2Laser-Based Long-Path Technique

Abstract Double-ended experimental arrangement using a small tunable TEA CO2 laser and a retroreflector was employed for differential absorption measurements of ethylene, freon 12 and ammonia concentrations in the atmospheric air in the distant sample chamber. Telescope collected return radiation was detected with a pyroelectric detector. Good agreement between remotely and in-situ measured concentrations was obtained. The system sensitivity to investigated gases was found to be of the order of several ppb-kilometers.

High accuracy differential absorption and velocity measurements in relaxing acetate solutions

Relaxation of acetate ions has been studied in dilute aqueous solutions using an improved differential ultrasonic technique. The technique uses a Carstensen type differential cell which can be completely submerged in the temperature regulated bath. A phase sensitive detection scheme accurate to 2 × 10−4 signal periods permits the measurement of relative velocities with an accuracy of 0.03 cm s−1. A precise waveguide beyond cutoff attenuator has been incorporated into a differential pulse comparison scheme in order to obtain attenuation accurate to 2 × 10−3 dB cm−1. These improvements permit measurements in solutions much more dilute than those previously studied. Results of both velocity and attenuation in very dilute solutions of zinc and copper acetate for frequencies from 1 to 35 MHz will be presented and compared with previous results.

Laser Detection of Pollution

Spectroscopic analysis is a useful technique for identifying and quantitatively determining the presence of specific gaseous constituents. Development of high-power tunable lasers has made the spectroscopic technique for detection of trace constituents in the atmosphere very attractive for practical applications. In this article three of the currently used modes for laser detection of pollution are reviewed: (i) long-path measurements, (ii) laser Raman (differential absorption) measurements, and (iii) optoacoustic detection. Progress in the field has been extremely rapid in the last few years and very useful and reliable data on air pollution can now be obtained routinely with the techniques described.

Infra-red differential absorption analysis for monodisperse aerosols

The investigation of a monodisperse, nitrogen suspended model aerosol of tricresyl phosphate showed that infra-red spectrometry may facilitate to some extent a valid method for quantitative analysis of particulate matter. In addition, the type of organic compound forming the aerosol may be identified due to the occurrence of characteristic group frequencies in the infra-red range. The additional beam attenuation due to light scattering of the particles can be separated from the specific absorption of the aerosol substance by differential absorption measurements. The usefulness of this technique, however, is limited by some dependence of the measured absorption coefficients upon the size parameters of the aerosol under investigation. For concentration measurements by infra-red spectrometry therefore, additional information on the particle size is required. In a particle size range, however, where the efficiency factor for absorption is proportional to the particle radius, the mass absorption coefficient of the aerosol represents a constant, which is independent of a particle size and can be used for the determination of concentrations. In this case, the scattering part of extinction is very small, so that, by means of differential absorption measurements, the absorption part of extinction can be well isolated. The experimental data are compared with theoretical results according to Mie (1908).

A novel type of cell for differential absorption measurements on liquids in the far infrared

A cell is described which features a fixed length, double chamber divided into two compartments by a transparent but movable septum. A suitable reference liquid, which might be the pure solvent in the case of solution spectroscopy, is placed in one compartment and the liquid or solution to be measured is placed in the other. The transmission spectrum of the doubly filled cell is then determined as a function of septum position and the resulting data are processed to give accurate absorption spectra in which the uncertainties due to reflection effects have been reduced to a very low level.

Remote Atmospheric Sensing with an Airborne Laser Absorption Spectrometer

A laser absorption spectrometer, using an ir laser transmitter and a heterodyne radiometer, can be used from an aircraft or spacecraft to measure altitude profiles of air pollutants and other atmospheric constituents. The technique involves measurement of differential absorption at several wavelengths, using the diffusely reflecting earth's surface to provide a return signal. The pressure broadening of absorption lines allows one to discriminate between high and low altitude absorbers. Application of the technique to measurements of ozone, nitric oxide, and water vapor are presented. CO(2) and CO lasers are considered as transmitters. The discussion includes altitude resolution limitations, atmospheric temperature dependence, and frequency stability requirements of the instrument.

Spectroelectrochemical Studies of the Oxidation of Dimethyl‐p‐phenylenediamine by Reflection‐Spectroscopy at SnO2‐Electrodes

AbstractThe two step oxidation of dimethyl‐p‐phenylenediamine was studied by attenuated total reflection spectroscopy (ATR) at transparent SnO2‐electrodes. The equilibrium constant for the formation of the semiquinone diimine (Wurster's Red) could be determined from the potential dependence of the ATR‐absorption as well as from differential absorption measurements (K = 13 at 3.5 < pH < 6 and K = 18 at pH < 2.5). The formation of the semioxidized species from the diamine and the diimine, which was formed by short oxidation pulses, was observed. From the time dependence of the ATR‐absorption (after 0.2 ms pulse) we obtained a rate constant of 5.2 . 105 IM−1 cm−1 at pH = 3.

Deduction of Ionospheric Electron Densities and Collision Frequencies from Differential Absorption and Faraday Rotation Measurements in the Quasi-Transverse Region

Rocket radio propagation technique is known to be a very useful and widely used method for obtaining the characteristics of the lower ionosphere. Though this technique is extensively used at high l...

Molecular Air Pollution Monitoring by Dye Laser Measurement of Differential Absorption of Atmospheric Elastic Backscatter

Molecular Air Pollution Monitoring by Dye Laser Measurement of Differential Absorption of Atmospheric Elastic Backscatter

D-region electron densities and collision frequencies from Faraday rotation and differential absorption measurements

A rocket technique for measuring electron density and collision frequency in the lower ionosphere is described. Absolute values of electron density were determined by a radio propagation experiment, and detailed height variations were measured with a Langmuir probe. In the derivation of the collision frequency profiles, a pressure profile was employed which was found from measurements of the absorption of solar Lyman-α radiation, made on the same flight. The analysis of results from one such flight is described in some detail. The payload was launched from South Uist, Scotland on 19 June 1969 at a solar zenith angle of 44° using a Petrel rocket. Electron density and collision frequency profiles are presented.

Differential Phase Shift of Partially Reflected Radio Waves

The addition of phase difference measurements to differential absorption experiments is shown to be both feasible and desirable. The phase information can provide a more sensitive measurement of electron density above about 75 km. The differential phase shift is only weakly dependent on collision frequency in this range, and so an accurate collision frequency profile is not a prerequisite. The differential phase shift and differential absorption measurements taken together can provide both electron density and collision frequency data from about 70 to 90 km.

Combined Differential Faraday and Differential Absorption Measurements at 40 Megahertz

Differential Faraday rotation measurements of the 40‐ and 41‐MHz beacons of satellite 1964–64A/BE‐B were made at London, Ontario (43°N, 81°W) through the use of a continuous output polarimeter of the phase comparison type, and simultaneous differential absorption measurements were made by use of the ordinary and extraordinary mode amplitudes at 40 MHz. Sufficient measurement accuracy was obtained to employ the second‐order expansion of the magnetoionic refractive and absorption index equations to extract total electron contents, the ratio of the density squared integral to the total electron content, a mean ionospheric electron collision frequency, and a parameter sensitive to the height of an electron density irregularity, from the data. Two passes, orbit 17239, March 17, 1968, and orbit 17280, March 20, 1968, were selected for analysis. Peak electron densities, mean plasma scale heights, and mean electron temperatures were computed from the reduced data by the assumption of an electron density height profile; they were found to correspond to within experimental error with comparable published measurements. During both passes examined, F region electron density profile broadenings were detected that were, for March 20, attributed to adiabatic expansions of the F region electron gas, which was driven by localized neutral gas motions, and for March 17 the broadenings were attributed to thermal expansions of the F region plasma. On both occasions, the fractional errors in the data were sufficiently small over some portions of the pass to permit a determination of the dominant ionospheric absorption mechanism.

The preparation of iodinated vancomycin and its distribution in bacteria treated with the antibiotic.

Vancomycin was radioactively labelled by iodination with (125)I.Iodinated vancomycin was only a little less potent as an antibiotic than vancomycin itself. It was shown, both by chromatography and differential absorption measurements, to combine with acyl-d-alanyl-d-alanine residues. Radioactive vancomycin was used to follow the fate of the antibiotic in bacteria that had been subjected to the least concentration required to inhibit growth. Most of the radioactivity was in the cell walls, although some was found in the membrane fraction. The latter proportion increased during longer incubations with the antibiotic. Pre-formed protoplasts adsorbed very little vancomycin. Mg(2+) removed labelled vancomycin from the mucopeptide of Bacillus licheniformis, but had little effect on the antibiotic adsorbed on Micrococcus lysodeikticus, either in vivo or on previously isolated cell walls. Specific peptide was shown to compete with cell walls for vancomycin and it also extracted from cell-wall samples the labelled compound that had been adsorbed on M. lysodeikticus living cells.

Seasonal variations of electron densities below 100 km at mid-latitudes—I Differential absorption measurements

The differential absorption experiment (D.A.E.) for measuring electron densities in the lower ionosphere, using partial reflections, is examined. A model of the scattering process which invokes sharply bounded horizontally stratified irregularities is found to be more satisfactory than one based on volume scattering. The ratio of calculated reflection coefficients for the two magneto-ionic components, R x R o , is found to be insensitive to the geometry of reflecting boundaries and the fractional changes in electron concentration, ΔN N , provided the refractive index n tends to unity; but is affected by the propagation angle with respect to the magnetic field. The nature of irregularities in the lower ionosphere is discussed, and it is concluded that perturbations in collision frequency, Δv v , are not significant for the calculation of R x R o . Models of collision frequency profile, v( h) for three seasons are derived from meteorological data. Differences in probable collision frequencies between northern and southern hemispheres are examined. The sensitivity of the method, to changes in assumed v( h), is then discussed. The capability of the D.A.E. to produce electron density profiles of good height resolution and accuracy is evaluated. Errors involved in the assumption of v( h) and the measurement of the amplitude ratio of the received magneto-ionic components, R x R o , are discussed.