A dual-wavelength light-emitting diode based detector for flow-injection analysis process analysers

In this paper, a small dual-wavelength light-emitting diode (LED) based detector for FIA process analysers is designed. The detector's optical parts include a flow cell, a dual-wavelength LED and a photodiode. Neither mirrors nor lenses are used. The optical paths for the different light beams are almost the same, distinguishing it from previously reported LED based detectors. The detector's electronic components, including a signal amplifier, an A/D and D/A converter, and an Intel 8031 single-chip microcomputer, are integrated on one small board. In order to obtain response signals of approximate intensity for the two colours, the D/A converter and a multiplexer are used to adjust the emission intensity of the two colours respectively. Under microcomputer control, light beams are rapidly electronically modulated. Therefore, dark current and intensity of the light beams are measured almost simultaneously; as a result, the effect of drift is negligible. While a solution of absorbance 0.875 was measured repeatedly, an RSD (relative standard deviation) of 0.24% could be reached. Furthermore, such a detector with a red/yellow LED has been coupled with the FIA technique for the determination of 10(-6)M levels of cobalt.     

An ultrasensitive method of real time pH monitoring with complementary metal oxide semiconductor image sensor

CMOS sensors are becoming a powerful tool in the biological and chemical field. In this work, we introduce a new approach on quantifying various pH solutions with a CMOS image sensor. The CMOS image sensor based pH measurement produces high-accuracy analysis, making it a truly portable and user friendly system. pH indicator blended hydrogel matrix was fabricated as a thin film to the accurate color development. A distinct color change of red, green and blue (RGB) develops in the hydrogel film by applying various pH solutions (pH 1–14). The semi-quantitative pH evolution was acquired by visual read out. Further, CMOS image sensor absorbs the RGB color intensity of the film and hue value converted into digital numbers with the aid of an analog-to-digital converter (ADC) to determine the pH ranges of solutions. Chromaticity diagram and Euclidean distance represent the RGB color space and differentiation of pH ranges, respectively. This technique is applicable to sense the various toxic chemicals and chemical vapors by situ sensing. Ultimately, the entire approach can be integrated into smartphone and operable with the user friendly manner.     

铝酸钠溶液的鲁米诺增强声致发光研究

Ultrasonic processing on sodium aluminate solutions was proved to have effects on the gibbsite crystallization process from sodium aluminate solution. In order to investigate the mechanism of the ultrasonic intensification, the sonofluorescence spectrum was detected by fluorescence spectrometer in sodium alumiante Luminol solutions, and the spectrum under the conditions of various ultrasonic power and different composition of sodium aluminate solutions were studied. It is found that the sodium aluminate Luminol solution can irradiate fluorescence by ultrasonic processing above the given power; the intensity of sonofluorescence are relatively low in sodium aluminate solutions with high concentration and low αk（mol ratio of Na2O/Al2O3 in sodium aluminate solution）. The relationship between the sonofluorenscence and ultrasonic intensification on gibbsite crystallization process from sodium aluminate solutions were also discussed. The conclusion that the ultrasonic effects are influenced by ultrasonic cavitation and intensity of sonofluorescence spectrum is deduced.     

A computer system for measuring fast-scan lowresolution mass spectra

A microprocessor-based satellite computer system (MASDAT) controls a low-resolution, fast-scan mass spectrometer for the measurement of series of spectra. Special digitization hardware (logarithmic A/D converter) and software algorithms are necessary to achieve a dynamic range (ratio of highest to lowest intensity) of about 10⁵ in peak heights. Up to three MASDAT satellites can be connected to a host computer. Synchronized parallel programs in the host system communicate with the operator, calibrate the mass scale, print an interscan report, and store final spectra and, optionally, unreduced data on mass storage devices. Host software is described for a RSX11M and for a VAX/VMS operating system.     

PHOTOASSOCIATION PHENOMENA IN CONCENTRATED ETHANOL SOLUTIONS OF 2-AMINO-PYRIMIDINE

Abstract— Besides fluorescence and phosphorescence of the monomer, concentrated ethanol and water solutions of 2-amino-pyrimidine show an additional red-shifted emission, whilst optical absorption spectra are independent of 2-amino-pyrimidine concentration. The maximum of this new band is red-shifted about 4000 cm^-1 with respect to that of monomer emission. The dependence of the intensity of this bathochromic emission on concentration and on temperature suggests that 2-amino-pyrimidine excimers form in ethanol solutions. In aqueous solutions the photoassociation product seems to involve more than two base molecules.     

Influence of heated spray chamber desolvation on the detectability in inductively coupled plasma atomic emission spectrometry

 A comparison study has been made of the performance of a heated spray chamber desolvation system for sample introduction into inductively coupled plasma. The heated spray chamber system Mistral replaces the normal spray chamber of an ICP-spectrometer and improves the efficiency of both aerosol generation and transport to the plasma [1]. 27 elements in 6 sample solutions with different mineralization were measured with and without the heated spray chamber system. The higher the mineralization of the sample solution, the less was the increase of the intensity of the spectral lines of the elements determined. An increase of the intensity by the same factor for most of the elements was observed in different sample solutions like drinking water (factor 6), fresh water (factor 5), sea water (factor 1.5) and acid solutions resulting from the digestions of soil (factor 3–4) and rock (factor 2) samples. A few elements in drinking and fresh water were only detectable by using Mistral. A clear improvement of the detection limits was found, but compared to the increase of the intensity not for all elements by the same factor. The detection limits for water samples are in the lower μg/L- and the higher ng/L-level by using Mistral. So the Mistral is an alternative to the ultrasonic nebulizer. Received: 28 November 1995/Revised: 15 February 1996/Accepted: 21 February 1996     

Terbium(III) Complexes with Pyrazolones-5 on Zirconium Phosphate: Synthesis and Luminescent Properties

Sorption of Tb³⁺ ions by zirconium phosphate (ZrP), their complexation with some pyrazolones-5, and composition of compounds formed on a solid matrix are studied. Unlike solutions with the ratio Tb : pyrazolone = 1 : 3, compounds formed on ZrP have the ratio Tb : L = 1 : 3, 1 : 2, and 1 : 1, depending on the availability and size of a substituent at the reaction site. The luminescence intensity of the adsorbed Tb pyrazolonates was found to correlate with a sum of the Hammet induction -constants of substituents in the ligand molecule. The luminescence intensity of the studied complexes on ZrP is two times and more higher than that in solutions, which makes it possible to use ZrP as a solid substrate.     

Electrochemical determination of the absolute cross-section of giant Raman light scattering by silver-silver adatom complexes

The procedure of the determining of changes in the background intensity in the giant Raman light scattering spectra at silver surface in solutions of silver salts, under the action of current changes during galvanostatic silver electrodeposition near the silver electrode equilibrium potential, suggested by authors, is substantiated. Expressions for the calculations of the quantitative values of the absolute background cross-section of the giant Raman light scattering, which is caused by the interaction of the metal electron plasma with silver adatoms, are derived. The relationship between the silver adatom concentration and the back-ground intensity in the giant Raman light scattering spectra allows estimating the absolute cross-section of the background of the giant Raman scattering for the metal-adatom complexes (1.02 × 10⁻²⁷ cm²/adatom) from preliminary experiments in sulfate solutions.     

Emission from the species CH3COC(OH)2CH3 in aqueous solutions of biacetyl

A previously unreported emission at 435 nm from solutions of biacetyl in water, methanol or ethanol has been observed. It results from excitation at the 280 nm absorption peak but not from excitation at the 405 nm absorption maximum; its intensity is proportional to the amount of water/acetonitrile mixtures, and is insensitive to air concentration. Comparison of the position and intensity of this new peak with the fluorescence maxima of simple ketones such as acetone suggest that it is emission from biacetyl hemi-hydrate or hemiketal, known to be the predominant species in aqueous solutions of biacetyl, and shown to be the predominant species in alcoholic solutions.     

BIPHOTONIC CHEMISTRY OF PHENANTHRENE UNDER 308 nm EXCIMER LASER IRRADIATION

Abstract— –The high intensity laser induced photochemistry of phenanthrene is complex and appears to be non-linear with respect to laser intensity. Photochemical products primarily involve the solvent (CH₂C1₂) and phenanthrene coupling. These species exhibit strong absorption and emission which are red-shifted from that of phenanthrene. In the presence of a-methyl styrene, styrene oligomers are formed, but no dimers, indicating that there are no a-methyl styrene cation radical reactions. In all cases of laser irradiation the solutions become acidic, which is ascribed to the deprotonation of the phenanthrene cation radical. Acid formation does not occur in the presence of a-methyl styrene under CW irradiation with a conventional Xe lamp. These differences are ascribed to photoionization from the singlet state for laser irradiation while under CW conditions triplet-triplet annihilation can produce the phenanthrene cation radical.     

A fully reversible fiber optic lactate biosensor based on the intrinsic fluorescence of lactate monooxygenase

Summary The intrinsic fluorescence intensity of the enzyme lactate monooxygenase is used as the analytical parameter in a new type of lactate biosensor. It is found that the fluorescence quantum yield of the coenzyme changes during its interaction with lactate at the point of saturation. The changes in intensity are fully reversible in the presence of molecular oxygen and can be monitored via fiber optic light guides. Enzyme solutions were entrapped at the fiber end using a semipermeable membrane which retains the enzyme. The change in fluorescence occurs within a rather small range of lactate concentration (0.5–1 mmol/l) with an lactate-invariable signal at higher levels. Response times of 7.5 to 25 min (to reach the full steady state) and regeneration times between 1 and 8 min are observed. Measurements are performed in flowing air-saturated solutions containing 0.1 mol/l pH 7.0 citrate buffer. The effect of pH has also been investigated. In order to achieve a more expanded analytical range (e.g., 1.4–10 mmol/l) and shorter response times, kinetic measurements are performed in a fashion similar to flow-injection analysis.

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Vollreversibler faseroptischer Lactatbiosensor aufgrund der Eigenfluorescenz der Lactatmonooxygenase

     

RESOLUTION ENHANCEMENT AND DECONVOLUTION INTO VIBRONIC BANDS OF THE FLUORESCENCE AND ABSORPTION SPECTRA IN THE RED REGION OF DILUTE SOLUTIONS OF CHLOROPHYLL a IN VARIOUS SOLVENTS

Abstract— The fluorescence spectra of chlorophyll a in less than 10–⁶ mol dm^-3 solutions of benzene, toluene, tetrahydrofurane, EPA and ethanol were determined at both room temperature and at 77 K. Resolution enhancement using Fourier transform methods revealed the presence of vibronic bands with essentially solvent-invariant separation between their origins; this was confirmed by the quantitative deconvolution of the spectra into Gaussian bands. It was concluded that the fluorescence is due to a single spectroscopically distinct species. The absorption spectra in the above solvents include a band absent from the fluorescence spectra which, from its position and intensity, may be identified as the longest wavelength X-polarized electronic transition of chlorophyll a. Differences observed between the shapes of the low-and high-temperature absorption spectra may be attributed primarily to the narrowing of bandwidths with decreasing temperature and to intensity redistribution within the bands; the apparent increase in the integrated intensity on cooling the solutions appears to be due largely to the increase in the volume concentration of the solute as a result of solvent contraction.     

FOURIER-TRANSFORM INFRARED SPECTROSCOPIC STUDY OF THE STRUCTURE OF CHLOROPHYLL a and CHLOROPHYLL b IN HIGHLY DILUTE WATER-SATURATED CARBON TETRACHLORIDE SOLUTIONS

Abstract— Fourier-transform (FT) infrared (IR) absorption spectra have been measured for chlorophyll a (Chi a ), chlorophyll b (Chi b ), pheophytin a (Pheo a ), and pheophytin b (Pheo b ) in highly dilute (10^-5-10^-6 M ) water-saturated carbon tetrachloride solutions. Frequencies of IR bands due to C=O stretching modes of the 9-keto group indicate that Chi a assumes largely a dimeric structure in the concentrated (10^-2-10^-3 M ) water-saturated carbon tetrachloride solutions but it remains mostly a monomer with one or two coordinated water molecules in dilute (10^-5-10^-6 M ) solutions. Although it seems that Chi b also assumes predominantly dimeric form in concentrated solutions and monomelic form in dilute solutions, the relative intensity change of two C=O stretching bands ascribed to the free and coordinated 3-aldehyde groups with decreasing concentration suggests that the aldehyde group is also involved in formation of the dimer. The relative intensity of two C=O stretching bands due to the free and coordinated aldehyde groups changes significantly for Pheo b in water-saturated carbon tetrachloride solutions. This observation suggests that some of Pheo b also assume dimeric form via the aldehyde group in concentrated solutions.     

Spectrofluorimetric trace determination of terbium(III) with potassium oxalate

Potassium oxalate acts as a specific reagent in enhancing the fluorescence intensity of terbium in aqueous solutions. Maximum fluorescence intensity is obtained by irradiating (at 255 mμ) terbium(III) dissolved in 0.01 M potassium oxalate solution at pH 7.8. The enhancement and quenching phenomena caused by other lanthanides, errors in the determination, and various examples of spectrofluorimetric analysis of traces of terbium in mixtures with other lanthanides are described. The sensitivity of the method is 5·10^-2μg/ml of terbium.     

Experimental determination of the absolute cross-section of giant Raman light scattering by metal-metal adatom complexes at silver electrode

Changes in the background intensities in giant Raman scattering spectra for silver surface in silver sulfate solutions, appeared at the varying of the silver galvanostatic deposition current near the silver electrode equilibrium potential, are measured. The connection between the silver adatom concentration and the intensity of the giant Raman scattering background allowed determining the absolute cross-section for the giant Raman scattering involving adatom-metal complexes: 1.02 × 10⁻²⁷ cm²/adatom in sulfate solutions.     

Vibrational dynamics of some anions in aqueous solutions from isotropic Raman scattering

From the I_VV and I_VH Raman spectra of a totally symmetric vibration, isotropic scattering profiles have been obtained for several anions in dilute aqueous solutions at various temperatures. The Raman spectrometer was connected to an A/D converter and a small computer, which allowed multiple scanning, data accumulation, and numerical processing of these profiles with good precision over a frequency range of about 20 times their full width at half peak height.The theoretical analysis of the isotropic Raman profiles was accomplished by assuming vibrational phase relaxation based on a MARKOV-GAUSS mechanism. Fitting procedures to the experimental data permitted the determination of the vibrational frequency distribution and its modulation time. Temperature effects are discussed in relation to the distribution and motional characteristics of the immediate environment of water molecules of the anions.     

Infrared,Raman, and cndo studies of the effect of ions on the electron density distribution in formamide

Infrared and Raman spectra of electrolyte solutions in formamide have been investigated for amide I and CH stretching regions. The effects of the cation-molecule and anion-molecule interactions on the frequency shift and IR intensity are discussed in terms of CNDO/2 calculations performed for the model formamide complexes with Li⁺ and F^? ions. It is suggested that the considerable CH frequency shift upon cornplexing with cation is due to the trans lone pair effect.     

Concentration dependence of the structure of aqueous solutions of lutetium nitrate according to X-ray diffraction

Aqueous solutions of lutetium nitrate over a wide range of concentrations are studied by X-ray diffraction under standard temperature and pressure. The low-angle peaks in experimental scattering intensity curves are interpreted. It is shown that the structure of these solutions can be of two types. It is found that a saturated solution and solutions concentrated to a molar ratio of 1: 20 have a quasi-crystalline structure resulting from interionic interactions. It is determined that dilute solutions form a water-like structure characterized by a tetrahedral network of hydrogen bonds between the water molecules. It is found that low-angle peaks also appear in the intensity curves of dilute solutions; this proves that the so-called “long-range” order is preserved in these solutions. It is revealed that in all the studied systems, the contributions to the total scattering pattern that are responsible for the occurrence of pre-peaks are intercationic interactions.     

Electrostatic correlations in polyelectrolyte solutions

The major attribute of polyelectrolyte solutions is that all chains are strongly correlated both electrostatically and topologically. Even in very dilute solutions such that the chains are not interpenetrating, the chains are still strongly correlated. These correlations are manifest in the measured scattering intensity when such solutions are subjected to light, X-ray, and neutron radiation. The behavior of scattering intensity from polyelectrolyte solutions is qualitatively different from that of solutions of uncharged polymers. Using the technique introduced by Sir Sam Edwards, and extending the earlier work by the author on the thermodynamics of polyelectrolyte solutions, extrapolation formulas are derived for the scattering intensity from polyelectrolyte solutions. The emergence of the polyelectrolyte peak and its concentration dependence are derived. The derived theory shows that there are five regimes. Published experimental data from many laboratories are also collected into a master figure and a comparison between the present theory and experiments is presented.     

X-ray diffraction investigations of the structure of concentrated ionic solutions

A liquid-type quasi-close-packing of molecular aggregates [In(NO₃)₂(H₂O)₄]⁺ is suggested as a model to interpret the scattered X-ray intensity of 2.27, 1.30, and 3.96 M aqueous solutions of indium nitrate; but the existence of another packing in the less concentrated solutions may not be excluded. Three different molecular models were tested to obtain agreement between the observed and calculated intensity, from s = (4π/λ)sinθ ≈ 0.7 to 13.0 Å⁻¹ for 2.27 and 1.30 M aqueous solutions.