Diagnostical measurements in a single electrode,atmospheric pressure,microwave plasma

Several important diagnostic parameters are determined for a single electrode atmospheric pressure plasma system described by HANAMURA et al. [1, 2]. These include excitation temperatures and electron number densities and electron temperatures for various plasma gases at several different input powers. The variation of emission intensity with various plasma gases and their mixtures is investigated, as well as the effect of the chemical form of the sample on emission intensity, for the purposes of optimizing operating conditions for emission spectrochemical analysis.     

Determination of bromophos residues by fluorogenic labelling with dansyl chloride and thin-layer. Chromatography

The use of a highly sensitive and inexpensive method for determination of residues of bromophos (an organophosphate pesticide) in peanut crops, by fluorogenic labelling and thin-layer chromatography (TLC) is described. The bromophos is hydrolysed and the product 4-bromo-2,5-dichlorophenol (BDCP) dansylated with dansyl chloride. The fluorescent dansylated BDCP is separated by TLC and detected fluorimetrically. Linear fluorimetric analytical curves are obtained for bromophos weights ranging between 0.5 and 50 ng. The minimum detectable quantity is estimated to be 0.5 ng. The method can be used to recover as little as 400 ng of bromophos residue from 25 g of peanut seeds.     

Conventional fluorescence spectrometry of polynuclear aromatic hydrocarbons in Shpol'skii matrices at 77 K

A simple fluorimeter assembled from commercial components and its use for the study and application of the Shpol'skii effect on polynuclear aromatic hydrocarbons (PAHs) in n-alkane matrices at 77 K are described. The correlation between the dimensions and geometries of PAHs and their corresponding Shpol'skii solvents is considered. Analytical figures of merit have been evaluated, and the power of the Shpol'skii technique with a conventional fluorimeter in the direct qualitative and quantitative determination of 11 PAHs in mixture is demonstrated. Comparisons with conventional room-temperature fluorescence and laser-excited Shpol'skii spectrometry are also commented upon.     

Photochemical analysis studies-III A fluorimetric and ultraviolet spectrophotometric study of the photolysis of chloroquine on silica-gel thin layers, and its analytical application

The photolysis of chloroquine on silica-gel thin layers has been studied by ultraviolet spectrophotometry and fluorimetry. It has been shown that a reversible photoisomerization of chloroquine takes place and yields a fluorescent photoproduct. The effect of pH, alkali-metal halides, and the eluent system on the fluorescence intensity of chloroquine and its photoproduct was investigated. The fluorescence on silica-gel thin layers is quenched by high concentrations of sodium hydroxide; this is explained in terms of interference of sodium ions in the hydrogen-bonded adsorption of chloroquine on the silica gel. The results have been used to develop a method for determination and separation of chloroquine at the nanogram level. Linear calibration plots are obtained, covering the range between 4 and 10(4) ng.     

Finite-field method calculations. IV. Higher-order moments,dipole moment gradients,polarisability gradients and field-induced shifts in molecular properties: Application to N2, CO,CN−, HCN and HNC

In this paper, theoretical methods developed in III are applied in calculating polarisabilities, polarisability gradients and field-induced shifts, by the finite-field method. Values of dipole moment gradients and higher-order moments, calculated from the unperturbed wavefunctions, are also reported. Results for N₂, CO, CN^?, HCN and HNC have been obtained at the SCF level; some CI results for the N₂ polarisability components and moments and for the dipole moment gradients of HCN are also given. The calculated polarisability gradients and dipole moment gradients have been used to estimate the Raman scattering intensities and depolarisation ratios and the IR absorption intensities. Model calculations of field-induced shifts in bond length, vibrational levels, spectroscopic constants, force constants and dipole moment gradient are reported for N₂ and CO.The discrepancy between the SCF and experimental bond dipole moment gradients for HCN, previously noted in the literature, has been re-examined and resolved by our CI results.     

Ring electrographic analysis of some ancient punch-marked silver coins from Soron, Allahabad, India

The chemical analysis of a number of punch-marked silver coins of the period 400-300 B.C., obtained from the archaeological site at Soron, Phoolpur Sub Division, Allahabad District, India, has been carried out nondestructively by a modified ring colorimetric method. On the basis of the compositions the order of their age has been suggested.     

A review of considerations for high-fidelity imaging of laboratory spectroscopic sources—II

In part I of this article the basic equations governing the astigmatism produced by a pair of mirrors were introduced. Here, the use of coupled pairs o     

Fluorimetric determination of dissociation constants and ph-controlled fluorescence analysis of purines and pyrimidines

Fluorimetrically determined pH-titration curves have been obtained for twelve purines and pyrimidines at room temperature, in aqueous solution. The pK(a) values for these compounds have been determined fluorimetrically and potentiometrically. Except for 6-mercaptopurine and uric acid, there is close agreement between the two sets of pK(a) values, but a large difference for the corresponding excited singlet-state values, pK(S1)(a), which were calculated previously. This indicates that the excited singlet-state proton-transfer rate is much slower than the fluorescence-decay rate of purines and pyrimidines in our experimental conditions. A direct, simple, pH-controlled fluorimetric method is proposed for the determination of purines and pyrimidines. The limits of detection vary between 60 ng ml and 5.4 mug ml .     

The crystal and molecular structure of trichlorogermylcobalt tetracarbonyl, Cl3GeCo(CO)4

The crystal and molecular structure of trichlorogermylcobalt tetracarbonyl. Cl₃GeCo(CO)₄, has been determined from three-dimensional X-ray data collected by counter methods. The structure has been resolved by vector-analysis and refined by least-squares techniques.It crystallizes in spacegroup C_c of the monoclinic system, with eight molecules in a cell of dimensions: a = 26.238 (3) å, b = 6.623 (5), c = 12.969 (2) and β = 106°12′ (2). The final conventional R factor for the 1647 reflections above background is 0.098.Both molecules in the asymmetric unit exhibit slight, but significant, deviations from C_3u symmetry. The coordination of the Co atoms is trigonal bipyramidal, and that of the Ge atoms is tetrahedral. The equatorial carbonyl groups are in a staggered conformation with respect to the chlorine atoms. The corresponding carbonyl-cobalt-germane angles are less than 90°. The average Ge-Co distance of the two molecules in the asymmetric unit is 2.31 å     

A review of considerations for high-fidelity imaging of laboratory spectroscopic sources—Part I

The use of mirrors, lenses, and combinations of optical elements for spatially resolving radiation from laboratory spectroscopic sources is discussed w     

The crystal structure of Mn(NO)3P(C6H5)3: The first x-ray analysis of a mononuclear metal trinitrosyl complex

The structure of Mn(NO)₃PPh₃ has been analyzed by single-crystal X-ray diffraction. It shows a tetrahedral geometry with essentially linear nitrosyl groups, and an eclipsed configuration around the MnP bond. Average distances and angles are: MnN 1.686(7) Å, MnP 2.315(2) Å, NO 1.165(10) Å, PC 1.815(4) Å, MnNO 177.2(7)°, PMnN 103.6(2)°, NMnN 114.7(4)°. Final R factor 7.3% for 2064 non-zero reflections. The structure of the five-coordinate nitrito complex Mn(NO)₂(ONO)(PEt₃)₂ is also mentioned briefly.     

Photochemical analysis studies-V Photochemical enhancement of the fluorescence signal of the antimalarial plasmocid in liquid solution and on silica-gel thin layers

Ultraviolet irradiation converts the antimalarial plasmocid into a highly fluorescent photoproduct. The effect of pH, solvent composition and irradiation time on the photochemical enhancement of the fluorescence signal of plasmocid has been investigated in solution and on silica-gell thin layers. A significant increase in the fluorescence intensity in very acidic medium is explained by the formation of a triprotonated plasmocid species. The photochemical-fluorescence enhancement factors are particularly large, ranging between about 10 and 20 on silica-gel thin layers. Linear calibration plots are obtained over a concentration range of nearly three orders of magnitude. The photochemical-fluorimetric detection limit of plasmocid on thin layers is 10 ng. The results presented demonstrate the potential of thin-layer phototochemical fluorimetry as a sensitive analytical method.     

Absorption spectra of dysprosium compounds in nonaqueous solutions. Spectral intensity analysis

Absorption spectra of dysprosium compounds were measured in amides and D₂O within the 5500–35000 cm^?1 region and in alcohols within the 7000–34300 cm^?1 region. The oscillator strengths of f-f absorptions bands below 35000 cm^?1 were determined. The intensities of the Dy³⁺ ground state absorption were analyzed according to the Judd-Ofelt theory of forced electric dipole transitions.A good fit to the measurements was obtained with the intensity parameter given in Tables 4–6. The polarizability effect on the intensity of the f-f transition with high value matrix elements U⁽⁴⁾ and U⁽⁶⁾ were considered.     

X-ray diffraction study of the bonding between sulphur and the elements of group IVB. The crystal and molecular structures of methylthiotriphenyl-methane, -silicon, -germanium, -tin and -lead

The X-ray analyses of the compounds methylthiotriphenyl-methane, -silicon, -germanium, -tin, and -lead were undertaken to see if the electronic interactions which affect the X-S bond could influence the molecular geometries. The five structures were solved or by direct methods or by Patterson and Fourier techniques and refined anisotropically to R = 0.053, 0.036, 0.031, 0.041, and 0.070 respectively. The central atom exhibits a distorted tetrahedral coordination; only the propeller shape orientation of the phenyl rings seems to be determined by differences in the electronic nature of the central atoms as well as by steric effects.     

A study of infrared absorption in the oxidation of zinc-substituted magnetites to defect phase γ and hematite

The effect of substitution extent on formation of superstructure-ordered vacancies in zinc-substituted lacunar spinels of type $\text{(}\text{Zn}{}^{\mathrm{2+}}{}_{\mathrm{x}}\text{Fe}{}^{\mathrm{3+}}{}_{\mathrm{1?x}}\text{)}{}_{\mathrm{A}}\text{(}\text{Fe}{}^{\mathrm{3+}}{}_{\mathrm{<mtext>(5+x)</mtext><mtext>3</mtext>}}\text{□}{}_{\mathrm{<mtext>(1?x)</mtext><mtext>3</mtext>}}\text{)}{}_{\mathrm{B}}\text{O}{}^{\mathrm{2?}}{}_4$ was investigated using ir spectrometry. Only those lacunar phases whose substitution extent x is less than about 0.3 show a vacancy ordering on octahedral sites. In addition, referring to the disappearance of the 635-cm^?1 absorption band, which is characteristic of these lacunar spinels, we show that the transformation temperature of the γ phases into αFe₂O₃ increases with zinc substitution extent. For the α phase obtained at 700°C we have found a linear variation between the intensity difference of the 390- and 450-cm^?1 absorption bands and the percentage of αFe₂O₃.     

The stereochemistry of N-methylhydrazido(2)-N′ ligands coordinated to group VIa metals. The structural characterisation of the bis(1,2-bis(diphenylphosphino)ethane)-bromo-N-methylhydrazido(2)-N′-tungsten(IV) and N-ethyl-N-phenylhydrazido(2)-N′-tris-(N,N-pentamethylenedithiocarbamato)molybdenum(VI) cations

The structure analyses of two substituted hydrazido(2) complexes has revealed the detailed stereochemistry of the uncoordinated nitrogen atom; the ligand electron density in several rhenium, tungsten and molybdenum complexes is commented upon in the light of the results.     

Methods for potentiostatic evaluation of heterogeneous kinetic parameters in the presence of an irreversible following chemical reaction

A theoretical study of Brdi?ka's adsorption waves and of the corresponding i-E curves in cyclic voltammetry and E-t curves in chronopotentiometry is presented under the following conditions: (a) the electrochemical reaction 0+ne?R is reversible; (b) both the oxidized and the reduced forms are strongly adsorbed; (c) the adsorption is rapid; (d) allowance is made in the isotherm for interactions between the molecules (Frumkin type isotherm). One mathematical function and its derivative are sufficient to describe the results in the three cases. The equations derived account in particular for the following experimental characteristics: (1) the linear variation of the half-wave potential of the adsorption wave (or of the chronopotentiogram) and of the voltammetric peak potential with the concentration c; (2) the changes in the slope of the wave when c varies and the discontinuous increase of current which is observed for high concentrations; (3) the changes in peak width and the hysteresis phenomenon observed in cyclic voltammetry; (4) the S-shaped experimental chronopotentiograms; (5) the appearance of prewaves (or postwaves) in cases where both O and R are equally adsorbed; (6) the fact that prewaves or postwaves usually appear for large molecules. The results show that the appearance of a Brdi?ka prewave or postwave is often caused by energy effects arising from the interactions between adsorbed molecules, rather than by energy effects caused by interactions with the electrode surface.     

Comparison of the effects of symmetric versus asymmetric H bonding on 2H and 17O nuclear quadrupole coupling constants: Application to formic acid and the hydrogen diformate anion

In this paper, we analyse the effects on the nuclear quadrupole coupling behaviour of ²H and ¹⁷O nuclei of a shift in H-bond character from asymmetric to symmetric. Using ab initio methods, the coupling amplitudes (nuclear quadrupole coupling constant e²_qQ/h) coupling anisotropies (asymmetry parameter η), and orientations of the electric field gradient (EFG) principal axis (PA) system of the H-bonded deuterium and oxygen nuclei in the formic acid dimer and related monomers, and the deuterium diformate anion are calculated. In addition, the relative contributions to the ²H and ¹⁷O EFGs of nuclear and electronic terms, and also the convergence of the EFG as a function of contributions from increasingly distant nuclei in the molecule are investigated. The trends in the calculated ¹⁷O EFGs on going from an asymmetric to a symmetric H-bonded environment are correlated with experimental nqr data in order to establish the hitherto unknown e²qQ/h sign, EFG assignments and PA orientation of symmetrically H-bonded oxygen. The possibility that the e²qQ/h value of deuterium is negative for symmetric H bonds is discussed, and difficulties in the computation of ²H EFGs for symmetric - as distinct from asymmetric - H-bonded systems are pointed out. In strong disagreement with assumptions in the literature, it is found that nearest neighbour terms do not dominate the ²H EFG in symmetrically H-bonded systems.     

A rapid microdetermination of chlorine dioxide in the presence of active chlorine compounds

A titrimetric and spectrophotometric procedure has been developed for the determination of ClO₂ in water samples. The procedure is rapid, accurate, and free of normal interferences present in water. It is based upon the reaction of ClO₂ with substituted halophenol indicators.     

Methods for the isolation and characterization of constituents of natural products XX. Rapid column procedures for forming isopropylidene derivatives of submicrogram to micromole amounts of diols

A simple, essentially instantaneous and complete reaction for the formation of isopropylidene (acetonide) derivatives of submicro- and microgram quantities of diols is described. The diol dissolved in acetone:hexane (1:4) is brought in contact with a column of Celite charged with a H₃PO₄P₂O₅ mixture and the resulting acetonide eluted for analysis. The procedure was modified so that micromole amounts of diols can be quantitatively derivatized in a continuously flowing column.