Pressure-induced shift and broadening of acetylene lines in the region 6580-6600 cm-1

Highly accurate measurements of pressure shift and broadening parameters of acetylene absorption lines in the region 6580-6600 cm-1 have been performed by tunable diode laser spectroscopy (TDLS). For these purposes the three channel spectrometer with distributed-feedback diode laser, operated at 1.53 microm was used. The laser is generating pulses of 4-10 ms duration at a repetition frequency of 40 Hz. A temperature-stabilization system, using a thermoelectric cooling unit affords a temperature stability of the order of 10(-4)K in the temperature range from -15 to +50 degrees C. A three channels acquisition system ensured simultaneous real time recording of the sample gas absorption spectrum and of two spectral calibration signals (Fabry-Perot fringes and low-pressure reference lines). We have measured the pressure-induced self-shift and broadening coefficients for six lines of the R-branch in the nu1+nu3 rotation-vibration band of acetylene 12C2H2. The self-shift coefficients have been determined for these lines in the wide pressure region. A non-linear behavior of the pressure dependence of the shift was observed. The temperature exponent n of pressure-induced broadening and shift are reported.     

Detection of OH on photolysis of styrene oxide at 193 nm in gas phase

Photodissociation of styrene oxide at 193 nm in gas phase generates OH, as detected by laser-induced fluorescence technique. Under similar conditions, OH was not observed from ethylene and propylene oxides, primarily because of their low absorption cross-sections at 193 nm. Mechanism of OH formation involves first opening of the three-membered ring from the ground electronic state via cleavage of either of two CO bonds, followed by isomerization to enolic forms of phenylacetaldehyde and acetophenone, and finally scission of the COH bond of enols. Ab initio molecular orbital calculations support the proposed mechanism.     

Near-IR bromine Laser Induced Breakdown Spectroscopy detection and ambient gas effects on emission line asymmetric Stark broadening and shift

Investigation via Laser-Induced Breakdown Spectroscopy of a near-infrared bromine emission line (827.2 nm) with an UltraViolet ablation laser and a gated detector is reported. The effects of ambient pressure and gas species (air, O₂, N₂ and He) on the atomic emission line strength and spectral profile were systematically investigated. Substantially improved signal strength and reduced background radiation are demonstrated near 100 mbar ambient pressure with all gases. Optimal results were achieved when helium was used. Asymmetric broadening and shift of the 827.2 nm bromine line, attributed to pressure-dependent Stark effect has been revealed. This effect is prominent when air, oxygen or nitrogen are present and is much less manifested when helium is used. Possible interpretations of this effect are presented.     

Theoretical and experimental values of the spectroscopic constant relative to the Hg 253.7 nm line at different temperatures.

The fundamental parameter (cm²/atom) relating the absorbance and the number of atoms, called “atomic absorptivity” (C.Th.J. Alkemade et al. Metal Vapours in Flames, Pergamon, New York, 1982) and herewith referred to as the “spectroscopic constant” k, can be either theoretically calculated or derived from experimental calibration curves. The comparison between these two values is useful because the theory can be refined and the operating conditions chosen with more confidence. One of the most important parameters needed is the variation of k with temperature, since a good control of the atomizer temperature is not easy due to difficulties in calibrating the sensor. In fact, if k is constant, there is no need to control the temperature, while if its variation is known, one can calculate the error caused by such inaccuracy. In this paper, some experimental and theoretical data for Hg, in the temperature interval 300–2400 K, are discussed.     

On the importance of line shift and peak broadening corrections in the evaluation of spectra in neutron activation analysis

The evaluation of -ray spectra achieved by Instrumental Neutron Activation Analysis (INAA) is improved if effects of line shift and peak broadening are taken into account, comparing the corresponding -lines in spectra from samples and standards. An algorithm which handles both effects is proposed and its realization in a computer program for routine analysis of archaeological ceramic samples is presented.     

Comparison of 1064 nm and 266 nm excitation of laser-induced plasmas for several types of plastics and one explosive

Comparative measurements of Laser-Induced Breakdown Spectroscopy (LIBS) for ultraviolet (UV) and near infrared (NIR) excitation wavelengths on a wide range of plastics and one kind of explosive are presented. The focus of work is on the influence of laser wavelength on the Signal-to-peak to peak noise ratio (SPPNR) for selected emission lines as well as the plasma thresholds for NIR and UV excitation wavelengths. The merits of both excitation wavelengths are discussed with respect to the detection of explosives.     

The three-body dissociation dynamics of Cl2O at 248 and 193 nm

The photodissociation of Cl₂O has been studied at 248 and 193 nm using photofragment translational spectroscopy (PTS) experiments with tunable VUV photoionization detection. The sole products observed were Cl, O and ClO fragments. Based on the derived translational energy distributions for the ClO and Cl photofragments we conclude that at 248 nm 15% of Cl₂O excitation results in three-body dissociation. At 193 nm no Cl₂ fragments are observed and we conclude that the oxygen atoms arise solely from three-body dissociation. Dissociation geometries derived from forward convolution fitting suggest two qualitatively distinct three-body dissociation pathways: asymmetric concerted dissociation and symmetric concerted dissociation in agreement with recent theoretical predictions.     

Automatic on line preconcentration and determination of lead in water by ICP-AES using a TS-microcolumn

A simple, sensitive, low-cost and rapid, flow injection system for the on-line preconcentration of lead by sorption on a microcolumn packed with silica gel funtionalized with methylthiosalicylate (TS-gel) was developped. The metal is directly retained on the sorbent column and subsequently then eluted from it by EDTA. Five variables (sample flow rate, eluent flow rate, eluent concentration, pH and buffer concentration) were considered as factors in the optimization process. Interactions between analytical factors and their optimal levels were investigated using two level factorial and Box-Behnken designs. The optimum conditions established were applied to the determination of lead by flow injection inductively coupled plasma atomic emission spectrometry (FI-ICP-AES). The proposed method has a linear calibration range from 10 to at least 500 ng ml⁻¹ of lead. At a sample frequency of 24 h⁻¹ and a 120 s preconcentration time, the enrichment factor was 41, the detection limit was 15.3 ng ml⁻¹ (S/N=3) and the precision, expressed as relative standard deviation, was 0.9% (at 100 ng ml⁻¹). Validation of the developed method was carried out against electrothermal atomic absorption spectrometry analysis without statistically significant differences between the proposed method and the atomic absorption method.     

Permittivity and electric conductivity of aqueous alumina (40 nm) nanofluids at different temperatures

Aiming to study the effect of nanoparticle size on electric properties, the effective relative permittivity and electric conductivity of suspensions of 40 nm particles of aluminium oxide (alumina) in base Milli-Q and Milli-Ro water were determined at six different temperatures in the range (298.15 to 348.15) K, and at eight different concentrations up to 7% mass (2% volume). Present results are compared with previously published values for the same colloids containing 15 nm particles. Empirical equations for describing the experimental data are given. This study demonstrates the importance of the particle size, volume fraction of nanoparticles, temperature and water purity on the effective relative permittivity and electric conductivity of alumina nanoparticles suspensions. Trends for changes in permittivity enhancement and in electric conductivity enhancement with temperature and concentration are examined and discussed. Classical theoretical models in the study of permittivity and conductivity are applied. A summary is given for the effect of size ((15 and 40) nm), concentration (0.25 to 2)% volume and temperature (298.15 to 348.15) K on the behavior of these nanofluids.     

What Caused the Formation of the Absorption Maximum at 421 nm in vivo Spectra of Rhodopseudomonas palustris

A spectral peak at ~421 nm appeared in vivo spectrum of Rhodopseudomonas palustris CQV97 cultured in acetate–glutamate medium (M1) but not in acetate–ammonium sulfate medium (M2). However, the spectral origin of 421 nm peak was not clear and frequently attributed to carotenoid component(s). In this study, comparative analysis of the extracted components showed that magnesium protoporphyrin IX monomethylester (MPE) was accumulated as one of the predominate components in M1 culture. The amounts of bacteriochlorophyll a in M1 culture were higher than that in M2, whereas the amounts of carotenoids were nearly identical in both cultures. A simple, rapid and minimum interference with carotenoid and bacteriochlorophyll method to efficiently extract the compounds involving in the formation of 421 nm peak was developed in this study. Assembly of purified MPE with protein components from R. palustris in vitro demonstrated that MPE caused the formation of 421 nm peak. The localization analysis in vivo demonstrated it is MPE associating to protein components and accounting for the peak at ~421 nm. This work clarified the 421 nm peak in vivo mainly originated from MPE accumulation, and will be very helpful to further explore the physiological roles of MPE or its derivatives in photosynthesis.     

Sum frequency generation at 365 nm by two diode lasers applied to the detection of mercury

365 nm laser light is produced by sum frequency generation in a LiIO₃ crystal using two continuous-wave single mode diode lasers. The efficiency of sum frequency generation as well as the applicability as a radiation source for the detection of mercury are discussed.     

Determination of nanomolar concentrations of lead and cadmium by anodic-stripping voltammetry at the silver electrode

Lead and cadmium have been determined by subtractive anodic-stripping voltammetry (SASV) in the square-wave mode at a silver electrode without removal of oxygen. The sensitivities and detection limits for the two metals differ considerably. Detection limits of 0.05 nM for lead and 1 nM for cadmium have been achieved following 90 s electrodeposition. The repeatability of consecutive SASV runs is good (for lead 0.5% at 20 nM for 30 s electrolysis, 5% at 0.3 nM for 60 s electrolysis; for cadmium 2.5% at 20 nM for 30 s electrolysis, 5% at 5 nM for 60 s). Hundreds of runs can be carried out without any pretreatment of the electrode. The high stability is attributed to renewal of the electrode surface that takes place during the electrodeposition step in a two-electrode cell: the silver counter/quasi-reference electrode generates silver ions that codeposit with lead and cadmium at the Ag-RDE, thus ensuring a continuity of the latter. Underpotential deposition (UPD) plays a central role in anodic-stripping voltammetry (ASV). During the deposition step, the adatom coverage of trace elements is in the range of 0.01-1% and no bulk deposition is invoked for metals that exhibit UPD. The UPD properties and, as a result, the ASV signals are strongly affected by the type and concentration of the supporting electrolyte. The effects of Cl⁻, Br⁻, SO₄²⁻ and NO₃⁻ are shown. The analysis of lead and cadmium in natural waters has been performed. Surfactants distort the SASV signal. In order to ensure surfactant-free solutions, the samples were pretreated by wet ashing.     

Tunable UV generation at 283 nm by frequency doubling and sum frequency mixing of two semiconductor lasers for the detection of Pb

High resolution atomic absorption measurements of lead at 283 nm in a vapor cell were performed by frequency doubling an 850 nm laser diode to obtain 425 nm light, followed by sum frequency generation of the harmonic radiation with a second 850 nm laser diode.     

β-Functionalized ethylchalcogenolate complexes of lead(II): Synthesis, structures and their conversion into lead chalcogenide nanoparticles

The reactions of Pb(OAc)₂·3H₂O with NaER yield homoleptic colorless to yellow complexes of composition, [Pb(ER)₂] (ER = SCH₂CH₂NMe₂ (1), SeCH₂CH₂NMe₂ (2) and SeCH₂CH₂COOMe (3)). These complexes were characterized by elemental analyses, UV–Vis and ¹H NMR data. Molecular structures of [Pb(ECH₂CH₂NMe₂)₂] (E = S or Se) have been established by single crystal X-ray diffraction analyses. These molecules have a distorted trigonal bipyramidal configuration around lead with the nitrogen atoms of the chelating chalcogenolate ligands occupying the axial positions. Thermal behavior of these complexes was studied by TG analysis. Pyrolysis in a furnace or in HDA (hexadecylamine) gave PbE nanoparticles which were characterized by UV–Vis, photoluminescence, XRD, EDAX, and TEM measurements.     

Isopiestic measurement and solubility evaluation of the ternary system (CaCl2 + SrCl2 + H2O) at T = 298.15 K

Water activities in the ternary system (CaCl₂ + SrCl₂ + H₂O) and its sub-binary system (CaCl₂ + H₂O) at T = 298.15 K have been elaborately measured by an isopiestic method. The data of the measured water activity were used to justify the reliability of solubility isotherms reported in the literature by correlating them with a thermodynamic Pitzer–Simonson–Clegg (PSC) model. The model parameters for representing the thermodynamic properties of the (CaCl₂ + H₂O) system from (0 to 11) mol ⋅ kg⁻¹ at T = 298.15 K were determined, and the experimental water activity data in the ternary system were compared with those predicted by the parameters determined in the binary systems. Their agreement indicates that the PSC model parameters can reliably represent the properties of the ternary system. Under the assumption that the equilibrium solid phases are the pure solid phases (SrCl₂ ⋅ 6H₂O and CaCl₂ ⋅ 6H₂O)_(s) or the ideal solid solution consisting of CaCl₂ ⋅ 6H₂O_(s) and SrCl₂ ⋅ 6H₂O_(s), the solubility isotherms were predicted and compared with experimental data from the literature. It was found that the predicted solubility isotherm agrees with experimental data over the entire concentration range at T = 298.15 K under the second assumption described above; however, it does not under the first assumption. The modeling results reveal that the solid phase in equilibrium with the aqueous solution in the ternary system is an ideal solid solution consisting of SrCl₂ ⋅ 6H₂O_(s) and CaCl₂ ⋅ 6H₂O_(s). Based on the theoretical calculation, the possibility of the co-saturated points between SrCl₂ ⋅ 6H₂O_(s) and the solid solution (CaCl₂ ⋅ 6H₂O + SrCl₂ ⋅ 6H₂O)_(s) and between CaCl₂ ⋅ 6H₂O_(s) and the solid solution (CaCl₂ ⋅ 6H₂O + SrCl₂ ⋅ 6H₂O)_(s), which were reported by experimental researchers, has been discussed, and the Lippann diagram of this system has been presented.     

Normal Spectral Emissivity at 684.5 nm of the Liquid Binary System Fe–Ni

Summary. Normal spectral emissivity at 684.5 nm of the liquid binary system Fe–Ni was measured by means of a fast ohmic pulse heating technique combined with fast ellipsometry. The experimental values observed of all liquid alloys are dependent on composition and temperature in the entire range of mixing. Spectral emissivity was measured for pure iron, Fe90Ni10, Fe80Ni20, Fe64Ni36, Fe50Ni50, Fe40Ni60, Fe30Ni70, Fe20Ni80, and pure nickel. Emissivity data as a function of temperature (at melting and in the liquid phase up to 2300 K) and as a function of the mixing ratio are presented and compared to the few existing literature-values.     

Mercury-free simultaneous determination of cadmium and lead at a glassy carbon electrode modified with multi-wall carbon nanotubes

A multi-wall carbon nanotube (MWNT) modified glassy carbon electrode (GCE) was described for the simultaneous determination of trace levels of cadmium and lead by anodic stripping voltammetry (ASV). In pH 4.5 NaAc-HAc buffer containing 0.02 mol/l KI, Cd²⁺ and Pb²⁺ first adsorb onto the surface of a MWNT film coated GCE and then reduce at −1.20 V. During the positive potential sweep, reduced cadmium and lead were oxidized, and two well-defined stripping peaks appeared at −0.88 and −0.62 V. Compared with a bare GCE, a MWNT film coated GCE greatly improves the sensitivity of determining cadmium and lead. Low concentration of I⁻ significantly enhances the stripping peak currents since it induces Cd²⁺ and Pb²⁺ to adsorb at the electrode surface. The striping peak currents change linearly with the concentration of Cd²⁺ from 2.5×10⁻⁸ to 1×10⁻⁵ mol/l and with that of Pb²⁺ from 2×10⁻⁸ to 1×10⁻⁵ mol/l. The lowest detectable concentrations of Cd²⁺ and Pb²⁺ are estimated to be 6×10⁻⁹ and 4×10⁻⁹ mol/l, respectively. The high sensitivity, selectivity, and stability of this MWNT film coated electrode demonstrated its practical application for a simple, rapid and economical determination of trace levels of Cd²⁺ and Pb²⁺ in water samples.     

Characterization of lead and lead leaching properties of lead glazed ceramics from the Solis Valley, Mexico, using inductively coupled plasma-mass spectrometry (ICP-MS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFT)

Ingestion of relatively small amounts of lead is now recognized to cause significant neurological and cognitive effects in humans. Large quantities may be fatal, yet lead poisoning, especially of children, is still a major public health concern in many parts of the world. In rural Mexican communities lead oxide (PbO) is added to ceramic glaze as a fluxing agent, lowering starting firing temperatures to 500 °C. The purpose of this study is to characterize the lead chemical forms in ceramic glazes from the Solis Valley, Mexico, to investigate lead leaching properties of these ceramics, and to demonstrate the applicability of lead isotope signatures as a means of tracing lead source origins. Ceramics were collected from the rural village of Santa Maria de Canchesda, State of Mexico, Mexico. Dried liquid glazes, post-fired glaze material, and pure PbO were analyzed by diffuse reflectance infrared Fourier transform spectroscopy (DRIFT). Results from DRIFT analysis indicate that PbO (1429 cm⁻¹ band) is the active form of lead found in liquid glazes and ceramics. Some shifting of 1429 cm⁻¹ PbO peak to lower wavenumbers occurs in post-fired ceramics, and this may be due to the formation of lead bisilicate during firing. Ceramics samples were leached in 0.02 M citric acid solution for 1 min, and leached lead concentrations were measured using inductively coupled plasma-mass spectrometry (ICP-MS). Lead concentrations in these leachates varied from 0.4-80.4 μg ml⁻¹, while the control pottery from the US leached only 0.1 μg ml⁻¹ lead. Elemental distributions on glaze surfaces were identified by laser ablation (LA)-ICP-MS. Nitric acid extracts of soils, teeth, and ceramic glazes were analyzed for lead isotope ratios (²⁰⁷Pb/²⁰⁶Pb vs. ²⁰⁸Pb/²⁰⁶Pb) using ICP-MS. Similarities of tooth and ceramic lead isotope ratios indicate that ceramics may be a substantial source of body lead burden in the Solis Valley. This study demonstrates the applicability of lead isotope ratios for lead source identification, and it identifies potential health risks from ceramic use induced lead toxicity within the Solis Valley.     

Contribution of migration current to the voltammetric deposition and stripping of lead with and without added supporting electrolyte at a mercury-free carbon fibre microdisc electrode

In order to assess the contribution and analytical significance of migration, electrochemical studies on the deposition and stripping of lead at a carbon fibre microelectrode (diameter of 10 μm) have been undertaken in aqueous solutions containing 1 mM lead ions with variable KNO₃ supporting electrolyte concentrations (10⁻¹ to 10⁻⁵ M), as well as in the total absence of deliberately added supporting electrolyte. The methodology involved the application of cyclic voltammetry to characterise the Pb²⁺ (solution)+2e⁻Pb (metal) process in both the reduction (Pb deposition) and stripping (Pb dissolution) directions. The use of a mercury-free carbon surfaces means that the lead stripping does not occur from the amalgam state, as is commonly the case in anodic stripping voltammetry. In the deposition step, the current rises sharply with potential in response to a lead nucleation-growth process and then reaches an almost potential independent limiting value. The stripping step, obtained on the reverse scan, exhibited oxidation peak currents resulting from the redissolution or stripping of the metal from the electrode surface. The influence of the electrolyte concentration and hence migration current at −0.8 V versus Ag/AgCl for the deposition process, as well on the redissolution peak current and the dependence of the voltammograms on scan rate (10–1000 mV) are discussed. Interestingly, neither deposition limiting nor stripping peak currents vary in a simple manner with added supporting electrolyte concentrations, with maximum values being observed at 10⁻⁵ M rather than zero concentration of added KNO₃. An important implication for the voltammetric determination of lead in low ionic strength media by the very sensitive technique of anodic stripping voltammetry is that use of the method of standard additions commonly employed to minimise unknown matrix problems, is prone to error when contributions to the process from migration current are important.