Ion chromatographic determination of traces of some oxoanions with direct spectrophotometric detection

Investigation of the use of a single analytical procedure using the non-suppressed ion chromatographic method with direct spectrophotometric detection capable of determining eight oxoanions simultaneously is presented in this paper. Potassium phosphate was found to be the most suitable eluent for UV absorbance detection at 205 nm. Oxoanions AsO³⁻₃, SeO²⁻₃, AsO³⁻₄, VO⁻₃, SeO²⁻₄, WO²⁻₄, MoO²⁻₄ and CrO²⁻₄ were detected at ng ml⁻¹ levels with well separated peaks at retention time < 25 min. The working range is in the range ng ml⁻¹ to 50 μg ml⁻¹. The method is sufficiently sensitive to determine As (V), V(V), Mo(VI) and Cr(VI) anions (and NO⁻₃) directly in a river water sample. The accuracy of these results was established by comparison with conventional atomic absorption methods.     

The enthalpy of mixing of liquid NaF and NaMgF3 from drop calorimetry

The enthalpy of mixing of three liquid mixtures of NaF and NaMgF₃ has been measured by drop calorimetry and was found to be negative. This energy release is attributed to a change in the equilibrium

Mg_1/4[MgF²⁻₄]_3/4+f⁻ å MgF²⁻₄ to the formation of complex MgF²⁻₄-ions. A ΔH^M diagram for the system NaF-MgF₂ up to 50 mol % MgF₂ has been constructed.     

Studies on the determination of dissolved oxygen in water

Studies on the decomposition rates of the Mn(III) complex of cyclohexanediaminetetra-acetate (DCTA) in light and in darkness have shown that this complex is more stable than the one derived from ethylenediaminetetra-acetate. The optimum pH range for the determination of dissolved oxygen by means of the Mn(III)-DCTA complex is found to be between 3 and 4. The absorbance of this complex is independent of the amount of DCTA used (in the range 0.2–1.0 g) with water samples containing a maximum of 3.2 ppm of dissolved oxygen. Significant interferences are caused by the presence of CO²⁻₃, HCO⁻₃, S₂O²⁻₃, PO³⁻₄, I⁻, NO⁻₂, SO²⁻₃, Ca²⁺, Fe²⁺ and Fe³⁺ at 500 times the oxygen concentration.     

Polarized infrared and Raman spectra of a CsHSO4 single crystal

The polarized absorption infrared (IR) and polarized Raman spectra of a CsHSO₄ single crystal at room temperature are presented and discussed in relation to the X-ray crystal structure. Breakdown of the selection rules for the X-ray determined C_2h factor group is observed. The vibrational factor group appears to be C₂. This implies C₁ site symmetry for the SO²⁻₄ ions. The polarization features of the HSO⁻₄ ion vibrations are predicted assuming that the longest S---OH bond vibrates independently of the SO₃ group vibrations. The ABC structure of the IR and Raman band arising from the νOH stretching vibration is explained on the basis of Fermi resonance.     

Spectroscopic investigation of ground state pyrrole (C4H5N): the NH stretch

We have recorded the infrared absorption spectrum of pyrrole at 0.005 cm⁻¹ spectral resolution using a Fourier transform interferometer. The rotational analysis of the fundamental N---H stretch (1¹₀) at 3530.811343(82) cm⁻¹ was performed. A set of 13 upper state rovibrational parameters was determined, allowing the 2715 assigned rovibrational lines to be reproduced with a standard deviation of 1.3 10⁻³ cm⁻¹. An attempt to record the fundamental band under slit-jet conditions is reported. The role of hot bands accompanying the series of the N---H stretch excitation is investigated. Effective vibrational parameters — ω⁰₁, X⁰₁₁, Y₁₁₁, X_1,24 — are obtained. The lower level in the hot band series is unambiguously identified as the V₂₄ = 1 level, by retrieving X_1,24 independently, from other spectral data. The observation of the complex band pattern accompanying the N---H series in the higher overtone range is discussed with the help of new data, recorded around the 1⁵₀ band at different temperatures using intracavity laser optoacoustic spectroscopy.     

The stereochemistry of quaternary N-methyl sparteinium cations, their derivatives, stereoisomers and analogues : Part II. Molecular and crystal structure, and IR spectra of methiodide and methperchlorate of 2-oxosparteine

The crystal and molecular structures of two quarternary salts of 2-oxosparteine (II), the methiodide (IICH⁺₃ • I⁻) and the methperchlorate (IICH⁺₃ • ClO⁻₄) have been determined on the basis of X-ray and IR data. The studies were performed by analogy to previously investigated quaternary salts of sparteine (I), the methiodide (ICH⁺₃ • I⁻) and the methperchlorate (ICH⁺₃ • ClO⁻₄). As expected, the configurations and conformations of cationic parts within the two pairs of quaternary salts are identical, except for the structure of their A/B fragments, which in ICH⁺₃ cations have the character of tertiary amines, but in IICH⁺₃ that of lactams.

On the basis of accumulated X-ray and IR data the similarities and differences in the modes of interaction of perchlorate and iodide anions with quaternary cations, and especially with their N⁺---CH₃ groups are discussed. In this discussion are also included the methiodide and methperchlorate of -isosparteine: IIICH⁺₃ • X⁻ (X⁻ = I⁻ or ClO⁻₄) where N⁺---CH₃ groups are cisoidally oriented to the basic nitrogen atoms. The most interesting observations are as follows: (i) When N⁺---CH₃ groups are easily accessible for direct quasi hydrogen bonding interactions with counter anions and when other positive charged groups, for instance lactam groups, are absent in quaternary cations, perchlorate anions interact more strongly than the iodide anions and in consequence introduce conformational changes into the ring with N⁺---CH₃ group as well as into further rings. (ii) Perchlorate and iodide anions interact with N⁺---CH₃ groups similarly and very weakly if at all, when the N⁺---CH₃ groups are for steric reasons inaccessible to counter anions or when in quaternary cations there are additional groups which attract the counter anions electrostatically. The last mechanism operates in both quaternary salts of 2-oxosparteine and this is the reason why their monocrystals are isosteric and IR spectra almost identical. (iii) The sterically hindered N⁺---CD₃ groups in both IIICD⁺₃ • X⁻ salts give rise in their IR spectra to two doubles of sharp, well resolved bands which indicate the presence of two different rotamers stabilized by two modes of weak intramolecular hydrogen bonds with basic N atoms. (iv) In IIICH⁺₃ • X⁻ and IIICD⁺₃ • X⁻ salts the perchlorate and iodide anions do not interact at all with the rotating and vibrating N⁺---CH₃ (N⁺---CD₃) group but the structures of these salts are not isosteric since the perchlorate anions interact more strongly than iodide anions with the A/B fragment of the IIICH⁺₃ cations. This is visible from the shapes and intensities of the so-called “trans” band in the IR spectra of both salts.     

Turbidimetric determination of sulphate in waters employing flow injection and lead sulphate formation

An analytical flow-injection procedure based on PbSO₄ colloidal formation is proposed as a turbidimetric determination of sulphate in natural waters. Ethanol-water was used as a medium in order to improve the sensibility of the method. Both chemical and flow variables as well as interfering species were studied. A detection limit of 0.3 μg SO²⁻₄ ml⁻¹ was found, and the analytical range (according to Beer's law) was 2–20 μg SO²⁻₄ ml⁻¹. The precision was better than 3% R.S.D. and the sample throughput was ca. 35 h⁻¹. The method, when compared with a standard methodology, gave good results when applied to water analysis.     

Antisymmetric resonance Raman scattering from the breathing mode of CuBr4

Circular polarization measurements establish a large antisymmetric component of the Raman scattering from the breathing vibration of CuBr²⁻₄ in acetonitrile when excited at 5145 Å in the first Br → Cu charge-transfer (π) absorption band. This is attributable to spin degeneracy and to the 700 cm⁻¹ spin-orbit splitting of the CT excited state.     

Untersuchungen zur atomspektroskopischen spurenanalyse in AB-halbleiter-mikroproben—II : Untersuchungen zur bestimmung von Ga-spuren in In und InAs und von In-spuren in Ga, GaAs und GaP durch AAS mit elektrothermischer atomisierung

The atomic-absorption determination of traces of Ga in In, P, As and InAs and of traces of In in Ga, P, As, GaAs and gap is described. The mechanism of the evaporation of the trace element according to the medium used (HCl or HNO₃) is discussed. Nitric acid medium is recommended for analytical determinations. The evaporation of the trace elements and matrices was investigated by means of absorbance vs. time curves. It is shown that a thermal fractionation of AsO³⁻₄ and PO³⁻₄ matrices and Ga and In traces is possible in the ashing step. In the case of Ga the thermal fractionation of the matrices (In³⁺, In³⁺/AsO³⁻₄) from the trace element is possible in the atomization step. The thermal fractionation of In traces from the matrices (Ga³⁺, Ga³⁺/AsO³⁻₄, Ga³⁺/Po³⁻₄) is impossible. The results and the reasons for the non-specific absorption are discussed. The absolute detection limits are Ga 45 pg, In 35 pg. The relative detection limits are 1 ppm in a 0.1 mg sample.     

Prompt and delayed photoejection of hydrated electrons in the UV photolysis of aqueous solutions of copper(I) complexes

The ejection of hydrated electrons from 266-nm laser-photoexcited solutions containing Cu(NH₃)⁺₃, CuCl²⁻₃, or CuBr²⁻₃ occurs through two pathways on the nanosecond time scale: a prompt ejection (ττ>laser pulsewidth) which follows a first-order rate law. This behavior is consistent with electron ejection from two excited states: the primary CTTS state, and longer-lived triplet species consisting of an exciplex and its precursor. The quantum yields for both prompt and delayed ejection are quite high, in the 0.15–0.4 range.     

Untersuchungen zur atomspektroskopischen spurenanalyse in AB-halbleiter-mikroproben—I : Verdampfbarkeit und unspezifische absorption von AB-verbindungen und ihren komponenten in der graphitrohrküvette

The evaporation of the species Ga³⁺, In³⁺, PO³⁻₄, AsO³⁻₄, Ga³⁺/AsO³⁻₄, Ga³⁺/PO³⁻₄ and In³⁺/AsO³⁻₄ in HCl and HNO₃ medium was investigated by measurement of the non-specific absorption at 250 nm, in a graphite cuvette, with a continuum light source. The maximum of the non-specific absorption is given for the ashing and atomizing phases as a function of the ashing temperatures. Ashing temperatures for analytical determinations can be derived from the results. The mechanisms of evaporation of the substances were investigated by means of extinction-time curves. Absorption spectra of the matrices and of the pure acids used were measured between 190 and 330 nm in the graphite cuvette at different ashing and atomizing temperatures. The InCl- and GaCl-bands of the C-system and new bands of GaO- and InO-molecules were found. The PO-band at 246 nm was detected. The results are discussed and can be applied for thermal fractionation and for background correction by the two-line method in trace analysis by electrothermal AAS.     

Indirect ultraviolet determination of silver with nickelocyanide ion by flow injection analysis

A flow-injection method for the ultraviolet spectrophotometric determination of silver, based on its reaction with nickelocyanide ion, Ni(CN)²⁻₄, in ammoniacal buffer medium (pH 10) and subsequent measurement of the decrease in the absorption of the Ni(CN)²⁻₄ complex at 275 nm is described. The calibration graph is linear in the range 10–400 μm silver. At a sampling rate of about 60 samples h⁻¹ with 35 μl sample injections, precision was about 1% relative standard deviation. The proposed method was successfully applied to the determination of silver in some common silver minerals.     

Field investigation of major and minor ions along Summit (Central Greenland) ice cores by ion chromatography

As a part of the European EUROCORE and GRIP (Greenland Ice Core Project) operations aimed at recovering deep ice cores at Summit (Central Greenland), we have for the first time successfully performed ion chromatography measurements in the field and investigated in detail the soluble impurities, including Na⁺, NH⁺₄, K⁺, Mg²⁺, Ca²⁺, F⁻, CH₃COO⁻, CH₂ OHCOO⁻, HCOO⁻, CH₃SO₃⁻, Cl⁻, NO⁻₂, SO₄²⁻ and C₂O₄²⁻, trapped in ice deposited over some 200 000 years in Greenland.     

Polarized infrared and Raman spectra of CsHSeO4 and CsDSeO4 single crystals

The polarized absorption infrared spectra of CsHSeO₄ and CsDSeO₄ single crystals and polarized Raman spectra of the CsHSeO₄ single crystal were measured at room temperature. The polarization features of the internal vibrations of the HSeO⁻₄ ions are predicted on the basis of the X-ray structure assuming strong couping between the vibrations of the two shortest Se---O bonds and an intermediate Se---O bond. The bending methods γOH and δOH of a hydrogen bond appear at 805 cm⁻ and 1258 cm⁻¹, respectively. The νOH absorption has the ABC structure due to Fermi resonance of νOH with the overtones of the δOH and γOH vibrations. A similar shape of the νOH band is observed in the Raman spectra. The νOD absorption has a different shape from that of νOH. Intra-chain coupling was observed for the νOH and νOD vibrations.     

The vapour pressure of di-arsenic pentoxide (As2O5)

The arsenic oxide pressure of As₂O₅ has been studied using mass spectrometry and a transportation method. Mass spectrometry revealed the presence of the species As₄O⁺₆, As₄O⁺₇, and As₄O⁺₈ in the vapour. The existence of volatile species up to As₄O₁₀(g) as a result of the reaction As₄O₁₀(g) As₄O_(10−y) (g) +1/2yO₂(g) has been assumed.

The oxygen pressure of this equilibrium builds up very slowly. The equilibrium pressure can be expressed by log(p_O2/atm) (880−952 K) = −(13940±930)/T + (14.53 ± 1.01)

A stationary arsenic oxide pressure has been measured using the transportation method. Since the oxygen pressure in the transportation gas did not influence the arsenic oxide pressure, it is assumed that only the As₄O₁₀(g) pressure has been measured. The results can be expressed by the linear function log(p_As4O10/atm) (865−1009 K) = −(15741 ± 410)/T + (13.87 ± 0.42).     

Gas-phase stability of cluster ions SF m + (SF6) n with m = 0–5 and n = 1–3

The gas-phase stabilities of cluster ions SF⁺_m (SF₆)_n with m = 0−5 were determined by using a high pressure mass spectrometer. The bond energies of SF⁺_m (SF₆)₁ were found to be less than 10 kcal/mol and to decrease with m = 0 → 5. There appear to be rather large gaps in the bond energies between n = 1 and 2 for the clusters SF⁺_m (SF₆)_n with m = 0−4. The structures of SF⁺₅, SF⁺ (SF₆)₁, SF⁺₃ (SF₆)₁, and SF⁺₅ (SF₆)₁ were investigated by ab initio molecular orbital calculations. For SF⁺₅, the D_3h geometry is found to be most stable andC_4v is a transition state of the Berry pseudorotation. For the ion-molecule complexes, the “on-top hat” models were found to be the most stable structures.     

Thermochemical study of the complex formation of ag(I) with some sulphur-containing aminopyridines

The enthalpies of formation of the complexes between the silver(I) ion and some sulphur-containing aminopyridines of general formula N(CH₂)_n−1-S-(CH₂)_m-NH₂ where n = 1, and m = 1,2; 1,3; 2,2; 2,3 have been determined by direct calorimetric titration at 25°C in 0.5 M (K)NO₃ solution. The corresponding entropy terms, ΔS, have been calculated using the obtained enthalpy values and the previously reported ΔG values.

In acid medium (pH < 3) coordination occurs through the thioether group and the protonated species AgLH³⁺₂ and AgL₂H⁵⁺₄ are enthalpy-stabilized and entropy-destabilized. At higher pH values (pH &>; 3) additional chelation through the pyridine nitrogen is obvious by a marked increase in the enthalpy of formation of the complexes AgL₂H⁴⁺₃, AgL₂H³⁺₂ and AgLH²⁺. The last complex dimerizes into a cyclic dimer Ag₂L, H⁴⁺₂. At still higher pH values (pH &>; 6) the participation of the amino group in the dimeric chelates Ag₂L₂H³⁺ and Ag₂L²⁺₂ is revealed again by a marked increase in the heat of complexation.     

First principles study of the structure, electronic state and stability of SinCm anions

Structure, electronic state and energy of Si_nC⁻ and Si_nC⁻₂ (n=1–7) anions have been investigated using the density functional theory. Structural optimization and frequency analysis are performed at the level B3LYP/6-311G(d). The charged-induced structural changes in these anions have been discussed. The strong C–C bond is also favored over C–Si bonds in the Si_nC⁻_m anions in comparison with corresponding neutral cluster. Among different Si_nC⁻ and Si_nC⁻₂ (n=1–7) anions, Si₃C⁻, Si₅C⁻ and Si₂C⁻₂ are most stable. Their stability has a decreasing tendency with the increase in the size of these clusters.     

Theoretical Study on Ionic Liquid Based on 1-Ethyl-3-Methyl- Imidazolium Cation and Hexafluorophosphate or Tetrafluoroborate

The Hartree-Fock and DFT/B3LYP methods have been employed to investigate the electronic structures of 1-ethy1-3-methyl-imidazolium cation(EMIM~ ),BF_4~-,PF_6~-,EMIM~ -BF_4~-,and EMIM~ -PF_6~- using the Gaussian-94 soft-package at 6-31 G(d,p)basis set level for hydrogen,carbon,nitrogen,boron, phosphorus,and fluorine atoms.Comparison of the electronic structures of the lowest energy of EMIM~ - BF_4~- and EMIM~ -PF_6~- pairs,and single EMIM~ ,BF_4~- and PF_6~- showed that the optimized EMIM~ -BF_4~- and EMIM~ -PF_6~- pair conformers were BF_4~- and PF_6~- outside the 5-ring plane between the ethyl group and the methyl group.The cohesion of C—H…F hydrogen bond between cation and anion is reinforced by charge assistance.The interaction energy between EMIM~ and PF_6~- is 328.8 kJ/mol at the B3LYP level and 326.6 kJ/mol at the Hartree-Fock level,whereas that between EMIM~ and BF_4~- is 353.5 kJ/mol at the B3LYP level and 350.5 kJ/mol at the Hartree-Fock level.The low energy interactions caused by bulky asymmetric EMIM~ ,and charge dispersion of cation and anion give rise to the low melting point of ionic liquid EMIM~ -BF_4~- and EMIM~ -PF_6~-.The two hydrogen bonding models of single hydrogen bond formation,and the hydrogen transfer between C_2 in EMIM~ and F in BF_4~- or PF_6~- were principally depicted.     

Density functional study of molecular properties of hydrazoic acid and methyl azide

Density functional calculations for hydrazoic acid HN₃ and methyl azide CH₃N₃ and for the respective singly ionized structures HN⁺₃ and CH₃N⁺₃ are reported. An analysis of the electrostatic solvent effects, based on the self-consistent reaction field approach, on the molecular properties and conformational equilibrium of CH₃N₃ is also reported. The results are sensitive to the basis set quality and show some dependence on the different representations for the exchange-correlation functions. For HN₃ very good agreement with experiment is observed for several properties, such as the geometry, dipole moment, vibrational frequencies and for the adiabatic first ionization energy. For CH₃N₃ the energy difference between eclipsed (ec) and staggered (st) conformers (δ_ec-st) is 2.5 kJ mol⁻¹, in good agreement with the experimental value (2.9 kJ mol⁻¹). However, for CH₃N⁺₃, δ_ec-st is −3.2 kJ mol⁻, reflecting a significant modification of the methyl group rotational potential after ionization. Solvent effects on the molecular properties of CH₃N₃ are important when it is solvated in a polar medium. The most significant modifications concern the dipole moment and the frequencies related to the CH₃ symmetric stretch and torsion vibrational modes.