Determination of total dissolved phosphorus in water samples by axial inductively coupled plasma atomic emission spectrometry

A procedure was developed to determine total dissolved phosphorus in groundwater-like samples using axial ICP-AES. Severe and peculiar matrix effects (strongly positive at lower and leveling off at higher matrix concentrations) in the presence of Na and Ca were observed. To reduce these matrix effects, a double approach was utilized consisting of a so-called minimum matrix in combination with an internal standard (Ga in this case). The ‘minimum matrix’ (small amounts of K, Mg and Na) was only added to the standard solution(s) used for the calibration. The detection limit for the whole procedure was 12 μg/L using the P213 nm line. Residual matrix effects were less than 3% (P213 nm line). Received: 21 February 1997 / Revised: 5 June 1997 / Accepted: 6 June 1997     

Analysis of seven chlorobiphenyl congeners by multidimensional gas chromatography

Chlorobiphenyl congeners (CBs) are used as indicator compounds in analysis performed to determine whether or not PCB concentrations in food products, waste mineral oil, and environmental samples comply with the maximum levels permitted by legislation. Seven of these compounds have been checked for coelution with other CB congeners by means of a multidimensional gas chromatographic method utilizing a combination of two narrow bore columns, one coated with a conventional non-polar stationary phase and the other with a liquid crystalline (smectic) stationary phase. Peaks of the relevant CBs have been transferred, by heart cutting, from the non-polar column to the liquid crystal column, on which unambiguous separation from possible coeluting CB congeners was obtained. It has been shown that if the seven congeners are analyzed solely on a single, non-polar capillary column the results obtained for two of them may be affected by coelution of other compounds.     

Photoreactions of aromatic compounds — XXVIII : Photo-induced reactions of 1-nitroazulene and derivatives with nucleophiles

The photosubstitutions of azulene, 1-nitroazulene and 3-substituted 1-nitroazulenes with nucleophiles have been investigated. In these azulenes the atom at position 1 proved to be the most reactive in accord with the calculated excited state charge densities. The photomethoxylation of 1-nitroazulene probably proceeds through a triplet state. The quantum efficiency of this reaction proved to be wavelength-dependent indicating that intersystem crossing from higher excited singlet states may occur.     

The mass spectra of some aliphatic and alicyclic sulphoxides and sulphones

Characteristic fragmentation processes of aliphatic sulphoxides and sulphones such as loss of hydroxyl, ‘alkene’ and/or ‘alkenyl’ are associated with hydrogen migrations to oxygen. A study of the mass spectra of di-n-butyl sulphoxide and sulphone, the saturated five-, six- and seven-membered ring sulphoxides and sulphones and their site-specifically deuterated analogues shows that these hydrogen migrations are nonspecific. Apparently steric factors play an important role in determining the relative contributions of initial hydrogen transfer from the various positions. The sites of abstraction probably determine the extent of competition between consecutive or concerted loss of hydroxyl, carbon-sulphur fission or other processes (e.g. McLafferty rearrangement). Apart from the McLafferty rearrangement only the loss of hydroxyl from sulphones shows a strong dependence on the site of initial hydrogen abstraction: γ-hydrogen is lost preferentially, yielding a cyclized [M ? OH] ion.     

X-ray crystal structure and EPR spectra of "arsenite-inhibited" Desulfovibriogigas aldehyde dehydrogenase: a member of the xanthine oxidase family

X-ray crystallography has been used to determine the structure of arsenite-inhibited aldehyde dehydrogenase from Desulfovibrio gigas, a member of the xanthine oxidase family of mononuclear molybdenum enzymes. The structure shows an AsO3 moiety bound to the molybdenum atom of the active site through one of the oxygen atoms. A reduced sample of arsenite-inhibited aldehyde dehydrogenase has a Mo(V) signal that shows anisotropic hyperfine and quadrupole coupling to one arsenic atom. This signal has a strong resemblance with a previously reported signal for arsenite-inhibited xanthine oxidase.     

Mass spectrometry of aralkyl compounds with a functional group—XII: Unorthodox elimination of hydrogen cyanide from hydrogen randomized molecular ions of benzylcyanide and of o-, m- and p-cyanobenzylcyanides,revealed by D-, 13C- acid 15N-labelling

Specific D-labelling in the side-chain and in the phenyl ring, ¹³C-labelling in the benzylic position and in the cyano group and ¹⁵N-labelling in the cyano group of benzylcyanide show, that the molecular ion, decomposing in the second field free region, i.e. having a low internal energy, loses hydrogen cyanide with participation of both side-chain carbon atoms (22% benzylic carbon and 78% cyano carbon) after a complete randomization of all hydrogens. This sharply contrasts with the loss of hydrogen cyanide from the hydrogen randomized molecular ion, decomposing in the ion source, where the original cyano group is involved exclusively. The molecular ions of (o, m, p)-cyanobenzylcyanides, decomposing in the ion source as well as in the second field free region, also lose hydrogen cyanide, involving to some extent (6 to 15%) a carbon atom, different from that of the side-chain cyano group, after an extensive randomization of hydrogens as shown by specific D-labelling in several positions and by ¹³C- and ¹⁵N-labelling in the side-chain cyano group. Furthermore, the molecule of hydrogen cyanide, eliminated in the ion source and in the second field free region, appears to contain predominantly the side-chain cyano group (±70%), thus suggesting that few or none of the molecular ions have rearranged to a seven membered ring.     

C-nitroso compounds—XXIV: Photolysis of some geminal nitro-nitrosoalkanes (“pseudonitroles”)

Photolysis of the “pseudonitrole” 1-nitro-1-nitrosocyclohexane with red light in the absence of oxygen occurs by homolytic C-NO fission, and generates a radical pair: NO and the α-nitro-cyclohexyl radical. If one radical of this pair adds to the NO-group of unchanged starting material, there results a paramagnetic nitroxide, that can combine with the other radical of the pair to a diamagnetic intermediate, forming two isomeric intermediate adducts to the NO double bond. The ratio in which these isomers are formed depends on solvent. In methanol, solvolysis leads to equimolar amounts of cyclohexanone and cyclohexanone-oxime, together with methyl nitrite. In benzene, the major product is cyclohexanone. Small amounts are formed of 1,1-dinitrocyclohexane, 1-nitrocyclohexene and nitrocyclohexane; arising directly from the α-nitrocyclohexyl radical. The nitroxide derived from this radical and the starting material can be detected by ESR.The photolytic behaviour of 1-nitro-1-nitroso-1-cyclopropylethane illustrates the strong interaction between a nitrogroup and an adjacent C-radical centre: only ring-closed products are formed, showing considerable spin delocalisation away from the cyclopropyl ring.     

Quadrupole mass spectrometer operating in the electron-capture negative ion mode as detector for comprehensive two-dimensional gas chromatography

A recently introduced rapid-scanning quadrupole mass spectrometer (qMS) with an electron-capture negative ion (ECNI) option, the Perkin-Elmer Clarus 500, was tested as a detector for comprehensive two-dimensional gas chromatography (GC x GC). The parameters influencing the data acquisition rate in the scan mode, such as scan time and inter-scan delay, and in the selected ion monitoring mode, such as dwell time and inter-channel delay, were evaluated. In the scan mode, good-quality mass spectra covering a range of 300 Da can be obtained at an acquisition rate of 23 Hz; in selected ion monitoring, an acquisition rate of 90Hz can be achieved when monitoring a single ion. Compared with electron ionisation, the use of electron-capture negative ionisation causes no extra peak broadening. As applications, mixtures of polychlorinated n-alkanes (PCAs), polybrominated diphenyl ethers (PBDEs) and polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) were analysed. The separation of PCAs based on their number of chlorine substituents was confirmed for the first time by using GC x GC-ECNI qMS in the scan mode and a significantly improved limit of detection was achieved for BDEs (10-150 fg injected) and CDD/Fs (10-700 fg injected) in the selected ion monitoring mode.     

The quadrupole momentQ 2+ of32S

The static quadrupole moment of the first excited 2⁺ state in³²S was determined by comparing, in coincidence with³²S ions backscattered from⁶⁰Ni, the gamma-ray yields of the 2 ₁ ⁺ →0 ₁ ⁺ transitions in both nuclei for bombarding energies around 70MeV. Depending on the sign of the interference term for transitions via the second excited 2⁺ state in³²S, the following two values were determined:Q ₂ ⁺ =(?18±4)e·fm² andQ ₂₊=(?15±4)e·fm².     

Monolayer nanosheets formed by liquid exfoliation of charge-assisted hydrogen-bonded frameworks

Hydrogen-bonded organic frameworks (HOFs) are a diverse and tunable class of materials, but their potential as free-standing two-dimensional nanomaterials has yet to be explored. Here we report the self-assembly of two layered hydrogen-bonded frameworks based on strong, charge-assisted hydrogen-bonding between carboxylate and amidinium groups. Ultrasound-assisted liquid exfoliation of both materials readily produces monolayer hydrogen-bonded organic nanosheets (HONs) with micron-sized lateral dimensions. The HONs show remarkable stability and maintain their extended crystallinity and monolayer structures even after being suspended in water at 80 °C for three days. These systems also exhibit efficient fluorescence quenching of an organic dye in organic solvents, superior to the quenching ability of the bulk frameworks. We anticipate that this approach will provide a route towards a diverse new family of molecular two-dimensional materials.

We report the liquid-phase ultrasonic exfoliation of two layered hydrogen-bonded frameworks into monolayer, micron-sized, and water-stable nanosheets (HONs) connected purely by hydrogen-bonding interactions.