Mercury Speciation in Fish by High-Performance Liquid Chromatography (HPLC) and Post-Column Ultraviolet (UV)-Photochemical Vapor Generation (PVG): Comparison of Conventional Line-Source and High-Resolution Continuum Source (HR-CS) Atomic Absorption Spectrometry (AAS)

An ultraviolet-photochemical generator (UV-PVG) capable of post-column on-line transformation of both organic and inorganic mercury species to cold vapor (Hg⁰) with subsequent detection by quartz tube-atomic absorption spectrometry (QT-AAS) was developed. Mercury(II), methylmercury(I), ethylmercury(I), and phenylmercury(I) were successfully detected after separation by reversed-phase high-performance liquid chromatography (RP-HPLC). Two types of AAS detectors were compared. The first was a commonly used line-source instrument while the second was a high-resolution continuum source (HR-CS) AAS. The latter provided better limits of detection: 0.47?µg?L^?1 for Hg(II), 0.84?µg?L^?1 for methylmercury(I), 0.80?µg?L^?1 for ethylmercury(I), and 2.0?µg?L^?1 for phenylmercury(I). The repeatability at 30?μg?L^?1 was 3.6%, 4.1%, 6.2%, and 4.5% for these species (n?=?10). These figures of merit were comparable with those reported for more sensitive atomic fluorescence spectrometry. Nine sample extraction procedures were investigated. Extraction by tetramethylammonium hydroxide and HCl at 75?°C was selected as the only method compatible with the proposed separation and detection steps providing high extraction efficiency and no changes in mercury speciation. The applicability of the proposed high-performance liquid chromatography–ultraviolet-photochemical vapor generation–quartz tube-atomic absorption spectrometry method was demonstrated using fish samples and certified reference materials (CRM) DOLT-4 (dogfish liver) and ERM-CE464 (tuna fish). The results were comparable to those obtained by a reference method based on L-cysteine extraction and high-performance liquid chromatography–inductively coupled plasma-mass spectrometry (HPLC–ICP-MS) determination.     

Theory and applications of ion-selective electrodes Part III

This review of ion-selective electrodes is arranged in the same way as Parts I and II. The continuous growth of the whole subject should be noted. Theory has particularly progressed through mechanistic studies. Among new types of electrodes, ISFET systems have become important. Among new applications of both solid and liquid membrane electrodes, the fluoride electrode still predominates, closely followed by potassium electrodes. In the field of biological and medical applications, the steady growth is significant. More than 800 papers published between mid-1976 and the end of 1978 are mentioned in the review.     

Magnetic and spectral properties of the coligand isomer pair: Cu{N(CN)2}2(pyrazole)2 and Cu{pyrazole · N(CN)2}2

Summary New coligand isomers of composition Cu{N(CN)₂}₂(pz)₂ and Cu{pz · N(CN)₂}₂ (pz = pyrazole) were prepared and studied by measuring their magnetic susceptibilities up to 4.2K and by aid of their e.s.r., ligand field and i.r. spectra. The susceptibility data have been analysed with various models for the exchange-coupled copper(II) polymers. It is shown that the resultant exchange coupling is ferromagnetic for Cu{N(CN)₂}₂(pz)₂ (J 1.1 - 1.4 cm^–1) but antiferromagnetic for Cu{pz · N(CN)₂}₂ (J –0.4 cm^–1). A polymeric chain structure is proposed for Cu{N(CN)₂}₂(pz)₂ havingpseudo-octahedrally coordinated copper(II) and CN-bridging dicyanamide ligands. Its coligand isomer contains anionic chelate ligands, formed by nucleophilic addition between N(CN)₂ and pz in the copper(II) coordination sphere, and giving with this central atom a square-planar system. Definite, but slight axial interaction takes place between these structure units.     

Solid-State NMR Study of Phase Separation and Order of Water Molecules and Silanol Groups in Polysiloxane Networks

Homogeneity and structure of organically modified polysiloxane networks prepared by sol-gel co-condensation, as well as location and nature of water molecules and silanol groups were studied by 1D and 2D solid-state NMR. ¹H–²⁹Si and ¹H–¹H interatomic distances were estimated from variable contact-time CP/MAS experiments, ¹H NMR chemical shifts and off-resonance WISE NMR. A structure model of these networks is proposed and discussed. The fraction of proton-inaccessible units Q⁴ in the networks decreases with increasing amounts of dimethylsiloxane (D) and methylsiloxane (T) units. In contrast to systems prepared by co-condensation of tetraethoxysilane (TEOS) with dimethyl(diethoxy)silane (DMDEOS), proton-inaccessible units form essential fraction in networks prepared by co-condensation of TEOS with methyl(triethoxy)silane (MTEOS). The proton-accessible part of the networks with high O/Si ratios is nano-heterogeneous phase, which is composed of water containing Q ⁱ particles separated by copolymer domains. The overall homogeneity and uniformity of binding sites around silanol groups increases by co-condensation TEOS with DMDEOS or MTEOS, while the amount of physisorbed water as well as the hydrogen bond strength decreases, as compared with neat silica gel prepared by polycondensation of TEOS.     

Transient absorption and laser output of YAG : Nd

YAG : Nd grown under 98% Ar 2% H₂ protective atmosphere free of nitrogen or hydrocarbons showed after UV irradiation broad absorption peaked at 1·9×10⁴ cm^–1 which disappeared relatively slowly at room temperature. It was more intensive in oxygen treated samples than in those annealed in hydrogsn. Transient absorption suppresses laser output by the increase of absorption at 0·94×10⁴ cm^–1 (1064 nm) and, particularly in CW mode, by the anomalous rod deformation. YAG : Nd containing Fe ions (2·10^–4 wt%) showed no transient absorption.     

A multi-angle magnetic spectrograph for nuclear reaction studies

A multi-angle magnetic spectrograph for recording spectra of charged particles emitted in nuclear reactions has been built. The apparatus and the beam transport system are described and their parameters are discussed.     

Magnetic Effects in Curved Quantum Waveguides

The interplay among the spectrum, geometry and magnetic field in tubular neighbourhoods of curves in Euclidean spaces is investigated in the limit when the cross section shrinks to a point. Proving a norm resolvent convergence, we derive effective, lower-dimensional models which depend on the intensity of the magnetic field and curvatures. The results are used to establish complete asymptotic expansions for eigenvalues. Spectral stability properties based on Hardy-type inequalities induced by magnetic fields are also analysed.     

Flavin–cyclodextrin conjugates: effect of the structure on the catalytic activity in enantioselective sulfoxidations

A series of flavin–cyclodextrin conjugates has been prepared and tested in the enantioselective oxidations of prochiral aromatic and aliphatic sulfides with hydrogen peroxide. The newly prepared conjugates contain isoalloxazinium or alloxazinium moieties attached to the primary rim of α- and β-cyclodextrins at the C-6 positions. In addition, flavinium units were attached to the secondary rim of the β-cyclodextrin macrocycle. The relationship between the structural features and the catalytic performance of the conjugates, including those recently reported by us, was analyzed. The rate and enantioselectivity of the sulfoxidations catalyzed by flavin–cyclodextrin conjugates are influenced mainly by the size of the cyclodextrin cavity, the type of flavin unit (alloxazine or isoalloxazine), and by the relative orientation of the flavin and cyclodextrin moieties.