Observation of several phase transitions in tetrachloro-o-benzoquinone using 35Cl nuclear quadrupole resonance

The temperature dependence of the ³⁵Cl nuclear quadrupole resonance spectra of tetrachloro-o-benzoquinone (TOB) is reported. An analysis of the change in line multiplicities suggests that TOB undergoes three phase changes in going from 77 to 330 K. The transition temperatures have been determined.     

Structural control in self-standing mesostructured silica oriented membranes and xerogels

Large pore (a = 150-200 A) wormlike and highly oriented cubic (IM3m space group) and 2D-hexagonal (P6m) mesostructured xerogels have been reproducibly synthesised by Evaporation-Induced Self Assembly (EISA). Mesostructure control was attained by changing the template (nonionic block copolymer) and water (h = [H2O]/[Si]) ratio.     

Solid-phase extraction using C(18) bonded silica disks: interferences and analysis of chlorotriazines in seawater samples

The interferences in C(18) Empore extraction disks were obtained by processing 5 1. of HPLC water with average blanks of 1 ng/l. A C(19) alkane, plasticizers and the antioxidant Nonox A were identified in the blanks as possible interferences. The extraction of the components of the disks was carried out with methanol, acetonitrile and/or ethyl acetate with subsequent analysis by gas chromatography-mass spectrometry (GCMS). The identification of interferences was a requirement for the determination of the chlorotriazine herbicides atrazine and simazine, and of a transformation product, de-ethylatrazine, at concentration levels varying between 2 and 140 ng/l. Seawater samples of 3-28 parts-per-thousand were pre-filtered through a 47-mm diameter of 0.7 mum and subsequently with 0.45 mum glass-fibre filters to trap particulate matter, followed by Empore extraction disks of 500 mg C(18) bonded silica. Water volumes of 5 1. could be processed within 150 min. The disks were extracted with methanol, the extract was blown down under nitrogen, and the analytes were quantified by GC with nitrogen-phosphorus detection (NPD) with further confirmation using GCMS in the selected ion monitoring (SIM) mode. The proposed method has been applied to the determination of the environmental levels of atrazine and simazine in seawater samples of varying salinity. The recovery of de-ethylatrazine was 10%, so the method was not appropriate for this compound. The concentration of the herbicides has been plotted against the salinity values, showing a decrease in the levels as the salinity increases, with two inflexion points that indicate a non-conservative mixing with loss of the herbicides in the mixing zone of the estuary.     

Determination of chloroquine in biological material by gas-liquid chromatography (author's transl)]

A method is developed for the gas chromatographic determination of chloroquine after extraction from biological material, using medazepam as the internal standard and a column filled with 3% OV-17 on Gas-Chrom Q. The detection limits are: 0.15 mug/ml of urine, 0.25 mug/ml of whole blood, and 1.50 mug/g of tissue. The technique can be applied in toxicological analysis and in monitoring drug levels.     

Simultaneous spectrofluorimetric determination of the rare earths with calcein

The reactivity of the fluorescent reagent calcein with the trivalent cations of the rare earths has been spectrofluorimetrically studied in aqueous solution. Optimum excitation and emission wavelengths were 492-497 and 519-522 nm, respectively. Optimum pH was in the range 6.0-9.2. The stoichiometry of the complexes was 1:1. A direct, rapid and sensitive method for the determination of rare earth mixtures has been proposed with a detection limit of 4.49x10(-8) M and a coefficient of variation of 0.82%.