Headspace solid phase microextraction for the analysis of the new antifouling agents Irgarol 1051 and Sea Nine 211 in natural waters

A simple and rapid extraction method based on headspace solid phase microextraction (HS-SPME) has been developed for the analysis of two antifouling agents, currently licensed for use in marine antifouling paints. Irgarol 1051 and Sea Nine 211 were extracted from aqueous solutions using polydimethylsiloxane-divinylbenzene (PDMS-DVB) 65 μm fiber and analyzed by gas chromatography (GC) with flame thermionic, electron capture and mass spectrometric detection. The extraction time, addition of Na₂SO₄ and the influence of organic matter, such as humic acid on extraction efficiency were examined in order to achieve a sensitive method. The optimized procedure was applied to spiked natural waters, such as sea water, river water and lake water in a concentration range of 0.5-50 μg l⁻¹ in order to obtain the analytical characteristics. The linear calibration curve obtained (R²>0.990) for both analytes indicate that the presence of interfering compounds had no significant effect due to the high affinity of both analytes to the PDMS-DVB 65 μm fiber coating. Recoveries were in relatively high levels over >82% in all types of natural waters. The limits of detection (LODs) ranged from 0.002 to 0.030 μg l⁻¹, depending on the detector and the compound investigated, with relative standard deviations in the range of 3-12% at all concentration levels tested. Finally, the proposed method was applied in real water samples from different marinas of Epirus region (NW Greece) in order to investigate its performance in precise and routine environmental analysis.     

Off-Line Concentration of Bisphenol A and Three Alkylphenols by SPE then On-Line Concentration and Rapid Separation by Reverse-Migration Micellar Electrokinetic Chromatography

A method for separation of four environmentally important compounds (three alkylphenols and bisphenol A) by cyclodextrin-modified reverse-migration micellar electrokinetic chromatography (CD-RM-MEKC) has been optimized. On-line concentration, stacking using reverse-migrating micelles and a water plug (SRW), was used to improve the limit of detection. Two main factors affecting the efficiency of enhancement by SRW, injection sample length and water-plug length, are discussed in detail. Compared with the normal 2-s injection, more than 121-fold enhancement of peak area and more than 71-fold enhancement of peak height were achieved with 120-s sample injection after 120-s water-plug injection. With this optimized separation method and SRW technology, limits of detection were found to be 0.089, 0.030, 0.0091, and 0.033 mg L^–1 for 4-nonylphenol, 4-tert-octylphenol, bisphenol A, and 4-tert-butylphenol, respectively. Calibration plots (R² 0.9968) and relative standard deviations (RSD, %) of corrected peak areas and migration time were also satisfactory. Combined with off-line concentration by solid-phase extraction (SPE) this method might be used to determine these contaminants at ppb levels in groundwater samples.     

A density functional study of N NQR parameters of imidazole derivatives and extrapolation to PfHRP2–Fe-PPIX complex

In this paper, density functional theory (DFT) was used to calculate ¹⁴N nuclear quadrupole coupling constants (NQCC), χ, and asymmetry parameters, η, for a series of imidazole derivatives: imidazole, 5-methylimidazole and histidine. These calculations were carried out with the PW91P86 method via the Gaussian 98 package. A systematic theoretical investigation of the different environmental effects on (χ, η) values of amino ¹⁴N1 and imino ¹⁴N2 of imidazole ring of these compounds, reveals that the local surrounding of nitrogen atoms play an important role in determining their χ and η values. Our calculations in solution show that adding explicit solvent molecules to the polarizable continuum model (PCM) has a strong effect on (χ, η) values, thereby indicating that for long-range effects, PCM, is not sufficient to describe the whole solvent effects. We also evaluate the influence of [Fe³⁺ (S = 1/2)] on the (χ, η) values of proximal and remote nitrogens of an axial ligand and compare with those of free ligands. The results show that Fe³⁺ has a strong effect on the (χ, η) values of proximal nitrogen unlike remote nitrogen. Finally, our results predict (χ = 1.56 MHz, η = 0.690) for proximal nitrogen and (χ = 2.75 MHz, η = 0.169) for remote nitrogen in PfHRP2–Fe³⁺-PPIX complex.     

Recognition characteristics of dibenzofuran by molecularly imprinted polymers made of common polymers

Dibenzofuran (DBF) recognition was studied by a molecularly imprinted polymer (MIP) made of commercially available polymers: polyvinyl chloride (PVC), polysulfone, polystyrene, and polyacrylonitrile. Preparation of MIPs was carried out by phase inversion of the polymer. Respective polymer solutions were coagulated with DBF template in water (non-solvent). In addition, reference polymers without the template were prepared in same manner as unimprinted polymers. After the DBF template was extracted from the solidified polymers by washing with methanol (MeOH), recognition experiments of DBF by the imprinted polymers were carried out for DBF in MeOH solutions. Equilibrium constants for DBF were calculated from saturation binding kinetics. Equilibrium experiment results reveal that recognition was effective for DBF binding to the DBF-imprinted polymer, especially for the imprinted PVC.     

Development and Evaluation of a Kinetic‐Spectrophotometric Method for Determination of Arginine

A kinetic method for the determination of micro quantities of amino acid arginine (Arg) is described in this paper. The catalytic activity of cobalt in the reaction of oxidation of purpurin (1,2,4‐trihydroxy‐antraquinone, PP) by hydrogen peroxide in alkaline buffer solution decreases in the presence of micro quantities of arginine, because of the formation of the complex. Operating conditions for the successful determination of arginine were optimized. The optimized conditions yielded a theoretical detection limit of 1.45 μg mL^?1. Kinetic equations are proposed for the investigated process. The interference effects of certain foreign ions and amino acids upon the reaction rate were studied and removed in order to assess the selectivity of the method. The developed procedure was successfully applied to the determination of arginine in various pharmaceutical samples. The typical feature of this procedure is that determination can be carried out at room temperature and in a short analysis time. The newly developed method is simple, inexpensive and efficient for use in the analysis of a large number of samples.     

Chemical Ecology—A Chapter of Modern Natural Products Chemistry

The chemical reaction of arthropods to their environment, i.e. their chemical ecology, can be studied particularly well with water beetles. Stenus comma, an aquatic beetle weighing only 2.5 mg, saves itself from drowning with the aid of an alkaloid, and the water beetle Ilybius fenestratus defends itself against small mammalian predators with a compound belonging to the same class. The water beetle Platambus maculatus employs a diterpene for precisely the same purpose and the whirligig beetle a norsesquiterpene, which also offers protection against troublesome microorganisms. As chemical artists, the ants can hardly be surpassed. In particular, the myrmecine ants guarantee their food supplies with plant growth substances. Since these compounds, depending upon concentration, can also act as inhibitors, we are confronted with an excellent example of an ecological equilibrium being established with the aid of organic chemicals. Even the little parasitic bombardier beetle Paussus favieri is tolerated, on account of its defensive chemistry, in the nest of the myrmecine ant Pheidole. In contrast, inorganic compounds are largely responsible for the stability of spiders' webs.     

Determination of thiopental in human serum and plasma by reversed-phase high-performance liquid chromatography

Summary A high-performance liquid chromatographic method for the analysis of thiopental in 100l of human serum or plasma is described. The procedure involves protein precipitation with acetonitrile. The supernatant is directly injected into a chromatograph containing a reversed-phase CLC-ODS (Shimadzu) column. A 5050 (v/v) mixture of water-acetonitrile, at a flow-rate of 1.0ml/min is used as the mobile phase. Detection is carried out ata wavelength of 280nm. Total analysis time per sample is 10min. The assay was found to be linear in the range of 0.1 to 120g/ml. Reproducibility was good, with intra-assay coefficients of variation from 1.780 to 3.208% and inter-assay coefficients of variation from 3.241 to 4.860%. The absolute recoveries were 97.4 to 101,4%. Other drugs were tested for potential interference with the assay, but none was found.     

A tandem-flow assembly for the chemiluminometric determination of hydroquinone

A direct chemiluminescent procedure for determination of hydroquinone based on the emergent flow methodology known as multicommutation or tandem-flow is presented for first time. The manifold was based on a set of three channels and three solenoid valves; and, the determination was performed at 60 °C and at flow-rate of 7.5 ml min⁻¹. The complete cycle lasted 35 s, which resulted in a sample flow trough of 103 h⁻¹. The chemical process was the hydroquinone oxidation with the system sulphuric acid-potassium permanganate; and the light emission was clearly enhanced by the presence of quinine sulphate and benzalkonium chloride reaching a detection limit of 30 μg l⁻¹. The dynamic interval was over the range 0.1-15.0 mg l⁻¹ and a large list of interferents were assayed; the chemical robustness was also tested. The method was applied to different type of samples: namely, pharmaceutical formulations, a photographic solution and irrigation and residual superficial waters.     

Use of environmental scanning electron microscopy to image the spore adhesive of the marine alga Enteromorpha in its natural hydrated state

The environmental scanning electron microscope (ESEM) has been used to image the adhesive secreted by zoospores of the marine alga Enteromorpha as they settle on a surface, under natural, hydrated conditions. Results reveal a featureless, swollen gel-like adhesive pad, in contrast to the fibrillar character of the adhesive when imaged by standard SEM. At high spore densities the adhesive is confluent. Dynamic hydration/dehydration events were followed by changing the water vapour pressure in the sample chamber. Rapid hydration and swelling were observed indicating a very hygroscopic material. Adhesive footprints were detected when surfaces from which spores had been removed by water jetting were examined.     

Microwave-assisted extraction versus Soxhlet extraction in the analysis of 21 organochlorine pesticides in plants

A method to determine 21 organochlorine pesticides in vegetation samples using microwave-assisted extraction (MAE) is described and compared with Soxhlet extraction. Samples were extracted with hexane–acetone (1:1, v/v) and the extracts were cleaned using solid-phase extraction with Florisil and alumine as adsorbents. Pesticides were eluted with hexane–ethyl acetate (80:20, v/v) and determined by gas chromatography and electron-capture detection. Recoveries obtained (75.5–132.7% for Soxhlet extraction and 81.5–108.4% for MAE) show that both methods are suitable for the determination of chlorinated pesticides in vegetation samples. The method using microwave energy was applied to grass samples from parks of A Coruña (N.W. Spain) and to vegetation from the contaminated industrial area of Torneiros (Pontevedra, N.W. Spain).