Nonlinear Optical Properties of Novel Metallophthalocyanines

Journal of Applied Spectroscopy - Detailed measurements of nonlinear optical properties and optical limiting for four phthalocyanine (Pc) derivatives (PcCo, PcCu, PcMn, and PcSi) are reported. The...     

Non-Parametric Regression Methods

The nature of the financial time series is complex, continuous interchange of stochastic and deterministic regimes. Therefore, it is difficult to forecast with parametric techniques. Instead of parametric models, we propose three techniques and compare with each other. Neural networks and support vector regression (SVR) are two universally approximators. They are data-driven non parametric models. ARCH/GARCH models are also investigated. Our assumption is that the future value of Istanbul Stock Exchange 100 index daily return depends on the financial indicators although there is no known parametric model to explain this relationship. This relationship comes from the technical analysis. Comparison shows that the multi layer perceptron networks overperform the SVR and time series model (GARCH).     

Phenol biosensor based on electrochemically controlled integration of tyrosinase in a redox polymer

An amperometric biosensor for the detection of phenolic compounds was developed based on the immobilization of tyrosinase within an Os-complex functionalized electrodeposition polymer. Integration of tyrosinase within the redox polymer assures efficient catechol recycling between the enzyme and the polymer bound redox sites. The non-manual immobilization procedure improves the reproducibility of fabrication process, greatly reduces the desorption of the enzyme from the immobilization layer, and, most importantly prevents fast inactivation of the enzyme by its substrate due to fast redox cycling. A two-layer sensor architecture was developed involving ascorbic acid oxidase entrapped within an electrodeposition polymer in a second layer on top of the redox polymer/tyrosinase layer. Using this sensor architecture it was possible to eliminate the current interference arising from direct ascorbate oxidation up to a concentration of 630 μM ascorbic acid. The effects of the polymer thickness, the enzyme/polymer ratio, and the applied potential were evaluated with respect to optimal sensor properties. The sensitivity of the optimized sensors for catechol was 6.1 nA μM⁻¹ with a detection limit of 10 nM, and for phenol 0.15 nA μM⁻¹ with a detection limit of 100 nM.     

Synthesis and polymerization of a new nitrogen‐containing bis‐ortho‐diynylarene monomer

This study focuses on the preparation, characterization, and optical properties of new bis(3,4‐diphenylethynylphenyl)phenylamine. This is the first nitrogen‐containing bis‐ortho‐diynylarene (BODA) monomer having a nitrogen atom as the spacer group. BODA monomers are usually prepared from common bisphenols, thereby providing great synthetic versatility and the opportunity to develop a wide array of novel polyarylene thermosets by varying the aromatic spacer group. The new bis(3,4‐bisphenylethynylphenyl)phenylamine was synthesized in five steps. This compound emits an intense blue color (λ = 438 nm) upon irradiation by UV light and may be suitable for use as an emitting layer in electroluminescent devices. Bis‐(3,4‐bisphenylethynylphenyl)phenylamine and its polymer have photoluminescence quantum yields 34 and 38%, respectively, and long excited‐state lifetimes of 3.2 and 3.6 ns, respectively. The structure of the monomer and its polymer were characterized using spectroscopic techniques including Ultraviolet–visible Spectrophotometer, Photoluminescence Spectrophotometer, Fourier Transform infrared spectroscopy, and Gel Permeation Chromatography. The polymerizations were studied by Differential Scanning Calorimeter. The amount of weight loss and the thermostability of the nitrogen‐containing polymer were determined from thermogravimetric analysis. The electrical conductivity of neat HCl‐doped BODA‐derived polymer film was measured according to the standard four‐point probe technique. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6988–6996, 2006     

Determination of trace elements in marine plankton by inductively coupled plasma mass spectrometry (ICP-MS)

A method has been developed for the determination of 23 elements in marine plankton in which inductively coupled plasma (ICP) source mass spectrometry (MS) was used to quantify the elements in the solution after digestion in a mixture of hydrofluoric and nitric acids in sealed PTFE vessels in a microwave field. The procedure was validated by the analysis of a standard reference soil (SRM 2709 San Joaquin Soil) and a standard reference fresh water plankton (CRM 414). The method was applied to the analysis of several marine plankton samples grown under controlled conditions including several whose growth media had been enriched with selenium. Matrix induced signal suppressions and instrumental drift were corrected by internal standardization. The suitabilities of germanium, indium, rhodium, scandium and yttrium as internal standard elements were evaluated. Neither scandium nor yttrium could be used due to the presence of these elements in the samples, germanium was used for the determination of As, Co, Cu, Fe, Ni, Se, Si and Zn, indium was used for Al, Ba, Ca, Eu, Sr, and Tl, and rhodium was used for Cd, Cr, Hg, Mg, Pb, Sb, Sn, and V. For Al, Ca, Cr, Cu, Fe, Mg, Mn, Ni, Si, Sr, V, and Zn internal standardization did not completely compensate for the suppressive effect of the heavier elements and the solutions were diluted. However, for As, Ba, Cd, Co, Eu, Hg, Pb, Sb, Se, Sn and T1, it was possible to obtain accurate results despite the 35-40% suppression in the signals. Isobaric overlap was only a problem in the cases of 42Ca and 78Se; 44Ca and 77Se, respectively, were used. Memory effects were only observed with Hg for which a nitric acid-sodium chloride solution was the most effective wash-out solution. The marine plankton samples were able to tolerate a higher concentration of Hg as the selenium concentration increased.     

Determination of calcium, magnesium and strontium in soils by flow injection flame atomic absorption spectrometry

Several procedures for the determination of Ca, Mg and Sr in soils have been compared on the basis of the accuracy of analysis of two NIST reference materials (Montana Soils SRM 2710 and SRM 2711). Samples were dissolved in a mixture of hydrofluoric and nitric acids in sealed vessels in a microwave oven and in teflon beakers on a hot plate. The digests obtained from both dissolution methods were evaporated to dryness in an attempt to remove silicon. Boric acid was added to prevent the precipitation of the lanthanum releasing agent (as lanthanum fluoride) and potassium was added as an ionization buffer. Determinations were made by flame atomic absorption spectrometry with both the nitrous oxide-acetylene flame and the air-acetylene flame, with calibration either by standard additions or against external standards matrix matched with respect to nitric acid, boric acid, lanthanum and potassium. The silicon remaining in the solution was also determined by external calibration. A single-line flow injection manifold was used to overcome any problems due to the presence of high dissolved solids. A volume of 300 mul was injected into a water carrier stream flowing at 8 ml min(-1). To determine Ca in the air-acetylene flame, it was necessary to remove silicon. Magnesium was determined in either flame without complete removal of the silicon, however, for the determination of Sr, it was necessary to remove the silicon and use the nitrous oxide-acetylene flame. The indicative value for Sr in SRM 2710 was too low: the value determined was 360+/-30 mug g(-1).     

Analysis of fish otoliths by electrothermal vaporization inductively coupled plasma mass spectrometry: aspects of precipitating otolith calcium with hydrofluoric acid for trace element determination

A method is developed for determination of trace elements, including Ag, As, Cd, Co, Cr, Cu, Mn, Ni, Se, Tl and Zn, in fish otoliths by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS). Hydrofluoric acid was used to precipitate calcium resulting from acid dissolution of otolith calcium carbonate. Initial acidity of the sample solution influenced the precipitation efficiency of calcium fluoride. Up to 99.5% of Ca was precipitated in solutions that contained less than 2% (v/v) HNO₃. Recoveries of the elements obtained from spiked artificial otolith solutions were between 90 and 103%. Stabilization of the elements within the ETV cell was achieved with 0.3 μg Pd/0.2 μg Rh chemical modifier that also afforded optimum sensitivity for multielement determination. The method was validated by the analysis of a fish otolith reference material (CRM) of emperor snapper, and then applied to the determination of the trace elements in otoliths of several fish species captured in Raritan Bay, New Jersey. Results indicated that fish physiology and biological processes could influence the levels of Cu, Mn, Se and Zn in the otoliths of fish inhabiting a similar aqueous environment. Otolith concentrations of Cr and Ni did not show any significant differences among different species. Concentrations for Ag, As, Cd, Co and Tl were also not significantly different, but were very low indicating low affinity of otolith calcium carbonate to these elements.     

Slurry sampling for determination of lead in marine plankton by electrothermal atomic absorption spectrometry

A slurry sampling method has been developed for the determination of Pb in marine plankton by ETAAS using a freshwater plankton certified reference material (CRM 414). Slurries were prepared in 1–3% m/v range with 1% v/v HNO₃ by ultrasonic agitation for 5 min. The effects of several chemical modifiers, including Ir(NO₃)₂, Mg(NO₃)₂, Pd(NO₃)₂, Pd(NO₃)₂ + Mg(NO₃)₂, and Mg(NO₃)₂ + NH₄H₂PO₄, were investigated for the stabilization of Pb during thermal pretreatment. Lead in slurries was effectively stabilized up to 1000 °C with Ir, Pd and Pd + Mg modifiers among which Pd + Mg provided the best results with complete atomization at 1850 °C. Firings in the presence of Ir were, problematic due to ash formation inside the atomizer. Water, dilute HNO₃ and HF were examined as suspension medium. Dilute HNO₃ (1–2% v/v) proved to be advantageous over water as it afforded extraction of Pb from plankton almost quantitatively in 5 min agitation. Hydrofluoric acid was the least suitable medium. Increasing HF concentration up to 5% v/v resulted in inaccuracy and substantial background absorption. Fast-heating furnace method provided comparable accuracy and precision to that of conventional-heating in slurries of CRM 414. Detection limits and characteristic masses were, respectively, 0.49 μg L^− 1 and 32 pg for the conventional method and 0.62 μg L^− 1 and 37 pg for the fast-heating method. However, fast-heating approach suffered from distorted peaks at high temperatures and incomplete pyrolysis of matrix at lower temperatures. Analysis of marine plankton samples for Pb was performed by using the conventional furnace program. The results showed a high correlation with those obtained by solution ICP-MS. Differences were statistically insignificant within 95% confidence interval.