Artificial neural networks for simultaneous spectrophotometric differential kinetic determination of Co(II) and V(IV)

A method for simultaneous analysis of V(IV) and Co(II) has been developed by using artificial neural network (ANN). This method is based on the difference of the chemical reaction rate of V(IV) and Co(II) with Fe(III) in the presence of chromogenic reagent, 1,10-phenanthroline. The reduced product of the reaction, Fe(II), can form a colored complex with 1,10-phenanthroline and make a visible spectrophotometric signal for indirect monitoring of the V(IV) and Co(II) concentrations. Feed forward neural networks have been trained to quantify considered metal ions in mixtures under optimum conditions. The networks were shown to be capable of correlating reduced spectral kinetic data using principal component analysis (PCA) of mixtures with individual metal ion. In this way an ANN containing three layers of nodes was trained. Sigmoidal and linear transfer functions were used in the hidden and output layers, respectively, to facilitate nonlinear calibration. Both V(IV) and Co(II) were analyzed in the concentration range of 0.1-4.0 μg ml⁻¹. The proposed method was also applied satisfactorily to the determination of considered metal ions in several synthetic and water samples.     

Highly sensitive and selective measurements of cobalt by catalytic adsorptive cathodic stripping voltammetry

A very sensitive and selective catalytic adsorptive cathodic stripping procedure for trace measurements of cobalt is presented. The method is based on adsorptive accumulation of the cobalt-MTB (methyl thymol blue) complex onto a hanging mercury drop electrode, followed by reduction of the adsorbed species by voltammetric scan using differential pulse modulation. The reduction current is enhanced catalytically by nitrite. The optimum conditions for the analysis of cobalt include pH 9.0 (ammonia buffer), 2.0 μM methyl thymol blue, 0.8 M sodium nitrite and an accumulation potential of −0.5 V (versus Ag/AgCl). The peak current is proportional to the concentration of cobalt over the entire concentration range tested (0.02–500 ng ml⁻¹) with a detection limit of 0.005 ng ml⁻¹ for an accumulation time of 60 s. The method was applied to determination of cobalt in a mineral water sample and some analytical grade salts with satisfactory results.     

Synthesis and cytotoxicity of novel chromenone derivatives bearing 4-nitrophenoxy phenyl acryloyl moiety

This work describes synthesis of novel chromenone derivatives bearing 4-nitrophenoxy phenyl acryloyl moiety through the reaction of 4-(4-nitrophenoxy)benzaldehydes and 3-acetyl-2H-chromen-2-ones in refluxing toluene. Cytotoxicity of all compounds was evaluated using a tetrazolium (MTT) colorimetric assay against human breast cancer cell line, MDA-MB-231.     

Design of an optical sensor for indirect determination of isoniazid

The characterization of an optical sensor membrane is described for indirect determination of isoniazid. The sensing membrane was consisted of immobilized 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine (PDT) on a triacetylcellulose membrane. The procedure is based on the reaction of Fe(III) with isoniazid in the presence of PDT. Fe(III) is reduced by isoniazid to Fe(II) which forms a complex with PDT. The complex shows an absorption maximum at 558nm. By measuring the absorbance of the complex at this wavelength, isoniazid can be determined in the range of 0.62-6.15mugmL(-1). This method was applied to the determination of isoniazid in pharmaceutical formulation and enabled the determination of isoniazid in microgram quantities.     

Independent component analysis of 2-D electrophoresis gels

We present a novel application of independent component analysis (ICA), an exploratory data analysis technique, to two-dimensional electrophoresis (2-DE) gels, which have been used to analyze differentially expressed proteins across groups. Unlike currently used pixel-wise statistical tests, ICA is a data-driven approach that utilizes the information contained in the entire gel data. We also apply ICA on wavelet-transformed 2-DE gels to address the high dimensionality and noise problems typically found in 2-DE gels. Also, we use an analysis-of-variance (ANOVA) approach as a benchmark for comparison. Using simulated data, we show that ICA detects the group differences accurately in both the spatial and wavelet domains. We also apply these techniques to real 2-DE gels. ICA proves to be much faster than ANOVA, and unlike ANOVA it does not depend on the selection of a threshold. Application of principal component analysis reduces the dimensionality and tends to improve the performance by reducing the noise.     

Direct Electrochemistry and Electrocatalytic Properties of Hemoglobin Immobilized on Carbon Nanotubes Ionic Liquid Electrode

Hemoglobin (Hb) was directly immobilized on a multiwalled carbon nanotubes ionic liquid electrode by immersing this electrode in a solution consisting of Hb and 1‐octyl‐pyridinium chloride as an ionic liquid. The immobilized Hb displayed a pair of well‐defined cyclic voltammetric peaks with a formal potential of ?0.187 V in acetate buffer solution, pH 5.0. This modified electrode exhibits fast response, a long linearity range, a low detection limit, high stability and excellent sensitivity through hydrogen peroxide detection with a detection limit (3σ) of 3.18 µM. The electrode was also used for electrocatalysis and voltammetric determination of oxygen and trichloroacetic acid.     

Active methods to control periodic acoustic disturbances invoking Q-learning techniques

This paper presents a new solution to the Active Noise Control problem based on the Q-learning algorithm. Unlike other common methods, this feedback method does not require any additional information about the primary and secondary transfer functions and it is fully robust to subsystems dynamics changes. The basic method is addressed for periodic acoustic disturbances at first. A number of challenges such as the need for the large memory block and long convergence time have led to the establishment of some new suggestions. These modifications have improved the system performances and decreased the computational burden. It is shown by simulation that these methods are robust not for in the subsystems dynamics changes but also at the presence of measurement noise.     

Silver‐Palladium Nanoalloys Modified Carbon Ionic Liquid Electrode with Enhanced Electrocatalytic Activity Towards Formaldehyde Oxidation

Electrocatalysis of the oxidation of formaldehyde on silver‐palladium‐modified carbon ionic liquid electrode (AgPd/CILE) was investigated in 0.1 M NaOH. The electrochemical performance of the AgPd/CILE was compared with those of Pd/CILE and Ag/CILE. Ag plays an important role in the catalytic performance of AgPd nanocatalyst and yields an excellent antifouling effect. Amperometric measurements showed that AgPd/CILE is a promising sensor for the detection of formaldehyde in the range of 10.0 µM–70.0 mM with a sensitivity of 240.6 µA mM^?1 cm^?2 and a detection limit of 2 µM. The method is free from interference of methanol, ethanol and formic acid.     

Wide range pH measurements using a single H(+)-selective chromoionophore and a time-based flow method

A hydrophilic transparent triacetyl cellulose membrane was adopted as a pH optode by immobilizing highly selective and sensitive Nile blue indicator on the membrane. Contrary to the common procedure for determinations using optodes, in which a steady state response is measured, a new approach is introduced in which the dynamic response of the optode is used as the analytical signal. While in common procedures, pH optodes exhibit limited linear dynamic range (often 2–4 pH units only), it is shown that in a time-based flow method, an optode with only one acid-base indicator can be used for measurement in the pH range of 0–10. The procedure is simple, inexpensive and rapid.     

Kinetic study and UV–Vis spectra of 1:2 complexation of free base para‐substituted meso‐tetraphenylporphyrins with trimethylsilyl chloride

The UV–Vis spectra for 1:2 complexation of four different para‐substituted meso‐tetraphenylporphyrin (H₂t(4‐X)pp) and meso‐tetraphenylporphyrins (H₂tpp) with trimethylsilyl chloride (TMSC) displayed large and different redshifts (28–32.4 nm) of Soret and (15–41.7 nm) Q_(0‐0) bands, whereas 1:2 complexation of the less flexible tetramesitylporphyrin (H₂tmp) with TMSC led to rather small redshift (24.8 nm) of the Soret band and blueshift (−7.4 nm) of the Q_(0‐0) band. The varying spectral behavior for the porphyrins complexation seems to essentially reflect the different extent of π‐interactions between the meso‐aryl groups and the presumably saddled porphyrin macrocycle, through their relative coplanarity. The observed order of the rate constants for the complexation of various para‐substituted porphyrins, H₂t(4‐OCH₃)pp (9.27 ± 0.03) × 10⁻³ > H₂t(4‐CH₃)pp (6.68 ± 0.05) × 10⁻³ > H₂tpp (3.2 ± 0.05) × 10⁻³ > H₂t(4‐Cl)pp (8.36 ± 0.06) × 10⁻⁴, clearly demonstrated a higher reaction rate for the porphyrins containing para‐substituents with stronger electron donor ability. The calculated order for porphyrins (0.9 ± 0.1) and for TMSC (1.0 ± 0.1) suggests rate = K[Por][TMSC] for the complexation. Attempts were made to explain the absence of spectral evidence for the presence of an intermediate 1:1 (TMSC) Por adduct in terms of its high reactivity and/or relative instability. © 2007 Wiley Periodicals, Inc. 39: 231–235, 2007