A Modified Z-Type Flow-through Cell for Optical, Electrochemical, and Optoelectrochemical Flow Injection Analysis Measurements

The design and construction of a modified Z-type flow-through cell that can be used for optical, electrochemical, and optoelectrochemical measurements are reported. In optical analysis, the proposed flow cell is placed in the light path of a spectrophotometer and worked as a commercial Z-type optical flow cell. In electrochemical analysis, the working and auxiliary electrodes are two platinum sheets placed at both ends of the cell cavity; the cell cavity is enclosed by two glass windows. The reference electrode is a saturated calomel electrode placed downstream in an overflow tube. The performance of the proposed electrochemical flow cell was studied by analysis of hexacyanoferrate solution as an electroactive species. In optoelectrochemical analysis, the proposed flow cell is operated optically and electrochemically, simultaneously. The flow cell is placed in the light path of a spectrophotometer, constant potential is applied to the electrodes, and the optical and electrochemical signals are recorded simultaneously by the use of two recorders.     

Thermodynamic characterization of weak association equilibria accompanied with spectral overlapping by a SVD-based chemometric method

A singular value decomposition (SVD)-based chemometric method is used for deconvolution of spectral information obtained from a single sample containing an equilibrium system with spectral overlapping at different temperatures. The output of analysis is the association constants at each temperature, thermodynamic parameters and the component spectral profiles. Thermodynamic characterization of charge-transfer complex formation between chloranil and some aromatic hydrocarbons are used as a model system for weak association equilibria and strong component spectral overlapping. The approach can be successfully applied for studying equilibrium systems, which cannot be treated with classical methods like Benesi-Hildebrand method due to the presence of systematic errors.     

Molecular emission cavity analysis: Part 27. Indirect Determination of Selenium,Tellurium, Arsenic and Antimony After Extraction as their Diethyldithiocarbamates

Measurement of S₂ emission of the diethyldithiocarbamates of As, Sb, Se and Te extracted into tetrachloromethane gives detection limits of 50, 150, 50 and 70 pg (in 5 μl), respectively. Tellurium in the presence of Se, and Sb in the presence of As, can be determined by extraction at pH 9.0. Calibration graphs are linear up to ca. 1 mg l^?1.     

Rapid kinetic determination of silver (I), using in-cuvette mixing and computerized data acquisition

 The determination of silver(I) based on its catalytic effect on the oxidation of indigo carmine with hexacyanoferrate(III) is described. The reaction is monitored spectrophotometrically by means of a home-made rapid system with computer data acquisition. The decrease in absorbance of indigo carmine at 612 nm, pH 6 and at a fixed concentration of hexacyanoferrate(III) and indigo carmine is proportional to the concentration of Ag(I). The acquired data based on the initial rate and fixed time are processed. Up to 100.0 μg/ml of silver are determined. The limit of detection and average relative standard deviation are 0.13 μg/ml and 1.9%, respectively. The effect of foreign ions on the determination of silver is also discussed. The proposed method is applied to the determination of Ag(I) in expired photographic film. Received: 17 June 1996 / Revised: 26 July 1996 / Accepted: 2 August 1996     

Single-step calibration, prediction and real samples data acquisition for artificial neural network using a CCD camera

An artificial neural network (ANN) model is developed for simultaneous determination of Al(III) and Fe(III) in alloys by using chrome azurol S (CAS) as the chromogenic reagent and CCD camera as the detection system. All calibration, prediction and real samples data were obtained by taking a single image. Experimental conditions were established to reduce interferences and increase sensitivity and selectivity in the analysis of Al(III) and Fe(III). In this way, an artificial neural network consisting of three layers of nodes was trained by applying a back-propagation learning rule. Sigmoid transfer functions were used in the hidden and output layers to facilitate nonlinear calibration. Both Al(III) and Fe(III) can be determined in the concentration range of 0.25-4 μg ml⁻¹ with satisfactory accuracy and precision. The proposed method was also applied satisfactorily to the determination of considered metal ions in two synthetic alloys.     

Flow injection chemiluminescence determination of sulfide by oxidation with N-bromosuccinimide and N-chlorosuccinimide

A rapid and sensitive flow injection chemiluminescence method is described for the determination of sulfide based on the chemiluminescence generated during its reaction with either N-bromosuccinimide (NBS) or N-chlorosuccinimide (NCS) in alkaline medium. The results of investigation of the sensitized and non-sensitized chemiluminescence reactions are presented. The emission intensity is greatly enhanced for both NBS- and NCS-sulfide chemiluminescence systems if dichlorofluorescein (for NBS-sulfide) and fluorescein (for NCS-sulfide) are presented in the reaction solutions. The methods were applied satisfactorily to the determination of sulfide in spring water samples.     

1H NMR based metabolic profiling in Crohn's disease by random forest methodology

The present study was designed to search for metabolic biomarkers and their correlation with serum zinc in Crohn's disease patients. Crohn's disease (CD) is a form of inflammatory bowel disease that may affect any part of the gastrointestinal tract and can be difficult to diagnose using the clinical tests. Thus, introduction of a novel diagnostic method would be a major step towards CD treatment. Proton nuclear magnetic resonance spectroscopy (¹H NMR) was employed for metabolic profiling to find out which metabolites in the serum have meaningful significance in the diagnosis of CD. CD and healthy subjects were correctly classified using random forest methodology. The classification model for the external test set showed a 94% correct classification of CD and healthy subjects. The present study suggests Valine and Isoleucine as differentiating metabolites for CD diagnosis. These metabolites can be used for screening of risky samples at the early stages of CD diagnoses. Moreover, a robust random forest regression model with good prediction outcomes was developed for correlating serum zinc level and metabolite concentrations. The regression model showed the correlation (R²) and root mean square error values of 0.83 and 6.44, respectively. This model suggests valuable clues for understanding the mechanism of zinc deficiency in CD patients. Copyright © 2014 John Wiley & Sons, Ltd.     

Kinetic spectrophotometric determination of sulfide, using in-cuvette mixing and titration techniques with computerized data acquisition

In-cuvette mixing and titration techniques have been used for the kinetic determination of sulfide based on its inhibition effect on the oxidation of indigo carmine with hexacyanoferrate(III) in the presence of silver. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of indigo carmine at 612 nm. Both initial rate and fixed-time methods were applied to the in-cuvette technique. Using in-cuvette mixing, sulfide up to 1800 ng was determined and detection limit and relative standard deviation for the determination of 120 ng of sulfide were calculated as 23.0 ng and 1.59%, respectively. On the basis of the titration technique, the upper limit of determination was 25 μg of sulfide and detection limit and average relative standard deviation for the determination of 1 μg of sulfide were 0.025 μg and 4.95%, respectively. The effect of foreign ions on the sulfide determination was studied. The proposed methods were applied to the determination of sulfide in water.     

Kinetic spectrophotometric determination of traces of sulfide in nonionic micellar medium

A sensitive kinetic spectrophotometric method for the determination of ng amounts of sulfide has been developed based on the reduction of Azure A by sulfide in the presence of Brij-35 at pH 7. The decrease in absorbance of Azure A at 600 nm is proportional to the concentration of sulfide over the range 25–1400 ng mL^–1. The variables affecting the rate of the reaction were investigated and the optimum conditions were established. The method is simple, rapid, precise, sensitive, and widely applicable. The limit of detection is 17 ng mL^–1, and the relative standard deviation of seven determinations of 500 ng mL^–1 sulfide was 2.1%. The method was applied to the determination of sulfide in spring water.