Structure-retention and mobile phase-retention relationships for reversed-phase high-performance liquid chromatography of several hydroxythioxanthone derivatives in binary acetonitrile-water mixtures

The reversed-phase high-performance liquid chromatographic (RP-HPLC) behavior of some newly synthesized hydroxythioxanthone derivatives using binary acetonitrile-water mixtures as mobile phase has been examined. First, the variation in the retention time of each molecule as a function of mobile phase properties was studied by Kamlet-Taft solvatochromic equations. Then, the influences of molecular structure of the hydroxythioxanthone derivatives on their retention time in various mobile phase mixtures were investigated by quantitative structure-property relationship (QSPR) analysis. Finally, a unified model containing both the molecular structure parameters and mobile phase properties was developed to describe the chromatographic behavior of the systems studied. Among the solvent properties, polarity/polarizability parameter (π^*) and hydrogen-bond basicity (β), and among the solute properties, the most positive local charge (MPC), the sum of positive charges on hydrogen atoms contributing in hydrogen bonding (SPCH) and lipophilicity index (log P) were identified as controlling factors in the RP-HPLC behavior of hydroxythioxanthone derivatives in actonitrile-water binary solvents.     

Determination of Cysteine at Bismuth Nanostructure – Carbon Ionic Liquid Electrode by Square Wave Voltammetry

Bismuth nanostructure‐carbon ionic liquid electrode has been employed for sensitive determination of cysteine (Cys). Bismuth nanostructure was incorporated into the carbon ionic liquid electrode (CILE) and applied for determination of cysteine. An interaction was taking place between bismuth nanostructure and the thiol group of cysteine. The bismuth cysteinate complex oxidation potential occurred at more negative potential compared to the cysteine oxidation peak obtained at bare carbon ionic liquid electrode (CILE). Square wave voltammetry (SWV) was used for the determination of the cysteine and satisfactory results were obtained. The calibration curve was linear in the concentration range of 1 to 500 µM and 0.5–2 mM of Cys. A low detection limit of 0.5 µM was achieved for Cys. The electrode showed a good selectivity for determination of cysteine in the presence of other amino acids. The proposed electrode was satisfactory applied for the determination of cysteine in human serum plasma sample.     

Highly Efficient and Stable Palladium Nanoparticles Supported on an Ionic Liquid Silica Sol?Gel Modified Electrode

A carbon ionic liquid electrode modified with a thin layer of silica sol? gel containing phosphinite ionic liquid was prepared for deposition of palladium nanoparticles. Palladium nanoparticles were formed easily by simple contact of the modified electrode with palladium chloride solution. The novel material overcomes the shortcomings of conventionally modified electrodes with a thin layer of silica sol? gel, due to the existence of ionic liquid in silica matrix. A crack‐free sol? gel matrix was obtained and also, the uniform porous structure of the ionic liquid‐sol? gel matrix resulted in a fast mass transport and increased ionic conductivity. The electrode exhibits high electrocatalytic effects towards hydrazine and ascorbic acid. It is very stable against repetitive cycling in the applied potential window.     

Analysis of narcotic drugs in biological samples using hollow fiber liquid�Cphase microextraction and gas chromatography with nitrogen phosphorus detection

We report on a method for trace analysis of the narcotic drugs alfentanil, fentanyl, and sufentanil in plasma and urine. Two?Cphase hollow fiber liquid?Cphase microextraction was combined with GC using nitrogen?Cphosphorus detection. Experimental parameters were optimized to give a viable analytical procedure whose limits of detection range from 8 to 15?ng L^?1 (at an S/N of 3). The calibration curves are linear between 0.1 and 50???g L^?1, with squared correlation coefficients (r ²) between 0.9953 and 0.9979. Precision values range from 2.4% to 3.3% (intra?Cday RSD) and 3.2 to 6.3% (inter?Cday RSD). The relative recoveries varied from 27.8% to 84.6% (for spiked plasma) and 75 to 85.2% (for spiked urine). The method consumes little solvent, is simple, fast, inexpensive, and well suitable for the analysis of complicated matrices.

Application of silica vanadic acid [SiO2-VO(OH)2] as a heterogeneous and recyclable catalyst for oxidative aromatization of Hantzsch 1,4-dihydropyridines at room temperature

A simple method for the oxidative aromatization of Hantzsch 1,4-dihydropyridines to the corresponding pyridines is described using hydrogen peroxide as green oxidant and silica vanadic acid as catalyst in acetonitrile at room temperature. The catalyst can be easily recovered and reused for 15 reaction cycles without considerable loss of activity.     

Spectrophotometric catalytic determination of ultra-trace amounts of selenium based on the reduction of resazurin by sulphide

A sensitive catalytic method for determining ng ml^? concentration of selenium is described. The method is based on the catalytic action of Se(IV) on the reduction of resazurin by sulphide, monitored spectrophotometrically at 605 nm. The linearity range of the calibration graph is dependent on the concentration of sulphide. 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. As low as 8.0 × 10^?4 μg ml^?1 of selenium can be determined. The relative standard deviation of seven determination of 10 ng Se was 0.7%. The determination of Se(IV) in the presence of Se(VI) and the determination of total selenium are also described.     

Investigation of the Role of Ionic Liquids in Imparting Electrocatalytic Behavior to Carbon Paste Electrode

In this paper, a survey has been undertaken to clarify the possible reasons for the electrocatalytic activity obtained by the presence of ionic liquid in carbon paste electrode (CPE). For this purpose, the effect of the addition of traces of ionic liquid to conventional CPE was investigated. Fe(CN)₆^3?/4? was used as a probe and two ionic liquids, namely n‐octylpyridinum hexafluorophosphate and 1‐octyl‐3‐methylimidazolium hexaflourophosphate were tested for their electrocatalytic activity. The reasons for this electrocatalytic behavior were evaluated and it was found that different factors such as increase in the ionic conduction of the binder, decrease in the resistance of the modified electrode, increase in ion exchange properties of the electrode and the inherent catalytic activity of ionic liquids are responsible for the considerable improved electrochemical response obtained in the presence of traces of ionic liquid.     

Indirect determination of cyanide ion and hydrogen cyanide by adsorptive stripping voltammetry at a mercury electrode

An indirect voltammetric method is described for determination of cyanide ions and hydrogen cyanide, using the effect of cyanide on cathodic adsorptive stripping peak height of Cu-adenine. The method is based on competitive Cu complex formation reaction between adenine at the electrode surface and CN⁻ ions in solution. Under the optimum experimental conditions (pH=6.42 Britton-Robinson buffer, 1×10⁻⁴ M copper and 8×10⁻⁷ M adenine), the linear decrease of the peak current of Cu-adenine was observed, when the cyanide concentration was increased from 5×10⁻⁸ to 8×10⁻⁷ M. The detection limit was obtained as 1×10⁻⁸ M for 60 s accumulation time. The relative standard deviations for six measurements were 4 and 2% for the cyanide concentrations of 5×10⁻⁸ and 2×10⁻⁷ M, respectively. The method was applied to the determination of cyanide in various industrial waste waters such as electroplating waste water and also for determination of hydrogen cyanide in air samples.     

Selective Extraction–Spectrophotometric Determination of Traces of Palladium in Catalysts

The simple, sensitive, and highly selective determination of palladium is based on the reaction between Pd(II) and 1,2-bis[methyl(2-aminocyclopentene carbodithioate)] ethane and extraction of the complex into dichloromethane. Beer's law is obeyed in the concentration range 0.19–10 μg ml⁻¹Pd. Relative standard deviations were 0.7–1.1%. The procedure has been successfully applied to the determination of palladium in different samples of catalysts.