Validated LC–MS/MS method for quantification of agomelatine in human plasma and its application in a pharmacokinetic study

An analytical method based on liquid–liquid extraction has been developed and validated for analysis of agomelatine in human plasma. Fluoxetine was used as an internal standard for agomelatine. A Betasil C18 (4.0 × 100 mm, 5 µm) column provided chromatographic separation of analytes followed by detection with mass spectrometry. The method involves simple isocratic chromatographic conditions and mass spectrometric detection in the positive ionization mode using an API‐4000 system. The proposed method has been validated with linear range of 0.050–8.000 ng/ml for agomelatine. The intra‐run and inter‐run precision values are within 12.12% and 9.01%, respectively, for agomelatine at the lower limit of quantification level. The overall recovery for agomelatine and fluoxetine was 67.10% and 72.96%, respectively. This validated method was used successfully for analysis of plasma samples from a pharmacokinetic study. Copyright © 2012 John Wiley & Sons, Ltd.     

On permanents of positive semidefinite matrices

It is shown in an elementary way that if A and B are positive semidefinite matrices, then per(A + B) ? per A + per B. The conditions under which equality may occur in this inequality are completely described, and some consequences are given.     

Oxidation of selenite by alkaline ferricyanide using osmium tetroxide as a catalyst

Summary Oxidation of selenite to selenate by alkaline ferricyanide catalysed by osmium tetroxide was followed by direct and indirect procedures. Either the ferrocyanide was titrated with selenite solution at 8–10% overall alkalinity or vice versa using amperometric or potentiometric end point. In the indirect procedure the excess ferricyanide was determined by amperometric titration with arsenious oxide at 10–15% alkalinity, and the ferrocyanide with ceric sulphate using o-phenanthroline or amperometric indicator. A cerimetric determination of ferricyanide based on this reaction is described.Sincere thanks of the authors are due to Dr. S. S. Joshi, D. Sc. (London), for kind interest in the work.     

Influence of surfactant and annealing temperature on optical properties of sol–gel derived nano-crystalline TiO2 thin films

Titanium dioxide thin films have been synthesized by sol–gel spin coating technique on glass and silicon substrates with and without surfactant polyethylene glycol (PEG). XRD and SEM results confirm the presence of nano-crystalline (anatase) phase at an annealing temperature of 300 °C. The influence of surfactant and annealing temperature on optical properties of TiO₂ thin films has been studied. Optical constants and film thickness were estimated by Swanepoel's (envelope) method and by ellipsometric measurements in the visible spectral range. The optical transmittance and reflectance were found to decrease with an increase in PEG percentage. Refractive index of the films decreased and film thickness increased with the increase in percentage of surfactant. The refractive index of the un-doped TiO₂ films was estimated at different annealing temperatures and it has increased with the increasing annealing temperature. The optical band gap of pure TiO₂ films was estimated by Tauc's method at different annealing temperature.     

Fragmentation dynamics of the methanol dication

Formation of di- and tri-atomic hydrogen molecular ions during the fragmentation of methanol dication is investigated by coincidence momentum imaging. Site-specific probability for such associative break-ups is determined. Two-body and three-body break-up channels involving association and migration of H atoms are identified. Three-body associative break-ups are found to occur sequentially, triggered by the loss of one H atom, followed by separation of charges. Based on the fragment momentum distributions we propose that H atom migration is induced in the first stage of a three-body sequential break-up, and suggest a structure for the intermediate dication.     

Application of colorimetric end-point to iodate : Procedures in presence of mercuric mercury

In the present investigations colorimetric titrations of arsenic(III), hydrazinc, thiosulphate and thiocyanate have been carried out by iodate procedures in the presence of mercuric ions. A Hilger Spekker absorptiometer unit (H 760) with a blue filter having a maximum transmission in the range of 450–500 mμ was employed for the titrations. Two end-points corresponding, respectively, to the reduction of iodate to iodide and the oxidation of the liberated iodide to iodine monochloride were obtained in HCl medium, the quantitative reduction of iodate to iodide being facilitated by the presence of mercuric ions. A study of the effect of the variation of acidity and dilution of the solution was carried out for both the end-points. As little as 5 mg of the reductants, could be determined with a precision of about 97% to 98%.     

Stable periodic motions of an impact-pair

The asymptotically stable motion of two rigid masses separated by a clearance is formulated most generally when the masses collide periodically. Predictions are shown to agree satisfactorily with comprehensive experimental results. Difficulties encountered in the practical application of this and similar stability theories are discussed with the help of empirical data. A technique is proposed for determining a clearance's dimensions in situ which could provide a basis for detecting progressive wear in mechanisms like gear trains.     

Doubly stochastic matrices with equal subpermanents

It has been conjectured that if A is a doubly stochastic n>× n matrix such that per A(i, j)≥perA for all i, j, then either A = J_n, then n × n matrix with each entry equal to $\text{1}\text{n}$, or, up to permutations of rows and columns, $\text{A =}\text{1}\text{2}\text{(I}{}_{\mathrm{n}}\text{+ P}{}_{\mathrm{n}}\text{)}$, where P_n is a full cycle permutation matrix. This conjecture is proved.