Simultaneous estimation of four proton pump inhibitors—lansoprazole,omeprazole, pantoprazole and rabeprazole: development of a novel generic HPLC‐UV method and its application to clinical pharmacokinetic study

A highly selective, sensitive and accurate HPLC method has been developed and validated for the estimation of four proton‐pump inhibitors (PPI), lansoprazole (LPZ), omeprazole (OPZ), pantoprazole (PPZ) and rabeprazole (RPZ), with 500 µL human plasma using zonisamide as an internal standard (IS). The sample preparation involved simple liquid–liquid extraction of LPZ, OPZ, PPZ and RPZ and IS from human plasma with ethyl acetate. The baseline separation of all the peaks was achieved with 0.1% triethylamine (pH 6.0):acetonitrile (72:28, v/v) at a flow rate of 1 mL/min on a Zorbax C₈ column. The total chromatographic run time was 11.0 min and the simultaneous elution of IS, OPZ, RPZ, PPZ and LPZ occurred at approximately 2.42, 4.45, 5.02 and 9.37 min, respectively. The method was proved to be accurate and precise at linearity range of 20.61–1999.79 ng/mL with a correlation coefficient (r) of ≥0.999. The limit of quantitation for each of the PPI studied was 20.61 ng/mL. The intra‐ and inter‐day precision and accuracy values were found to be within the assay variability limits as per the FDA guidelines. The developed assay method was applied to a pharmacokinetic study in human volunteers. Copyright © 2009 John Wiley & Sons, Ltd.     

Base-free monosulfonylation of amines using tosyl or mesyl chloride in water

A mild and efficient procedure has been developed for the monosulfonylation of various amines using mesyl or tosyl chlorides in water at room temperature to afford the corresponding sulfonamides in high yields.     

RP‐HPLC determination of phenylalkanoids and monoterpenoids in Rhodiola rosea and identification by LC‐ESI‐TOF

An HPLC method permitting the simultaneous determination of fourteen analytes (phenylalkanoids and monoterpenoids) from the roots of Rhodiola rosea was developed. A separation was achieved within 35 min using C₁₈ column material and a water–acetonitrile mobile phase, both containing a 0.05% phosphoric acid gradient system and a temperature of 53°C. The method was validated for linearity, repeatability, limits of detection and limits of quantification. The limits of detection and limits of quantification of 14 phenylalkanoids and monoterpenoids were found to be 0.20–1.0 and 0.5–3.5 µg/mL, respectively. The wavelengths used for quantification of phenylalkanoids and monoterpenoids with a diode array detector were 205, 220 and 251 nm. The method was used to analyze the roots of two species of Rhodiola and commercial extracts of R. rosea and provides preliminary evidence of phytochemical differences between North American and Eurasian populations of R. rosea. LC–mass spectrometry coupled with electrospray ionization (ESI) interface method is described for the identification of phenylalkanoids and monoterpenoids in various Rhodiola samples. This method involved the use of the [M + H]⁺, [M + NH₄]⁺ and [M + Na]⁺ ions in the positive ion mode with extractive ion monitoring (EIM). Copyright © 2009 John Wiley & Sons, Ltd.     

Quantitative determination of chemical constituents from seeds of Nigella sativa L. using HPLC-UV and identification by LC-ESI-TOF

An HPLC method was developed for the simultaneous determination of nine compounds of Nigella sativa L. The separation was achieved within 23 min by using C18 column material, a water-acetonitrile mobile phase, both containing 0.1% acetic acid gradient system and a temperature of 35 degrees C. The method was validated for linearity, repeatability, LOD, and LOQ. The LOD and LOQ of nine compounds were in the range of 0.09-10 and 0.3-25 microg/mL, respectively. The wavelength used for quantification with the diode array detector was 205 and 260 nm. LC/MS coupled with electrospray ionization interface method is described for the identification of compounds in N. sativa L. samples. This method involved the use of [M+H]+ and [M+Na]+ ions in the positive ion mode with extracted ion chromatogram.     

Analysis of primaquine and its metabolite carboxyprimaquine in biological samples: enantiomeric separation, method validation and quantification

The clinical formulation of primaquine (PQ) is a mixture of (−)‐(R)‐ and (+)‐(S)‐ primaquine enantiomers which may show different pharmacokinetic and pharmacodynamic properties. To assess the efficacy and toxicity of primaquine enantiomers, a method using LC‐MSD‐TOF has been developed. The enantiomers were well separated using a Chiralcel OD column (250 × 4.6 mm, 10 µm) with a linear gradient of mobile phase consisting of acetonitrile (0.1% formic acid) and aqueous ammonium formate (20 mm ; 0.1% formic acid) adjusted to pH 5.9 at a flow rate of 0.7 mL/min. The method was validated for linearity, precision, accuracy and limits of detection and quantification. The calibration curves were linear with all correlation coefficients being >0.999. The average recoveries of (−)‐(R)‐ and (+)‐(S)‐primaquine and (−)‐(R)‐ and (+)‐(S)‐carboxyprimaquine were 88 and 92%, respectively, in spiked human plasma and 89 and 93% respectively in spiked mouse plasma samples. The RSD of (−)‐(R)‐ and (+)‐(S)‐primaquine and (−)‐(R)‐ and (+)‐(S)‐carboxyprimaquine were 2.15, 1.74, 1.73 and 2.31, respectively, in spiked human plasma and 2.21, 1.09, 1.95 and 1.17% in spiked mouse plasma, respectively. The intra‐day and inter‐day precisions expressed as RSD were lower than 10% in all analyzed quality control levels. The method as reported is suitable for study of the pharmacokinetic and pharmacodynamic properties of the enantiomers of primaquine. The method was successfully applied to study plasma pharmacokinetic profile of enantiomers of primaquine and carboxyprimaquine in mice administered with primaquine in racemic form. The analytical method was found to be linear, accurate, precise and specific. Copyright © 2010 John Wiley & Sons, Ltd.     

Carbon solubility and superconductivity in MgB2

Successful replacement of B by C in the series MgB_2−xC_x for values of x upto 0.3 is reported. Resistivity and ac susceptibility measurements have been carried out in the samples. Solubility of carbon, inferred from the observed change in the lattice parameter with carbon content indicates that carbon substitutes upto x=0.30 into the MgB₂ lattice. The superconducting transition temperature, T_c measured both by zero resistivity and the onset of the diamagnetic signal shows a systematic decrease with increase in carbon content upto x=0.30, beyond which the volume fraction decreases drastically. The temperature dependence of resistivity in the normal state fits to the Bloch–Gruneisen formula for all the carbon compositions studied. The Debye temperature, θ_D, extracted from the fit, is seen to decrease with carbon content from 900 to 525 K, whereas the electron–phonon interaction parameter, λ, obtained from the McMillan equation using the measured T_c and θ_D, is seen to increase monotonically from 0.8 in MgB₂ to 0.9 in the x=0.50 sample. The ratio of the resistivities between 300 and 40 K versus T_c is seen to follow the Testardi correlation for the C substituted samples. The decrease in T_c is argued to mainly arise due to large decrease in θ_D with C concentration and a decrease in the hole density of states at N(E_F).     

Structural studies on fullerenes

Amongst the other physical properties, the structure of fullerene solids, and the structural transformations with temperature, pressure and doping have all evoked considerable interest and during the last two years tremendous progress has been made in this area. This paper provides a brief review of the studies on the structural properties of pristine and doped fullerenes. The results of our own investigations are also presented.     

In-beam gamma-ray and electron spectroscopy following the75As(p,n)75Se reaction

The level scheme of⁷⁵Se has been studied through the⁷⁵As (p, n) reaction at proton energies from 1.5 to 5.0 MeV.γ-ray and internal conversion electron measurements were made using NaI (T1) and Ge(Li) detectors and a six-gap electron spectrometer. A proportional counter and a thin window NaI(T1) detector were used to detectγ-rays with energies less than 30 keV. The level scheme has been established by observing the thresholds of variousγ-rays and byγ-γ and e^?-γ coincidence measurements. New levels at 133.0, 293.2, 790.0, 953.0, 1020.8, 1184.3, 1198.5 and 1258.2 keV not observed in earlier (p, n) studies have been established. Conversion coefficients of most of the low-lying transitions have been determined. Angular distributions of some of theγ-rays were also measured and compared with the statistical model calculations. DefiniteJ ^π assignments have been made to most of the low-lying levels. Life-times of the 112.1, 133.0, 286.7 and 293.2 keV levels have been measured to be 0.69±0.12, 5.3±0.6, 1.35±0.15 and 31±2 nsec respectively. The reduced transition probabilities for various low-lying transitions have been determined and compared with recent calculations. The 1/2^? and 9/2⁺ levels hitherto unknown in this nucleus has been identified. The structure of the low-lying levels is discussed in terms of the existing models.     

The interpretation of the Theory of Relativity

The presently accepted interpretation of the (Special) Theory of Relativity is considered by the author to be inadequate in certain respects. An alternative interpretation is suggested     

Intrinsic paramagnetic defects probe the superionic phase transition in mechanochemically synthesized AgI nanocrystals

Electron paramagnetic resonance (EPR) of two intrinsic paramagnetic centers generated by soft mechanochemistry of Ag and I to yield zinc blende gamma-AgI nanoparticles (approximately 38 nm) has been used for the first time to probe the gamma-alpha (body centered cubic) superionic phase transitions in AgI at (423 +/- 1) K. These results are agreeable with the differential scanning calorimetric studies. A transmission electron microscope picture shows the average crystallite size in the range of approximately 30-40 nm. A hole-type Ag-related paramagnetic center (Ag2+) with an average g = 2.21025 value is remarkably sensitive to the first-order phase transition exhibiting sharp drops at the phase transition temperature (T(t)) and complete reversibility. The T(t) is characterized by a sharp, abrupt rise in the inverse paramagnetic susceptibility 1/chi by 1 order (7.4 x 10(10) to 3.17 x 10(11) in kg m(-3)) which reflects changes in the bonding of the material. Furthermore, a sharp signal at g = 2.0019 (deltaH(PP) = 10 G) due to an electron-excess center (Ag0) as a result of Ag metal nanoclusters also formed during the mechanochemical reaction (MCR) yields an abrupt and drastic decrease in the intensity observed at T(t) = 423 K. From high-temperature (323 to 433 K) I-V characteristics, the evolution of nonohmic behavior is observed on the order of 10(-9)-10(-6) A with increasing temperature until below T(t) which becomes ohmic thereafter. The reason could be the creation of an electronic defect such as Ag0 metal nanoclusters formed during the near-equilibrium mechanochemical reaction, with the increased excess free energy favoring the formation of gamma-AgI nanoparticles.