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991.
Jeyakumar S Mishra VG Das MK Raut VV Sawant RM Ramakumar KL 《Journal of separation science》2011,34(6):609-616
The retention behavior of U and Th as their 2,6-pyridine dicarboxylic acid (PDCA) complexes on a cation exchange column was investigated under low pH conditions. Based on the observed retention characteristics, an ion chromatographic method for the rapid separation of uranium and thorium in isocratic elution mode using 0.08 mM PDCA and 0.24 M KNO(3) in 0.22 M HNO(3) as the eluent was developed. Both uranium and thorium were eluted as their PDCA complexes within 2 min, whereas the transition and lanthanide metal cations were eluted as an unresolved broad peak after thorium. Under the optimized conditions both U and Th have no interference either from alkali and alkaline earth elements up to a concentration ratio of 1:500 or from other elements up to 1:100. The detection limits (LOD) of U and Th were calculated as 0.04 and 0.06 ppm, respectively (S/N=3). The precision in the measurement of peak area of 0.5 ppm of both U and Th was better than 5% and a linear calibration in the concentration range of 0.25-25 ppm of U and Th was obtained. The method was successfully applied to determine U and Th in effluent water samples. 相似文献
992.
George M Ramesh V Srinivas R Giblin D Gross ML 《International journal of mass spectrometry》2011,306(2-3):232-240
The collisionally activated mass spectral fragmentations of N-(2,4-dinitrophenyl)alanine and phenylalanine [M - H](-) may be gas-phase analogs of the base-catalyzed cyclization of N-(2,4-dinitrophenyl)amino acids in aqueous dioxane. This latter reaction is one source of the 2-substituted 5-nitro-1H-benzimidazole-3-oxides, which are antibacterial agents. The fragmentation of both compounds, established by tandem mass spectrometric experiments and supported by molecular modeling using DFT methods, indicate that the [M - H](-) ions dissociate via sequential eliminations of CO(2) and H(2)O to produce deprotonated benzimidazole-N-oxide derivatives. The gas-phase cyclization reactions are analogous to the base-catalyzed cyclization in solution, except that in the latter case, the reactant must be a dianion for the reaction to occur on a reasonable time scale. The cyclization of N-(2-nitrophenyl)phenylalanine, which has one less nitro group, requires a stronger base for the cyclization than the compound with a second nitro group at the 4-position. Following losses of CO(2) and H(2)O are expulsions of both neutral molecules and free radicals, the latter being examples of violations of the even-electron ion rule. 相似文献
993.
994.
Sangeetha K Babu RR Bhagavannarayana G Ramamurthi K 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,79(5):1017-1023
Cu2+ and glycine doped L-arginine monohydrochloride monohydrate (LAHCl) single crystals were grown by slow solvent evaporation technique. The grown single crystals were confirmed by X-ray diffraction study and the interaction of dopants with LAHCl molecule was identified in Fourier transform infrared spectra. The crystalline perfection of pure and doped crystals was analyzed by high resolution X-ray diffraction studies. Vickers microhardness and UV-visible spectroscopy were carried out respectively to study the mechanical stability and optical transmittance of pure and doped LAHCl single crystals. He-Ne laser of wavelength 632.8 nm was used to measure refractive index and birefringence of grown crystals. The second harmonic generation efficiency was also measured for pure and doped LAHCl single crystals using Nd:YAG laser. 相似文献
995.
Ramesh M Raju B Srinivas R Sureshbabu VV Narendra N Vasantha B 《Journal of mass spectrometry : JMS》2010,45(12):1461-1472
Four pairs of positional isomers of ureidopeptides, FmocNH‐CH(R1)‐φ(NH‐CO‐NH)‐CH(R2)‐OY and FmocNH‐CH(R2)‐φ(NH‐CO‐NH)‐CH(R1)‐OY (Fmoc = [(9‐fluorenyl methyl)oxy]carbonyl; R1 = H, alkyl; R2 = alkyl, H and Y = CH3/H), have been characterized and differentiated by both positive and negative ion electrospray ionization (ESI) ion‐trap tandem mass spectrometry (MS/MS). The major fragmentation noticed in MS/MS of all these compounds is due to ? N? CH(R)? N? bond cleavage to form the characteristic N‐ and C‐terminus fragment ions. The protonated ureidopeptide acids derived from glycine at the N‐terminus form protonated (9H‐fluoren‐9‐yl)methyl carbamate ion at m/z 240 which is absent for the corresponding esters. Another interesting fragmentation noticed in ureidopeptides derived from glycine at the N‐terminus is an unusual loss of 61 units from an intermediate fragment ion FmocNH = CH2+ (m/z 252). A mechanism involving an ion‐neutral complex and a direct loss of NH3 and CO2 is proposed for this process. Whereas ureidopeptides derived from alanine, leucine and phenylalanine at the N‐terminus eliminate CO2 followed by corresponding imine to form (9H‐fluoren‐9‐yl)methyl cation (C14H11+) from FmocNH = CHR+. In addition, characteristic immonium ions are also observed. The deprotonated ureidopeptide acids dissociate differently from the protonated ureidopeptides. The [M ? H]? ions of ureidopeptide acids undergo a McLafferty‐type rearrangement followed by the loss of CO2 to form an abundant [M ? H ? Fmoc + H]? which is absent for protonated ureidopeptides. Thus, the present study provides information on mass spectral characterization of ureidopeptides and distinguishes the positional isomers. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
996.
Charagondla Krishnaiah Anumula Raghupathi Reddy Ramesh Kumar Khagga Mukkanti 《中国化学会会志》2010,57(1):68-74
A simple, rapid, selective and sensitive high performance liquid chromatographic method was developed for the separation and quantification of o‐Toluene Sulphonamide and its positional isomers which is an intermediate of Zafirlukast drug substance using a chiral column. Elution time was below 10 min in normal phase mode and ultra violet detection was carried out at 220 nm. Efficient separation was achieved on a Chiralcel OD‐H column using of n‐Hexane and 2‐Propanol mixture (50:50 v/v) as isocratic at 1.0 mL min−1 flow rate. Resolutions between m‐Toluene Sulphonamide and p‐Toluene Sulphonamide isomers of o‐Toluene Sulphonamide were found to be >; 2.5. The calibration graphs for m‐Toluene Sulphonamide and p‐Toluene Sulphonamide isomers of o‐Toluene Sulphonamide were linear (R2 > 0.999) when ranging from the limit of quantitation to 0.5%. The method is found to be selective, precise, linear, accurate and also robust. It was used for not only Quality assurance but also monitoring the synthetic reactions involved in the process development of Zafirlukast. The liquid chromatographic method is found to be specific and reliable for the determination of unreacted levels of positional isomers in reaction mass. This method was successfully validated according to the International Conference Harmonization (ICH) guidelines (Validation of Analytical Procedures: Test and Methodology Q2). 相似文献
997.
Enantiomeric differentiation of β‐amino alcohols under electrospray ionization mass spectrometric conditions
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R. Karthikraj Ramesh Kumar Chitumalla Kotamarthi Bhanuprakash S. Prabhakar M. Vairamani 《Journal of mass spectrometry : JMS》2014,49(1):108-116
The enantiomeric differentiation of a series of chiral β‐amino alcohols (A) is attempted, for the first time, by applying the kinetic method using L‐proline, L‐tryptophan, 4‐iodo‐L‐phenylalanine or 3, 5‐diiodo‐L‐tyrosine as the chiral references (Ref) and Cu2+ or Ni2+ ion (M) as the central metal ion. The trimeric diastereomeric adduct ions, [M+(Ref)2+A‐H]+, formed under electrospray ionization conditions, are subjected for collision‐induced dissociation (CID) experiments. The products ions, formed by the loss of either a reference or an analyte, detected in the CID spectra are evaluated for the enantiomeric differentiation. All the references showed enantiomeric differentiation and the Rchiral values are better for the aromatic alcohols than for aliphatic alcohols. Notably, the Rchiral values of the aliphatic amino alcohols enhanced when Ni2+ is used as the central metal ion. The experimental results are well supported by computational studies carried out on the diastereomeric dimeric complexes. The computational data of amino alcohols is correlated with that of amino acids to understand the structural interaction of amino alcohols with reference molecule and central metal ion and their role on the stabilization of the dimeric complexes. Application of flow injection MS/MS method is also demonstrated for the enantiomeric differentiation of the amino alcohols. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
998.
Thippani Ramesh Pothuraju Nageswara Rao Ramisetti Nageswara Rao 《Journal of separation science》2014,37(4):368-375
A rapid, specific, and reliable isocratic LC–MS/MS method has been developed and validated for the identification and characterization of the stressed degradation products of Entecavir (ETV). ETV, an antiviral drug, was subjected to hydrolysis (acidic, alkaline, and neutral), oxidation, photolysis and thermal stress, as per the international conference on harmonization specified conditions. The drug showed extensive degradation under oxidative and acid hydrolysis stress conditions. However, it was stable to thermal, acidic, neutral, and photolysis stress conditions. A total of five degradation products were observed and the chromatographic separation of the drug and its degradation products were achieved on a Waters Symmetry C18 (250 mm × 4.6 mm, id, 5 μm) column using 20 mM ammonium acetate (pH 3)/acetonitrile (50:50, v/v) as a mobile phase. The degradation products were characterized by LC–MS/MS and its fragmentation pathways were proposed. The LC–MS method was validated with respect to specificity, linearity, accuracy, and precision. No previous reports were found in the literature regarding the degradation behavior of ETV. 相似文献
999.
Eulalia Ramirez-Oliva Jorge Cervantes Francisco Cervantes-Lee Ramesh N. Kapoor Keith H. Pannell 《Journal of organometallic chemistry》1996,510(1-2):57-62
A transition metal-substituted silylacetylene [(η5-C5H5)Fe(CO)2SiMe2C]2, [FpMe2SiC]2 (I) was synthesized and characterized spectroscopically and structurally. I crystallized in the monoclinic space group P21/n, A = 13.011(3) Å B = 12.912(3) Å, C = 13.175(5) Å, β = 94.95(2). The acetylene linkage is reactive toward Co2(CO)8 to form I. Co2(CO)6 (II) which was also characterized spectroscopically and by single crystal X-ray diffraction. II crystallized in the orthorhombic space group Pbca, A = 17.64(2) Å, B = 14.225(10) Å, C = 24.49(2) Å. 相似文献
1000.
Solvent extraction of some selected metals from an aqueous buffered solution by LIX26 extractant has been studied. The pH1/2 values (at which 50% of metal ion is extracted) for extracting different metals by 1 v/v% LIX26 extractant in methyl isobutyl
ketone have been obtained. The order of extraction of metals by LIX26 extractant as a function of pH1/2 value is Pd(II)<Cu(II)<Sb(III)<Fe(II)<Co(II)<Zn(II)<Ni(II) <Pb(II)<Mn(II)<Cd(II). 相似文献