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991.
992.
表面活性剂增敏2.5次微分极谱测定香豆素 总被引:1,自引:0,他引:1
王福民 《理化检验(化学分册)》2003,39(3):138-141
拟定了表面活性剂增敏、2 .5次微分极谱测定香豆素的方法。在含 6.0× 10 -6 mol·L-13 氯 2 羟丙基 三甲基氯化铵的 0 .1mol·L-1KH2 PO4 Na2 HPO4 (pH 6.8)缓冲液中 ,香豆素还原波 [峰电位Ep=- 1.60V(vs .SCE) ]的 2 .5次微分极谱峰峰电流e″p 与其浓度在 4 .0× 10 -7~ 6.0× 10 -5mol·L-1范围内呈良好线性关系 (r =0 .9998,n =10 ) ,检出限为 1.2× 10 -7mol·L-1。 13次平行测量 8.0× 10 -6 mol·L-1香豆素的峰电流 ,RSD为 1.5 %。该方法可用于中药白芷中香豆素的直接测定 相似文献
993.
Low molecular weight poly(dimethylsiloxane) and poly(methylphenylsiloxane) were synthesized and blended with polyimide (PI) at its precursor poly(amic acid) stage. FTIR analysis has proven the retention of polysiloxanes in polyimide after the ultimate curing of blends. Differential scanning calorimetric analysis was performed on polysiloxanes to elucidate the structures present in polymers while thermogravimetric analysis (TGA) was performed on polysiloxanes, polyimide as well as their blends to evaluate the thermal stability and to analyze the effect of polysiloxane incorporation in blends. Blends have shown synergistic improvement as compared to neat polyimide. 相似文献
994.
The intermolecular interaction energy for reacting systems in singlet, triplet and doublet states was partitioned by the perturbation expansion method into the chemically meaningful five interaction terms: the Coulomb, exchange-repulsion, induction, dispersion, and charge-transfer energies. In the local ZDO approximation, these energy terms were evaluated for the dimerization of methylenes (1,3CH2), the additions of carbenes (1,3CH2 and1,3CF2) as well as amino radicals (2NH2 and2NF2) toward ethylene, and the hydrogen abstractions by methylenes (1,3CH2), nitrene (3NH), and hydroxyl radical (2OH) from methane. It has been found that the reaction path is much influenced by the spinmultiplicity, and that the charge-transfer and exchange-repulsion terms play a dominant role in determining the course of reactions. 相似文献
995.
Measurements of acoustic absorption and velocity as a function of frequency and concentration in KH2PO4–K2HPO4 buffers at 4°C and pH 5-7 are reported. The dependence of the observed acoustic relaxation parameters on concentration is consistent with that to be expected from perturbation of a monomer-dimer equilibrium with an equilibrium constant [for 2H2PO
4
–
(H2PO4)2
2–] of 0.21 M–1, a bimolecular rate constant of 5×108 M–1-sec–1 and a standard volume change of –5 cm3 mole. The equilibrium constant for H2PO
4
–
+ HPO4
2–H3(PO4)2
3– is estimated to be 0.7 M–1. 相似文献
996.
Tomazela DM Gozzo FC Mayer I Engelmann FM Araki K Toma HE Eberlin MN 《Journal of mass spectrometry : JMS》2004,39(10):1161-1167
Ten homologous or isomeric singly, doubly, triply and quadruply charged cationic macrocyclic complexes I-Va, bn+ (n = 1-4) formed by the coordination of [Ru(bipy)2Cl]+ to the pyridyl N-atoms of a series of meso-(phenyl)m-(meta or para-pyridyl)n-porphyrins (m + n = 4) were transferred to the gas phase and structurally characterized by electrospray ionization (ESI) mass (MS) and tandem mass (MS/MS) spectrometry. Previously known to be stable in solution and in the solid state, I-Va, bn+ are found to constitute also a new class of stable, long-lived multiply charged gas-phase ions with spatially separated charge sites. Increasing intramolecular electrostatic repulsion from Ia, b+ to IVa, b3+ facilitates in-source and tandem collision-induced dissociation (CID). However, for the quadruply charged ions Va, b4+, electrostatic repulsion is alleviated mainly by ion pairing with the CF3SO3- counterion forming the salt clusters [Va,b/CF3SO3]3+ and [Va,b/(CF3SO3)2]2+ with reduced charge states. Ion-pairing that yields [IVa,b/CF3SO3]2+ is also observed as a minor ESI process for the triply charged ions IVa, b3+. The gaseous ions I-Va, bn+ (n = 2, 3 or 4) dissociate by sequential 'charge partitioning' with the formation of two cationic fragments by the release of [Ru(bipy)2Cl]+. The meta (a) and para (b) isomers and the positional isomers II2+ and III2+ display nearly identical ESI-MS and ESI-MS/MS spectra. ESI-MS/MS of I-Va, bn+ shows that the Ru-py(P) is, intrinsically, the weakest bond since this bond breaks preferentially upon CID. 相似文献
997.
Kozhevnikov D. N. Kataeva N. N. Rusinov V. L. Chupakhin O. N. 《Russian Chemical Bulletin》2004,53(6):1295-1300
A simple procedure was developed for the synthesis of 1,2,4-triazines and their 4-oxides containing the ClCH2, Cl2CH, or CCl3 group at position 3 by cyclization of 2-aryl-2-hydrazono-1-oximinoethanes with the corresponding chloroacetonitriles. The reaction pathway depends on the number of halogen atoms in the acetonitrile used. The reactions with trichloroacetonitrile, monochloroacetonitrile, and dichloroacetonitrile afford 3-trichloromethyl-1,2,4-triazines, 3-chloromethyl-1,2,4-triazine 4-oxides, and a mixture of the corresponding dichloromethyltriazines and their 4-oxides, respectively. The reactions of 3-trichloromethyl-1,2,4-triazines with indoles and phenols are accompanied by tele-substitution with elimination of halogen from the trichloromethyl group to give 5-indolyl- (or 5-hydroxyphenyl)-3-dichloromethyl-1,2,4-triazines. 相似文献
998.
评述了液晶态分子在分析化学中的应用进展,包括其超分子的分子识别作用,液晶在色谱,光谱探针,核磁共振谱等分析化学领域中的应用。 相似文献
999.
Summary Electrophoretic mobility measurements in the pH 2‐10 range are described for several commercial HPLC silica microparticles
and a laboratory-produced product. The content of metal impurities for the silicas was also determined by AAS. An acidic/hydrothermal
treatment was used to generate a more homogenous surface for some of the silicas. The zero points of charge (zpc) for both
a native and a treated silica plus several commercial HPLC silicas were compared. The electrophoretic mobility method may
be useful in predicting the utility of certain types of silica supports for chromatographic separations. 相似文献
1000.
The ion product of water and the dissociation constants of carbonic acid have been determined in 0.1, 1.0, 3.0, and 5.0M NaClO4 at 25°C. The ion product of water K
w
'
has been evaluated by emf measurements with a combined glass electrode in NaClO4 solutions containing 0.001–0.1M HCLO4 or NaOH. The product K
H
'
K
l
'
K
2
'
of the Henry constant for CO2 and the dissociation constants for H2CO3 have been determined by titration of carbonate solutions equilibrated with pCO2 =10–3.52 atm, and K
2
'
has been evaluated by potentiometric titration and by measuring the H+ concentration at fixed HCO
3
–
and CO
3
2-
concentrations. The ion interaction (Pitzer) equations are applied to describe the constants K
w
'
, K
2
'
and K
H
'
H
1
'
K
2
'
as a function of the NaClO4 concentration. The experimental data are used to evaluate the mixing parameters
i/ClO
4 and
i/ClO
4
-/Na+ fori = OH
-,HCO
3
-
andCO
3
2- 相似文献