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Summary The reaction of secondary amines R2NH with disulfur dichloride S2Cl2 in dichloro methane yields mixtures of bis-dialkylamino polysulphides R2N–Sn–NR2 with sulphur chain lengths varying from ns=2 to 14. The S chains are believed to be non-branched. The compounds form homologous series in each of which sulphur atoms give a constant contribution to retention. The sulphur retention index depends slightly on the carbon number in the terminal alkyl groups R. The presence of nitrogen lowers retention. The index increment of N is ca. –160 units, which is distinctly less negative than values found in alkylamines. 相似文献
4.
Summary The microcomputer-assisted retention prediction system in C18 reversed-phase HPLC is described. The system is based on the use of the hydrophobic parameter and the correlation factor of alkylbenzenes and polycyclic aromatic hydrocarbons (PAHs) which are highly correlated to their retention in reversed-phase HPLC. The system is evaluated by comparing the retention data between measured and predicted values. One of the typical examples applied for PAH analysis in the extracts of diesel particulate matter shows the high potential of the system investigated. 相似文献
5.
Summary The reversed-phase ion-pair liquid chromatographic behaviour of several metal complexes with 5-sulphoquinoline-8-ol (HQS)
on an octadecyl-modified silica column was investigated by using a fluorescence detector. The aluminum complex gave two peaks
on the chromatograms when eluents containing phosphate buffer were used. The effects of the pH of the eluent, HQS concentration,
the nature of anions in the eluent, and the column temperature on the retention behaviour of the aluminum complex are discussed
on the basis of the equilibria and the kinetics of the complexation of the aluminum ion with HQS and anions in the eluent.
The equilibrium constant for the interconversion reaction between the two Al(III)-HQS species which correspond to the two
peaks observed and the second stepwise formation constant for the Zn(II)-HQS complex were evaluated from the HPLC data obtained. 相似文献
6.
The effects of Na+, K+ and Li+ cations on the fluorescence spectra of benzo[15]crown-5, benzo[18]crown-6 and dibenzo[18]crown-6 were investigated in acetonitrile. The alkali cation role observed was usually the complexation-enhanced quenching fluorescence effect (CEQF) in acetonitrile due to the increased fluorescence quenching rate of the complexed fluoroionophore. The association constants for 1 :1 stoichiometry InK
a have been obtained using the relationship 1/K
a[L
0] = (1 –P)2/P. It was shown that the preferential interaction rule of compatibility of cationic radii and macrocyclic ring size is in excellent agreement with the association constants obtained by fluorescence spectroscopy. The order of InK
a found for benzo[15]crown-5 complexation was Li+ > Na+ > K+ and K+ > Na+ > Li+ for benzo[18]crown-6 in acetonitrile.Presented at the Sixth International Seminar on Inclusion Compounds, Istanbul, Turkey, 27–31 August, 1995. 相似文献
7.
Summary The effects of eluent pH and organic modifier concentration on the capacity factor (k) and selectivity of dipeptide isomers were investigated. It has been observed that the variation in the logarithm of the capacity factor of the dipeptide isomers is linearly dependent on the organic modifier concentration (Cb), however, the selectivity is almost independent of it. Both capacity factor and selectivity were seriously affected by the pH of the eluent. Both the capacity factor and the intercept of the ln k vs. Cb plot increased with increasing van der Waals volume of the non-polar amino acid subunit of the dipeptides. 相似文献
8.
F. Dondi G. Blo Y. D. Kahie G. Lodi C. Pietrogrande P. Reschiglian 《Chromatographia》1988,25(5):423-429
Summary Reversed-phase HPLC retention behaviour of different flavonoid compounds in different columns and with a range of methanol-buffer
eluents was examined. Repeatibility and reproducibility of logk′ and Δlogk′ values were analyzed. Sharp group contributions,
expressed as Δlogk′, were observed. These did not depend significantly on acid modifier type, column packing characteristics
(C8 and C18) and dimensions (5,7 and 10μm) or the percentage of methanol in the mobile phase. A list of twelve group contributions
is presented which is in agreement with literature data. 相似文献
9.
Summary The retention behaviour of an homologous series of phosphorylated oligodeoxythymidylic acid (pd(T)5–18) oligonucleotides was studied using reversed-phase ion-pair chromatography with isocratic elution conditions. The effects
of temperature, pH, eluent ionic strength, percentage organic modifier, concentration and alkyl chain length of the ion-pairing
reagent were investigated. The retention behaviour was generally explicable by current theoretical models of ion-pair chromatography.
However, the marked effect of mobile phase pH on the retention of the oligonucleotides was unexpected, and this was ascribed
to the presence of ionisable residual silanols on the surface of the reversed-phase packing material. 相似文献
10.
The reactions between alkali metal ions and crown ethers, aza crown ethers, and cryptands in propylene carbonate were studied by potentiometric and calorimetric titrations. The most stable complexes formed by macrocyclic and macrobicyclic ligands are when the ligand and cation dimensions are comparable. On comparing the complex stabilities of crown ethers and aza crown ethers of the same size, crown ethers were, on the whole, found to form the most stable complexes, with the exception of the lithium cation. Enthalpic factors are responsible. Substitution of the amino group protons of the aza crown ethers by benzyl groups leads to a high increase in values of the reaction enthalpy. This effect is partly compensated by entropic contributions. The bulky benzyl groups reduce the ligand solvent interactions and induce a ligand conformation with the lone pair of electrons from the nitrogen donor atoms which are more or less directed inside the cavity. The thermodynamic data for the transfer from methanol to propylene carbonate indicate that the ligands containing nitrogen show specific interactions with methanol.This paper is dedicated to Professor H. Strehlow on the occasion of his 70th birthday. 相似文献
11.
Summary The twelve structural C2 isomers of naphthalene are resolved on a single capillary column using , , or cyclodextrin as the stationary phase. A change in elution order is seen upon going from to and then cyclodextrin which can be related to the size of the cyclodextrin cavity and the stereochemical fit of the isomer. A crown-ether column and a liquid-crystal column were found to be unable to separate all of the isomers. 相似文献
12.
Summary It is shown theoretically that when the concentration of organic solvent in the mobile phase increases, or solute size decreases, log k values of small solutes in reversed-phase liquid chromatography (RPLC) will tend to have a minimum value called the convergence point. A theoretical model for evaluating the convergent coordinates of small solutes is presented by using a stoichiometric displacement model for retention (SMDR). The physical meaning of the coordinates of each kind of convergence are also elucidated. The convergence points have either two-dimensional coordinates with a common ordinate (the logarithm of the phase ratio of the column, log ) or threedimensional corrdinates with two common axes: — log and the logarithm of the molar concentration of the pure displacing agent in mobile phase, log aD. The other axis relates to the nature of the solutes, such as carbon number of a homolog, van der Waal's surface area, hydrophobic fragment constant etc. for the latter and those and/or concentration axis for the former. The model was tested with published data and found to give a good fit. 相似文献
13.
The RPLC retention of 1,n-halo(alkylthio)alkanes on an ODS phase with methanol/water (95%/5%) has been investigated. Replacement of a methyl group in a dialkyl sulphide R-S-R by a halogen atom X, to yield the title compounds X-(CH2)n-S-R, generally results in a retention decrease. This retention loss results either from the halogen atom proper, or from its immediate vicinity, or from a reduced retention contribution of the alkyl units. The methylene groups (n) between halogen and sulphur produce somewhat greater retention than the methylene groups in the alkyl groups R. 相似文献
14.
Extraction and determination of crown ethers from water samples using a membrane disk and gas chromatography 总被引:2,自引:0,他引:2
A method for rapid extraction and determination of some crown ethers in aqueous matrices using octadecyl-bonded silica membrane disks and gas chromatography is presented. Extraction efficiency and the influence of vacuum pressure. pH, and type and least amount of eluting solvent used to extract the crown ethers from the membrane disks were evaluated. Extraction efficiencies > 95% were obtained for benzo-15-crown-5, benzo-18-crown-6 and dicyclohexyl-18-crown-6 using 5 ml of acetonitrile as eluting solvent. The limit of detection of the proposed method for the determination of the crown ethers is reported. 相似文献
15.
The retention of small peptides can be predicted by summing the hydrophobic contribution to retention of each amino acid of
peptides. But the retention time of peptides larger than 10–15 residues are less than that predicted by summing the retention
coefficients of each constitutive residue. A new prediction model, considering the effects of the peptide length and contact
area of each amino acid with the stationary phase for larger peptides was proposed. The model was validated by 136 peptides
identified by nano-flow 2-D-LC-ESI-MS-MS platform and other retention data observed from literature. The high degree of correlation
between the observed and predicted retention time by using the new model is not only good evidence for the accuracy of our
predictive method, but supports the supposition that the peptide length and contact area of each amino acid with stationary
phase are important factors affecting peptide retention time for larger peptide. In addition it is found that the range of
peptide length is wider, the accuracy of prediction is better. The ratio coefficient of surface area of non-polar, polar and
charged amino residues contacting with the stationary phase were all calculated to be less than one.
Revised: 30 June and 11 August 2005 相似文献
16.
A conductance study concerning the interaction between hydronium ion and several crown ethers in acetonitrile, nitrobenzene and 1,2-dichloroethane solutions has been carried out at 25°C. The stability constants of the resulting 1:1 complexes in acetonitrile and nitrobenzene solutions were determined from the molar conductance-mole ratio data and found to vary in the order 18C6>DB30C10>DC18C6>DB18C6>DB21C7>DB24C8>B15C5. In 1,2-dichloroethane solution, the complexation process results in the dissociation of ion pairs. There is an inverse relationship between the stabilities of the complexes and the Gutmann donicity of the solvents. In nitrobenzene solution, some evidence for the formation of a 2:1 sandwich adduct between the smaller crowns (i.e., B15C5 and 18-crowns) are observed from the molar conductance-mole ratio data which is supported by the1H NMR data. 相似文献
17.
P. L. Zhu 《Chromatographia》1986,21(4):229-233
Summary An equation is derived which can describe how the retention of solutes is influenced by the composition of the mobile phase
in reversed-phase liquid chromatography, the retention of solutes in alkyl bonded stationary phase regarded as the complexation
between solute molecule and the active sites on the surface of the stationary phase. When the stationary phase is not fully
saturated by the organic modifier, the activity of the active sites, the activity coefficient of the adsorbed solute as well
as the activity coefficient of the solute in the mobile phase depend on the composition of the mobile phase. However, when
the stationary phase is fully saturated, the composition of the mobile phase mainly influences the activity coefficient of
the solute in the mobile phase. In addition, the selectivity of retention is discussed in terms of the derived equation. 相似文献
18.
Jos W. H. M. Uiterwijk Gerrit J. van Hummel Sybolt Harkema Veronika M. L. J. Aarts Kari Daasvatn Jan Geevers Herman J. den Hertog Jr. David N. Reinhoudt 《Journal of inclusion phenomena and macrocyclic chemistry》1988,6(1):79-100
The preparation and X-ray structure determinations of six complexes of urea and (O-n-butyliso)uronium salts with crown ethers are presented. Urea forms isostructural 5:1 adducts with 18-crown-6 (1) and aza-18-crown-6 (2), in which two urea molecules are each hydrogen bonded to two neighbouring hetero atoms of the macroring. The remaining urea molecules form two-dimensional layers alternating with crown ether layers. In both complexes the macroring has theg
+
g
+
a ag
–
a ag
–
a g
–
g
–
a ag
+
a ag
+
a conformation withC
i symmetry. In the solid 1:1 complex of O-n-butylisouronium picrate with 18-crown-6 (3) two types of conformations of the macroring were observed: theg
+
g
+
a ag
–
a ag
+
a ag
–
g
–
ag
–
a ag
+
a conformation with approximateC
m symmetry and to a lesser extent theg
+
g
+
a ag
–
a ag
+
a g
+
g
+
a ag
–
a ag
+
a conformation with approximateC
2 symmetry. Both conformations allow the guest to form three hydrogen bonds to the macrocyclic host. Three complexes of 18-crown-6 and uronium salts have been prepared and characterized by X-ray crystallography. The 1:1 complexes with uronium nitrate (4) and uronium picrate (5) both exhibit the sameC
2 conformation and the same hydrogen bonding scheme as in the least occupied form of the previous complex. A 1:2 complex with uroniump-toluenesulphonate (6) has a different hydrogen bonding scheme (two hydrogen bonds per cation to neighbouring oxygen atoms of the macroring) and a different conformation of the host molecule (theag
+
a ag
–
a ag
+
a ag
–
a ag
+
a ag
–
a conformation with almostD
3d symmetry). An attempt to prepare a solid uronium nitrate complex with diaza-18-crown-6 in the same way as the 18-crown-6·uronium nitrate (1:1) complex did not yield the expected result. Instead X-ray analysis revealed that the uronium ion is dissociated, resulting in the nitrate salt of the diprotonated diaza crown ether (7).
Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82058 (26 pages). 相似文献
19.
Summary The retention data of isomeric xylenes, ethyltoluenes and diethylbenzenes, and of mesitylene, benzene, toluene and ethylbenzene were obtained on a reversedphase column using methanol-water and ethanol-water mobile phases at four different temperatures. This database was used to relate the dependence of solute retention and resolution on the polarity of the mobile phase, solute dipole moment, and column temperature. The additivity of the free energy of the transfer of solute molecules or solute segments from the stationary phase to the mobile phase, was examined for the isomeric compounds. For this, the logarithm of the net retention volume was substituted for the free energy. Deviations from the additivity of free energies indicate that the separation of isomeric substituted alkylbenzenes is governed by their differential interactions with both the polar mobile phase and nonpolar stationary phase. Among the disubstituted alkylbenzenes,ortho-isomers favor the mobile phase more andpara-isomers tend to prefer the stationary phase more. Themeta-isomers are found to follow the additivity rule closely. These trends are amplified as the polarity of the mobile phase is increased indicating that these isomers are resolved better in water-rich mobile phases. These findings are substantiated by analogous results from gas-liquid chromatographic retention data, estimation of dipole moment effects, and examination of the entropic and enthalpic contributions to the net retention volume.Dedicated to Professor Leslie S. Ettre on the occasion of his 70th birthday. 相似文献
20.
Summary Retention prediction of small peptides (up to four residues) in reversed-phase liquid chromatography has been investigated,
considering the contributions of side chains in each position to the peptide retention. In isocratic elution the retention
of peptides could be predicted within about 8% relative error. 相似文献