共查询到20条相似文献,搜索用时 15 毫秒
1.
Summary Pressure and temperature have significant influence on retention in HPLC. This study investigates the effect of pressure and
temperature on the retention behavior of aromatic hydrocarbons (toluene, ethyl benzene, butyl benzene, pentyl benzene) and
polar, acidic and basic samples (phenol, acetophenone, N,N-dimethyl aniline, benzophenone) on a reversed phase column. The
effect has been studied on non-porous, tetradecyl (C14) coated silica particles. We found that the adsorption-induced decrease of the partial molar volume of the solutes investigated
was between ΔV
m
=5–15 cm3 mol−1. The increment of the decrease of the partial molar volume due to the addition of one CH2 group, for the homologous series of the aromatic hydrocarbons is approximately ΔV
CH2
=2.3 cm3mol−1.
Presented at Balaton Symposium '01 on High-Performance Separation Methods, Siófok, Hungary, September 2–4, 2001. 相似文献
2.
Summary The pressure applied in liquid chromatography (LC) can influence the capacity factor of analytes. Using commercial equipment,
column (33×4.6 mm) and 1.5 μm non-porous, tetradecyl (C14) coated silica particles, a moderate but significant change in the capacity factor was observed with increasing pressure.
Depending on the experimental conditions the relationship was found to be either linear or non-linear. In the latter case
the retention increased at first, but later tended to decrease at still higher pressure. The results direct attention to the
role of the pressure (and hence of flow rate and heat of friction) in determining capacity factors.
Presented at Balaton Symposium on High Performance Separation Methods, Siófok, Hungary, September 1–3, 1999 相似文献
3.
Summary A new reversed-phase (RP) HPLC method has been developed and validated for the separation of the main opium alkaloids morphine,
codeine, thebaine, papaverine and noscapine on a non-porous (micropellicular) stationary phase. On this phase quantification
of the compounds by internal standardization with brucine was achieved extremely rapidly, in ca 1.5 min, only. Thus, the analysis
time for the opium alkaloids was approximately one tenth of that on porous stationary phases. Different opium samples were
investigated using non-porous and porous packings. The correlation between the results was excellent.
Presented at Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 1–3, 1999 相似文献
4.
Summary This paper demonstrates the possibilities in transfering HPLC methods from porous to non-porous stationary phases. The procedures
are transferred from 125 or 250 mm columns packed with porous stationary phases to 33 mm columns packed with non-porous particles.
It is demonstrated that fast HPLC using non-porous columns reduces analysis times by a factor four to eight. Precision is
comparable to HPLC with porous stationary phases. The costs for HPLC with porous and with nonporous packing materials are
similar. The implementation of these fast HPLC columns is easy because standard equipment can be used. 相似文献
5.
Summary The aim of this work was to evaluate reversed-phase chemically bonded non-porous (micropellicular)d
p=1.5 μm stationary phases. On these modern phases the time for analysis of complex mixtures of solutes—whether monomeric or
polymeric (e.g. drugs, vitamins, peptides, or protein)—is very short compared with that on porous phases. Different surface
chemistries were elaborated for the separation of different types of sample. For the separation of small molecules a long-chain
(C14) hydrocarbon-coated phase seems to be optimum; a short chain (C6) hydrocarbon bonded to the surface of the silica seems better for the separation of polymers.
The efficiency, the low analysis times, and sensivities were demonstrated by separation of different proteins, peptides, drugs,
alkaloids, and mixtures of water and fat-soluble vitamins. 相似文献
6.
B. T. Mathews A. E. Beezer M. J. Snowden M. J. Hardy J. C. Mitchell 《Chromatographia》2000,53(3-4):147-155
Summary The reversed phase chromatographic properties of the [G1]-L-glutamic and ethyl ester-AC-silica (1), [G2]-L-glutamic acid ethyl ester-AC-silica (2) and the [G1]-L-glutamic acidt-butyl ester-AC-silica (3) dendrimer stationary phases were evaluated. Initial studies involved the comparison between these phases with a classic
reversed phase (i.e. ODS1) by the separation of a standard reversed phase test mixture composed of dimethylphthalate, nitrobenzene,
anisole, diphenylamine and fluorene. Separations were achieved with comparable performance to those obtained with the conventional
reversed phase (ODS1). However, it was apparent that the chromatographic selectivity exhibited by the dendrimer stationary
phases was different from that of the ODS1 phase. On a per mole basis, the dendrimers exhibited similar (and sometimes greater)
affinity for these analytes compared with the ODS1 ligand. Subsequent chromatographic experiments were conducted upon the
dendrimer chiral stationary phases using chiral analytes under reversed phase and normal phase conditions. Chiral resolution
was not observed. 相似文献
7.
Summary The synthesis of a nitric acid ester NP-LC stationary phase (organonitrate phase), by nitrating a commercial polyol phase
(Serva, Polyol Si 100, 5 μm) with mixed sulfuric-and nitric acid, is reported. The nitric acid ester bond is quite stable
towards hydrolysis. To examine its possible use as a stationary phase for the group separation of alkyl nitrates, several
bifunctional polar alkyl nitrates (di-nitrates, hydroxy-nitrates, keto-nitrates) have been synthesized. In order to simplify
their names a new abbreviating nomenclature for multifunctional organic nitrates is presented. With our new stationary phase
it is possible to separate mono-, di-, and hydroxy-nitrates as groups completely, a major advantage in sample preparation
in the chemistry of smog formation. However a co-elution of di- and keto-nitrates is observed. A distinction of the latter
two organonitrate groups is possible by gas chromatography-mass spectrometric detection (MSD). Apart from the fragment ion
NO2
+ (m/z=46 amu), which is nearly specific for alkyl nitrates, aliphatic di- and keto-nitrates show different characteristic
fragment ions. 相似文献
8.
Summary L-N-(3,5-dimethoxyoxybenzoyl)isoleucine, ionically bonded to γ-aminopropyl silica, has been tested as a chiral stationary
phase for the separation of racemates by HPLC. The phase shows good selectivity towards different types of racemates and in
particular for those having an electron-poor aromatic group in their molecule. The separation of benzoin racemate can be achieved
on the developed chiral phase with an α value of 1.10. 相似文献
9.
Summary The employment of three chiral stationary phases (CSPs) obtained by derivatizing γ-mercaptopropyl-silanized silica gel with
quinine, quinidine and N-methyl-quinium iodide, for the separation of organic racemates, is presented. They are quite useful
in the resolution of alkylarylcarbinols, binaphthyl derivatives, amides and other substances of pharmaceutical interest. 相似文献
10.
A study of the mechanisms involved in the separation of metal ions with a mixed-bed stationary phase
Summary The optimization of chromatographic methods for the determination of metal species require an understanding of the mechanisms
involved. In this work, the separation of Cd, Co, Cu, Fe(II/III), Mn, Pb and Zn using a mixed bed column (IonPac CS5A) and
a cation-exchange column (IonPac CS2) is studied as a function of mobile phase composition. The type and concentration of
complexing agent and of ionic strength modificators were evaluated. The charge of analytes were calculated using the classical
ion exchange approach to highlight the effect of eluent composition on retention. The comparative study enabled us to identify
an optimal eluent composition for the separation of the nine metal species. 相似文献
11.
G. -S. Yang M. -B. Huang Q. Dai R. -Y. Gao Q. -S. Wang A. -Q. Du G. -L. Li 《Chromatographia》2001,53(1-2):93-95
Summary The enantiomers of eightO,O-dialkyl-2-benzyloxycarbonyl-aminoarylmethyl-phosphonates are directly separated on anN-(3,5-dinitrobenzoyl)leucine (DNBleu) column. The influence of the mobile phase composition and the column temperature on
the retention and the enantioselectivity are investigated. The influence of the length and steric hindrance of alkoxyl groups
of the phosphonate ester and the nature of the substituentp-Cl and pH on the benzene ring which is attached to the chiral carbon atom on chiral separation are discussed also. 相似文献
12.
Summary The retention behavior of dansyl amino acids in micellar liquid chromatography has been examined by using ionexchange-induced stationary phases. Several parameters affected the retention of the analytes, including the type and concentration of micellar agent and modifier ion and the concentration of acetonitrile in the mobile phase. The order of elution of dansyl amino acids obtained with the micellar mobile phase was very different from that observed in conventional reversed-phase liquid chromatography. Fluorescence intensities of some dansyl amino acids were enhanced by the micellar mobile phase. 相似文献
13.
Summary Mixed-ligand or “mixed-interaction” stationary phases are composed of bonded silanes possessing both ionic and hydrophobic
character. The complex retention properties exhibited by these phases have been particularly useful in separating large biomolecules,
such as synthetic single-stranded oligodeoxyribonucleotides. By isolating the individual properties of separate ligands present
in mixed-ligand stationary phases a better understanding of the heterogeneous surface was sought. Specifically a dilute anion-exchange
mixed-ligand phase of 5% surface coverage showed dramatically different selectivity for oligomers compared to hydrophobic
stationary phases. Of particular interest was the increased selectivity observed in separating oligonucleotides differing
on the 3′ end over conventional reversed-phases supports. 相似文献
14.
Summary N(9-methylanthracene)aminopropyl silica gel is introduced as a new reversed-phase packing material. It has specific selectivity for some aromatic compounds. In this paper the anthracene phase is compared with commercial octadecyl-, phenyl- and aminopropyl-bonded silica gels. 相似文献
15.
《Journal of separation science》2018,41(6):1450-1459
Thirteen pairs of enantiomers belonging to the same structural family (phenylthiohydantoin‐amino acids) were analyzed on two polysaccharide chiral stationary phases, namely, tris‐(3,5‐dimethylphenylcarbamate) of amylose (Chiralpak AD‐H) or cellulose (Chiralcel OD‐H) in supercritical fluid chromatography with a carbon dioxide/methanol mobile phase (90:10 v/v). Five different temperatures (5, 10, 20, 30, 40°C) were applied to evaluate the thermodynamic behavior of these enantioseparations. On the cellulose stationary phase, the retention, and separation trends were most similar among the set of probe analytes, suggesting that the chiral cavities in this stationary phase have little diversity, or that all analytes accessed the same cavities. Conversely, the retention and separation trends on the amylose phase were much more diverse, and could be related to structural differences among the set of probe analytes (carbon chain length in the amino acid residue, secondary amine in proline, existence of covalent rings, or formation of pseudo‐rings via intramolecular hydrogen bonds). The large variability of behaviors on the amylose phase suggests that the chiral‐binding sites in this chiral stationary phase have more variety than on the cellulose phase, and that the analytes did access different cavities. 相似文献
16.
Summary Racemic resolution of aromatic and aliphatic amino acid esters into L-amino acid and D-amino acid ester via LC and HPLC is
achieved by using enzyme reactors as chromatographic columns. For this purpose α-chymotrypsin and trypsin are immobilized
on Eupergit C, Sepharose 4B and Lichrosorb-Diol. 相似文献
17.
Summary Using two polycyclyic aromatic hydrocarbons as solutes, a comparison is made between a bonded liquid crystal stationary phase and a conventional polymeric C-18 phase. The bonded nematic liquid crystal phase was the silanized form of 4-[4-(allyloxy)benzoyl-oxy]biphenyl and the polymeric phase was Vydac 201TP. Both phases display shape and planarity selectivity as indicated by the results of the variable temperature and mobile phase composition studies. The slot theory of retention can be used to explain these results. However, the liquid crystal phase is more sensitive to molecular geometry, probably due to its more ordered structure on the surface. Variable temperature experiments which compare retention during both heating and cooling provides additional support for this conclusion. With the polymeric bonded C-18 phase, each solute had identical retention at the same temperature during both the heating and cooling cycles. On the bonded liquid crystal phase, measurable differences in retention were observed at identical temperatures depending on whether the column was heated or cooled. This effect is attributed to a degree of partially reversible disordering which occurs as the column temperature was increased. However, conditioning with the appropriate mobile phase can restore the original retention characteristics of the bonded liquid crystal phase. 相似文献
18.
Polysiloxane-encapsulated stationary phase for reversed-phase high-performance liquid chromatography
Summary Silica beads of 6-μm average diameter were silanized with methylvinyldiethoxysilane and then subjected to encapsulation with
poly(methylvinylsiloxane). The resulting product is a new stationary phase for reversed-phase high performance liquid chromatography
(RP-HPLC) which has superior ability for the separation of polar, non-polar and basic compounds. The chromatographic peaks
are symmetric. Its stability has been studied; after continuous use for three months the carbon content and chromatographic
behaviour of the phase were unchanged. on to the silica surface to given an uniform organic film. Material prepared in this
way has both good chromatographic behaviour and superior selectivity. Because contact of the silica matrix with the mobile
phase is avoided, the alkali-resisting ability of the stationary phase is increased. The non-specific adsorption of alkaline
solutes on to the silica surface is also avoided because of the complete coverage of surface silanol groups. Reports of stationary
phases encapsulated with polystyrene [6], polybutadiene [I] and octadecylsiloxane polymers have recently appeared in the literature
[3].
In this paper we report the encapsulation of poly-(methylvinylsiloxane) (analogous to the phase SE-31 often used in GC) on
to a silica matrix previously modified with methylvinyldiethoxysilane. The resulting phase has superior performance in reversed-phase
HPLC. 相似文献
19.
Separation of the stereoisomers of racemic fluoroquinolone antibacterial agents on a crown-ether-based chiral HPLC stationary phase 总被引:1,自引:0,他引:1
Summary A chiral stationary phase derived from (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid has been successfully used for the
direct separation of the enantiomers of recemic fluoroquinolines containing a primary amino group being investigated as antibacterial
agents. The chromatographic resolution behavior was found to depend on the content and the type of acidic and organic modifiers
in the mobile phase and on the column temperature. 相似文献
20.
Summary The separation of enantiomers of substituted cyclohexanecarboxamides, benzamides and chemical precursors of Rho-kinase inhibitors
was achieved using derivatized polysaccharide-based chiral stationary phases. Separations were by normal phase HPLC with a
mobile phase ofn-hexane-alcohol (methanol, ethanol or 2-propanol) in various proportions, and a silica-based cellulose tris-3,5-dimethylphenylcarbamate
(Chiralcel OD-H), tris-methylbenzoate (Chiralcel OJ), a silica-based amylose tris-(S)-1-phenylethylcarbamate (Chiralpak AS), or tris-3,5-dimethylphenylcarbamate (Chiralpak AD). The effects of cencentration
of various aliphatic alcohols in the mobile phase were investigated. The effect of structural features on the discrimination
between the enantiomers was examined. The isolation of milligram amounts of enantiomers of two derivatives was performed on
an analytical column by multiple repetitive injections under overload conditions. 相似文献