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1.
The reversed-phase liquid chromatographic analysis of basic pharmaceuticals can be problematic. Both the properties of the eluent and the stationary phase can influence the chromatographic performance. Therefore selection of suitable experimental conditions for the analysis of basic compounds can be difficult. This paper shows that the organic modifier and the nature of the buffer influence the eluent properties. Moreover, the nature and amount of modifier also influence the basicity of the analytes. Investigations showed that the nature of the buffer can have a significant influence on retention and peak shape of basic compounds. Test procedures using basic analytes as test probes provided relevant information with respect to selecting columns to analyse basic pharmaceutical compounds. Test procedures using compounds like aniline, phenol and benzene were found to be less suitable.  相似文献   

2.
Reversed-phase liquid chromatography using silica-based columns is successfully applied in many separations. However, also some drawbacks exist, i.e. the analysis of basic compounds is often hampered by ionic interaction of the basic analytes with residual silanols present on the silica surface, which results in asymmetrical peaks and irreproducible retention. In this review, options to optimise the LC analysis of basic pharmaceutical compounds are discussed, i.e. eluent optimisation (pH, silanol blockers) and stationary phase optimisation (development of new columns with minimised ionic interactions). The applicability of empirical based, thermodynamically based and test methods based on a retention model to characterise silica-based reversed phase stationary phases, as well as the influence of the eluent composition on the LC analysis of basic substances is described. Finally, the applicability of chemometrical techniques in column classification is shown.  相似文献   

3.
Stationary phases were investigated for HPLC coupled with electrospray ionization mass spectrometry (ESI-MS) for the analysis of basic drugs. Tricyclic antidepressants (TCAs) and beta-blockers were used as model solutes. The functional groups, pentafluorophenyl (PFP), OH, CN or CH3 were attached to the silica via a propyl chain. The effects of these stationary phases as well as C8 and C18 phases on retention and peak shape of the basic drugs were studied. The CN and PFP phases adequately retained (tR of 2 to 6 min) the basic drugs when the mobile phase was composed of 90% acetonitrile, whereas with the C4, C8 and C18 phases, less than 40% acetonitrile had to be used to provide adequate retention of the basic drugs. Because acetonitrile provides better desolvation in ESI than an aqueous solvent, it produces an increased MS signal. As an example of the HPLC-ESI-MS analysis of the beta-blocker, pindolol, on a CN phase, the use of 90% acetonitrile in the mobile phase increased the ESI-MS signal by 790% when compared to a C18 phase which could use only 5% acetonitrile in the mobile phase for retention of the solute. In addition, the CN and PFP phases provided better peak shape than the OH phase and the hydrophobic phases (C4, C8 and C18) and ion-pairing or ion-suppressing agents were not required. The retention behavior of the TCAs and beta-blockers on each of the phases is described.  相似文献   

4.
This paper focuses on the classification or differentiation of RP-HPLC columns based on measured chromatographic properties. A chemometric study has been conducted on a published data set consisting of 85 RP-HPLC columns and on a data set consisting of 47 self-tested columns. Principal component analysis enables determination of the number of parameters necessary for a rational differentiation. The results show that reducing the number of parameters for such differentiation still allows classification of the columns just as a higher number did. It is shown that three test parameters produce a classification similar to that obtained with five parameters.  相似文献   

5.
The protein ribonuclease A (RNase A) represents a good model protein for studying reversible conformational refolding during gradient elution. Work is described utilizing RNase A under gradient conditions to evaluate several different reversed-phase materials. Columns (10 cm x 4.6 mm I.D.) were packed with Partisil C18, Vydac C18, Nucleosil C4, Nucleosil C18 and an adamantyl-modified Partisil silica. Measurements of the apparent first-order rate constant of refolding, as a function of temperature, are presented and compared for each stationary phase. Comparisons of peak shapes as functions of flow-rate and temperature are also discussed.  相似文献   

6.
A chemically bonded phase with a peptide group (PB) for reversed-phase high-performance liquid chromatography (HPLC) is described. This packing was prepared by a two-stage modification of the surface of silica gel with mono- and trifunctional 3-aminopropylsilane and then with an appropriate derivative of a fatty acid. Packings prepared in this way were compared with standard C18 materials used in HPLC. Surface characteristics of the packings before and after chemical modification were determined by different physico-chemical methods, e.g., porosimetry, elemental analysis, 13C and 29Si cross-polarization magic angle spinning NMR and HPLC. Chromatographic properties of these packings were evaluated by comparison between log k' of one phase and log k' of a second phase for substances with different chemical natures. The PB packing was found to be especially useful for the separation of basic substances.  相似文献   

7.
The preparation of stationary phases for HPLC using polymers deposited on silica usually includes an immobilization step involving cross-linking by free radicals induced by ionizing radiation or by other radical initiators. The present paper reports changes which occur at ambient temperature in the character of poly(methyloctylsiloxane) deposited on porous silica particles as a function of the time interval between particle loading and column packing. Column performance and retention factors increase with time and these changes are attributed to rearrangement (self-assembly) which result in "self-immobilization" of the polymer molecules on the silica surface.  相似文献   

8.
The availability of a variety of stable organic stationary phases for columns has been a key factor in the development of HPLC as a major scientific tool. This paper explores the history and rationale used in the development of some important stationary phases and attempts to identify some of the strengths and limitations of these materials. Some of the author's experiences in stationary phase development illustrate approaches leading to present-day columns that exhibit a broad range of selectivity coupled with a high degree of reproducibility. Suggestions also are made for additional stationary phases that may be needed to complete column selectivity potential for HPLC separations.  相似文献   

9.
Recent developments of polysaccharide-based chiral stationary phases (CSPs) for the direct separation of enantiomers in high-performance liquid chromatography (HPLC) are mainly reviewed together with the results on mechanistic studies by means of chromatography, NMR and mass spectroscopies, and computational methods. Miscellaneous applications of polysaccharide derivatives to the newly developed, chiral dynamic high-performance liquid chromatography (DHPLC) for obtaining a nonracemic compound are also described.  相似文献   

10.
11.
The separation of C60 and C70 fullerenes on four different polysiloxane stationary phases was examined. It was determined that polar solvents can be used as mobile phases effectively for the separation of fullerene molecules. Unlike previously published work, a polymeric octadecyl siloxane (ODS) stationary phase provided higher separation factors for C70/C60 than did monomeric ODS stationary phases or phenyl substituted stationary phases. For example, for a methanol-diethyl ether (50:50, v/v) mobile phase and C60, k' approximately 5.0 separation factors, alpha = 3.3, were achieved with polymeric ODS compared to alpha = 2.2, with a monomeric ODS stationary phase. A linear solvation energy relationship (LSER) was used to model the importance of solvent interactions and stationary phase interaction to solute retention.  相似文献   

12.
A fast screening strategy was developed in capillary electrochromatography (CEC) for the chiral separation of basic and bifunctional compounds. The screening conditions were determined on polysaccharide chiral stationary phases using 15 pharmaceutical compounds. The content and type of organic modifier, as well as the pH of the mobile phase appeared to have the largest influence on the chiral resolution. It was seen that for acidic compounds, our approach was not suitable. A generic mobile phase for basic and bifunctional compounds was determined. The testing on 20 additional compounds showed that the proposed mobile phase performed well since enantioselectivity was observed for 86% of the investigated compounds. A comparison of CEC and reversed-phase liquid chromatography (RPLC) results was attempted to demonstrate the potential of the used technique for chiral method development.  相似文献   

13.
In this paper, we present a combination of a key-solute test based on retention and separation factors of large probe solutes (carotenoid pigments) and a quantitative structure-retention relationship analysis based on the retention factors of small probe solutes (aromatic compounds), both performed in supercritical fluid chromatography, to investigate the different chromatographic behaviour of octadecylsiloxane-bonded stationary phases of all sorts: classical, protected against silanophilic interactions or not, containing polar groups (endcapping groups or embedded groups). The results indicate that the two approaches chosen (carotenoid test and solvation parameter model) are complementary and provide precise information on the chromatographic behaviour of ODS phases. The applicability of the classification to the selection of stationary phases is evidenced with some examples of separations.  相似文献   

14.
We have evaluated and compared the performance of several conventional C18 phases with those possessing either a polar-endcapping group or a polar-embedded group within the primary alkyl ligand and found distinct differences in the chromatographic behavior among the three groups, as well as a high degree of variability within each group. The trend is for the polar-endcapped phases to display similar hydrophobic retention characteristics as the conventional C18 columns, but to express higher hydrogen bonding capacities and silanol activity. The polar-embedded phases displayed the opposite behavior, with a greatly reduced hydrophobic nature compared to the conventional and polar-endcapped C18 phases, and also a very much reduced silanol activity. Most interestingly, it appears that ionic or dipole interactions play a significant role in the overall retention behavior of the polar-embedded phases towards basic and acidic analytes.  相似文献   

15.
At present, in high-performance liquid chromatography (HPLC) for the majority of analyses, reversed-phase liquid chromatography (RPLC) is the separation mode of choice. Faster method development procedures using aggressive eluents under elevated temperature conditions, the need for improved selectivities, efficiencies and resolution, the reduction of solvent consumption and also the decrease of analysis times require reversed-phase (RP) columns of high chemical and thermal stability. Until now, the majority of columns for RPLC separations are manufactured from silica substrates. Silica has many favorable properties making this material nearly ideal as a support for RP columns. However, its solubility, that increases considerably in eluents of pH above +/-7, is a drawback preventing its widespread use over the entire pH range. In addition, also the thermal stability of silica is limited. Recently, however, substantial progress has been made in the synthesis of RPLC silica-based stationary phases showing satisfactory thermal and chemical stability under many different experimental conditions. Also, new substrates mainly based on other inorganic substrates like, e.g. alumina and zirconia have been developed now as a starting material for the preparation of RPLC stationary phases of improved chemical and thermal stability. In addition, for the same reasons, many efforts have also been made to synthesize polymer and also polymer-coated phases. These latter phases, more particularly those based on zirconia, but also polymer phases show a high degree of chemical and thermal stability compared to silica counterparts. In this paper, an overview will be given of the state-of-the-art of the thermal and chemical stability of the different available stationary phases for RPLC.  相似文献   

16.
C30 stationary phases for the analysis of food by liquid chromatography   总被引:3,自引:0,他引:3  
The introduction of a polymeric C30 liquid chromatographic column by Sander et al. [Anal. Chem., 66 (1994) 1667] designed for the separation of carotenoid isomers, has led to the development of improved analytical methods for these compounds. Subsequent commercial availability of polymerically bonded C30 columns has facilitated these advances, and applications to a wide variety of separation problems with biological samples have been described. This report provides a comprehensive review of applications of polymeric C30 columns, utilized in the determination of carotenoids, retinoids, and other nutrients and related compounds in complex, natural-matrix samples.  相似文献   

17.
Several C18 stationary phases were found to behave non-ideally when insulins and proinsulins were eluted with shallow acetonitrile gradients in 0.1% trifluoroacetic acid, resulting in poor peak shapes or no elution at all. With triethylammonium phosphate or ammonium sulphate as buffer components, the insulins and proinsulins were eluted with excellent peak shapes, presumably owing to better masking of residual silanol groups on the stationary phases. Similar use of trifluoroacetic acid-acetonitrile gradients on the less hydrophobic C4 or C3 stationary phases resulted in excellent peak shapes. The difficult separation of rat proinsulin I and II, which are important for the study of rat insulin biosynthesis, was only achieved with two different stationary-mobile phase combinations.  相似文献   

18.
Silica-polypyrrole particles have been used as a composite stationary phase for liquid chromatography. Determination of capacity factors (k') of a wide number of polycyclic aromatic hydrocarbon (PAH) molecular probes allows the characterisation of the chromatographic properties of the silica-polypyrrole stationary phase. Capacity factors in the range of 0.10 up to 6.1 were determined, thus demonstrating the high affinity of the PAH probes towards the stationary phase. The selectivity of the composite stationary phase was also evaluated as a function of the planarity of the molecular probes injected. Capacity factors determined for PAHs (two-dimensional molecular probes) are higher than those measured for phenyl-substituted PAHs (phenyl-PAHs, three-dimensional molecular probes). Determination of capacity factors, dependence on the composition of the mobile phase demonstrates the reverse alpha-phase properties of the composite stationary phase. The acid-base properties of the composite silica-polypyrrole stationary phase were investigated using benzene derivative molecular probes (i.e., toluene, phenol, benzoic acid and aniline). Capacity factors in the range of 0.45 to 1.0 were determined. This study clearly demonstrates that this composite stationary phase exhibits selective interactions towards PAHs and phenyl-substituted PAHs and strong acid-base properties depending on the structure, the geometry and the acid-base properties of the molecular probes eluted.  相似文献   

19.
Selectivity of 15 stationary phases was examined, either commercially available or synthesized in-house. The highest selectivity factors were observed for solute molecules having different polarizability on the 3-(pentabromobenzyloxy)propyl phase (PBB), followed by the 2-(1-pyrenyl)ethyl phase (PYE). Selectivity of fluoroalkane 4,4-di(trifluoromethyl)-5,5,6,6,7,7,7-heptafluoroheptyl (F13C9) phase is lowest among all phases for all compounds except for fluorinated ones. Aliphatic octyl (C8) and octadecyl (C18) phases demonstrated considerable selectivity, especially for alkyl compounds. While PBB showed much greater preference for compounds with high polarizability containing heavy atoms than C18 phase, F13C9 phase showed the exactly opposite tendency. These three stationary phases can offer widely different selectivity that can be utilized when one stationary phase fails to provide separation for certain mixtures. The retention and selectivity of solutes in reversed-phase liquid chromatography is related to the mobile phase and the stationary phase effects. The mobile phase effect, related to the hydrophobic cavity formation around non-polar solutes, is assumed to have a dominant effect on retention upon aliphatic stationary phases such as C8, C18. In a common mobile phase significant stationary phase effect can be attributed to dispersion interaction. Highly dispersive stationary phases such as PBB and PYE retain solutes to a significant extent by (attractive) dispersion interaction with the stationary phase ligands, especially for highly dispersive solutes containing aromatic functionality and/or heavy atoms. The contribution of dispersion interaction is shown to be much less on C18 or C8 phases and was even disadvantageous on F13C9 phase. Structural properties of stationary phases are analyzed and confirmed by means of quantitative structure-chromatographic retention (QSRR) study.  相似文献   

20.
Summary A reversed-phase liquid chromatographic (RPLC) column, with which large oligodeoxynucleotides (oligo-DNAs) can be separated in well-resolved peaks, has been developed. The column contains only specially selected silica bonded with monochlorodimethyloctadecylsilane. The carbon content of the column packing is the predominant factor to achieve good results. With this column several mixtures containing different large oligo-DNAs could be separated with excellent resolution. Dedicated to Professor Morio Ikehara of Osaka University, on the occasion of his retirement in March 1986.  相似文献   

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