Interpretation of the excess adsorption isotherms of organic eluent components on the surface of reversed-phase adsorbents

Kazakevich, Yuri; LoBrutto, Rosario; Chan, F.; Patel, Tarun S.

doi:10.1016/s0021-9673(00)01239-5

Cited by 166 publications

(146 citation statements)

References 47 publications

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“…For excess isotherm measurements, each column was equilibrated with mobile phase of decreasing concentration of organic solvent in water (100, 98, 94, 90, 80, 70,60,50,40,30,20,10,8,4,0) by pumping at least 30 mL of solvent mixture. Perturbation of the baseline was done by a 5-mL injection of the mixture with higher concentration of organic solvent than the plateau concentration.…”

Section: Excess Isotherm Measurementmentioning

confidence: 99%

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Modeling solvation on the chemically modified silica surfaces

Buszewski

Bocian

Nowaczyk

2010

J of Separation Science

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A detailed molecular-level description of the retention mechanism in RP-HPLC is a point of great interest to analytical chemists. For this purpose, the solvent adsorption on the octadecyl stationary-bonded phase was investigated. Preferential adsorption of solvents from the acetonitrile-water mobile phase was modeled on the silica surface with one, two, three and four organic ligands, which represents a series of non-end-capped-bonded phases with different coverage density of bonded ligands. As a result of the computer simulation, the increase of adsorbed acetonitrile around bonded ligands is observed. The number of water molecules near the modeled surface is observed as well. The results are in agreement with experimental measurement of acetonitrile excess adsorption isotherms on the series of in-house made stationary-bonded phase.

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Section: Excess Isotherm Measurementmentioning

confidence: 99%

“…The solvent used as a mobile phase forms a diffuse layer on the surface [4,30]. Hence, the effecting stationary phase in RP systems consists of the organic ligand, residual silanols and extracted solvent molecules [31].…”

Section: Introductionmentioning

confidence: 99%

Modeling solvation on the chemically modified silica surfaces

Buszewski

Bocian

Nowaczyk

2010

J of Separation Science

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“…However, ACN in the mobile phase was problematic. We suspected that the different behavior was due to the tendency for ACN to more extensively solvate C18 type stationary phases compared to MeOH [23,24]. When a diluent containing a stronger solvent such as IPA or THF solvent was injected in a mobile phase containing ACN, it apparently displaced some of the adsorbed ACN from the stationary phase, causing a pulse of ACN-rich mobile phase to migrate through the column.…”

Section: Use Of Solvents In the Mobile Phasementioning

confidence: 99%

Using strong injection solvents with 100% aqueous mobile phase in RP-LC

Loeser¹,

Drumm

2006

J. Sep. Sci.

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When samples are dissolved for HPLC analysis, organic solvents are often used to enhance the solubility of the sample components. However, when the diluent becomes significantly stronger than the mobile phase, peak shape distortions may develop during injection. This is a serious problem for weakly retained analytes under 100% aqueous mobile phase conditions. Under these extreme conditions, even small amounts of solvent in the diluent can cause serious broadening or distortion effects. However, if the organic solvent used in the diluent elutes significantly after the analyte, the peak shape of the analyte will be relatively unaffected, even when a relatively strong solvent such as THF is used. This phenomenon is counterintuitive considering the usual practice of keeping the sample diluent as weak as possible. This report describes the potential analytical utility and limitations of this approach for the analysis of weakly retained analytes.

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“…Many models are proposed to express the analyte distribution between the eluent and the stationary phase. [30][31][32][33] Recent investigations have shown that alkyl chains bonded to the silica surface are densely packed or liquid-like 32) and that methanol forms a monomolecular adsorbed layer on a silica surface on the top of collapsed bonded layer.…”

Section: Resultsmentioning

confidence: 99%

Hydrophobicity Parameters Determined by Reversed-Phase Liquid Chromatography. XV: Optimal Conditions for Prediction of log Poct by Using RP-HPLC Procedures.

Yamagami

Kawase

Iwaki

2002

CHEMICAL & PHARMACEUTICAL BULLETIN

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Recently, in connection with the remarkable development of computational technologies for rational drug designs, the necessity has become apparent of rapid measurement or estimation of molecular properties of chemicals having a potential for medical use. In particular, hydrophobicity (as expressed by the logarithm of 1-octanol/water partition coefficient, log P oct ) is identified as one of the most important properties that govern potencies; its prediction has attracted much attention from medicinal chemists, agrochemists and many investigators in various fields such as pharmacology, toxicology, environmental chemistry and food chemistry. 1,2)Instead of measuring log P oct by the standard but time-consuming shake-flask method, reversed-phase chromatography (RP-HPLC) has increasingly been used as a powerful tool to predict log P oct from the readily accessible retention factor, log k, (given by kϭ(t R Ϫt 0 )/t 0 where t 0 and t R express elution times of the non-retained substance and sample, respectively).Extensive studies have been made to establish an optimal RP-HPLC system providing a good linearity between log P oct and log k.3-10) Many workers have used an ODS-type column with methanol-water mobile phases to obtain a normalized parameter, log k W (k W : the retention factor extrapolated to 0% organic modifier), as an alternative to log P oct . 3,5,8) In our experience, this log k W approach works well for non-polar solutes but tends to provide overestimated log P oct values for strong H-acceptors. [10][11][12][13][14][15] From systematic studies of log k obtained under various HPLC conditions for typical heteroaromatic compounds such as (di)azines, furans and thiophenes, we were led to the conclusion that the use of an eluent containing around 50% methanol, which usually provides a more direct correlation with log P oct , is the most convenient and practical procedure for rapid estimation of log P oct provided H-donors (amphiprotic compounds) are treated separately.11-15) Our results so far obtained are illustrated graphically in Fig. 1. This conclusion has been derived from the following results.First, we have shown that, for each series of monosubstituted (di)azines, log P oct can be excellently correlated with log k in different compositions of methanol-water eluents by a general formula Eq. 1 containing two terms correcting for H-bonding effects: 16) log kϭalog P oct ϩrs I ϩsS HA ϩconst.( 1) where the s I parameter represents the Charton's inductive electronic substituent constant, 17) and S HA designates the substituent H-acceptor scale that we have recently defined where the value of S HA is set at unity for H (the unsubstituted * To whom correspondence should be addressed. The use of log k derived from reversed phase (RP)-HPLC retention times provides a convenient method for estimating log P oct values (P oct : 1-octanol/water partition coefficient). In order to establish optimal HPLC conditions, the difference between chromatographic (C18 modified column and aqueous methanol eluents) and bulk solve...

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Interpretation of the excess adsorption isotherms of organic eluent components on the surface of reversed-phase adsorbents

Cited by 166 publications

References 47 publications

Modeling solvation on the chemically modified silica surfaces

Modeling solvation on the chemically modified silica surfaces

Using strong injection solvents with 100% aqueous mobile phase in RP-LC

Hydrophobicity Parameters Determined by Reversed-Phase Liquid Chromatography. XV: Optimal Conditions for Prediction of log Poct by Using RP-HPLC Procedures.

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