Reversed‐Phase HPLC

LoBrutto, Rosario; Kazakevich, Yuri

doi:10.1002/9780470087954.ch4

Cited by 17 publications

(6 citation statements)

References 152 publications

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“…[52] Upon ion interaction (either in mobile phase or adsorbed on the stationary phase surface) with the solvated protonated basic analyte, leads to the disruption of the analyte solvation shell and increase in the relative hydrophobicity of the analyte or the ion-associated species, which results in an increase in retention of the basic analyte. [14] Kazakevich, LoBrutto, et al assumed the existence of an equilibrium between solvated and desolvated analyte molecules and counteranions, and this was described mathematically. The Langmuir-type dependence of analyte retention increases with an increase of counterion concentration and has been explained on the basis of solvation-desolvation equilibrium.…”

Section: Ion-pairing Vs Ion Associationmentioning

confidence: 99%

“…They are characterized by significant delocalization of their charge, primarily symmetrical, usually in spherical shape, and at the same time they do not have deleterious properties of surfactant agents (surface modification of the bonded phase). [14] Recent developments in application of liophilic ions as mobile phase additives for basic compounds offer additional advantages in variation of selectivity and efficiency. In contrast to the irreversible adsorption of amphiphilic ions on the reversed phase surface, liophilic ions shows relatively weak interactions with the alkyl chains of the bonded phase.…”

Section: Liophilic Ionsmentioning

confidence: 99%

“…The influence of liophilic ions on the retention of basic analytes can be best described with three different possible mechanisms: [14] 1. Ion-pairing, which involves the formation of neutral ion-pairs and their retention according to the reversed-phase mechanism.…”

Section: Ionic Interactions With Liophilic Ionsmentioning

confidence: 99%

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Liophilic Mobile Phase Additives in Reversed Phase HPLC

Makarov

LoBrutto

Kazakevich

2008

Journal of Liquid Chromatography & Related Technologies

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The separation of basic compounds can be challenging and the use of inorganic mobile phase additives have been successfully used in chromatographic methods development. About fifteen years ago the role of these additives as ioninteraction agents for selectively adjusting retention of ionic analytes was discovered and the theory of chaotropicity was applied to reversed phase chromatography. In the last ten years the studies of the influence of these counterions on the retention of ionizable analytes and the interaction with the stationary phase in various hydro-organic eluents has expanded our knowledge of this phenomenon.The general view and understanding of the process have been significantly updated and the use of these ionic additives (liophilic ions) in the mobile phase has become regular practice in the pharmaceutical industry for optimization and fine tuning of complex separations. This paper reviews the latest developments in the field and discusses the modification and expansion of our theoretical understanding of the process. The paper also describes their application in practical separations for a wide variety of analytes, from small molecules to peptides and even chiral separations.

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Section: Ion-pairing Vs Ion Associationmentioning

confidence: 99%

Section: Liophilic Ionsmentioning

confidence: 99%

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Liophilic Mobile Phase Additives in Reversed Phase HPLC

Makarov

LoBrutto

Kazakevich

2008

Journal of Liquid Chromatography & Related Technologies

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“…Known also as ionic associations or ionic association complexes, ion pairs are pairs of oppositely charged ions held together by Coulomb attraction without formation of a covalent bond [1]. The lifetime of an ion pair was determined to be of at least 10 −5 seconds, equivalent to about 10 8 molecular vibrations, demonstrating that ion pairs can be considered as independent species [2].…”

Section: Introductionmentioning

confidence: 99%

Ion-Pair Spectrophotometry in Pharmaceutical and Biomedical Analysis: Challenges and Perspectives

Florea¹,

Ilie²

2017

Spectroscopic Analyses - Developments and Applications

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Experimental and theoretical studies of the mechanisms that underlay ion-pair formation, their properties and applications in various fields have been and still are focused by researchers since the introduction of the concept in 1926, by Bjerrum. Ion pairs are distinct chemical entities, electrically neutral, formed between ions of opposite charge and held together by Coulomb forces, without formation of a covalent bond. Investigation methods used are various, from classical conductometric measurements to up-to-date methods, such as spectrophotometry, chromatography and capillary electrophoresis. In the pharmaceutical field, ion pairs were used to develop methods of separation, identification and assay for the active substances in complex matrices, to obtain pharmaceutical formulations with controlled release and to explain the mechanisms of transport and action for certain drugs. The chapter is an attempt to describe new trends in the spectrophotometry of ion pairs and their applications in the pharmaceutical field. The development of the concept and types of ion pairs are first presented; further, examples of applications using molecular absorption, fluorimetry and resonance light scattering spectrophotometry are presented. Based on the literature data and the authors' experience in the field, challenges and perspectives in the ion-pair spectrophotometry are also considered.

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“…Elution of bonded phase hydrolysis products containing amine groups from these stationary phases may interfere with ESI MS detection [17,18]. Organic polymer-based mixed-mode columns have been reported to be stable over a wide pH range (e.g., [1][2][3][4][5][6][7][8][9][10][11][12][13][14], but suffer from low efficiencies [19]. Recent work to improve the hydrolytic stability of silica-based mixedmode RP/AX materials used a polymer-coating approach and functionalization via thiol-ene click reactions [18].…”

mentioning

confidence: 99%

Characterization of a highly stable mixed‐mode reversed‐phase/weak anion‐exchange stationary phase based on hybrid organic/inorganic particles

Walter

Alden

Field

et al. 2021

J of Separation Science

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We have characterized Atlantis ethylene‐bridged hybrid C18 anion‐exchange, a mixed‐mode reversed‐phase/weak anion‐exchange stationary phase designed to give greater retention for anions (e.g., ionized acids) compared to conventional reversed‐phase materials. The retention and selectivity of this stationary phase were compared to that of three benchmark materials, using a mixture of six polar compounds that includes an acid, two bases, and three neutrals. The compatibility of the ethylene‐bridged hybrid C18 anion‐exchange material with 100% aqueous mobile phases was also evaluated. We investigated the batch‐to‐batch reproducibility of the ethylene‐bridged hybrid C18 anion‐exchange stationary phase for 27 batches across three different particle sizes (1.7, 2.5, and 5 μm) and found it to be comparable to that of one of the most reproducible C18 stationary phases. We also characterized the acid and base stability of the ethylene‐bridged hybrid C18 anion‐exchange stationary phase and the results show it to be usable over a wide pH range, from 2 to 10. The extended upper pH limit relative to silica‐based reversed‐phase/weak anion‐exchange materials is enabled by the use of ethylene‐bridged hybrid organic/inorganic particles. The improved base stability allows Atlantis ethylene‐bridged hybrid C18 anion‐exchange to be used with a wider range of mobile phase pH values, opening up a greater range of selectivity options.

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Reversed‐Phase HPLC

Cited by 17 publications

References 152 publications

Liophilic Mobile Phase Additives in Reversed Phase HPLC

Liophilic Mobile Phase Additives in Reversed Phase HPLC

Ion-Pair Spectrophotometry in Pharmaceutical and Biomedical Analysis: Challenges and Perspectives

Characterization of a highly stable mixed‐mode reversed‐phase/weak anion‐exchange stationary phase based on hybrid organic/inorganic particles

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