Systematic investigations of peak distortions due to additives in supercritical fluid chromatography

Emelie Glenne,Jörgen Samuelsson,Hanna Leek,Patrik Forssén,Magnus Klarqvist,Torgny Fornstedt

doi:10.1016/j.chroma.2020.461048

Emelie Glenne, Jörgen Samuelsson + Show 4 more

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https://doi.org/10.1016/j.chroma.2020.461048

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Abstract

The impact of eluent components added to improve separation performance in supercritical fluid chromatography was systematically, and fundamentally, investigated. The model system comprised basic pharmaceuticals as solutes and eluents containing an amine (i.e., triethylamine, diethylamine, or isopropylamine) as additive with MeOH as the co-solvent. First, an analytical-scale study was performed, systematically investigating the impact of the additives/co-solvent on solute peak shapes and retentions, using a design of experiments approach; here, the total additive concentration in the eluent ranged between 0.021 and 0.105 % (v/v) and the MeOH fraction in the eluent between 16 and 26 % (v/v). The co-solvent fraction was found to be the most efficient tool for adjusting retentions, whereas the additive fraction was the prime tool for improving column efficiency and peak analytical performance. Next, the impacts of the amine additives on the shapes of the so-called overloaded solute elution profiles were investigated. Two principal types of preparative peak deformations appeared and were investigated in depth, analyzed using computer simulation with mechanistic modeling. The first type of deformation was due to the solute eluting too close to the additive perturbation peak, resulting in severe peak deformation caused by co-elution. The second type of deformation was also due to additive–solute interactions, but here the amine additives acted as kosmotropic agents, promoting the multilayer adsorption to the stationary phase of solutes with bulkier aryl groups.

Highlights

Preparative supercritical fluid chromatography (SFC) is an important technique in the pharmaceutical industry and of increasing interest in the scientific community
The selection of the amine additive is based on several considerations, such as the effect on the chromatographic performance, the detector used in controlling the fractioning, post-purification removal, and reactivity
We will systematically investigate the impact on retention and peak/band shapes of both co-solvent and amine additives in the more complicated separation systems required for analysis of basic components

Summary

Introduction

Preparative supercritical fluid chromatography (SFC) is an important technique in the pharmaceutical industry and of increasing interest in the scientific community. In SFC, the mobile phase usually contains highly pressurized carbon dioxide (CO2) as the main weak solvent, with a polar co-solvent added to control retention. The addition of an amine additive will generally decrease the retention and improve the peak shapes for basic solutes in SFC [5,6], as was demonstrated in the early 1980s in reversed-phase liquid chromatography (RPLC) [7]. The selection of the amine additive is based on several considerations, such as the effect on the chromatographic performance, the detector used in controlling the fractioning, post-purification removal, and reactivity. The component ammonium hydroxide has been introduced as a water rich additive for improved chromatographic separation and purification of highly polar pharmaceuticals and peptides [9]

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