Fluoroalkylamines: Novel, Highly Volatile, Fast-Equilibrating, and Electrospray Ionization-Mass Spectrometry Signal-Enhancing Cationic Ion-Interaction Reagents.

Bassam Lajin,Walter Goessler

doi:10.1021/acs.analchem.0c02138

Bassam Lajin, Walter Goessler

Open Access

https://doi.org/10.1021/acs.analchem.0c02138

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Journal: Analytical Chemistry	Publication Date: Jun 22, 2020
Citations: 6	License type: cc-by

Affiliation: University of Graz

Abstract

A new class of cationic ion-interaction reagents for reversed-phase chromatography is introduced in the present work. Compounds belonging to a homologous series of linear fluoroalkyl chains including trifluoroethylamine (TFEAm), pentafluoropropylamine (PFPAm), heptafluorobutylamine (HFBAm), and nonafluoropentylamine (NFPAm) were tested and compared with ammonia and triethylamine (TEA) for the separation of selected organic acids of general interest such as the herbicides glyphosate, ethephon, and fosamine and arsenic metabolites methylarsonic acid and dimethylarsinic acid as well as other compounds. Depending on the carbon and fluorine atom number, the fluoroalkylamines were shown to be effective cationic ion-interaction reagents, significantly enhancing the retention of organic acids on a C18 reversed-phase column. Contrary to the general behavior of ion-interaction reagents (a broader term than ion-pairing reagent), significant (up to 5-fold) and consistent enhancement in the electrospray ionization mass spectrometry signal (ESI-MS) was observed relative to ammonia and triethylamine. Overall, among the tested series HFBAm was found to offer the best overall properties among the tested series as it provided a good compromise between column equilibration time (ca. 25 column volumes) and retention behavior (up to a 10-fold increase in the retention factor of acids relative to ammonia) while providing the same general advantages found for the fluoroalkylamines such as fast washout times from the ESIMS system (ca. 30 min) and a 3–5-fold signal enhancement. The fluoroalkylamines are a new class of cationic ion-interaction reagents with clear advantages over the currently employed alkylamines and may revive the general interest in ion-interaction chromatography.

Highlights

A new class of cationic ion-interaction reagents for reversed-phase chromatography is introduced in the present work
This application of the fluoroalkylamines was not described before, and there has been a single report about the incorporation of a fluoroalkylamine in liquid chromatography, in which Kamiusuki et al briefly mentioned the addition of heptafluorobutylamine to the mobile phase as a “masking agent of the adsorption point” within the course of a study that involved investigating the retention behavior of organic compounds on a polyfluoroalkylsilane stationary phase in an attempt to achieve an improvement in the separation of three fluoroaniline isomers.[22]
Our choice of fluoroalkylamines to be included in the present study was based on three interrelated criteria: (1) water solubility/miscibility at concentrations normally employed in ion-interaction chromatography (1−10 mM) under acidic pH values where the fluoroalkylamine is positively charged; (2) volatility and a sufficiently low boiling point (

Summary

Introduction

A new class of cationic ion-interaction reagents for reversed-phase chromatography is introduced in the present work. Driven by some of the positive aspects and widespread use of the fluorinated carboxylic acids in reversed-phase chromatography, the aim of the present work was to investigate the use of commercially available fluoroalkylamine compounds as cationic ion-interaction reagents This application of the fluoroalkylamines was not described before, and there has been a single report about the incorporation of a fluoroalkylamine in liquid chromatography, in which Kamiusuki et al briefly mentioned the addition of heptafluorobutylamine to the mobile phase as a “masking agent of the adsorption point” within the course of a study that involved investigating the retention behavior of organic compounds on a polyfluoroalkylsilane stationary phase in an attempt to achieve an improvement in the separation of three fluoroaniline isomers.. The compounds were purchased from Sigma-Aldrich (Steinheim, Germany) and prepared in pure water (18.2 MΩ cm) at a concentration in the range of 0.1−15 mg L−1 in a mixture which was used for the chromatographic investigations (see below)

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