SFC–MS Versus RPLC–MS for Drug Analysis in Biological Samples

Abstract

Keywords: MS • plasma • SFC-MS • supercritical fluid chromatography • urine Brief overview of modern supercritical fluid chromatography & coupling of SFC with MSThe advantages of supercritical fluid chromatography (SFC) over LC have been widely described in the past and include enhanced kinetic performance, due to the lower fluid viscosity and better solute diffusion coefficient; lower consumption of organic solvents; highly efficient chiral separation in presence of a supercritical fluid; and improvement of productivity at the preparative scale [1][2][3]. However, all these benefits were restricted by the lack of robustness/reliability, limited sensitivity and poor quantitative performance of old-generation SFC systems. This is certainly why SFC has never been considered as a forefront separation technique since its discovery in 1962 [4]. Over the last few years, a new generation of instruments and columns has appeared on the market. These new systems tackle the above-mentioned shortcomings. In addition, they also make SFC compatible with the most recent column types, such as the ones packed with fully porous sub-2 μm particles, or with sub-3 μm superficially porous particles [5].When dealing with the analysis of biological samples, another important aspect to consider is compatibility of the separation technique with MS, as this detector allows improving selectivity, sensitivity and identification power [6]. In theory, the coupling of SFC with ESI source should be straightforward since the mobile phase is composed of a high proportion of CO 2 , which should enhance the evaporation step during the ionization process. However, it is also important to keep in mind that CO 2 is decompressing through the transfer line between SFC and MS, leading to possible analyte precipitation and poor retention time repeatability. For these reasons, the coupling of SFC with ESI/MS involves the use of a dedicated interface. Among the existing interfaces, some of them are more universal or user friendly, while others are more sensitive [7]. Today, the most advantageous interface seems to be the pre-back pressure regulator (BPR) splitting interface using a make-up pump, as it offers good flexibility in terms of applicable chromatographic conditions, extended robustness and ease of use [7]. Which analytes are compatible with SFC-MS?In the early days of SFC, the mobile phase was exclusively composed of supercritical CO 2 , possessing a polarity close to that of hexane. Therefore, SFC was only suitable for the analysis of highly lipophilic compounds such as petroleum fractions, and remained hardly compatible with drugs and other compounds of biological interest [1,2]. To increase the mobile phase polarity and extend the range of compounds compatible with SFC, an organic modifier (in average between 5 and 40% methanol) is generally added to the supercritical CO 2 . With such a mobile phase, and considering the wide range of stationary phase chemistries available for SFC operation (e.g., polar, nonpolar, aromatic and mixedmode), this sep...

Supercritical fluid chromatography tandem mass spectrometry employed with evaporation‐free liquid–liquid extraction for the rapid analysis of cinnarizine in rat plasma

“…CNZ is a lipophilic compound, so an LLE method was developed. Considering the good compatibility of the SFC-MS/MS system with nonpolar solvents [29], the LLE method without nitrogen evaporation was further investigated. Different extraction solvents including ethyl acetate, dichloromethane, n-hexane, and MTBE were evaluated with extraction recoveries and matrix effects as indicators.…”

“…Such mobile phase is well suited for the elution of the lipophilic CNZ. In addition, unlike HPLC-MS/MS, SFC-MS/MS has good compatibility with nonpolar organic solvents [29], which makes it possible to omit the step of evaporation and reconstitution in LLE. Up to now, there is no report on the determination of CNZ concentrations in plasma by SFC-MS/MS method.…”

Instrumental and Technical Evolution Over the Past Decade in Bioanalysis

“…It offers high sensitivity MS detection since the mobile phase is inherently volatile and generally has complementary selectivity to reversed-phase LC applications mainly due to the nature of the fundamental hydrogen-bonding interactions, in contrast to reversed-phase LC. Broadly speaking, SFC remains to be fully established since a limited number of studies have been completed and reported, and this applies to matrix effect investigations in particular; however, it certainly constitutes an exciting complement of alternate and orthogonal selectivity to existing LC-MS techniques [27], not to mention a very green analytical tool.…”

Supercritical Fluid Chromatography in Natural Product Analysis – An Update

“…Due to the low concentration, complex matrices and wide range of active ingredients, appropriate sensitive and selective analytical methods are indispensable [65]. In comparison to LC-MS, the method of choice for most approaches, SFC is still in its infancy and the number of publications is meagre [66]. Therefore, the following two approaches are noteworthy, as they underline the auspicious potential of SFC in this sector that will surely gain in value in the future.…”