Davy Guillarme

Modern analytical supercritical fluid chromatography using columns packed with sub-2 μm particles: a tutorial.

This tutorial provides an overview of the possibilities, limitations and analytical conditions of modern analytical supercritical fluid chromatography (SFC) using columns packed with sub-2 μm particles. In particular, it gives a detailed overview of commercially available modern SFC instrumentation and the detectors that can be employed (UV, MS, ELSD, FID, etc.). Some advice on the choice of the stationary phase dimensions and chemistries, the nature of the mobile phase (choice of organic modifier and additives) and its flow rate as well as the backpressure and temperature are also provided. Finally, several groups of potentially problematic compounds, including lipophilic compounds, hydrophilic substances and basic drugs, are discussed in detail. All these families of analytes can be resolved with SFC but require specific analytical conditions.

Intact protein analysis in the biopharmaceutical field

In recent years, a growing number of biopharmaceutical proteins have been produced and are already available, or will be soon available, in the market. These molecules are more complex to analyze than conventional low molecular weight drugs, and thus need powerful analytical approaches for the entire development and delivery process. This review summarizes the analytical techniques available for intact protein determination and the main development steps in which they are applicable. A strong emphasis has been put on separation techniques, liquid chromatography and electrophoretic techniques, but mass spectrometry and spectroscopic approaches are also mentioned. Overall, we highlight how several analytical strategies are necessary to obtain global information.

Comparison of ultra-high performance supercritical fluid chromatography and ultra-high performance liquid chromatography for the analysis of pharmaceutical compounds.

Currently, columns packed with sub-2 μm particles are widely employed in liquid chromatography but are scarcely used in supercritical fluid chromatography. The goal of the present study was to compare the performance, possibilities and limitations of both ultra-high performance liquid chromatography (UHPLC) and ultra-high performance supercritical fluid chromatography (UHPSFC) using columns packed with sub-2 μm particles. For this purpose, a kinetic evaluation was first performed, and van Deemter curves and pressure plots were constructed and compared for columns packed with hybrid silica stationary phases composed of 1.7 and 3.5 μm particles. As expected, the kinetic performance of the UHPSFC method was significantly better than that of the UHPLC. Indeed, the h(min) values were in the same range with both strategies and were between 2.2 and 2.8, but u(opt) was increased by a factor of >4 in UHPSFC conditions. Another obvious advantage of UHPSFC over UHPLC is related to the generated backpressure, which is significantly lower in the presence of a supercritical or subcritical fluid. However, the upper pressure limit of the UHPSFC system was only ∼400 bar vs. ∼1000 bar in the UHPLC system, which prevents the use of highly organic mobile phases at high flow rates in UHPSFC. Second, the impact of reducing the particle size (from 3.5 to 1.7 μm) was evaluated in both UHPLC and UHPSFC conditions. The effect of frictional heating on the selectivity was demonstrated in UHPLC and that of fluid density or decompression cooling was highlighted in UHPSFC. However, in both cases, a change in selectivity was observed for only a limited number of compounds. Third, various types of column chemistries packed with 1.7 μm particles were evaluated in both UHPLC and UHPSFC conditions using a model mixture of acidic, neutral and basic compounds. It has been shown that more drastic changes in selectivity were obtained using UHPSFC columns compared to those obtained by changing UHPLC columns. In addition, there was a good complementarity between the two separation modes. Finally, by combining the use of small particles with supercritical fluids as a mobile phase, it was possible to achieve the analysis of pharmaceutical compounds in less than 1 min or to attain a peak capacity of more than 250 in approximately 40 min, both with a high degree of repeatability.

Theory and practice of size exclusion chromatography for the analysis of protein aggregates

Size exclusion chromatography (SEC) is a historical technique widely employed for the detailed characterization of therapeutic proteins and can be considered as a reference and powerful technique for the qualitative and quantitative evaluation of aggregates. The main advantage of this approach is the mild mobile phase conditions that permit the characterization of proteins with minimal impact on the conformational structure and local environment. Despite the fact that the chromatographic behavior and peak shape are hardly predictable in SEC, some generic rules can be applied for SEC method development, which are described in this review. During recent years, some improvements were introduced to conventional SEC that will also be discussed. Of these new SEC characteristics, we discuss (i) the commercialization of shorter and narrower columns packed with reduced particle sizes allowing an improvement in the resolution and throughput; (ii) the possibility of combining SEC with various detectors, including refractive index (RI), ultraviolet (UV), multi-angle laser light scattering (MALLS) and viscometer (IV), for extensive characterization of protein samples and (iii) the possibility of hyphenating SEC with mass spectrometry (MS) detectors using an adapted mobile phase containing a small proportion of organic modifiers and ion-pairing reagents.

Coupling ultra high-pressure liquid chromatography with mass spectrometry: Constraints and possible applications

The introduction of columns packed with porous sub-2μm particles and the extension of the upper pressure limit of HPLC instrumentation to 1300bar (ultra-high pressure liquid chromatography, UHPLC) has opened new frontiers in resolution and speed of analysis. However, certain constraints appear when coupling UHPLC technology with mass spectrometry (MS). First, the most significant limitation is related to the narrow peaks that are produced by UHPLC that require a fast duty cycle, which is only available on the latest generations of MS devices. Thus, certain analyzers are more readily compatible with UHPLC (e.g., QqQ or TOF/MS) than others (e.g., ion trap or FT-MS). Second, due to the reduction of the column volume, extra-column band broadening can become significant, leading to a reduction in the kinetic performance of the UHPLC-MS configuration. Third, as the mobile phase linear velocity is higher in UHPLC, the electrospray ionization source must also be able to provide high sensitivity at flow rates of up to 1mL/min. Despite these limitations, the UHPLC-MS/MS platform has successfully been employed over the last decade for various types of applications, including those related to bioanalysis, drug metabolism, multi-residue screening, metabolomics, biopharmaceuticals and polar compounds.

A systematic investigation of the effect of sample diluent on peak shape in hydrophilic interaction liquid chromatography

The aim of this study was to evaluate the importance of sample diluents to improve peak shapes in hydrophilic interaction liquid chromatography (HILIC), using low molecular weight (<1000 Da) analytes as well as peptides (with MW ranging between 1000 and 6000 Da) as model compounds. Various solvents were tested including water, acetonitrile, methanol, ethanol, propan-2-ol, dimethyl sulfoxide, and a number of combinations of them. For the analysis of small MW compounds, best peak shapes were obtained with sample dissolved in pure ACN but, IPA or a mixture of ACN/IPA (50:50, v/v) could represent a viable alternative in the case of solubility issues with pure ACN. For drug discovery applications, DMSO can be employed but in combination with at least 80% of ACN. For peptides analysis, acetonitrile, EtOH and IPA as sample diluents, provided similar chromatographic profiles, but pure EtOH or IPA were recommended to limit denaturation and samples solubility issues. Finally, whatever the nature of the compounds, it is recommended to add the lowest amount of water to the sample diluent, to maintain suitable peak shapes.

New trends in reversed-phase liquid chromatographic separations of therapeutic peptides and proteins: theory and applications.

In the pharmaceutical field, there is considerable interest in the use of peptides and proteins for therapeutic purposes. There are various ways to characterize such complex samples, but during the last few years, a significant number of technological developments have been brought to the field of RPLC and RPLC-MS. Thus, the present review focuses first on the basics of RPLC for peptides and proteins, including the inherent problems, some possible solutions and some directions for developing a new RPLC method that is dedicated to biomolecules. Then the latest advances in RPLC, such as wide-pore core-shell particles, fully porous sub-2 μm particles, organic monoliths, porous layer open tubular columns and elevated temperature, are described and critically discussed in terms of both kinetic efficiency and selectivity. Numerous applications with real samples are presented that confirm the relevance of these different strategies. Finally, one of the key advantages of RPLC for peptides and proteins over other historical approaches is its inherent compatibility with MS using both MALDI and ESI sources.

Evaluation of various HILIC materials for the fast separation of polar compounds.

In recent years, numerous works have been reported on hydrophilic interaction chromatography (HILIC) columns, but there is a growing demand for fast separations with improved resolution. Such analyses can only be obtained with the new generation of columns and instrumentation. In the present study, HILIC columns packed with porous sub-2 microm particles or with superficially porous particles of 2.7 microm were evaluated. A set of 15 compounds with diverse physicochemical properties was selected. The aim of this study was to compare the chromatographic behavior of three selected columns. Concerning kinetic performance, the fused-core column offers a backpressure two times lower than the sub-2-microm particle columns. However, these superficially porous particles also generated a 30% lower efficiency. The complex mechanism of HILIC was also investigated on bare silica columns, confirming that the mechanism is a mixture of partitioning, adsorption and ion exchange in different proportions according to the nature of the analytes, the composition of the mobile phase and the characteristics of the analytical support. Finally, a rapid separation of three drugs and their corresponding metabolites was carried out. The analysis time was reduced to less than 4 min while maintaining acceptable backpressure and sufficient resolution.

UPLC–TOF-MS for plant metabolomics: A sequential approach for wound marker analysis in Arabidopsis thaliana ☆

The model plant Arabidopsis thaliana was studied for the search of new metabolites involved in wound signalling. Diverse LC approaches were considered in terms of efficiency and analysis time and a 7-min gradient on a UPLC-TOF-MS system with a short column was chosen for metabolite fingerprinting. This screening step was designed to allow the comparison of a high number of samples over a wide range of time points after stress induction in positive and negative ionisation modes. Thanks to data treatment, clear discrimination was obtained, providing lists of potential stress-induced ions. In a second step, the fingerprinting conditions were transferred to longer column, providing a higher peak capacity able to demonstrate the presence of isomers among the highlighted compounds.

Importance of instrumentation for fast liquid chromatography in pharmaceutical analysis

In the last decade, an important technical evolution has occurred in pharmaceutical analysis with numerous innovative supports and advanced instruments that have been proposed to achieve fast or ultra-fast separations in LC with an excellent sensitivity and ease of operation. Among the proposed strategies to increase the throughput, the use of short narrow-bore columns packed with sub-3 μm core-shell and porous sub-2 μm particles have emerged as the gold standards. Nevertheless, to take the full benefits of these modern supports, a suitable chromatographic system has to be employed. This review summarizes the instrumental needs and challenges in terms of extra-column variance, dwell volume, maximum system pressure, detector data acquisition rate, and injection cycle time. In addition, because of their reasonable pressure drop, the use of columns packed with sub-3 μm core-shell particles on a conventional LC instrument is discussed in detail. A methodology is proposed to check the compatibility between stationary phase and instrument, and some solutions are proposed to improve the performance of standard instruments. Finally, because the column technology is evolving faster than instrumentation, it is nowadays possible to purchase short, narrow-bore columns packed with 1.3 μm core-shell particles. Micro columns (1 mm I.D.) packed with 1.7-1.9 μm porous particles are also available from several providers, which limit frictional heating effects and reduce solvent and sample consumption. However, it remains difficult to find instruments compatible with such column geometries and a severe loss of performance may be observed due to the system itself.