Applicability of supercritical fluid chromatography - mass spectrometry to metabolomics. I - Optimization of separation conditions for the simultaneous analysis of hydrophilic and lipophilic substances.

The aim of this study was to evaluate the suitability of SFC-MS for the analysis of a wide range of compounds including lipophilic and highly hydrophilic substances (log P values comprised between -6 and 11), for its potential application toward human metabolomics. For this purpose, a generic unified chromatography gradient from 2 to 100% organic modifier in CO2 was systematically applied. In terms of chemistry, the best stationary phases for this application were found to be the Agilent Poroshell HILIC (bare silica) and Macherey-Nagel Nucleoshell HILIC (silica bonded with a zwitterionic ligand). To avoid system overpressure at very high organic modifier proportion, columns of 100 × 3 mm I.D. packed with sub-3 µm superficially porous particles were selected. In terms of organic modifier, a mixture of 95% MeOH and 5% water was selected, with 50 mM ammonium formate and 1 mM ammonium fluoride, to afford good solubility of analytes in the mobile phase, limited retention for the most hydrophilic metabolites and suitable peak shapes of ionizable species. A sample diluent containing 50%ACN/50% water was employed as injection solvent. These conditions were applied to a representative set of metabolites belonging to nucleosides, nucleotides, small organic acids, small bases, sulfated/sulfonated metabolites, poly-alcohols, lipid related substances, quaternary ammonium metabolites, phosphate-based substances, carbohydrates and amino acids. Among all these metabolites, 65% of the compounds were adequately analyzed with excellent peak shape, 23% provided distorted peak shapes, while only 12% were not detected (mostly metabolites having several phosphate or several carboxylic acid groups).

First inter-laboratory study of a Supercritical Fluid Chromatography method for the determination of pharmaceutical impurities.

Supercritical Fluid Chromatography (SFC) has known a strong regain of interest for the last 10 years, especially in the field of pharmaceutical analysis. Besides the development and validation of the SFC method in one individual laboratory, it is also important to demonstrate its applicability and transferability to various laboratories around the world. Therefore, an inter-laboratory study was conducted and published for the first time in SFC, to assess method reproducibility, and evaluate whether this chromatographic technique could become a reference method for quality control (QC) laboratories. This study involved 19 participating laboratories from 4 continents and 9 different countries. It included 5 academic groups, 3 demonstration laboratories at analytical instrument companies, 10 pharmaceutical companies and 1 food company. In the initial analysis of the study results, consistencies within- and between-laboratories were deeply examined. In the subsequent analysis, the method reproducibility was estimated taking into account variances in replicates, between-days and between-laboratories. The results obtained were compared with the literature values for liquid chromatography (LC) in the context of impurities determination. Repeatability and reproducibility variances were found to be similar or better than those described for LC methods, and highlighted the adequacy of the SFC method for QC analyses. The results demonstrated the excellent and robust quantitative performance of SFC. Consequently, this complementary technique is recognized on equal merit to other chromatographic techniques.

Evaluation of stationary phases packed with superficially porous particles for the analysis of pharmaceutical compounds using supercritical fluid chromatography.

Superficially porous particles (SPP), or core shell particles, which consist of a non-porous silica core surrounded by a thin shell of porous silica, have gained popularity as a solid support for chromatography over the last decade. In the present study, five unbonded silica, one diol, and two ethylpyridine (2-ethyl and 4-ethyl) SPP columns were evaluated under SFC conditions using two mixtures, one with 17 drug-like compounds and the other one with 7 drug-like basic compounds. Three of the SPP phases, SunShell™ 2-ethylpyridine (2-EP), Poroshell™ HILIC, and Ascentis(®) Express HILIC, exhibited superior performances relative to the others (reduced theoretical plate height (hmin) values of 1.9-2.5 for neutral compounds). When accounting for both achievable plate count and permeability of the support using kinetic plot evaluation, the Cortecs™ HILIC 1.6µm and Ascentis(®) Express HILIC 2.7µm phases were found to be the best choices among tested SPPs to reach efficiencies up to 30,000 plates in the minimum amount of time. For desired efficiencies ranging from 30,000 to 60,000 plates, the SunShell™ 2-EP 2.6µm column clearly outperformed all other SPPs. With the addition of a mobile phase additive such as 10mM ammonium formate, which was required to elute the basic components with sharp peaks, the Poroshell™ HILIC, SunShell™ Diol and SunShell™ 2-EP phases represent the most orthogonal SPP columns with the highest peak capacities. This study demonstrates the obvious benefits of using columns packed with SPP on current SFC instrumentation.

Automated approach for the rapid identification of purification conditions using a unified, walk-up high performance liquid chromatography/supercritical fluid chromatography/mass spectrometry screening system.

Integration of supercritical fluid/mass spectrometry (SFC/MS) and reversed phase liquid (HPLC/MS) chromatographic screening techniques into a single chromatographic system and utilized in "walk up" mode, enabled us to produce an orthogonal data set for selecting purification conditions for medicinal chemistry compounds. To streamline the overall workflow, we also demonstrate the use of automated batch data processing of individual data files to identify suitable separation conditions without user intervention. We have addressed the chromatographic challenges that hinder the identification of the intended target and thus the selection of ideal purification conditions. For instance, multiple component-of-interest (COI) peaks, co-elution of impurities with the COI, and chromatographic suitability factors such as retention times and peak shapes are all important considerations when selecting appropriate methods for purification and, therefore, are bottlenecks to an automated approach. Since SFC and HPLC data were collected in parallel from separate instruments in our workflow, the time required for the separation scientist to analyze acquired data from both systems was a time-limiting factor. To reduce data processing time and accelerate or "FastTrack" samples to purification, two unique and automated solutions were introduced. We describe the implementation of an integrated, multi-column, walk-up HPLC/SFC/MS system, and the implementation of an intelligent, automated method selection application which uses advanced data evaluation criteria to selectively score and identify the most practical separation conditions for SFC/MS and HPLC/MS methodologies.

High-throughput bioassay-guided fractionation: a technique for rapidly assigning observed activity to individual components of combinatorial libraries, screened in HTS bioassays.

In this paper, we describe an automated, high-throughput analytical tool for the unambiguous characterization of the active component(s) of a combinatorially derived reaction mixture. We call this technique high-throughput bioassay-guided fractionation (BGF). The novel aspects of this communication are the systematization of the BGF concept, the application of BGF to combinatorial chemistry, and the high-throughput nature of the identification technique. The identification of the active component in a well mixture is an essential step for subsequent resynthesis or isolation of the active component(s) or for removal of intractable wells from further consideration. We believe the technique described is also applicable to any mixture library, provided the expected component (or components) of each well is (are) known. Example mixture libraries would include collections of synthetic chemicals and collections of purified natural products. The mixture need not come from libraries produced using parallel synthesis. The BGF tool described herein allows full utilization of highly diverse combinatorial libraries, thereby obviating costly up-front purification or extensive prescreening characterization efforts.