Supercritical fluid chromatography for the enantioseparation of pharmaceuticals

A rapid and highly specific method to evaluate the presence of 2-(2-phenylethyl) chromones in agarwood by supercritical fluid chromatography-mass spectrometry

The detection and structural characterization of the major constituents of agarwood, 2-(2-phenylethyl)chromones, are important to quality control and the establishment of the authenticity of agarwood samples. However, a highly specific and rapid method for the evaluation of 2-(2-phenylethy)chromones in agarwood has not been reported to date. In this study, we developed a method using super- critical fluid chromatography in combination with mass spectrometry (SFC-MS). Tropylium ions, the characteristic product ions of 2-(2-phenylethyl)chromones in tandem mass spectrometric experiments, were selected for the targeted detection of 2-(2-phenylethyl) chromones. This method used precursor ion scans for tropylium ions with different possible substitutions on a triple-quadrupole mass spectrometer. To evaluate the usefulness of the developed method, a diethyl ether extract from a Chinese agarwood "Qi-Nan" sample was first separated using SFC, and the elutes were later subjected to precursor ion scans, which searched for 15 common substituted tropylium ions to evaluate the 2-(2-phenylethyl)chromones. In the precursor ion scans, a total of 29 2-(2-phenylethyl)chromones were detected and investigated further using tandem mass spectrometry (MS/MS) to obtain more detailed structural information. By comparing the retention times and m/z values of the precursor ions with reference standards, nine of the detected compounds were unequivocally identified. The remaining compounds were tentatively identified by analyzing the MS/MS spectra. This method provides a rapid and efficient method for evaluating the 2-(2-phenylethyl)chromones present in a sample, which aids in quality control and the establishment of the authenticity of the agarwood sample.

Impact of injection solvents on supercritical fluid chromatography

Even though there has been a rapid development in instrumentation and applications of supercritical fluid chromatography (SFC), relatively little is known about retention mechanisms compared to high-performance liquid chromatography (HPLC). Much effort has been made to characterize the influence of injection solvents on chromatographic efficiency in HPLC, however has been left rather uninvestigated in the domain of SFC. In this study properties of different injection solvents have been studied and correlated with properties of seven various analytes on three different columns, a C18, a 2-ethylpyridine and a bare-silica column. Aided by calculations of correlation coefficients and principal component analysis (PCA), the physical properties of injection solvents and the interactions between injection solvent, solute and stationary phase were investigated. The findings of this work shows that interactions capable of masking accessible silanol groups on a C18 column are of importance in order to maximize the plate number. While solvents with dipolar and hydrogen bond interaction properties are associated negatively with chromatographic efficiency using polar columns. Properties such as molar density, vapor pressure and boiling point were related to sharper peaks, mostly likely because of solubility issues of the injection solvent into the methanol-modified carbon dioxide. However, no additional solubility due to hydrogen interactions between the injection solvent and the carbon dioxide in SFC was observed. Surface tension and viscosity was not particularly associated with a decrease in plate numbers. By increasing the injection volume a stronger correlation between solubility related properties and plate numbers were obtained. Additional experiments showed that the resistance in solubility became an issue when performing partial-loop injection where additional washing solvent entered the system, thus providing broadened peaks.

Chiral derivatizations applied for the separation of unusual amino acid enantiomers by liquid chromatography and related techniques

Amino acids are essential for life, and have many functions in metabolism. One particularly important function is to serve as the building blocks of peptides and proteins, giving rise complex three dimensional structures through disulfide bonds or crosslinked amino acids. Peptides are frequently cyclic and contain proteinogenic as well as nonproteinogenic amino acids in many instances. Since most of the proteinogenic α-amino acids contain at least one stereogenic center (with the exception of glycine), the stereoisomers of all these amino acids and the peptides in which they are to be found may possess differences in biological activity in living systems. The impetus for advances in chiral separation has been highest in the past 25 years and this still continues to be an area of high focus. The important analytical task of the separation of isomers is achieved mainly by chromatographic and electrophoretic methods. This paper reviews indirect separation approaches, i.e. derivatization reactions aimed at creating the basis for the chromatographic resolution of biologically and pharmaceutically important enantiomers of unusual amino acids and related compounds, with emphasis on the literature published from 1980s. The main aspects of the chiral derivatization of amino acids are discussed, i.e. derivatization on the amino group, transforming the molecules into covalently bonded diastereomeric derivatives through the use of homochiral derivatizing agents. The diastereomers formed (amides, urethanes, urea and thiourea derivatives, etc.) can be separated on achiral stationary phases. The applications are considered, and in some cases different derivatizing agents for the resolution of complex mixtures of proteinogenic d,l-amino acids, non-proteinogenic amino acids and peptides/amino acids from peptide syntheses or microorganisms are compared.

UHPLC: The Greening Face of Liquid Chromatography

Pharmaceutical analysis based on chromatographic separation is an important part of studies aimed at developing routine quality analysis of drugs. High-performance liquid chromatography (HPLC) is one of the main analytical techniques recommended for drug analysis. Although it meets many criteria vital for analysis, it is time-consuming and uses a relatively high amount of organic solvents compared to other analytical techniques. Recently, Ultra-high-performance liquid chromatography (UHPLC) has been frequently proposed as an alternative to HPLC, which means introducing an environment-friendly approach to drug analysis achieved by reducing the consumption of solvents. It also offers greater chromatographic resolution and higher sensitivity as well as requiring less time due to faster analysis. This review focuses on the basics of UHPLC, compares that technique with HPLC and discusses the possibilities of applying UHPLC for the analysis of different pharmaceuticals and biopharmaceuticals.