A graphical method for understanding the kinetics of peak capacity production in gradient elution liquid chromatography

High temperature-ultra performance liquid chromatography-mass spectrometry for the metabonomic analysis of Zucker rat urine

The applicability and potential of using elevated temperatures and sub 2-microm porous particles in chromatography for metabonomics/metabolomics was investigated using, for the first time, solvent temperatures higher than the boiling point of water (up to 180 degrees C) and thermal gradients to reduce the use of organic solvents. Ultra performance liquid chromatography, combined with mass spectrometry, was investigated for the global metabolite profiling of the plasma and urine of normal and Zucker (fa/fa) obese rats (a well established disease animal model). "Isobaric" high temperature chromatography, where the temperature and flow rate follow a gradient program, was developed and evaluated against a conventional organic solvent gradient. LC-MS data were first examined by established chromatographic criteria in order to evaluate the chromatographic performance and next were treated by special peak picking algorithms to allow the application of multivariate statistics. These studies showed that, for urine (but not plasma), chromatography at elevated temperatures provided better results than conventional reversed-phase LC with higher peak capacity and better peak asymmetry. From a systems biology point of view, better group clustering and separation was obtained with a larger number of variables of high importance when using high temperature-ultra performance liquid chromatography (HT-UPLC) compared to conventional solvent gradients.

Peak capacity in unidimensional chromatography

The currently existing knowledge about peak capacity in unidimensional separations is reviewed. The majority of the paper is dedicated to reversed-phase gradient chromatography, covering specific techniques as well as the subject of peak compression. Other sections deal with peak capacity in isocratic chromatography, size-exclusion chromatography and ion-exchange chromatography. An important topic is the limitation of the separation power and the meaning of the concept of peak capacity for real applications.

Comparison of the practical resolving power of one- and two-dimensional high-performance liquid chromatography analysis of metabolomic samples

Two-dimensional liquid chromatography (2DLC) has become a mainstay of proteomics research due to its higher peak capacity compared to one-dimensional LC (1DLC). Because of the long analysis times typically associated with 2DLC (tens of hours) and its use primarily in proteomics applications, 2DLC in the context of general HPLC has been regarded as a niche technique for use in analysis of mixtures containing hundreds to thousands of components compared to the far more common techniques of isocratic and gradient elution 1DLC. A significant next step in the analytical development of 2DLC is to consider using its higher resolving power to reduce the analysis time of rather "simple" mixtures, in the range of only tens to hundreds of chemical constituents. The chief objective of this paper is to provide guidance to practitioners who need to decide whether 1DLC or 2DLC gives the superior separation in a given analysis time. Conditional peak capacities are predicted for fully optimized 1DLC and practical 2DLC separations of the low molecular weight constituents of an extract of corn seed at several analysis times using a model based on the chromatographic properties of compounds that are representative of real mixtures of lower molecular weight species. Two important corrections to the ideal 2DLC peak capacity are made to account for both incomplete usage of the separation space and the serious effect of first-dimension undersampling; this allows, we believe for the first time, a fair comparison of the resolving power of 1D- and 2DLC under realistic conditions. The predicted optimum conditions are then used to carry out experimental separations of low molecular weight corn seed extract, and peaks are counted in each 1D- and 2DLC chromatogram. Based on comparisons of both the predicted peak capacities and number of peaks observed in experimental chromatograms, we believe that practical 2DLC will be superior to fully optimized gradient 1DLC for separations lasting more than only about 10 min. This crossover time is much shorter than intuitively expected, and we believe this finding will inevitably have a major impact on the practice of 2DLC in liquid-phase separations in general.

Fast, comprehensive two-dimensional liquid chromatography

The absolute need to improve the separating power of liquid chromatography, especially for multi-constituent biological samples, is becoming increasingly evident. In response, over the past few years, there has been a great deal of interest in the development of two-dimensional liquid chromatography (2DLC). Just as 1DLC is preferred to 1DGC based on its compatibility with biological materials we believe that ultimately 2DLC will be preferred to the much more highly developed 2DGC for such samples. The huge advantage of 2D chromatographic techniques over 1D methods is inherent in the tremendous potential increase in peak capacity (resolving power). This is especially true of comprehensive 2D chromatography wherein it is possible, under ideal conditions, to obtain a total peak capacity equal to the product of the peak capacities of the first and second dimension separations. However, the very long timescale (typically several hours to tens of hours) of comprehensive 2DLC is clearly its chief drawback. Recent advances in the use of higher temperatures to speed up isocratic and gradient elution liquid chromatography have been used to decrease the time needed to do the second dimension LC separation of 2DLC to about 20s for a full gradient elution run. Thus, fast, high temperature LC is becoming a very promising technique. Peak capacities of over 2000 and rates of peak capacity production of nearly 1 peak/s have been achieved. In consequence, many real samples showing more than 200 peaks with signal to noise ratios of better than 10:1 have been run in total times of under 30 min. This report is not intended to be a comprehensive review of 2DLC, but is deliberately focused on the issues involved in doing fast 2DLC by means of elevating the column temperature; however, many issues of broader applicability will be discussed.

Gradient elution separation and peak capacity of columns packed with porous shell particles

The separation of the tryptic digests of myoglobin and bovine serum albumin were carried out in the gradient elution mode, using water, acetonitrile and TFA as the mobile phase components and columns packed with a new type of shell particles, Halo C(18). These particles give very high efficiencies, characterized with an unusually low eddy diffusion contribution and a small mass transfer contribution. However, because the molecular diffusivities of the peptides in the digest are small, the mobile phase velocity corresponding to the optimum velocity for maximum efficiency is also small, of the order of 0.3 mm/s. The gradient slopes also must be small. Peak capacities of 400 were achieved, with analysis time of the order of an hour.

Practice and theory of high temperature liquid chromatography

High temperature liquid chromatography (HTLC) exists in a temperature region beyond ambient (ca. 40 degrees C) and below super critical temperatures. The promises of HTLC, such as increased analysis speed, enhanced separation productivity, "green" LC with pure water mobile phases coupled to universal FID detection, and fast analysis of complex samples by combination with fast 2-D techniques, have become an option for routine practice. The focus of this paper is to review the key developments that have made the application of HTLC a practical technique and draw attention to new developments in 2-D techniques that incorporate HTLC that offer an opportunity to vastly increase the usefulness of HPLC for the analysis of complex samples.

Comprehensive two-dimensional liquid chromatography in analysis of Lamiaceae herbs: Characterisation and quantification of antioxidant phenolic acids

A fast and effective dynamic sonication assisted ethanol extraction method was developed for extracting phenolic acids from basil, oregano, rosemary, sage, spearmint and thyme of the Lamiaceae family. The results were compared with results obtained by conventional solvent extraction techniques. A comprehensive two-dimensional liquid chromatography (LC x LC) system interfaced to electrospray ionisation time-of-flight (TOF) mass spectrometry was then optimised for analysis and quantification of the herb extracts. The optimised LC x LC system employed a combination of C18 and cyano columns. The relative standard deviations for the retention times were better than 0.05% (rosmarinic acid 0.1%) and those for the peak areas 2-14% (2 mg/l, n=3). Limits of detection were 18-90 ng/ml. The LC x LC-MS method was applied to the quantitative analysis of phenolic acids, and the results were compared with those obtained with conventional LC-MS.

Characterization of the chemical composition of a block copolymer by liquid chromatography/mass spectrometry using atmospheric pressure chemical ionization and electrospray ionization

Liquid chromatography/mass spectrometry (LC/MS) with electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) in the positive and negative ion modes was used for the characterization of a block copolymer consisting of methoxy poly(ethylene oxide) (mPEO), an epsilon-caprolactone (CL) segment and linoleic acid (LA), used as surfactant in water-based latex paints. Chromatographic separation was obtained based on the number of CL units in the polymer species and the presence of an mPEO and/or LA tail. Different ionization methods were found to be complementary and only their combination allowed the qualitative profiling of the chemical composition. The LC/MS method has proven valuable for following the reaction in time, as well as for comparison of different polymeric surfactants.