Development of an on-line size exclusion chromatographic — reversed-phase liquid chromatographic two-dimensional system for the quantitative determination of peptides with concentration prior to reversed-phase liquid chromatographic separation

Comprehensive multi-dimensional liquid chromatographic separation in biomedical and pharmaceutical analysis: a review

'Multi-dimensional' liquid separations have a history almost as long as chromatography. In multi-dimensional chromatography the sample is subjected to more than one separation mechanism; each mechanism is considered an independent separation dimension. The separations can be carried out either offline via fraction collection, or directly coupled online. Early multi-dimensional separations using combinations of paper chromatography, electrophoresis and gels, in both planar and columnar modes are reviewed. Developments in HPLC have increased the number of measurable analytes in ever more complex matrices, and this has led to the concept of 'global metabolite profiling'. This review focuses on the theory and practice of modern 'comprehensive' multi-dimensional liquid chromatography when applied to biomedical and pharmaceutical analysis.

Prototype for integrated two-dimensional gel electrophoresis for protein separation

Two-dimensional gel electrophoresis practitioners have long waited for a fully automated system. This article presents an integrated platform that is capable of complete automation from sample introduction to spots detection. The strip gel for the first dimensional separation is fixed on the edge of a discrete planar stage before separation. A pair of platinum pin electrodes for isoelectric focusing (IEF) makes contact from underneath the stage. IEF is performed directly after rehydration and protein loading. After the first dimensional separation, sodium dodecyl sulfate (SDS) equilibration is done on the same stage without moving the gel. The IEF stage is then moved horizontally to couple with a precast second dimensional gel. The <0.5 mm gap between the two gels is filled with poly (ethylene oxide) solution. After SDS-polyacrylamide gel electrohporesis separation, a charge-coupled device camera is used to detect spots via protein native fluorescence excited by a Hg (Xe) lamp with the gel inside the running cell. Potential for full automation is demonstrated with 0.5 microg of Escherichia coli proteins on this miniaturized platform. More than 240 spots are detected in a total experiment time of <2.5 h.

Development of a LC-LC-MS complete heart-cut approach for the characterization of pharmaceutical compounds using standard instrumentation

A total heart-cut LC-LC-MS technique is described for the analysis of pharmaceutical compounds. Utilizing ordinary LC-MS equipment, a standardized multi-dimensional, highly selective approach was developed. The system was developed on synthetic mixtures containing ten active pharmaceutical compounds. The methodology would be further deployed for the impurity characterization of batches of active chemical, process intermediates, and reference standards. Column-switching was employed to heart-cut sequential fractions from one set of LC conditions to another set of LC conditions. Two high efficiency columns, including the Merck Chromolith C18, for fast LC-LC analysis were used. The system provides a highly automated, turnkey, multi-dimensional approach applicable to a variety of complex mixtures with little user intervention. It is envisioned that this idea could be viewed as a platform for other types of LC-LC analyses including peptide and achiral-chiral analyses.

On-line coupling of SEC and RP-LC for the determination of structurally related enkephalins in cerebrospinal fluid

On-line coupled analytical techniques can be advantageous in the assay of smaller peptides in complex biological matrices such as plasma, cerebro-spinal fluid (CSF) and tissues. The present study shows the feasibility of the recently reported on-line coupled size exclusion chromatography (SEC) and reversed phase liquid chromatography (RP-LC) separation system for the quantitation of structural related peptides in biological matrices, as demonstrated for a number of enkephalins in CSF. The degradation of the peptides, caused by endogenous peptidases in the matrix, could sufficiently be inhibited with imipramine HCL to allow an assay with satisfactory linearity and intraday (0.70-4.9%) precision. The sensitivity of the method, with a concentration limit of quantitation (LOQ) of 2 microgram/ml is comparable with other kinds of assays for peptides and sufficient for the quantitation of peptide drugs with higher therapeutic ranges in biological matrices. However, for the assay of low concentrations of peptides, such as endogenous components of a biological matrix, the sensitivity may need improvement. The LOQ cannot be improved by increasing the sample amount, because of interference of other endogenous components of the CSF. This indicates that a larger selectivity is desired. The LOQ may be improved by using more sensitive and selective detection methods such as mass spectrometry or fluorescence after post-column derivatization. Miniaturization of the system, combined with on-line trapping may also contribute to a better sensitivity.