Yvan Vander Heyden

Chromatographic separation techniques and data handling methods for herbal fingerprints: a review.

As herbal medicines have an important position in health care systems worldwide, their current assessment and quality control are a major bottleneck. Over the past decade, major steps were taken not only to improve the quality of the herbal products but also to develop analytical methods ensuring their quality. Nowadays, chromatographic fingerprinting is the generally accepted technique for the assessment and quality control of herbal products. This paper briefly considers the evolution of the regulations and guidelines on the quality control of herbal medicines, and reviews the established analytical techniques for herbal fingerprinting with an emphasis on the most recent developments, such as miniaturized techniques, new stationary phases, analysis at high temperatures and multi-dimensional chromatography. Accessory to the new analytical techniques, the chemometric data handling techniques applied are discussed. Chemometrics provide scientists with useful tools in understanding the huge amounts of data generated by the analytical advances and prove to be valuable for quality control, classification and modelling of, and discrimination between herbal fingerprints.

Experimental designs and their recent advances in set-up, data interpretation, and analytical applications

In this review, the set-up and data interpretation of experimental designs (screening, response surface, and mixture designs) are discussed. Advanced set-ups considered are the application of D-optimal and supersaturated designs as screening designs. Advanced data interpretation approaches discussed are an adaptation of the algorithm of Dong and the estimation of factor effects from supersaturated design results. Finally, some analytical applications in separation science, on the one hand, and formulation-, product-, or process optimization, on the other, are discussed.

HILIC methods in pharmaceutical analysis

In this review, hydrophilic interaction liquid chromatographic (HILIC) applications for pharmaceutical analysis are discussed. The HILIC technique uses an aqueous/organic modifier mobile phase with a high organic modifier fraction and a hydrophilic stationary phase (SP). In general, the SPs are silica or polymer based. The silica-based columns are most often applied and are divided into bare-silica particle, chemically bonded silica particle, and monolithic phases. The bare-silica columns are most frequently used. The much less applied polymer-based columns are also divided into particle and monolithic phases. In this review, the applications are grouped and discussed according to the SP type used. Whenever possible, the considered HILIC application is compared with other HILIC methods, e.g. on other SPs, and/or with other separation modes, for that application. The advantages and drawbacks of HILIC are also discussed, as well as the method validation issues, when executed.

Method development for HILIC assays

In this review, method development for hydrophilic interaction LC (HILIC) is highlighted. HILIC is a chromatographic technique that uses aqueous-organic solvent mobile phases with a high organic-solvent fraction, and a hydrophilic stationary phase. It is mainly applied for the separation of polar and hydrophilic compounds. Method development, in general, can be done uni- or multivariately. In the univariate approach, the factors that are expected to potentially affect the separation of the compounds will be examined sequentially and one-at-a-time. All HILIC methods found in the literature were developed in this way. For these methods, the analytes, the considered factors, the selected responses, and the finally chosen experimental conditions are discussed in this review. Where examined, the method validation and the comparison with other analytical assay methods is also described. For the multivariate method-development approach, which is based on the use of experimental designs, only a possible strategy is presented, because of the lack of relevant publications in the literature.

Supercritical fluid chromatography for the enantioseparation of pharmaceuticals

Chirality has a significant impact on drug discovery and development processes in the pharmaceutical industry. As the number of enantiopure drugs launched onto the market is yearly increasing, the need for fast and performant enantioseparation methods with minimal costs is becoming more compelling. In this context, sub- and supercritical fluid chromatography (SFC), being applicable at an analytical, as well as at a preparative scale is gaining more interest. In this review a practical overview is given of the different parameters that are important in supercritical fluid chromatographic separations. A comparison is made between the applicability for chiral separations of SFC and conventional high-performance liquid chromatography (HPLC), and illustrated by means of examples. Different aspects of method development and the upscaling feasibility in SFC are discussed. This review aims to give the reader a practical insight in the use of supercritical fluid chromatography for the chiral separation of pharmaceutical compounds.

Rapid screening for chiral separations by short-end injection capillary electrophoresis using highly sulfated cyclodextrins as chiral selectors

Two series of amino acid derivatives and phenylamines were used to evaluate the potential of highly sulfated cyclodextrins (HS‐CDs) for the screening for chiral separations by capillary electrophoresis (CE). HS‐CDs showed to be very versatile and to exhibit very high enantioselectivity. The use of short‐end injection allowed to reduce dramatically the analysis time. From the results obtained, a scheme for the rapid screening of enantiomeric molecules was developed and applied to various chiral drugs. Results are very satisfying as almost all compounds (62 out of 67) could be baseline‐resolved. Usually, less than three experiments were necessary to obtain very good separation.

Characterisation of reversed-phase liquid chromatographic columns by chromatographic tests. Evaluation of 36 test parameters: repeatability, reproducibility and correlation.

The European Pharmacopoeia (Ph. Eur.) or other official compendia give only a general description of the stationary phase in the description of a liquid chromatographic method. Therefore the selection of a column giving suitable selectivity presents difficulties. Earlier, a test procedure was proposed that allows measurement of a number of parameters which are reported to be representative for stationary phase characteristics. This paper describes how the test procedure was applied on 69 RP-LC C18 columns. Chromatographic parameters obtained as test results were evaluated, and their repeatability, reproducibility and correlation were examined.

Characterisation of reversed-phase liquid chromatographic columns by chromatographic tests. Rational column classification by a minimal number of column test parameters.

The European Pharmacopoeia (Ph. Eur.) and other official compendia give only a general description of the stationary phase in the description of a liquid chromatographic method. Therefore the selection of a column giving suitable selectivity presents difficulties. Earlier, a test procedure was proposed that allows to measure 36 chromatographic parameters which have been described for characterising stationary phases. This procedure was carried out on 69 reversed-phase liquid chromatography (RP-LC) columns. This paper focuses on the classification of RP-LC stationary phases based on chromatographic parameters. A chemometric study was conducted using 24 parameters that could be measured in a repeatable and reproducible way. Principal component analysis was used to classify the columns and to estimate the minimal number of parameters necessary for a rational classification. It is shown that after reducing the number of parameters from 24 to four or three, similar classifications were obtained. The column classifications were compared to the European Pharmacopoeia stationary phase description and to the column properties obtained from the manufacturers.

Minimal number of chromatographic test parameters for the characterisation of reversed-phase liquid chromatographic stationary phases

This paper focuses on the classification or differentiation of RP-HPLC columns based on measured chromatographic properties. A chemometric study has been conducted on a published data set consisting of 85 RP-HPLC columns and on a data set consisting of 47 self-tested columns. Principal component analysis enables determination of the number of parameters necessary for a rational differentiation. The results show that reducing the number of parameters for such differentiation still allows classification of the columns just as a higher number did. It is shown that three test parameters produce a classification similar to that obtained with five parameters.

Chiral separations in sub-and supercritical fluid chromatography

Sub- and supercritical fluid chromatography (SFC) received more and more attention in pharmaceutical analysis during the last years. Especially for chiral separations, this technique is becoming increasingly popular. This review gives an overview of most chiral separation applications using SFC, covering the literature from 2000 on.