Stationary phase screening

The approach to method development is similar to the one described for HPLC and can be characterized as a rapid stationary phase screen using column and solvent switching with gradient elution followed by development of an isocratic preparative method. SFC has been successfully applied to the analytical and preparative separation of achiral and chiral compounds. 

In addition to the development of the powerful chiral additive, this study also demonstrated that the often tedious deconvolution process can be accelerated using HPLC separation. As a result, only 15 libraries had to be synthesized instead of 64 libraries that would be required for the full-scale deconvolution. A somewhat similar approach also involving HPLC fractionations has recently been demonstrated by Griffey for the deconvolution of libraries screened for biological activity [76]. Although demonstrated only for CE, the cyclic hexapeptides might also be useful selectors for the preparation of chiral stationary phases for HPLC. However, this would require the development of non-trivial additional chemistry to appropriately link the peptide to a porous solid support. 

The series of regioisomeric amines 48-50, methamphetamine (29) and phentermine (31), can be identified in forensic screening analyses by RP-HPLC-UVD (254/280 nm dual accessory) using a Cis stationary phase and a mobile phase buffered at pH 3.0. The capacity factors and retention times increase in the order 48 < 49 < 29 < 31 < 50. Other methods for identifying these compounds failed for example, the base peak in MS is m/z = 58 for all five compounds, corresponding to a loss of a benzyl group from the molecular peak also their IR and UVV spectra are too similar to be useful for this... 

Kordel W, Stutte J, Kotthoff G. 1993. HPLC-screening method for the determination of the adsorption-coefficient on soil comparison of different stationary phases. Chemosphere 27(12) 2341 - 2352. 

Most screening and optimization approaches in HPLC were defined using polysaccharide chiral stationary phases (CSP), thanks to their broad chiral recognition ability toward a large number of compounds. 

Kennedy et al. [57] have described the use of an intelligent chiral resolution system using a rapid screening of conditions on polysaccharide CSP, aiming to transfer the separation to preparative LC afterward. For the analytical part of the strategy, lO-pm particles were used for the preparative section, the particles had a 20-ttm diameter. The screening performs 11 experiments on analytical columns, which are displayed in Table 3.3. Chiralpak AD, Chiralcel OD, Chiralcel OJ, and Chiralpak AS are the considered stationary phases, and they are analyzed either in POSC or NPLC mode. The... 

Geiser et al. [50,51] illustrated the screening of different chiral stationary phases and the separation of highly polar amine hydrochlorides using EEL methanol/C02 mixtures and the columns, Chiralpak-AD-H, Chiralpak-AS. This method is advantageous because no acid or base additive was required to achieve base line separation of the racemates and conversion to free base form for enantiomer separation was not required. Preparative-scale separations of the amine-hydrochloride were accomplished using similar mobile phase conditions [51], Furthermore, this is believed to be the first chiral separation of highly polar solutes without the addition of acid or base additive to effect the separation. 

In summary, the use of RPLC is ideal for pharmaceutical analyses because of the broad range of commercially available stationary phases because the most common RPLC mobile phases (buffers with acetonitrile or methanol) have low UV cut-off wavelengths, which facilitate high sensitivity detection for quantitation of low-level impurities and because selectivity can readily be controlled via mobile phase optimization. Additionally, the samples generated for selectivity screening (as detailed above) are typically aqueous based. In subsequent phases of pharmaceutical development, aqueous-based sample solvents are ideal for sample preparation and are, under limited constraints, compatible with MS detection required to identify impurities and degradation products. 

Ion chromatography has become an essential tool of the pharmaceutical analytical chemist. The high sensitivity of the technique, coupled with the wide dynamic operating range made possible with modern high-capacity stationary phases makes it ideal for the analysis of ions in pharmaceutical applications. The combination of gradients and suppressed conductivity detection provides a powerful screening... 

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