Chiral HPLC for Chemists: Ultimate Solvent Choice with High Capacity Using Astec’s P-CAP™ Series

By: Denise Wallworth, Reporter EU Volume 28

Solvent Choice and Reversal of Elution Order

The polyamide chiral stationary phase (CSP) features a thin, ordered polymer layer, chemically bonded to 5 μm or 3.5 μm spherical silica, using a patented radical polymerization. This results in two effects; there is a high permeability across the surface and, as a synthetic polymer, it can be identically manufactured in R, R and S, and S enantiomeric forms, enabling a predictable reversal of elution order in the same mobile phase (Figure 1). As a bonus there are no memory effects, so the same column can be used in a number of different mobile phases without any detrimental effects. These phases form a new generation bridge between the traditional ‘brush’ type CSPs and the conventional polymeric phases.

Figure 1. Predictable reversal of elution order for an analogue of Lorazepam (Conditions: 95/5: DCM/MeOH, 1.0 mL/min )

Chiral method development is typically carried out either in normal phase (heptane/IPA or ethanol) or polar organic (acetonitrile/methanol) mode. For the optimization of a method, a wide range of organic solvents can be used; from acetone to dichloromethane to dioxane and many others. For acids and bases, the addition of 0.1% TFA often increases resolution and efficiency, and decreases retention times. There are no known limitations on the kind of solvents that can be used with these phases.

For MS detection volatile acids and buffers, such as ammonium acetate, can be added to enhance peak efficiency, or to enhance ionization when needed.

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High Capacity for Preparative HPLC

The high loading capacity makes P-CAP and P-CAP-DP excellent for both analytical and preparative scale separations. The separation of furoin enantiomers is shown in Figure 2 using an analytical 25 cm x 4.6 mm (R,R) P-CAP-DP column and a mobile phase of 20/80 EtOH/Hexane. Excellent separation is demonstrated with an injection of 8 μg of the furoin racemate; increasing the load to 1 mg of furoin on this analytical column demonstrates the high loading capacity of this phase. In a further loading study, 10 mg of binaphthol was separated without overload on an analytical column (1). Solvent flexibility on the P-CAP will further enhance this column’s applicability in prep and process LC.

Figure 2. Furoin (referenced above: 35024AST)

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Applications

P-CAP CSPs have been used for a wide variety of molecular types and are ideal for medium to high polarity compounds. The mechanism of separation is either through hydrogen bonding for P-CAP, or through both hydrogen bonding (donor and acceptor) with additional π-π interaction for the P-CAP-DP. Both also use dipole-dipole and steric interactions. Examples of the separations completed to date are shown in table 1.

Table 1: Examples of chiral separations on the P-CAP series of CSPs

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Summary

P-CAP and P-CAP-DP are rugged chiral HPLC phases, experience no memory effects, and can be run in a wide variety of solvents with speed and high efficiencies. For preparative applications, a combination of wide solvent choice and high capacity make them ideal for large-scale purification. Initial studies also show that they appear to be very applicable to SFC.

 

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Materials

     

References

  1. Professor F Gasparrini, Università “La Sapienza”, Rome. Data given at the Supleco Sigma-Aldrich seminar in Rome, May 2007.

With thanks also to Professor D A Armstrong for recent data

 

 

Trademark Attributes

  • P-CAP is a trademark of Sigma-Aldrich Co. LLC

 

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