Astec® CHIRALDEX® Column Selection

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Frequently Asked Questions - over 60 topics to assist you with chiral chromatography

Certain phases are more selective for given molecular structures. While many compounds can be enantiomerically resolved on multiple Astec CHIRALDEX phases, often an advantage can be found in selectivity, elution order, and/or analysis speed from one phase to another.

The patented G-TA is the first choice of the fifteen phases. This phase has been shown to be the most broadly selective phase for the pharmaceutical industry, especially in the analysis of chiral intermediates and drug studies in various stages of clinical trials. Separations occur without the inclusion mechanism and are typically faster and more efficient than most chiral stationary phases. This phase does not contain a polysiloxane carrier and, therefore, there are no deleterious effects at low temperatures. The ability of this phase to separate the parent drug enantiomers and their metabolites has proven quite beneficial. In a number of cases, multiple chiral metabolites have been resolved on 10 meter columns.

The G-DP phase was added to enhance selectivity for both aliphatic and aromatic amines in additional to aliphatic and some aromatic esters. This phase is especially useful for polar racemates. This phase demonstrates better hydrolytic and thermal stability than the G-TA.

A modified version of the G-TA is the G-PN. It functions like the G-TA but shows higher selectivity toward certain amines (amphetamine, methamphetamine). This phase is more stable to moisture than the G-TA.

The G-BP phase can be used as a general purpose column but it is especially useful for amino acids.

Note: The subtle differences in functional groups between the G-TA, G-DP, G-PN, and G-BP often allow for minor enhancements in chiral and achiral selectivity when changing from one derivative to another.

The second major stationary phase in the Astec CHIRALDEX line is the B-DM. Through special derivatization techniques, the concentration of the cyclodextrin has been substantially increased in the polysiloxane carrier. The B-DM is very useful for a number of free acids and bases and is the only chiral GC phase that can do this type of separation. The B-DM is the phase of choice when elution temperature exceeds 200 °C. The B-DM is considered a second-generation B-PM (β-cyclodextrin, permethyl derivative) phase and will do most of the separations done on the B-PM but with higher resolution. There are a few occasions when selectivity differences occur between these two phases, but more often selectivity on the B-DM is higher. The selectivity of the B-DM covers applications of both the B-PM and B-PH although with superior performance.

The B-PM phase can be used as a general purpose column for the separation of a wide variety of compounds. This phase is useful for the analysis of alcohols and diols in their underivatized form and also of analytes with polar groups (i.e. tertiary amines).

The third most useful phase is the B-DA because it demonstrates the strongest size selectivity. This phase requires analytes to minimally contain two ring structures, one of which is unsaturated (aromatic). The mechanism of this phase is strongly dependent on the inclusion mechanism and as such is able to differentiate changes in the base structure. Because the DA phases most effectively separate multi-ring analytes, analysis temperatures are often higher than 150 °C. The fact that there are three different size cyclodextrins (α-, β-, and γ-) allows for separation of a wide variety of different size analytes. This product is, therefore, primarily used for fingerprinting raw materials and identifying structural differences.

The B-PH shows at least some selectivity to a great variety of analytes but is especially effective for saturated analytes with minimal functionality, saturated cyclics, and saturated bicyclics. This phase often shows a reversal of elution order (enantioreversal) compared to the B-DA phase.

Materials

     
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