Chiral e-Times 2009 Volume 2


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  1. Web focus: Follow ChiralChrom on Twitter
  2. Application focus: Chiral Amino Acids, SMB for Chiral Separations
  3. Product spotlight: CHIRALDEX and Supelco DEX: Unique and valuable GC chiral separations
  4. Chiral Services update: Expanded Options for Preparative LC Capabilities
  5. Partner update: Pharmorphix®-SAFC Crystallization Resolution Services
  6. Tradeshows and Seminars: Chirality Tradeshow and Analytical Seminar Schedule
  7. Tips and Tricks: Flow rate considerations in chiral HPLC
  8. New Literature: Chiral Method Development Poster
  9. Special Offers

1. Web focus: Follow ChiralChrom on Twitter back to top

Are scientists using Twitter? Apparently yes. The new social networking site, Twitter, is a cross between blogging, texting, and instant messaging. Using Twitter, members communicate in real time with short bursts of information. If you aren’t familiar with Twitter and are interested in learning, there are loads of tutorials on the web; just query your favorite search engine.
How are we using Twitter? We “tweet” (communicate) ideas, tips & tricks, seminar and show updates, industry news, special offers; we even ask our “followers” questions about chiral chromatography.
To view ChiralChrom updates on Twitter, go to www.twitter.com/chiralchrom. Become a follower, if you already have a twitter account.


2. Application focus: Chiral Amino Acids, SMB for Chiral Separations back to top

CHIROBIOTIC chiral stationary phases (CSPs) possess ionic functional groups and, unlike cellulose-based CSPs, they are not limited to normal phase operation. They are therefore very useful for separating ionic/ionizable compounds, like amino acids. They operate in mobile phases that are MS-compatible, and that can be optimized based on sample solubility, an important consideration for all forms of preparative separations, including SMB.

Chiral Amino Acids
Most amino acids are chiral, with the L-form dominating in nature. D-Amino acids and the ratio of D to L-forms are studied for various reasons, including pharmaceutical research and to explore their extraterrestrial origins. Astec chiral HPLC and GC stationary phases  are uniquely suited for chiral amino acid separations, including native amino acids and their N-blocked derivatives. CHIROBIOTIC CSPs have ionic functional groups and therefore permit chiral discrimination of compounds with ionic or ionizable groups. They also operate in mobile phases that are MS-compatible and in which amino acids are freely soluble. Other phases, notably Astec CLC and various CYCLBOND chemistries, also have found utility for amino acid enantiomer separations.

The decision tree below is a general guideline on choosing an HPLC CSP for chiral amino acid separations. Many applications and a bibliography are available on our web site sigma-aldrich.com/chiral-chromatography. Please consult our technical services group for further assistance.

(click image for a larger view)

A product information flier and technical presentations on Astec CHIROBIOTIC CSPs for SMB applications are available in our learning center

View the selection of SMB chiral columns in our online catalog.


3. Product spotlight: CHIRALDEX and Supelco DEX: Unique and valuable GC chiral separations back to top

Astec CHIRALDEX and Supelco DEX lines comprise the widest range of derivatized cyclodextrin (CD) phases for chiral GC separations available today. The 26 different phases cover three different cyclodextrins and nine different derivatives. The phases are grouped into three general categories based on the derivative and types of interactions they are proposed to undergo with analytes.

Group 1 is termed “Surface Interactions/Complex Derivatives.” Because the predominant mechanism of retention for phases in this group is based on surface interaction, the gamma-cyclodextrin, with 8 glucose molecules, has been shown to be the most useful. Compared to alpha- and beta-cyclodextrins, the greater number of glucose molecules in a gamma-cyclodextrin results in the greater number of 2,3,6-position hydroxyl functional groups available for derivatization. High derivative concentration is beneficial for maximizing surface interactions. Astec CHIRALDEX G-TA, G-DP, G-PN and G-BP belong to this group. Although the G-TA is by far the dominant player, there are subtle chiral and achiral selectivity differences between the members.

Group 2 is termed “Surface & Inclusion Interactions/Simple Derivatives.” This group includes the popular dimethyl and permethyl derivatives. The beta-cyclodextrin has shown the greatest applicability for phases with these derivatives. Astec CHIRALDEX B-DM, B-PM, and Supelco ß-DEX 110, ß-DEX 120, ß-DEX 325 and ß-DEX 225 belong to this group.

Group 3 is termed “Inclusion Interactions.” Obviously, this group relies on inclusion interactions as the dominant retention mechanism. The three different size cyclodextrins (alpha, beta, and gamma) allow for separation of a wide variety of different size analytes. Astec CHIRALDEX B-DA and CHIRALDEX B-PH belong to this group. The Astec CHIRALDEX B-DA 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 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. This phase is primarily used for fingerprinting raw materials and identifying structural differences. The Astec CHIRALDEX 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. Interestingly, B-PH and B-DA often exhibit reversal of elution order (enantioreversal).

The table below gives some guidelines on the choice of chiral GC phase based on the analyte functional group. Please consult our technical services group if you need any help in deciding which GC CSP is best for your separation. Please also note the limited-time promotion on our chiral GC columns in the Special Offers section.

(Click image for a larger view)
click for larger image

4. Chiral Services update: Expanded Options for Preparative LC Capabilities back to top

Sample solubility in the mobile phase is an important consideration when performing preparative HPLC separations and purifications. Generally, the higher the solubility, the more mass per injection and the higher the throughput. Our Chiral Services Laboratory was founded upon using the Astec CHIROBIOTIC phases for preparative as well as analytical scale chiral separations. Now, we have expanded our capabilities to include normal phase preparative separations using cellulosic-type CSPs. With this addition, our Services Laboratory is unique in having expertise in normal phase, reversed-phase, polar-ionic and polar-organic chiral separations. This expertise can be applied to perform all types of chiral services, from rapid column screening using an automated MS protocol to supplying gram-quantities of purified enantiomers.

Preparative Chiral Purification


To learn more about our Chiral Services, please visit www.sigma-aldrich.com/chiral_services


5. Partner update: Pharmorphix-SAFC Crystallization Resolution Services back to top

The most popular method of resolving racemic mixtures for process-scale operations is still the crystallization of diastereomeric salts. However a non-rationalized approach to the screening of resolving agents can often result in poor recovery, low chiral purity and inefficient, non-scalable crystallization protocols.

Experience of the Pharmorphix team has shown that the solid state characterization of the diastereomeric salts is critical for an understanding of the resolution process as different polymorphic forms and / or solvates can provide varying resolution results.

For small molecule compounds that lack an ionizable center, separation of racemic mixtures can be possible and can be sometimes achieved by a process of kinetic entrainment.

Key Pharmorphix capabilities for crystallization resolution studies include:

  • Rapid screening and characterization of crystalline diastereomeric salts.
  • Diverse selection of chiral acids and bases for diastereomeric resolution of racemic acids and bases.
  • Comprehensive suite of complementary physicochemical techniques (e.g. DSC, TGA) for the characterization of physical properties of individual and combined crystalline forms.
  • Single crystal X-ray diffraction (SXD) studies for structure determination and absolute stereochemistry determination for regulatory submission.
  • Expertise in crystallization-based purification.

For more information on crystallization development and scale-up or the solid-state services offered by Pharmorphix, please contact Paul.Hirst@sial.com or view our Pharmophix Crystallization Development page.


Crystal of R(-)-phenylglycinol-R-mandelate hydrate

6. Tradeshows and Seminars: Chirality Tradeshow and Analytical Seminar Schedule back to top

Chirality 2009 (July 12 - 15, 2009, Breckenridge, CO)

Our complimentary vendor seminar on chiral method development received a high response, and we were overbooked – we truly appreciate the interest in our talk!

Analytical Open Seminar Schedule
Beginning in August 2009 and continuing throughout the remainder of the year, we will be conducting a series of regional, open-venue Innovation Seminars across the US. The aim of these seminars is to convey information about our innovative products for chromatography and sample prep, and to show how these innovations can be put to practical use by all chromatographers. Chiral Chromatography is one of the featured topics.

The first seminar series will be conducted August 10 – 13 in the NJ-PA-DE region. To find out more, including locations, abstracts, speaker biographies and to register online, please visit sigma-aldrich.com/analytical-seminars, or send an email to ac_seminars@sial.com.

To see our complete tradeshow schedule for 2009, visit www.sigmaaldrich.com/analytical-events


7. Tips and Tricks: Flow rate considerations in chiral HPLC back to top

Once enantiomeric selectivity is achieved on a chiral stationary phase, resolution of the enantiomers may be improved by changing mobile phase composition, temperature, and/or flow rate. A flow rate of 1.0 mL/min. is often used during method development on 4.6 mm I.D. columns packed with 5 µm particles. For method optimization, if enantiomers are separated but not fully resolved at 1 mL/min., decreasing the flow below 1.0 mL/min. may further increase resolution. Van Deemter studies performed on 4.6 mm I.D., 5 µm particle CHIROBIOTIC T and V2 columns in reversed-phase, polar-ionic, and polar-organic modes have shown that the greatest peak efficiency is achieved at flow rates between 0.2 and 0.15 mL/min. (linear velocities between 0.2 and 0.3 mm/s; reduced linear velocities between 0.61 and 0.81). Therefore, decreasing the flow rate beyond the norm may enhance the efficiency of each peak, and thus, improve the resolution of the enantiomers.

Knox Plot of Fluoxetine on CHIROBIOTIC V2 (5 µm)
Knox Plot of Fluoxetine on CHIROBIOTIC V2

8. New Literature: Chiral Method Development Poster back to top

Method development and optimization on Astec CHIROBIOTIC and CYCLOBOND CSPs follows a simple, logical protocol that also permits optimization for MS and evaporative detection methods. To help our customers, we have updated the familiar Astec poster on Chiral Method Development to include new information, strategies and tips. The poster should be a welcome addition to any laboratory where chiral HPLC methods are developed.

Click on the image to request your copy of the poster.

click to request the poster


9. Special Offers back to top

For a limited time --
25% off chiral GC Columns

Specify Promotion Code 632 to receive a 25% discount off any Astec CHIRALDEX or Supelco DEX chiral GC column.
Limit one per customer. US customers only. Offer good through August 31, 2009.

View our Ordering Information for a list of columns.