46


September 2009


absorbance detectors (UV) and much less sensitive than mass spectrometers (MS). However UV and MS do not offer insight into optical activity.


Figure 5: SFC separation of Cypermethrin with 3 chiral centers, SFC


We use Advanced Laser Polarimeters (ALPs) to track enantiomer elution order, differentiate enantiomers from impurities, identify components inmultiple chiral center


compounds, detect compounds without chromophores, and control peak collection in HPLC/SFC purification.


Figure 6: Gentamicin Semi-Prep Separation with ALP Detection


chromophore, and exhibit limited dynamic range. Polarimeter detectors are not absorbance based so do not require a chromophore and can exhibit very large dynamic range depending on design. Chiral detectors are generally less sensitive that


See Figure 5 where an ALP was used to purify cypermethrin enantiomers using SFC. Cypermethrin has three chiral centers and eight enantiomers. There are no commercially available cypermethrin single enantiomer standards. The ability of ALP to


identify enantiomers by peak polarity and area was a big help in interpretation of UV chromatograms and peak identification for prep scale separations. The last peak in this chromatogram is an impurity, not a cypermethrin enantiomer. This was easy to


see with a supplemental ALP chromatographic trace.


Figure 6 illustrates where ALP was used to purify Gentamicin analogs using HPLC. Many antibiotics are relatively small molecules with a molecular weight less than 2000 Da. UV detection is challenging because this compounds lack a UV absorbing chromophore. All analogs (C1A, C2, C2A, C2B, C2A, and C1) are separated along with impurities and sisomicin. Method details are Column - Phenomenex Gemini, 4.6 x 250 mm, 5 µm; Eluent - water + TFA 0.04M buffer / methanol, 97/3; Flow - 1 mL/min; Injection - 100µL; Sample – Gentamicin 5mg/mL in water; Temperature - 35°.


Results and Conclusions Using the procedures and equipment mentioned above we are usually able to go from racemic samples we have never seen before to purified enantiomers in one week. This performance is partially due to efficient system configurations and procedures but is also partially due to intelligently limiting the methods we consider to a reasonable set. The systems and equipment described herein are not particularly expensive when compare to the results they deliver. We use ALP detectors on all systems to provide complementary information to UV detection.


Acknowledgements The Authors wish to acknowledge our Customers and Mother Nature for continuously supplying us with challenges and our Collaborators from both industry and academia for helping us to understand underlying principles and navigate towards positive results.


New automated solid phase extraction instrument


The newAutoTrace 280 systemfromDionex (USA) is an automated solid phase extraction (SPE) instrument designed to be usedwith large volume (20mL - 4 L) samples for the isolation of trace organics inwater or aqueousmatrices.


The instrument traps compounds of interest on SPE adsorbents (in cartridge or disk format) and then elutes them with strong solvents to generate an analysis-ready extract thus saving time, solvent, and labor, and ensuring high reproducibility for analytical laboratories. The instrument can process up to 6 samples in 2-3 h with only 15 min of operator involvement. Powerful pumps (no check valves) and a proven, positive- pressure technology efficiently process even the most difficult samples.


The AutoTrace 280 instrument features a new multiple port-switching valve, improved electronics, and a USB port for connecting to a PC. Up to 24 methods can be stored in the instrument and each method can be uploaded from the front panel using the software which includes a new feature for method editing.


Current analytical methods that could require SPE sample preparation include GC, GC-MS, LC, and LC-MS.


Latest ultra-inert ODS phase, Inertsil ODS-4.


GL Sciences have announced the launch of their latest ultra- inert ODS phase, Inertsil ODS-4. This phase is ideal for acidic, basic, neutral and chelating compounds. GL Sciences Inertsil ODS-4 offers improved peak shape, enhanced sensitivity, high resolution, fast equilibration and is compatible with 100% aqueous mobile phases. For further information on this new phase or to request a free sample column visit www.inertsil.com or contact UK distributor Hichrom at technical@hichrom.co.uk or Tel: 0118 930 3660.


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60