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MS Quantitation of Chiral Molecules by the Kinetic Method

! Theory of the Kinetic Method

Potential diagram for the chiral r e c o g n i t i o n o f a n a l y t e A ( A R a n d A based on the formation of diasteromeric ions through CID of a metal ion (M)-bound cluster. S )

B* is the chiral reference compound.

C h i r a l s e l e c t i v i t y , R c h i r a l ( = R R / R S ) , related to !(!G). i s

A CID of a trimeric transition metal ion-bound cluster ions (composed of three chiral ligands: one of the analyte and two of the reference compound) which give rise to diastereomeric product ions.

Chiral selectivity of compounds is determined by the relative abundances of the product ions caused by differences in the energy required for their formation.

A two-point calibration curve, derived from the kinetic method,allows rapid quantitation of enantiomeric excess of chiral mixtures.

Cooks: Anal. Chem. 2004, 76, 663. JACS 2000,122, 10598.

MS Quantitation of Chiral Molecules by the Kinetic Method

! Resolution of Pseudoephedrine

Chiral recognition of ephedrine by the kinetic formation of diastereomeric ions [Cu(L-Tyr)(A) - H]+ (m/z 431, where A is (+)-and (–)-ephedrine) via CID of [Cu(L-Tyr)2(A) - H]+ (m/z 635).

The common product is [Cu(L-Tyr)2 - H]+ (m/z 470) is the internal standard.

3-D models show a stronger !-cation interaction in one of the diastereomers.

OH

H N

Me

Me (–)-Ephedrine

Enantiomeric determination of pseudophedrine. The average error is 2.6 % ee for the range of –99% to 99% ee.

OH

H N

After calibration the measurement of one sample is less than 30 seconds.

Me

Me (+)-Ephedrine

Cooks: Anal. Chem. 2004, 76, 663 & JACS 2000,122, 10598.

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