Acid/base ratio, enantiomeric separation

With the increased popularity of LC-MS, the problem of overlapping enantiomer peaks from other amino acids has largely been resolved. The mass spectrometer can act as an additional dimension of separation (based on mass to charge ratio). Thus, only amino acids having the same mass-to-charge ratio must be separated achirally (see Desai and Armstrong, 2004). This additional dimension of separation also has implications for the applications in the matrices discussed previously. With the ability of the mass spectrometer to discriminate on the basis of mass, this lessens the need for complete achiral separation. For example, an LC-MS method was recently developed to study the pharmacokinetics of theanine enantiomers in rat plasma and urine without an achiral separation before the enantiomeric separation (Desai et al., 2005). In such matrices, proteins must still be removed by appropriate sample preparation. 

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