Cavity-enhanced fourier transform spectroscopy for chiral analysis

A method, comprising:

• electrically obtaining a first response elicited from a first diastereomeric complex including a chiral analyte and a racemic mixture comprising a chiral tag;
• and
• electrically obtaining a second response elicited from a second diastereomeric complex including the chiral analyte and a specified-enantiopurity form of the chiral tag;
• wherein the first and second responses are elicited by electrically exciting a range of molecular rotational resonances.

An apparatus, comprising:

• a sample cell including a resonant cavity;
• a source electrically coupled to the sample cell to electrically excite at least one mode of the resonant cavity;
• a receiver electrically coupled to the sample cell to obtain a response elicited from a diastereomeric complex formed by a chiral analyte and a chiral tag within the sample cell, in response to excitation of the resonant cavity using the source, the receiver comprising an analog-to-digital converter to provide a digital representation of a time-domain response obtained from the sample cell;
• and
• an isolator to isolate the source from the sample cell at least when the receiver is receiving the response elicited from the sample;
• wherein the sample cell comprises at least two sample introduction ports, including at least one sample introduction port to receive the chiral analyte and the chiral tag.

A method of measuring enantiomeric excess of a chiral analyte of unknown enantiopurity, the method comprising:

• injecting a first gas-phase sample of the chiral analyte and a racemic mixture of a chiral tag into a sample cell, the first gas-phase sample of the chiral analyte containing first enantiomers of the chiral analyte that form a first diastereomeric complex with the racemic mixture of the chiral tag and second enantiomers of the chiral analyte that form a second diastereomeric complex with the racemic mixture of the chiral tag in the sample cell, the first diastereomeric complex exhibiting a molecular rotational resonance (MRR) spectrum different than an MRR spectrum of the chiral analyte and the second diastereomeric complex exhibiting an MRR spectrum different than the MRR spectrum of the chiral analyte and different than the MRR spectrum of the first diastereomeric complex;
• obtaining a molecular rotational resonance (MRR) spectrum of the first gas-phase sample of the chiral analyte and the racemic mixture of the chiral tag, the MRR spectrum of the first gas-phase sample of the chiral analyte and the racemic mixture of the chiral tag containing contributions from both the first diastereomeric complex and the second diastereomeric complex;
• injecting a second gas-phase sample of the chiral analyte and an enantiopure form of the chiral tag into the sample, the second gas-phase sample of the chiral analyte and the enantiopure form of the chiral tag;
• obtaining an MRR spectrum of the second gas-phase sample of the chiral analyte and the enantiopure form of the chiral tag, the MRR spectrum of the second gas-phase sample of the chiral analyte and the enantiopure form of the chiral tag containing contributions from either the first diastereomeric complex or the second diastereomeric complex;
• and
• determining the enantiomeric excess of the chiral analyte based on the MRR spectrum of the first gas-phase sample of the chiral analyte and the racemic mixture of the chiral tag and on the MRR spectrum of the second gas-phase sample of the chiral analyte and the enantiopure form of the chiral tag.