Development of real-time sensitive chiral analysis technique using quartz crystal analyzer

A rapid and highly sensitive chiral sensing technique was developed for the chiral discrimination of mandelic acid (MA) using a quartz crystal microbalance (QCM) modified with an amide-type S-MA derivative. After the modification, the response difference when exposed to the target R-MA and S-MA was measured using a low concentration range from 10 μM to 3 mM combined with a novel analysis technique. For the given target concentrations, the chiral discrimination factor between S-MA and R-MA was 5.7 when using the normal frequency measurement. Remarkably, the novel sensing technique produced a chiral discrimination factor up to 9.4 based on an additional parameter at the same experimental condition. In addition, the interaction properties between the enantiomers and the chiral selector were investigated in detail using the F–R model. The main advantages of the novel sensing technique are that it is based on a real-time technique, requires a short detection time, and is highly sensitive within a 10–300 μM concentration range. In particular, the excellent sensitivity for a low target concentration was because the novel analysis method revealed the mechanical difference of the intermolecular binding properties between the target enantiomers and the selector.