Ultrasound-Controlled Chiral Separation of Four Amino Acids and 2,2,2-Trifluoro-1-(9-anthryl)ethanol

Chiral separation of 4-hydroxyphenylglycine, phenylglycine, tryptophan, methionine, and 2,2,2-trifluoro-1-(9-anthryl)ethanol (TFAE) was performed under ultrasound reduction at room temperature and high temperature (50 °C). At high temperature (50 °C), both α and Rs were improved slightly under ultrasound reduction as compared to those under non-ultrasonic and ultrasonic irradiation (50 watt/L) conditions. Even at low temperatures, the largest α was observed under ultrasound reduction conditions, except in the case of methionine. However, at low temperature, Rs was reduced under ultrasound (50 watt/L) irradiation, but was improved under ultrasound reduction rather than under the continuous ultrasonic irradiation. Similar to the fact that gradient elution (based on solvent polarity) can improve α, ultrasound reduction can improve α and Rs. Ultrasound reduction is demonstrated to aid the rapid separation of chiral compounds with improved resolution, especially, at high temperatures. Although chromatographic separation using ultrasound has been rarely dealt with until now, ultrasound can be used as an external field in chromatography.