Ultrasonic acoustic wave detection of single or capillary electrophoretically resolved underivatized amino acids

Acoustic wave detection of various underivatized amino acids that were injected into and electrokinetically migrated along a capillary tube has been achieved. Acoustic wave detection of underivatized leucine was obtained in the ultrasonic frequency range of 100 kHz - 20 MHz. This was accomplished by measuring the insertion loss from the vector ratio of the signal voltage to the source voltage obtained at the generating and receiving piezoelectric transducers. Linear concentration dependence of the insertion loss of underivatized leucine was established. The effects of capillary internal diameter, capillary geometry (square/circular), buffer composition and acoustic wave frequency on the insertion loss were investigated. Subsequently, separations of underivatized amino acids (leucine/histidine, and leucine/tryptophan) were performed under different buffer conditions and different capillary geometry. The principle of acoustic wave detection will be discussed.