Chirality discrimination of D/L-malic acid and its diethyl ester based on terahertz polarization time-domain...

Terahertz time-domain spectroscopy (THz-TDS) technology offers unique advantages for biomedical applications and non-destructive testing. Unlike X-rays, THz technology does not damage the materials being tested, especially active substances. However, traditional THz-TDS techniques still struggle to distinguish between chiral substances. This study presents a terahertz polarization time-domain spectroscopy system (THz-PTDS) that utilizes a 2 × 2 GaAs photoconductive array to detect the polarization of terahertz waves. This system enables the non-destructive and rapid identification of chiral forms of malic acid and its diethyl ester enantiomers. The results indicated that the polarization parameter curves for both solid and solution forms of malic acid showed significant chiral differences at frequency of 0.6 THz. Moreover, the polarization parameter curve of a malic acid diethyl ester-ethanol solution displayed significant chiral differences at 0.93 THz, while the pure malic acid diethyl ester showed significant chiral differences at 1.013 THz. Furthermore, the rotation direction of the polarization ellipse at the corresponding THz frequencies can be used to distinguish between enantiomers. This method provides an innovative approach for the rapid identification of chiral enantiomers in food and pharmaceuticals, with significant application prospects and potential benefits.