Rapid analysis of tetracycline hydrochloride solution by attenuated total reflection terahertz time-domain spectroscopy

•ATR THz-TDS was applied for detecting the TCH in solutions.•Complex refractive indices of TCH in pure water and in pure milk were determined.•The present of TCH in solutions led to a lower complex refractive index.•The SLR models could be used for predicting the TCH concentration.

Despite numerous methods for the detection of antibiotic residues, they are usually destructive and require tedious pre-treatment. Terahertz time-domain spectroscopy (THz-TDS) is an emerging technology that has advantages for analyzing chemical and biological compounds since THz waves are very sensitive to the molecular vibrational modes. Here we incorporated attenuated total reflection technique into the THz-TDS and demonstrated that this technology (ATR THz-TDS) allowed to determine the complex refractive indices of tetracycline hydrochloride (TCH) solutions with high accuracy and could be used to predict their concentrations. Our results from the simple linear regression models indicated that the complex refractive index exhibited a monotonic decrease with an increase in the TCH concentration. This study will provide new knowledge about the concentration determination of a liquid sample that couldn't be elucidated with the conventional THz-TDS technologies.