The effect of magnetic field on the hydration of cation in solution revealed by THz spectroscopy and MDs

Quantitative detection of potassium chloride solutions at different concentrations using terahertz waves

Terahertz detection, utilizing electromagnetic waves within the terahertz spectral band, offers a sophisticated approach for the analysis and identification of materials. This technique capitalizes on the distinctive resonant interactions between terahertz waves and the vibrational modes of various non-polar substances and biochemical entities. A notable challenge arises in the terahertz time-domain spectroscopy (THz-TDS) when applied to water-rich samples, owing to the significant absorption characteristics of water molecules at these frequencies. Although various methodologies exist for the detection of potassium chloride, a common substance with extensive applications, its analysis using THz-TDS, particularly in aqueous solutions, remains unexplored in literature. This investigation delineates the terahertz spectral behavior of potassium chloride in powdered form and extends to evaluate aqueous solutions with concentrations ranging from 3 to 60 mmol/L. The findings indicate a pronounced absorption peak within the terahertz range for potassium chloride solutions, which progressively lowers in intensity as the concentration increases. Consequently, THz-TDS emerges as a swift, precise, non-invasive, and safe modality for the quantification of potassium chloride in solutions.

Terahertz time-domain attenuated total reflection spectroscopy integrated with a microfluidic chip

The integration of a microfluidic chip into terahertz time-domain attenuated total reflection (THz TD-ATR) spectroscopy is highly demanded for the accurate measurement of aqueous samples. Hitherto, however little work has been reported on this regard. Here, we demonstrate a strategy of fabricating a polydimethylsiloxane microfluidic chip (M-chip) suitable for the measurement of aqueous samples, and investigate the effects of its configuration, particularly the cavity depth of the M-chip on THz spectra. By measuring pure water, we find that the Fresnel formulae of two-interface model should be applied to analyze the THz spectral data when the depth is smaller than 210 μm, but the Fresnel formula of one-interface model can be applied when the depth is no less than 210 μm. We further validate this by measuring physiological solution and protein solution. This work can help promote the application of THz TD-ATR spectroscopy in the study of aqueous biological samples.