In this paper, we employed terahertz time
domain spectroscopy (THz-TDS) to investigate the nitrate
() concentration in four types of nitrate solution (sodium
nitrate, aluminum nitrate, calcium nitrate and magnesium
nitrate). Their absorption coefficient and refractive index
were calculated in 0.2–2.5 THz, and a logarithmic
relationship was observed between NO – 3 concentrations
and selected optical parameters regardless of the kinds of
nitrate solution. Partial least square (PLS) model was built
between THz-TDS and NO – 3 concentration. The correlation
coefficient of PLS model was calculated. The results make
the quantitative analysis of NO – 3 concentration possible by
THz-TDS and indicate the bright future in practical
application.

• Detecting NO 3 -- concentration in nitrate solutions using terahertz time-domain spectroscopy