Patent ID: 8374800

Claim:
A method for determining a concentration of a first substance in a liquid mixture containing water, the first substance and other substances, the method applies self-referenced reflection THz spectroscopy and comprises: on a section of a plane window of thickness d and refractive index n win having a front and a back side, providing the mixture in contact with the back side; irradiating coherent THz radiation with frequencies within the range 0.05-2 THz on the front of the window section at an angle of incidence θ, the incident radiation resulting in a reference signal reflected from the front of the window section and a sample signal reflected from the back side of the window section; recording the reference and sample signals in the time domain; calculating by a processor at least one component of the complex index of refraction of the mixture {circumflex over (n)} mix (ω) or the complex reflection coefficient {circumflex over (r)} win/mix (ω), each of the at least one component being determined for at least two frequencies in said range; and comparing the calculated component(s) with a set of corresponding components being previously recorded and calculated for said at least two frequencies using the above steps on a set of samples with known concentrations of the first substance in water, thereby estimating a concentration of the first substance in the mixture.