The measurement principle is based on the intense UV absorption of organic molecules at 254 nm according to the Lambert-Beer law:
[C] = k log (Iin / Iout)
[C]: concentration of the sample
k: extinction coefficient
Iin: sample input light intensity
Iout: light output sample intensity
Turbidity, organic substances, suspended solids or dirt in the measuring cell are automatically compensated by a differential measurement with a second detector with a different wavelength.