TOC-5000 Online TOC Analyzer Many organic substances dissolved in water absorb ultraviolet light. Therefore, by measuring the absorption of these organic substances by ultraviolet light at a wavelength of 254 nm, the total amount of organic pollutants in water can be measured. The TOC sensor uses two light sources, one 360, one 360mm UV reference light, which can automatically compensate the optical path attenuation and turbidity effects, thus achieving more stable and reliable measurement values.