Comparison of nephelometric turbidity measurements using wavelengths 400–600 and 860 nm

Two turbidimeters with a spectral peak response of the detection systems between 400 and 600 nm have been compared with one that measures scattered light with a wavelength of 860±10 nm according to ISO 7027 (EN 27027). Water colour reduced readings of formazine suspensions with instruments that do not meet the requirements in ISO 7027. For natural water and drinking water the latter instruments produced lower readings regardless of water colour. The experimental results were confirmed in a nationwide interlaboratory comparison.