This article was featured in International Labmate - July 2008
Turbidity measurement represents a method appearing quite simple with a very complex background. Its complexity is shown by the fact that possibilities for objective and reproducible measurements were developed just about in the 2nd half of the 20th century. Turbidity is caused by dispersion of undissolved particles varying in size and form being suspended in the solution. The greatest challenge for correct measurement was given in the development of suitable calibration standards generally reflecting the composition and properties of the turbidity showing a ‘linear’ correlation. This already presents a singularity: Due to scattered light properties depending on particle size and their number, the linearity over a wide measuring range is not given; on the contrary the measuring ranges are linear within sections. Depending on the degree of turbidity, there are different applicable measuring techniques. Modern turbidimeters such as the WTW Turb 430 Series provide an automatic measurement range changeover.