Types of Assays - Turbidity

Turbidity
Cloudy or hazy solutions are called "turbid". Measuring turbidity is important in many common procedures, such as testing the purity of drinking water or measuring the concentration of microorganisms in lab procedures. Turbidity is due to the presence of very small suspended particles in the liquid that scatter light. To measure the scatter of light, as opposed to its absorbance, the detector in turbidity assays is placed at 90^o to the direction of the light path. Click here for the Turbidity Assay page.

Figure 1. Turbidity of a milk solution. The amount of scattered infrared (940 nm) radiation is proportional to the concentration of milk.

Terms and definitions

Turbidity assay - A procedure (assay) that measures the concentration of particulate suspensions.

Standard solutions - A set of solutions with known concentrations of the chemical species being assayed. Used to make a standard curve.

Standard curve - A graph that relates the output of the photometer (on the y-axis) to the concentrations of the solutions (on the x-axis). The curve based on the standard solutions is used to determine concentrations of unknown solutions.