Trübtests

Trübtests, in German often called turbidity tests, are analytical procedures used to assess the cloudiness of liquids caused by suspended solids such as silt, organic matter, or microorganisms. The primary goal is to quantify turbidity, which serves as a key indicator of water quality, process cleanliness, and product stability in various industries.

Most trübtests rely on nephelometric measurement, where light is projected into the sample and the instrument detects light scattered at about a 90-degree angle from the incident beam. Results are typically expressed in nephelometric turbidity units (NTU) or, in some contexts, Formazin nephelometric units (FNU), reflecting the calibration standard. Calibration standards commonly involve Formazin turbidity solutions, and measurements may follow standards such as ISO 7027 or DIN EN ISO 7027.

Procedure elements usually include collecting a representative sample, thorough mixing to ensure uniform suspension, removing air bubbles, instrument calibration, and adherence to specified temperature and measurement conditions. The measurement range often spans from near 0 up to several hundred NTU, with regulatory and process requirements guiding acceptable limits (for example, drinking water frequently targets low NTU values).

Applications of trübtests cover drinking water and bottled beverages, wastewater and environmental monitoring, and various industrial processes where turbidity correlates with filtration performance or product quality. Limitations include interference from sample color or dyes, oils, or fine particles that affect light transmission and scattering; high turbidity can saturate detectors; and results can depend on particle size distribution and sample handling.

See also: Turbidity, Nephelometry, Water quality testing.