The primary standard for calibrating a nephelometer is:

The primary standard for calibrating a nephelometer is formazin. Formazin is a polymer that is created by the reaction of hydrazine sulfate and sulfuric acid with an aldehyde, and is widely used in the field of water quality testing. It produces a stable and reproducible scattering of light, which is essential for the accurate calibration of nephelometers, instruments that measure the turbidity of water by detecting the amount of light scattered by particles suspended in the liquid.

The use of formazin allows for consistent turbidity readings, as it mimics the scattering behavior of natural particulates found in various water samples. This property makes it an ideal choice for laboratory settings, where precise measurements are critical for assessing water quality.

Formazin’s stability over time and its ability to be prepared in various concentrations provide flexibility for calibrating nephelometers, making it a standard practice in water treatment and environmental monitoring.