Nephelometric Method of Measuring Turbidity

In this nephelometric method of measuring turbidity post we have briefly explained about nephelometric method’s principle, procedure, requirements, and results. 

Nephelometric Method

Depending on its intended purpose, water must meet precise composition and purity requirements. Each body of water must be assessed on a regular basis to ensure its suitability.

All options range from simple field testing for a single study through laboratory-based multi-component instrumental analysis. Water quality measurement is a time-consuming and precise process that uses a number of quantitative analytical methods.

Turbidity refers to the amount of suspended particle matter in water. Turbidity is a metric that measures how light is scattered by suspended solids: the more light that is scattered, the higher the turbidity.

The turbidity of a sample solution can be determined using a nephelometer. The turbidity is measured in nephelometric turbidity units (NTU) or Jackson turbidity units (JTU).


Nephelometric method compares the intensity of light scattered by a sample under defined conditions to the intensity of light scattered by a standard reference suspension under the same conditions.

As the intensity of scattered light increases, so does the turbidity. A popular primary standard reference suspension is formazin polymer. A formazin suspension’s turbidity at a certain concentration is defined as 400 NTU.



1. Nephelometer

2. Light source

3. Sample cells


1. Water Sample

2. Hydrazinesulphate (NH2)2.H2SO4

3. Hexamethylenetetramine (CH2)6N4

4. Working standards

5. Secondary standards

Sample storage

The material cannot be preserved; analysis should begin as soon as possible. Refrigeration or icing to 4°C is suggested to prevent microbial breakdown of solids.


1. Gently stir the sample using a moderate agitator. Before pouring the sample into the cell, wait for the air bubbles to disappear.

2. Fill the cell with a well-mixed sample and place it in an ultrasonic bath for 1 to 2 seconds to remove all bubbles, or use vacuum degassing to eliminate all bubbles. The turbidity of the water can be determined directly from the instrument display.

3. Calibrate continuous turbidity monitors for low turbidities using a laboratory-model nephelometer by determining the turbidity of the water flowing out of them.

4. Alternatively, calibrate the instruments using a formazin primary standard or a suitable secondary standard, as directed by the manufacturer.


Low values are caused by the presence of floating debris and coarse sediments that settle out quickly. Finely separated air bubbles will have a good effect on the outcome.

True color, the color of water formed by dissolved compounds that absorb light, reduces turbidity, albeit this effect is rarely seen in finished waters.

Further Readings