Formazin Turbidity Standards

Formazin has been used as a turbidity standard to test cloudiness in water for many decades. The standard unit of measurement is the NTU or nephelometric Turbidity Unit. Stock solutions are typically at 4000 NTU’s. This concentration is stable for at least 1 year, although our customers frequently report stability/reliability/consistency up to the 2 year date from manufacture.

The nature of formazin is such that the particle size varies- between 0.01-10 microns, and because of this characteristic formazin resembles closely to what is described as “real world’ samples. Formazin is an insoluble polymer formed by the reaction of 2 compounds.

Another benefit /advantage to formazin is that it is recognised worldwide as the only true primary standard for turbidity measurement. Of course, it is EPA approved. It is accepted and reliable for reporting of lab test results. All other “standards” are reliable only to the extent that they are traceable to formazin.

The other key benefit to a formazin turbidity standard is that it is compatible with any turbidity meter, unlike some modern synthetic substitutes which are sensitive to differences in turbidity meter brands. Formazin turbidity standards are also much more economical to use.

The one disadvantage of a formazin turbidity standard is stability with low concentrations. These must be prepared on a daily basis when required from a stronger 2000 or 4000 NTU solution. As always, any formazin standard needs to be shaken briefly before each use. Reproducible results from dilutions of Exaxol offers certified Formazin turbidity standards at competitive prices, and with a quick order turnaround. Different values of NTU are listed on our website with their respective shelf life.