What is UV254?

UV254 is a water quality test parameter it provides a fast simple reagent free measurement of the organic content in water.

Ultraviolet transmittance (UVT) refers to the percentage of light that passes through a sample at the wavelength of 254 nm.

UV254 is absorbed and scattered by the organics, colloids, and suspended solids.

UV Absorbance often expressed as A254 or ABS is the light absorbed by a sample.

Absorbance and Transmission are related terms and are related logarithmically

How is UV254 Measured?

Ultraviolet (UV) light, at the wavelength of 254 nm, is passed through a sample. This is compared to the light intensity in deionized water.

The result UVT is given as a percentage transmitted %T = I/Io 

Alternatively, this can be expressed as absorbance ABS = log10 ( 1 / %T )

How is concentration related to ABS/UVT?

The absorbance is related to the concentration by Beer lamberts law

ABS = L ε C


ABS - Absorbance
L - The path length
ε - Molar absorptivity
c - Concentration

What is SUVA? (Specific UltraViolet Absorbance)

SUVA is calculated by dividing the UVA value by the DOC (Dissolved organic content)


SUVA is a method of normalising UV254 with the total organic content (TOC). This is needed as UV254 only measures aromatic content ​

How does UV254 / UVT relate to BOD, COD, TOC and DOC?

All aromatic surrogates concentration grow linearly with UV254 absorption. Doubling the surrogate concentration doubles the UV254 absorption

What is Turbidity Compensation?

Turbidity is the merkyness of water and this can interfere with your UV254 measurement.

UV254 / UVT is blocked/absorbed by particles aswell as organic content.

To compensate for the turbidity we use an infra-red light source to measure the absorption of the particles and subtract it from the UV measurement

What absorbs at 254nm?

TOC, BOD, COD, and DOC all absorb light at a wavelength of 254nm. The proporties that this group of parameters have is the aromatic bonds that they contain.

These aromatic hydrogen bonds will absorb light that means we can know they are present by a drop in light intensity through the sample. Twice the aromatic bonds will have twice the UVT  uv254 absorption. Twice absorption means twice the concentration of organic material.


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