UV254 Analyzer – UV254Sense

The UV254Sense UVA/UVT monitor provides real time organic UVA (ultra-violet absorbance) and UVT (ultra-violet transmission) analysis. The real time monitoring of organics in water has improved greatly with technological improvements in spectral analysis of the ultraviolet light range using the UV254 analyzer which as standard comes with UV transmittance and UV absorbance outputs. It does this by passing a low flow of water continuously through a fixed silica cuvette and by shining a UV254 light through the water measuring how much is absorbed (UVA) and how much is transmitted (UVT).

What is the UV254Sense UV254 Analyzer?

The concentration of contaminants such as the organics that lead to disinfection by products (DBPs) can be determined by measuring the light absorbed by a water sample at a particular wavelength (254nm). The absorbance of light used in UV254 monitors provides an indication of the amount of aromatic (or reactive) organic matter in water, making it an excellent choice as a surrogate measurement for total organic carbon (TOC) in monitoring organics removal from a process.

UV254 analyzers from Pi allow for the detection of natural organic matter (NOM) which is found in all waters and has a bias towards aromatic compounds which provides significant benefit for monitoring DBP formation potential.

If you have any questions or would like to find out more about UV254Sense get in touch with one of our technical experts.

Focus On

Focus Ons are a series of short articles distributed by email providing technical information regarding instrumentation, process measurement in potable, waste, process and pool waters. If you would like to join the mailing list, please contact us.


UV254 refers to the particular wavelength of light (254nm) that is shone through water. Contaminants (that may be either particulate matter or organics) in the water absorb light at that wavelength, and this is the basis of measurement.

This technology is employed in two main ways, ultraviolet absorption (UVA) and ultraviolet transmission (UVT). The UV254Sense can be used in either of these modes.

UVA measures how much of the light is absorbed and is used for measuring the level of organics; it can also be used as a surrogate measurement for COD, TOC and DOC. Water treatment works, and sites using coagulation control commonly use this measurement.

UVT measures how much light passes through the water and is used to determine the power required in UV-based disinfection processes.

Because UVA and UVT are different ways of interpreting how the same UV254 source is affected by the sample, there is a direct mathematical relationship between them:

UVA = 2 – log10 UVT

Because the organics in raw water that are detected using UV254 are often also the cause of color, color analysis is often used for the same purpose. However, the issue with color analysis is that many organics do not reflect in the visible light spectrum (causing low readings) and there are many color-causing substances (such as manganese) that aren’t relevant for organic analysis (causing high readings).

UV254 instruments are also useful for monitoring disinfection by-products (DBPs) as they are more sensitive to the aromatics which can react with chlorine to form them. This is another advantage over color analysis and is particularly useful in coagulation control.  

In addition to the 254nm light used for measurement within the UV254Sense, the sensor also measures the absorbance of a second wavelength closer to the visible light spectrum. This second wavelength is not absorbed by organics, and so monitoring the difference between these two wavelengths allows for continuous turbidity compensation.

Continuously measuring total organic carbon (TOC) is both expensive and difficult, and so a common alternative is to use UV254 as a surrogate measurement. Because every water source is different, a correlation needs to be determined for each site; this relationship can then be entered into the analyzer, and a continual surrogate TOC output can be produced.

The quality of this correlation will depend upon the makeup of the TOC in the water; the higher the proportion of UV254 absorbing organics, the better the correlation will be. The opposite is also true, as non-absorbing organics will not be detected by the sensor. However, we typically find that the correlations in wastewater and municipal applications are very good.


Need help deciding what you need? Fill in the form and we will call you

The latest company & industry news from Pi

Subscribe to receive technical and applications information in the following categories:

Pi Logo

This website uses cookies to ensure you get the best experience on our website. Read our cookies policy here.