UV254nm is the total amount of light, at a frequency of 254nm absorbed by dissolved and undissolved components within the sample. SAC is the Spectral Absorption Coefficient of the sample and is performed on a filtered sample to 0.45 micron as defined by DIN38 404 and EN ISO 7887:1994.

Suspended solids also absorb transmitted light and interfere with the measurement. It is therefore recommended that samples be filtered before analysis. The absorption from a single pre-focussed, pulsed beam passing through a fixed path length can then be continuously reported. The technique is often referred to as reagent-less but cleaning solutions are typically required to maintain and clean optics. Aromatic hydrocarbons and solvents absorb at this frequency.

The results are often arbitrary and need to be carefully interpreted. Only organic chemicals containing a double bond within their structure absorb UV254nm, single bonded chemicals do not. Every organic chemical absorbs different amounts of UV254nm. The technique is not suitable for applications where the contaminant is unknown or variable in its chemical form. The technique can be applied to a known process or to simply alarm but not quantify the presence of some organic chemicals.

Total Organic Carbon - TOC can be used to report the dissolved organic compounds in less than 3 minutes. The test is not compound sensitive and does not suffer interference affects from suspended solids. By determining the TOC or dissolved organic component of a sample stream, a correlation may be set up with other test such as COD and BOD. Peak organic loads may therefore be determined in real-time.