Specific UV absorbance at 254 nm (SAC254) is a recognised surrogate for organics content in water.

It is often included in compliance criteria for many environmental applications.

As the s::can UV/Vis systems measure the entire spectrum between 230nm and 730nm the 254 nm. Absorbance can be provided by the s::can G series carbo::lyser, UV ::lyser and spectro::lyser units.

It needs to be noted the A254 as a lab standard method involves the pretreatment of the water by filtering using a 0.45-µm filter. The assumption is that the remaining absorbance is due to soluble material. This is often not the case as fine colloidal material tends to pass through such a lab filter. Some examples where this can be problematic are.

  • Treated municipal wastewater
  • Treated and untreated industrial wastewater
  • Environmental waters such as the Murray River and others containing colloidal clays etc.

The s::can units mathematically compensate for the presence of these particulates and will therefore give a lower A254 than the lab when the lab measurement is being interfered with by colloidal material. Verification of this can be achieved by simply refiltering the 0.45 micron filtrate with a 0.22 micron filter after checking the A254.

The A254 is often used as a surrogate for determining TOC or DOC in a water sample due to the complexity and cost of DOC/TOC testing. The lab test for these involves sample oxidation by chemical or heat to form Carbon Dioxide (CO2) which is then measured with a UV detection system. It needs to be noted that the A254 will provide good correlations to DOC/TOC while the composition of the water is relatively stable however this relationship will normally break down during times of compositional change which is often when the reading is needed most.

DCM can provide the equipment to not only provide you with raw and filtered 254 values plus transmissivity, the systems can tell you when the composition is changing and you need to recheck your 254 to DOC correlations.