IANZ Accredited Spectrophotometric Method for Colour Testing | Hill Laboratories - NZ


IANZ Accredited Spectrophotometric Method for Colour Testing

Date: 10 Nov 2021
Author: Hill Laboratories

Colour is an aggregate water quality parameter that is useful in determining the suitability of a water for a range of applications. While colour in water can often be a concern for aesthetic reasons, colour from dissolved organic matter can contribute to the formation of undesirable by-products during the chlorine treatment process, most notable when treating water for drinking or process water purposes. In addition, some highly coloured wastewaters may not be suitable for direct discharge into waterways. Recently Hill Laboratories moved to a spectrophotometric method for analysing Hazen colour in water. The spectrophotometric method replaces our previous colour method which was the visual comparison method referencing APHA 2120 B.

Hazen colour units, defined as the colour produced by 1mg/L of platinum in the form of the chloroplatinate ion, are widely used to quantify the yellowish or yellow-brown colour that can be observed in waters; with the presence of Hazen colour mostly attributed to dissolved organic matter, notably humic and fulvic acids.  

The spectrophotometric - single wavelength method, referencing APHA 2120 C, measures the absorbance of a sample at 455 nm. The absorbance measurement is converted to Hazen colour units utilizing the established relationship between sample absorbance and colour. For the spectrophotometric method, all samples are laboratory filtered prior to analysis and results are a ‘true colour' measurement, with any ‘apparent colour’, e.g. from suspended particles, being removed by the filtering process.  

Our IANZ accredited spectrophotometric method will be used for all colour testing at Hill Laboratories, including for the MPI Recognised Laboratory Programme (RLP) and for testing required for Drinking Water Standards New Zealand. The spectrophotometric method APHA 2120 C method is listed on our MPI Recognised Laboratory Programme (RLP) certificate and our Drinking Water Testing Laboratory certificate.  

If you would like further information on this, or any other water quality testing, please contact us at env.csm@hill-labs.co.nz