TEST METHOD: Colour
Revised 26 February 2003 (calibration notes changed to reflect new spectrophotometer)
Assess Safety, Health, Quality and Environmental aspects of each specific step.
Colour of natural waters varies considerably. The following methods are used for measuring colour in waters.
|SPECIFIC JOB STEPS||RISK ASSESSMENT||RISK CONTROL|
|Colour is measured using a spectrophotometer. A sample is placed in a cell and a beam shone through it.||The machine may need calibration.||The Vega spectrophotometer is zeroed against a blank, and then stores the zero value until its next calibration is due.|
|"Apparent" Colour/Turbidity Testing:
Record the absorbance of the sample at 425nm and 580nm. As colour and turbidity affect each other, correct by plotting the readings on the Nomogram Chart that is stored in the laboratory.The chart is derived from AT Palin (1955) "Photometric determination of the colour and turbidity of water." Water & Water Engineering, 59:341-345. Record colour as HAZEN's or Colour Units, in the laboratory day book.
|The nomogram is depenndant on the path length of the spectrometer cell||Charts are available for 10mm and 10cm path lengths|
|"True" Colour Testing:
Should a sample need testing for hue, saturation and luminance, the method as specified in Standard Methods for the Examination of Water and Wastewater (APHA) should be followed.
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