Water quality- Examination of colour

[Urmas Muinasmaa]

Hi,

I have question about a simple parameter: colour.

There is 2 methods according to ISO 7887:1994 :
1) Visual comparison against Pt-Co standards;
2) Photometric measurement of absorption (436, 525, 625 nm).

I don't believe that many laboratories use visual examination nowadays,
specially for (many) 100-s of samples a day. The same time drinking water
quality requirements specify the limit in mg/l Pt-Co scale in many
countries and the use of Pt-Co scale is common.

Is it correct to calibrate spectrophotometer using Pt-Co standards? What
would be correct wavelength then ? 436 nm? Probably this isn't following
ISO 7887:1994 standard any more?

Does anybody know how is colour measured in water industry laboratories?

Urmas

[R Molony]

The test procedures are usually carried out on cylinders with path
length of up to half a meter for some low colour waters.
normal commercial spectros do not have a long enough pathlength.
This is why cylinders and artificial colour standards are used.
I understand Tintometer produce a artificial glass disc colour
standard.

Bob