Nitrate test kits

["Greger Lindstrand" <greglind at algonet_se>]

Kevin wrote:

From: Kevin.Buckley at uk_neceur.com
> Subject: Re: Nitrate test kits
> 
> One of the issues I've always struggled with is exactly where do you hold
> the sample with respect to the white background on the colour chart.

My suggestion:
Lessen your guessing with this method. I've written it in swedish but you will get the meaning from the pictures alone.
Else, a translation on altavista or someplace might be of assistance.
http://www.hjortgatanszoo.se/main/default/default.cfm?navID=169

Short in english:
Vessels shall have a flat bottom and be of equal size. Plastic or glas doesnt matter as long as they are of the same sort and brand IE. identical.
The drilled holes shall have an edge at the bottom, preventing the vessel from falling thru and drops of liquid from the paper. Use two drills with different size.
Use equal amounts of liquid IE. 5 ml water from the tank and 5 ml testliquid in the other vessel.

Principle is to look from above thru the tankwater on the papercolour and compare it to the testsample against white paper.
Hint: look with unfocused eyes between the two samples from a distance and move the holder from left to right until the two vessels appear to have the same colour.

Using this comparative method gives an acuracy of 2-3 ppm when your inbetween two colours.
Weather the light comes from above, left or right doesn't matter much. You'll get the same result anyway (unlike holding a testtube against the coloursample).

Best regards
Greger