Tests for total N and P (1 Viewer)

[slip]

what are the tests used to find the concentration of total nitrogen and total phophorus??

 

[Paroissien]

Just use a colorimeter

 

[slip]

can you elaborate a little bit??

 

[jumb]

We just used one of those little magic boxes.

 

[Tommy_Lamp]

I don't believe we need to know this.

 

[Paroissien]

A colorimeter can be used to determine the concentration in ppm of nitrogen (shouldn't exceed 600ppm) and phosphorus (shouldn't exceed 60ppm). If ratio of N exceeds 10:1 this indicates that eutrophication has began.
Can't remember exactly how colorimeter works, has something to do with the amount of light that passes through the sample, but anyway you don't need to know that

 

[nit]

phosphate conc is measured by addition of ammonium molybdate, nitric acid, then ascorbic acid, followed by colorimetry, while nitrates are converted into nitrites and then into a reddish/purple organic complex and spectrophotometric tests are carried out on that.

As for the N ratio, that's really a very dodgy measure of eutrophication - it basically only gives info abt the limiting reagent and not so much on levels of the nutrients in water bodies. I'd be careful quoting figures for it, though 10:1 seems to be the "accepted" value. I've seen 7:1 in other places for biological systems. Unless a question asks specifically for the ratio, I'm not sure it's worth mentioning at all.

 

[Paroissien]

Ok, sounds reasonable. Saying colorimetric processes would be enough though wouldn't it? There won't be too many marks for a question like this

 

[randhi]

i'm sorry, i don't know if i'm wrong or not but isn't the ratio of N when its 10:1 meaning that it is most likely the water body won't be affected by eutrophication

 

[KungPow]

i'm sorry, i don't know if i'm wrong or not but isn't the ratio of N when its 10:1 meaning that it is most likely the water body won't be affected by eutrophication

Yes. They were saying when it exceeds that ratio.

 

[smallcattle]

i'm sorry, i don't know if i'm wrong or not but isn't the ratio of N when its 10:1 meaning that it is most likely the water body won't be affected by eutrophication

when it exceeds the ratio of 10:1, then eutrophication begins i think

 

[Paroissien]

Well I didn't actually say that, but thats what I meant

 

[randhi]

lol sorry thanks

 

[beta-omega]

further elaborating,

USING COLORIMETRY for...

phosphate ions:
Molybdate ions were added followed by the addition ascorbic acid. If phosphate ions are present, then the solution should be a blue to purple colour. Use for colorimetry to determine the concentration of phosphate ions.

nitrate ions:
Firstly the NO3- is reduced to NO2- by passing sample through granulated cadmium tube. 2 organic substances are added successively for intense a red colour.