Sciencemadness Discussion Board

Having trouble with nitrate test kits

Little_Ghost_again - 13-12-2014 at 15:08

Hi
I have several aquariums, one in particular is a planted dutch tank and uses CO2 injection for enhanced plant growth.
I use a aquarium test test to measure the nitrate levels and other stuff. If gets expensive testing with these kits as the aquarium runs so well it eats up the nutrients at a huge rate, so I add in ferts etc.
I need to test often tomake sure the nitrate levels etc are correct.
I found the MSD for the aquarium test kits, but got to thinking........... A company called sparkfun do a small unit that detects colour and gives you a voltage based on this, now it would be pretty easy to use a micro to read a test tube detect the colour and have a LCD give you the nitrate or nitrite reading.
But Even with the msd sheets I cant work out how to replicate the kit.
For example Nitrite

the test kit data sheet for bottle one
http://www.regulatory-info-hsx.com/pdf/english/MSDS-A7826.pd...

for the second bottle you use
http://www.regulatory-info-hsx.com/pdf/english/MSDS-A7827.pd...

they give you a little container and you add 5ml water to test tube then add 5 drops from bottle 1, next you add 5 drops from bottle 2 and wait two mins, the colour is then compared on a chart, obviously instead of the chart I am aiming to do this electronicaly.
But my problem is the msd is a bit vague about whats in the bottles.
For example it say bottle 1 contains Sulfanilic acid conc 0.1%-1%
Hydrochloric acid 1%-5%

Bottle 2
1,2propanediol 60%-100% ??
Acetic acid 10%-30%
N-(1-nNaphytal-Ethyllendiamine Dihydrochloride

So I am not sure exactly what proportions of each chemical are in the bottles, once I know that I could copy it and just work out how much was in a drop by measuring it. No idea what the chemicals cost but has to be way cheaper to buy the chemicals and make my own kits?
Anyone got any ideas on this?
Many thanks
There are others but I wanted to start here. I cant find the link to the light detector but they are cheap and seem to work (I have used one for something else)
LG

Its not the sensor I will use but its similar to this one for anyone interested
https://www.sparkfun.com/products/10904

[Edited on 13-12-2014 by Little_Ghost_again]

IrC - 13-12-2014 at 22:06

http://www.ebay.com/itm/TCS230-TCS3200-Detector-Module-Color...

Little_Ghost_again - 14-12-2014 at 01:31

Hi
Thanks for that, I have that side covered, I am asking about the chemistry side and what strength of chemicals to use etc

nezza - 14-12-2014 at 01:33

I had a look at some nitrate test kits a while ago. The best one I found used coarsely ground zinc to reduce nitrate to nitrite which was reacted with sulfanilic acid in HCl to give a diazonium salt. This is then added to alpha naphthol in alkali to give a red colour. I modified the test and use this as a method myself :-

Test for nitrate (NO3-)

Principle

In acid solution nitrate is reduced to nitrite by zinc and hydrochloric acid. This is used to diazotise aniline or sulfanilic acid. This then reacts with alpha naphthol to give a red coloured diazo dye.


Reagents

Hydrochloric acid (4N) containing sulfanilic acid or
Hydrochloric acid (4N) containing aniline

Coarsely powdered zinc

Alpha naphthol in ethanol

Sodium hydroxide (6N)


Method

1. Add 3 drops of the acid to 4ml of test solution.

2. Add a small spatula of zinc powder.

3. Leave for 2 minutes mixing occasionally.

4. Add 1 drop of alpha naphthol.

5. Add 4 drops of 6N Sodium hydroxide.

The development of a pink-red colour indicates the presence of nitrate in the water. A control of deionised water should be run at the same time.

Little_Ghost_again - 14-12-2014 at 03:54

Quote: Originally posted by nezza  
I had a look at some nitrate test kits a while ago. The best one I found used coarsely ground zinc to reduce nitrate to nitrite which was reacted with sulfanilic acid in HCl to give a diazonium salt. This is then added to alpha naphthol in alkali to give a red colour. I modified the test and use this as a method myself :-

Test for nitrate (NO3-)

Principle

In acid solution nitrate is reduced to nitrite by zinc and hydrochloric acid. This is used to diazotise aniline or sulfanilic acid. This then reacts with alpha naphthol to give a red coloured diazo dye.


Reagents

Hydrochloric acid (4N) containing sulfanilic acid or
Hydrochloric acid (4N) containing aniline

Coarsely powdered zinc

Alpha naphthol in ethanol

Sodium hydroxide (6N)


Method

1. Add 3 drops of the acid to 4ml of test solution.

2. Add a small spatula of zinc powder.

3. Leave for 2 minutes mixing occasionally.

4. Add 1 drop of alpha naphthol.

5. Add 4 drops of 6N Sodium hydroxide.

The development of a pink-red colour indicates the presence of nitrate in the water. A control of deionised water should be run at the same time.


Hi will this give a quantitative result? or just indicate yes/no for nitrate?

blogfast25 - 14-12-2014 at 08:08

That's very neat, nezza.

What's the estimated detection limit? Would it be suitable for photometric determinations?

nezza - 14-12-2014 at 10:47

Hi folks. It reacts down to 10 or so ppm of nitrate. As for how quantitative it is higher concentrations do give a deeper colour but I suspect a set of standards would have to be run with any unknowns. The absorption max with sulfanilic acid is about 550nm. Other phenols can be used in alpha naphthol is not available. Thymol gives an orange colour but is not as sensitive.

[Edited on 14-12-2014 by nezza]