Re: NO3 testing (multiple)

["Philippe Lemaire" <ph.lemaire at CompaqNet_be>]

Thanks to all !

See my interspersed remarks/questions...


> Date: Thu, 16 May 2002 05:56:49 -0400
> From: Jared Weinberger <jared at brainyday_com>
> Subject: Re: NO3 testing 
> 
> <<Nitrate test kits do not measure nitrate directly. The first step is to 
> reduce nitrate to nitrite. It is the nitrite that actually forms the color. 
> The 10-20 minute waiting period is to allow sufficient time for the nitrate 
> in your sample to be fully reduced. --Bill >>
> 
> Yes, in fact LaMotte tells you that you would first have to perform a step 
> to get rid of any nitrite before measuring the nitrate. Of course we plant 
> folks (correctly) assume there isn't appreciable nitrite around. From the 
> LaMotte site about their various nitrate kits: "The nitrate is reduced to 
> nitrite by cadmium or zinc and this undergoes diazotization/coupling to 
> form a pink color. All kits below use cadmium except #3354, which uses zinc 
> and which also contains a reagent that eliminates nitrite interference. Kit 
> #3519 tests both nitrate and nitrite"
> 
> Jared

OK Nitrites are less than 0.05 mg/l (Don't remember between N+ or NO2)

> ~~~~~~~~~~~~~~~~~~~~~~~
> Jared Weinberger
> http://www.brainyday.com/jared


> Date: Thu, 16 May 2002 10:38:46 -0500
> From: Bill Warner <lww at ictech_net>
> Subject: Re: NO3 testing
> 
> > Date: Wed, 15 May 2002 22:06:42 +0200
> > From: "Philippe Lemaire" <ph.lemaire at CompaqNet_be>
> > Subject: Re: NO3 testing
> > 
> > So more you wait more accurate it is ?
> 
> Sorry, Philippe, but no.  The "if some is good more is better" philosophy
> does not apply here.  For maximum accuracy you should follow the
> directions that came with your test kit exactly.  The azo dye that is
> formed is not very stable and if you wait too long the color will begin to
> fade as the dye degrades.

My Tetra and Sera kits (that use grey powder [zinc oxide ?]) go from yellow
to red so losing saturation will not affect the hue that much.

Tetra ask for 20sec. mixing with Zinc and Sera just once...
Some times ago shaking the Tetra kit after 10 min. seems to go back
in time (i.e. less Nitrates)

> 
> - -- 
> Bill

------------------------------


> Date: Thu, 16 May 2002 10:25:59 -0700
> From: Jeff Coart <rapdfire at pacbell_net>
> Subject: Re: NO3 testing
> 
> >Date: Thu, 16 May 2002 10:38:46 -0500 
> >In-reply-to: <200205160748.g4G7m2M28470 at acme_actwin.com> 
> >References: <200205160748.g4G7m2M28470 at acme_actwin.com>
>  
> >Sorry, Philippe, but no.  The "if some is good more is better"
> >philosophy does not apply here.  For maximum accuracy you should follow
> >the directions that came with your test kit exactly.  The azo dye that
> >is formed is not very stable and if you wait too long the color will
> >begin to fade as the dye degrades.
> 
> For what its worth, I use a Salifert NO3 kit and the longer I let the
> sample sit the pinker it gets. The instructions say wait 3 minutes after
> which time there is no color at all. If I let it sit around for an hour
> or so it turns a little pink.

My NO3 Salifert kit as well as Sera Fe kit use a pink hint from light
to intense as indication.  With both more waiting also means more
saturation...

> 
> Anybody have any experience with Salifert kits? Are they reliable? I
> guess I need to mix a sample of water with a known NO3 concentration to
> determine if the thing works correctly.


Stupid question : Are all the NO3 on earth equal ?  
Do they switch to NO2 at the same speed ?
Could another tank parameter modify the reaction ?

Regards,

Philippe