Re: Measuring CO2

To: Aquatic-Plants at actwin_com
Subject: Re: Measuring CO2
From: ac554 at freenet_carleton.ca (David Whittaker)
Date: Tue, 12 Sep 1995 07:00:30 -0400

Roger Crowther writes....

>George makes a good argument for the limited accuracy of estimating
>CO2 concentrations by interpolating from KH/pH tables.  So I suppose I 
>will have to invest in *another* test kit.  What kits are recommended? 
>Joanne (I think) mentioned the LaMotte kit. Is there any consensus about 
>this?

The best method of which I am aware is to titrate a fresh sample with
sodium carbonate (N/22). Free CO2 combines with NA2CO3 to form NaHCO3
which is colourless in the presence of phenolphthalein indicator. The
sample turns red at the point at which no free CO2 exists and excess
Na2CO3 is present. It is then a matter of calculating the result. If
one is careful, the result is fairly accurate. Free mineral acid, if
present, will be measured in the test. The lab equipment will cost you
a few bucks though. Seems a bit of a bother to me.

ppm free CO2 = ml N/22 sodium carbonate X 1000/ml sample


Dave

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