Re: Measuring CO2

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 

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