eutech-instruments carbon dioxide gas User Manual

Instruction Manual 

 

Carbon Dioxide Electrode

 

 

14

 
Free CO

2

, bicarbonate, and carbonate - the total amount of carbonate - in ground water or seawater, 

will depend on location, temperature, depth, and pH. Using the measurement procedure in the 

 section, the carbonate level in groundwater or seawater can be measured. Grab 

samples taken in the field or ocean can be preserved for laboratory testing by following the 
procedures given in the 

 section. 

 
Since carbon dioxide is easily absorbed by highly basic solutions, concentrated ammonium 
hydroxide often contains carbonate as an impurity. By a variation of the direct measurement 
procedure, the amount of carbonate in concentrated ammonium hydroxide can be measured. By 
adding increments of a 10,000 ppm standard to an acid reagent, a calibration curve is constructed, 
the sample concentration is determined from the calibration curve, taking the dilution factor into 
account. 
 
The required equipment is found in the 

 section. You will also need a 1 ml 

graduated pipet and a 10 ml pipet. 
 
In addition to the solutions found in the 

 section prepare the following: 

 

1. 

A standard solution of 10,000 ppm carbonate, CO

3

-2

. To prepare this solution from your 

own laboratory stock, half fill a one liter volumetric flask with distilled water, add 14.0 
grams of reagent-grade sodium bicarbonate (NaHCO

3

). Swirl the flask to dissolve the 

solid. Fill to the mark with distilled water, cap, and upend several times to mix the 
solution. 

 
2. 

3M sulfuric acid reagent. To prepare this solution from your own laboratory stock, add 
approximately 500 ml of distilled water to a one liter volumetric flask. Using a hood and 
protective safety equipment and extreme caution, add 167 ml of concentrated sulfuric acid 
(18M H

2

SO

4

) to the flask.  Swirl the flask slowly after small additions to mix the acid and 

dissipate the heat. Finally, add remaining distilled water to the mark. Allow the solution to 
cool to room temperature. Upend the stoppered flask several times to mix the solution. 

 

To measure a sample: 

 
1. 

To a clean, dry 150 ml beaker, add 100 ml of 3 M sulfuric acid to a 150 ml beaker. Place 
the beaker on the magnetic stirrer and begin stirring at a constant rate. Lower the electrode 
tip in the solution. Add the standard solution (10,000 ppm), using the steps given in Table 
4 below. Record the mV reading after each addition. Plot the concentration (log axis) 
against the mV potential (linear axis) on semi-logarithmic paper. The plotted concentration 
is eleven times the actual concentration due to sample dilution. 

 
2. 

To another 150 ml beaker, add 100 ml of the acid reagent. Place the beaker on the 
magnetic stirrer and begin stirring at a constant rate. Lower the tip of the electrode in the 
solution. Add 10 ml of the sample to the beaker and record the mV reading. Determine the 
concentration from the calibration curve.