1. Firstly connect a latex tube with a glass tube at one end on the sampling pipe
2. Open the sampling valve to drain water, the draining time shall not be less than 5 minutes to ensure no bubble in the water,
3. Add 2 drops of phenolphthalein indicator and a certain amount of 0.1 N NaOH standard solution to the sampling bottles in advance.
4. Slowly insert the glass tube into the sampling bottle bottom, after the water sample flows to the carved water sample volume scale, quickly pinch the latex tube to make water not to flow, and immediately pull out the sampling tube.
5. Immediately use 0.05 M sulfuric acid standard solution for neutralization until the red clour disappears, this consumption is not recorded.
6. Add 2 drops 0.5% of methyl orange indicator into water sample, continue to use 0.05 M - H2SO4  for titration until water sample turns into orange red from yellow, record the consumption - H2SO4 volume a, the calculation is shown as follows:
                        a·n·44
        CO2=                      ×1000 mg/L
                           V
 Where:
a - showing the consumed volume of HaSO4 standard solution for titration of the second time, mL.
N - showing that the equivalent concentration of H2SO4 standard solution used, meg/L.
44 - showing CO2 milligram equivalent, g/meq.
V - Showing the volume of water sample, mL.（zjl）