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Stage 2
Determine the influence of CO
2
Note: Stability criteria <0.5 %/min corresponds in fact to a change in
conductivity <0.02 mS/cm per minute (equivalent to 0.1 mS/cm per
5 minutes), as required in the Stage 2 USP document.
• Transfer a sufficient amount of water (100 mL or more) to a thermostatic
vessel, and stir the test specimen. Adjust the temperature and maintain it
at 25 ±1 ºC. We recommend using a thermostatic bath.
• Rinse the cell carefully with deionized water. Place the conductivity probe
on the Sample and dip it in the thermostatic vessel containing the sample.
Check that the 4 rings are immersed in the solution.
• Press Step 2.
• When the conductivity value is stable, if the conductivity is not greater than
2.1 mS/cm the water meets the requirements of the test, for conductivity.
If the conductivity is greater than 2.1 mS/cm proceed with stage 3.
Stage 3
Determine the combined effect of the CO
Use a Hanna Instruments pH meter.
Take care that the instrument be calibrated in at least two points using
pH 4.01 and pH 7.01 Hanna buffers.
Perform the following test within approximately 5 minutes of the conductivity
determination while maintaining the sample temperature at 25±1 ºC.
• Add the Saturated KCl Solution to the same (0.3 mL per 100 mL of the test
specimen), and determine the pH to the nearest 0.1 pH unit.
• Press Stage 3 key, then enter the corresponding pH reading.
• Referring to the Stage 3 pH and conductivity requirement table the
instrument determines the conductivity limit at the measured pH value. If
the measured conductivity is no greater than the conductivity requirements
for the pH determined the water meets the requirements of the test for
conductivity. If the measured conductivity is greater than this value or the
pH is outside of the range of 5.0 to 7.0, the water does not meet the
requirements of the test for conductivity.
and pH.
2
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