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pH of Purified Water

What is requirement for pH of purified Water. Whether Purified Water USP require pH specification / control

Water systems

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      There is no pH specification for Purified Water in USP. Conductivity specifications take care of pH. If the water passes conductivity test pH automatically will fall in the range of 5.0-7.0. For Purified Water USP conductivity limits is defined through three stages. For example in Stage 1 when conductivity is measured at 25 degC,  conductivity should not be greater than 1.3uS. If this is not met proceed to Stage 2 testing, and conductivity should not be greater than 2.1uS (at 25 degC). If this is also not met, in Stage 3, test the pH of the Stage II sample. For the specified pH of purified water, conductivity shall not be greater than the value specified in the table. For example, if pH of the water is 7.0, conductivity should not be greater than 4.6uS. European PHarmacopea – Purified Water (Ph. Eur) also do not specify pH, and only specify conductivity test.

      References:

      1. FAQs: Water for Pharmaceutical and Analytical Purposes (USP)
      2. USP: Water Conductivity <645>

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