Electrical Conductivity of Water for Injection

Electrical Conductivity of Water for Injection


  • Post By : Kumar Jeetendra

  • Source: Microbioz India

  • Date: 05 May,2020

In the pharmaceutical industry, varying grades of water are an essential and highly used raw material. As per the United States Pharmacopeia (USP), Water for Injection (WFI) is a grade of water that is purified by reverse osmosis or distillation; such water must continually undergo tests for conductivity to ensure purity via standard method USP.

This method has also been adopted by other pharma companies as the primary method for the determination of inorganic/ionic impurities in Purified Water and WFI. USP includes three stages of testing; once a stage is passed, no further testing is required.

Stage 1 requires a non-temperature compensated conductivity reading to be met based on the temperature of the sample and excluding carbondioxide (CO₂) dissolution. This Stage 1 test can be performed either inline or in an appropriate container that does not affect the conductivity of the testing solution in any appreciable way (i.e. PTFE containers).

Stage 2 requires a conductivity limit of less than 2.1μS/cm at 25°C (±1°). During Stage 2 testing, the sample must be stirred in order to permit CO₂ dissolution and a change in conductivity of less than 0.1 μS/cm per 5 minute interval.

Stage 3 is the final stage that must be performed within 5 minutes of Stage 2 while maintaining a temperature of 25°C. If this third stage is necessary, 0.3 mL of saturated potassium chloride is added for every 100 mL of testing solution; based upon the pH of the solution, the testing solution must be below the specified conductivity limit.

Hanna Instruments HI5321 Compliant Research Grade Benchtop Meter with the HI76312 Conductivity Probe met all the guidelines as Per USP.

HI5321 is an advanced research grade benchtop EC/TDS/Salinity/Resistivity meter that is completely customizable with a large color LCD, capacitive touch keys, and USB port for computer connectivity.The HI5321 can be calibrated up to four points with a choice of six pre-programmed conductivity standards or user defined custom standards. Resistivity, TDS, Practical Salinity (PSU) and Natural Seawater Scale are calibrated through conductivity. The % NaCl is calibrated to single point with the HI7037 salinity standard.
All readings are performed with the HI76312 four-ring conductivity probe with a built in temperature sensor for automatic temperature correction. The four rings are made with platinum and the body of the electrode is made of Polyetherimide (PEI) plastic that is resistant to many harsh chemicals.

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