Operation, Cleaning & Calibration of pH Meter

Operation, Cleaning, and Calibration of pH Meter

A. pH Measurement by Orion Star™ A211 Benchtop pH Meter

  1. Measure the pH at a temperature of 25°C ± 2°C, unless prescribed otherwise. Record the temperature in to the measurement System.
  2. Rinse the electrode with distilled water before use.  If the pH electrode is dehydrated soak it for 30 minutes in KCl/ Distilled Water.
  3. Clean the pH meter with a clean cotton cloth before starting the operation.
  4. Start the measurement and wait for its stabilization.
  5. If the meter is AUTO READ mode (default setting), press Measure to start the measurement.
  6. When the AR icon stops flashing, record the pH and the temperature of the sample.
  7. As per requirement set the mode For example two-mode option:
    1. Continuous mode ,
    2. Timed Mode
  8. Continuous Mode: The enter will immediately start taking a measurement and update the display whenever the measurement changes. Wait for the display to show “READY” and record the pH and the temperature of the sample.
  9. Timed Mode: Will log measurements at the preselected time interval, regardless of the measurement stability. The meter will update the display whenever the measurement changes, so the pH and temperature of the can be recorded when the display shows READY.
  10. Wash and rinse the electrode with distilled water and Keep the electrode immersed in saturated KCL or distilled water when not in use.
Procedure, Cleaning and Calibration of pH -Meter A211

Electrode Storage:

  1. Electrode shall be stored in electrode storage solution readymade available in the market or 3 M KCL or pH 4.0 buffer solution
  2. Preparation of in-house electrode storage solution shall be recorded.

Cleaning Procedure:

  1. Clean the instrument with dry clean cotton cloth.
  2. Wash pH electrode with Distilled water.
  3. For General Cleaning, prepare a 0.1 M hydrochloric acid (HCl) or 0.1 M Nitric acid solution.
  4. For oil or grease, prepare 0.1 to 0.5 % Liquid detergent solution mixed with hot water.
  5. Soak the electrode in the 0.1 M HCl or HNO3 for half an hour and stir the solution at a moderate rate.
  6. If a refillable electrode is used, drain the reference chamber and refill the electrode with a fresh ROSS fill solution.

Calibration Procedure (Five Point Calibration):

  1. Calibration frequency: Before routine use Rinse the electrode with purified water and dry with a tissue.
  2. Five-point buffer calibrations will be carried out. Standard buffer solutions of pH 1.68, 4.01, 7.00, 10.01 and 12.45.
  3. Note: pH value may vary on a different brand of standard buffer solution as example 4.00 instead of 4.01.
  4. Press F1(Cal), First place the electrode into the buffer pH 1.68, then press F3 (Start), to start calibration. The screen will display P1. When the pH value is stable, it shows pH 1.68 Automatically. Press f2 (Accept) and then f2 (Next) to proceed next buffer.
  5. Rinse the electrode with purified water and dry it with a tissue. Put it into the buffer pH 4.01, then press F3 (Start). The screen will be displayed P2. When the pH value is stable, it shows pH 4.01 Automatically. Press f2 (Accept) and then f2 (Next) to proceed next buffer. 
  6. Rinse the electrode with purified water and dry it with tissue. Put it into the buffer pH 7.00, then press F3 (Start). A screen will display P3. When the pH value is stable, it shows pH 7.00 Automatically. Press f2 (Accept) and then f2 (Next) to proceed next buffer. 
  7. Rinse the electrode with purified water and dry it with a tissue. Put it into the buffer pH 10.01, then press F3 (Start). The screen will display P4. When the pH value is stable, it shows pH 10.01 Automatically. Press f2 (Accept) and then f2 (Next) to proceed next buffer.
  8. Rinse the electrode with purified water and dry it with a tissue. Put it into the buffer pH 12.45, then press F3 (Start). The screen will display P5. When the pH value is stable, it shows pH 12.45 Automatically. Press f2 (Accept) and then f3 (Cal done) to complete calibration
  9. The meter will display the calibration summary including the average slope. Press f1 (means) to export the data to the Calibration log
  10. Record the slope.
  11. Verify the pH buffer 7.00 by measuring the pH as per the procedure previously enlisted and also measured the offset value in pH 7.00 buffer and record it.
  12. Acceptance criteria:
    1. Slope: 90.0% to 105.0%
    2. Verification: pH value should be ± 0.05 from the actual pH of verification buffer and offset value ± 30 mV

Precaution for pH meter :

  1. Care the electrode for scratches, cracks, and salt crystal build up.
  2. Do not store the electrode in De-ionized water.
  3. Clean electrodes after and before use and always store it in electrode storage solution.
  4. Make sure the calibration has been performed before use.
  5. Periodically check the level of electrolyte solution in electrode and electrode storage solution has not evaporated.
  6. The electrode should not be immersed in dehydrating solutions such as sulphuric acid and ethanol.
  7. USA Buffer Group and DIN Buffer set mV range should be as display in below table,
  8. Always use NIST/DIN or Traceable standard for calibration.
  9. Use Buffer solution within 6 months once the bottle is opened or before its expiry which is earlier.
USA Buffer Group and DIN Buffer set with mV range

NIST: National Institute of Standards and Technology

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