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SOP for Operation and Calibration of pH Meter


Standard operating procedure to operate & calibrate the pH meter and activation of pH electrode.

1.0  PURPOSE

       To lay down the procedure to perform the Operation and calibration of pH meter. 

2.0  SCOPE

       It is applicable to pH meter installed in Quality control department.

3.0  RESPONSIBILITY

       QC Analyst / Microbiologist

4.0  ACCOUNTABILITY

       Head of Department

5.0  PROCEDURE

5.1  Key function of pH meter

5.1.1  ON/OFF Press the ON/OFF button of the pH meter to switch on the meter and switch off the meter.
5.1.2  CAL/MEAS
CAL: - Press the CAL button to activate the pH calibration mode and activate the temperature calibration mode.
MEAS: - Press the MEAS to allow return to measurement mode when canceling or terminating any operation.
5.1.3  HOLD/ENTER
HOLD: - Press the HOLD to Activate/Deactivate freezing of the measured reading while in measurement mode.
ENTER: - Press the ENTER to confirm the measured reading for print.
5.1.4  MI/
MI (memory input): - Press MI to capture the measured readings of the pH with its corresponding temperature values and store them in memory.
▲: Scroll through each SETUP and its sub group menu
5.1.5  MR/
MR (memory recall): - Press MR to retrieve the stored data from memory.
: - Scroll through each SETUP and its sub group menu.
5.1.6  SETUP: -Press SETUP to activate the parameter setting menu to customize meter configuration, view calibration points and electrode offset data, select auto power off, reset meter and clear memory.
5.1.7  MODE: - Select the measurement parameter option between pH with temperature.

5.2  General

5.2.1  Electrode Cleaning: Electrodes, which are mechanically intact, can often be restored to normal performance by one or combination of the following procedures.
5.2.2  Salt Deposits: Dissolve the deposit by immersing the electrode in raw water for ten to fifteen minutes. Then thoroughly rinse with de-ionized water.
5.2.3  Oil / Grease Films: Wash electrode pH bulb in a little detergent and water. Rinse electrode tip with de-ionized water.
5.2.4  Clogged Reference Junction: Heat a dilute KCl solution to 60-80°C. Place the sensing portion of the pH electrode into the heated KCl solution for approximately 10 minutes. Allow the electrode to attain room temperature while immersed in some unheated KCl solution.
5.2.5  Electrode Activation: In case of dehydration/electrode showing sluggish response, the bulb can be re-hydrated by immersing the electrode in an ideal storage solution (e.g. buffer pH 5.00/5.01 solution) for 1-2 hours. If this fails, proceed for the electrode rejuvenation. 

5.3  Operation of pH meter to determine pH of solution

5.3.1  Press ON to switch on pH meter. The MEAS annunciator appears on the top center of the LCD. The ATC indicator appears in the lower right hand corner to indicator automatic temperature compensation.
5.3.2  Rinse the electrode with de-ionized or distilled water before use to remove any impurities adhering to the probe body.
5.3.3  Maintain the temperature of the sample to 25°C ± 2°C, unless otherwise specified in the individual monograph and dip the electrode along with the temperature sensor into the sample.
5.3.4  When dipping the electrode into the sample the sensor or the glass bulb of the electrode must be completely immersed into the sample, Stir the probe gently in the sample to create a homogeneous sample.
5.3.5  Allow time for the reading to stabilize.
5.3.6  If the READY indicator has been activated the READY annunciator lights when the reading is stable.   
5.3.7  Press the HOLD to freezing of the measured reading and Press the ENTER to confirm the measured reading.
5.3.8  Record the observed values of pH and Temperature in the respective test data sheet or technical information sheet.
5.3.9  Wash the electrode in de-Ionized water after use and store the electrode in storage solution or pH buffer 5.00/5.01 or 7.00/7.01 buffer solution.

5.4  Calibration of pH meter

Frequency : Daily (Prior to use)
5.4.1  Before starting the calibration make sure that the correct measurement mode is selected.
5.4.2  Wash the electrode thoroughly with de-Ionized water or a rinse solution. Do not wipe the electrode; this causes a build-up of electrostatic charge on the glass surface.
5.4.3  Maintain the temperature of the buffers to 25°C ± 2°C, unless otherwise specified in the individual monograph and dip the electrode along with the temperature sensor into the buffers.
5.4.4  Perform the five point calibration using standard buffers of pH 1.68, 5.01/5.00, 7.00/7.01, 10.00/10.01 and 12.45.
5.4.5  Dip the electrode into the calibration buffer. The end of the electrode must be completely immersed into the sample. Stir the electrode gently to create a homogeneous sample.
5.4.6  Press CAL/MEAS key to enter pH calibration mode .The CAL indicator will be shown. The primary display will show the measured reading while the smaller secondary display will indicate the pH standard buffer solution reading.
5.4.7  Wait for the measured pH value to stabilize.
5.4.8  Press HOLD/ENTER key to confirm calibration. The meter is now calibrated to the current buffer.
5.4.9  Fist rinse the electrode with de-ionized water, which is followed by next buffer solution and
place it in the buffer solution.
5.4.10  Follow steps 5.5.5 to 5.5.9 for additional calibration points.
5.4.11  When all the calibration points set in the unit configuration set up are completed the meter returns to the measurement mode automatically. However calibration can be terminated without completing the number of points as set in the unit configuration. It can be done by pressing CAL\MEAS to return to pH measurement mode. Record the calibration details and Temperature.
5.4.12  Change the calibration buffer every week or whenever required and record.

5.5  Determination of pH Electrode Slope

Frequency : After each calibration.
5.5.1  Press the SETUP key to enter Set Up mode.
5.5.2  Press the MI/▲or MR/▼ keys to scroll through subgroups until you view parameter P3.0.
5.5.3  Press the HOLD/ENTER key. The display show the electrode offset value. If you have not calibrated at any buffer, the primary display show ‘----‘
5.5.4  Press the HOLD/ENTER key to proceed to electrode slope display.
5.5.5  The display shows electrode slope in percentage. Slope displayed will be the current slope of the slope zone to which a measurement is made or calibration is done. Record the electrode slope.

5.6  Storage

5.6.1  Always keep the electrode bulb wet, preferably in the pH 5.00/5.01 buffer. Raw water is also acceptable storage media, but avoid storage in de-ionized water.
5.6.2  During handling of pH meter, check if electrode is broken, replace the same with new electrode and enter the details in instrument usage log book for pH meter.

5.7  Electrode Rejuvenation

5.7.1  If the electrode fail to give appropriate result during calibration, the same shall be Rejuvenated as mentioned below: -
5.7.1.1  Dip and stir the electrode in ethyl alcohol for 5 minutes.
5.7.1.2  Leave the electrode in tap water for 15 minutes.
5.7.1.3  Dip and stir the electrode in concentrated acid (e.g. Hydrochloric Acid, Sulphuric Acid) for 5
minutes.
5.7.1.4  Leave the electrode in tap water for 15 minutes.
5.7.1.5  Dip and stir the electrode in strong base (Sodium Hydroxide) for 5 minutes.
5.7.1.6  Leave for 15 minutes in raw water.
5.7.1.7  Test with standard calibration buffer solution.
5.7.1.8  If the electrode still fails to restore the normal electrode response, the electrode rejuvenation steps (5.7.1.3 – 5.7.1.6) shall be repeated.
5.7.1.9  If the response does not improve, then the electrode has completed its useful life and same shall be replace with a new electrode.
5.7.1.10  Record the Electrode Rejuvenation details.

6.0  ABBREVIATIONS

SOP - Standard Operating Procedure
KCl - Potassium chloride
M - Molarity
ÂșC - Degree centigrade




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