Sop for Operation and Calibration of pH METER.

This document describes (Standard Operating procedure) Sop for Operation and Calibration of pH METER.

SOP for Operation and Calibration of pH METER.

I. Purpose & Scope:

  • The purpose of this SOP is to lay down a procedure for Sop for Operation and Calibration of pH METER.
  • This Standard operating procedure shall be applicable for Operation and Calibration of pH METER  of Pharmaceutical products in Microbiology section.

II. Responsibilities:

• All Quality Control and microbiology department personnel shall be responsible to follow and implement this SOP.

Introduction and Procedure:

Preliminary Check:

  • Check and ensure that the instrument is clean and free from dust.
  • Check that the instrument is connected to 230 V stabilized power supply.
  • Check that the temperature probe and electrode are properly connected to the instrument.
  • Ensure that the temperature probe is always dipped in purified water.
  • Always preserve the electrode in pH 4.0 buffer containing 1 % v/v of saturated potassium chloride. Do not preserve the electrode in purified water.

Basic Operation and Calibration of pH meter :

Key functions:

  • H.S. Keys : Alphanumeric Dual Function ( A~Z , 1~9 ), Zero (0) with Dash (-), Dot (.),Slash(/), decimal point ( . ) and Clear Entry( CE )
  • Description of Functional Keys:


MEM CLEAR To Clear the Stored Readings / Calibration data of the selected Mode from meter Memory.
RESET To Reset the meter
CAL  To perform CALIBRATION within the selected Operating Mode
FWD TEMPCO   This key has dual function, (a) To check the readings in scan mode, (b)To select Auto / Manual temperature compensation.
SCAN To SCAN / read the stored readings with the help of FWD/TEMCO Key
PRINT  To     To Print the Stored Readings / Calibration data of the selected Mode from meter Memory with GLP format
MODE To Select Meter Operating Mode
ENTER To acknowledge the Entered value.
CE BACK To clear the wrong entry & to go backward for previous display   screen
GLP To Select the GLP or Standard Mode between sample measurement &storage.
GLP Mode         In this selection, the sample related detail such

As Sample Name and ID. No. can be entered after each Measurement.

Standard Mode In this selection, Direct Measurement can be done with-out entering the Sample related details.


Measurement/Functional Modes: 

  • The modes can be selected by pressing MODE key repetitively till desired mode / function is displayed and later acknowledged by pressing ENTER key.
  • Please note the Second Line of the display shows the Active Keys. The very first Mode Displayed is pH Mode.
  • For pH Mode: Press ENTER or MODE
  • After desired Measurement / Functional Mode is displayed and then Enter Key is pressed to confirm the selection.

pH Measurement:

  • Select the pH Mode, The Instrument Display reads, • “Wait Stabilising” – indicates, the instrument is checking Electrode signal Stability and once the signal is steady it shows the measured pH, mV and temperature.

Electrode Maintenance and Precautions: 

  • When not in use the electrode tip should be immersed in pH 4.0 buffer containing 1 % v/v of a saturated potassium chloride solution.
  • Do not allow the solution to evaporate and crystallize on the electrode.
  • Always blot dry the electrode with a clean tissue paper. Do not wipe the electrode as this may cause polarization and slow response.
  • Inspect the electrode for scratches and cracks.

Cleaning Procedures : –

  • General – Soak in 0.1 M hydrochloric acid or 0.1 M nitric acid for half an hour.
  • Removal of membrane/junction deposits.
  • Protein – Soak in 1 % pepsin in 0.1 M hydrochloric acid for 15 minutes.
  • Inorganic – Soak in 0.1 M tetra sodium EDTA solution for 15 minutes
  • Grease and Oil – Rinse with mild detergent or methanol.

 Calibration Protocol :

  • Calibration frequency : Daily
  • Prepare standard buffer solution of pH 1.0, 4.0, 7.0, 10.0 and 12.0 using respective tablets / capsules OR Alternatively use pH buffer solutions of make Reagecon or Merck or from any other reputed company with a certificate of quality traceable to NIST.
  • Rinse the electrode with purified water.

Calibration with Linear Regression interpolation method as Standard :

  • Rinse the pH electrode with Purified water 2~3 times , remove the excess water by soaking it with tissue paper and insert the pH electrode and RTD in Acidic pH buffer.
  • Press CAL: Slope = 100.91% Offset = -05.55 mV will display.
  • Press ENTER: Enter password will display then Enter password XXXX.
  • Press ENTER : Enter Buf1 = ………will display

  Note: As a GLP Sequence the User should Perform Calibration from   Acidic buffer and end it with higher pH or Basic side buffer.

  • The CE key is used to Terminate / complete the calibration when using less than 5 buffers. Max 5 pH buffers can be used.
  • Enter the First Calibration Buffer Value Enter pH = 1.0
  • Press ENTER: Wait! Stabilising….. will display. Followed by pH =…………..
  • Press ENTER : Enter Buf2 = ………will display
  • Now remove the pH electrode from the 1.00 pH solution and rinse it thoroughly with distilled water, soak the excess water with tissue paper. Insert the pH electrode and RTD in beaker having 4.00 pH buffer.
  • Enter the First Calibration Buffer Value Enter pH = 4.00
  • Press ENTER: Wait ! Stabilising….. will display. Followed by pH =………….
  • Instrument checks the Slope of the Electrode obtained.
  • If the Slope is Within Limits, Enter Buf3= ………will display.
  • Repeat the above sequence with 7.00 pH buffer, 10.00 pH buffer, 12.00 pH buffer.
  • When the last (5th) buffer is completed, instrument checks the Slope of the Electrode obtained and If the Slope is Within Limits Full Calibration Report is Printed with values Buffers used and the Slope Obtained.

Acceptance criteria:

Slope value should be between 92 % to 105%

Preparation of Buffer Solutions : 

  • STANDARD BUFFER SOLUTION: Dissolve one buffer tablet/capsule of individual pH in 50 ml of purified water and dilute to 100 with purified water in 100 ml volumetric flask.
  • When readily available pH buffer solution with NIST certificate are received, Dispense about 50 ml of each of standard buffer solutions pH 1.0, pH 4.0, pH 7.0, pH 0 and pH 12.0 in a glass bottle having screw cap and label appropriately.
  • Prepare / dispense the buffer solutions weekly or in between if the solution shows turbidity or sedimentation.
  • Certificate for the same should mention the product number, Lot Number and expiry date.


  1. Do not use buffer solution after the expiry date.
  2. Validity of the dispensed buffer solution is one week.
  3. Check the clarity of buffer solution before use.
  4. Record the observed values in daily pH calibration data sheet (Annexure I)

    Note: If instrument does not comply with any of the calibration requirement, then follow the relevant procedure of instrument breakdown.

Annexure -I

pH Meter Calibration Record


Instrument : pH Meter                                                   Make :

Instrument ID No.                                                           Model :

Date Observed reading of Buffer Slop

Value (S)



Checked by Remark
pH 1.00 ±0.05 pH 4.00 ±0.05 pH 7.00 ±0.05 pH 10.00 ±0.05 pH 12.00 ±0.05
pH Temp


pH Temp


pH Temp


pH Temp


pH Temp





You may also like...

Leave a Reply

Your email address will not be published. Required fields are marked *