Standard operating procedure for operation and calibration of pH Meter (Lab india Pico+ model)
1.0 Purpose:
To lay down a procedure for operation and calibration of pH Meter Lab India (PICO+ model).
2.0 Scope:
This procedure is applicable for the operation and calibration of pH meter having Make: Lab India PICO+ pH Meter.
3.0 Responsibility:
Officer/ Designee : To perform operation, calibration and maintain the usage log book as per SOP.
Head/ Designee – QC : To review and implementation and ensure compliance of SOP.
Head/ Designee – QA : To approve, implement and ensure compliance of SOP.
4.0 Procedure:
4.1 Requisites:
4.1.1 Sufficient amount of fresh Purified water, standard pH buffers (1.68, 4.01, 6.86, 9.18 & 10.01) and 3M KCl for pH electrode activation.
4.1.2 Tissue paper roll and suitable container for waste disposal.
4.2 Storage / Care of pH Electrode:
4.2.1 For fast response of the pH electrode during sample measurements, the electrode is to be soaked in a slightly acidic solution. Also pH electrodes should always be stored in a moist condition with 3M KCl solution between routine measurements.
4.2.2 Place the pH electrode into electrode storage solution (3M KCl solution).
4.2.3 Never store an electrode in distilled water or de-ionized water as this causes migration of the ions from the electrode, thus decreasing the response.
4.3 Operation:
4.3.1 Using the Instrument:
4.3.1.1 After the Meter is powered ON, only two keys are active, i.e. RESET and MODE. RESET key is used to initialize the Meter. By pressing the RESET key Meter gives Beep and Display reads like this-
4.3.1.2 Mode key is important key, as it allows the user to select the Operating and Measurement Mode. Select pH mode by pressing MODE key and after that press ENTER for confirmation of selection.
4.3.1 pH Measurement:
4.3.1.1 Before starting the pH measurement, Ensure the Instrument is Setup properly.
The Instrument Display reads like this-
4.3.1.2 “Wait Stabilizing” – indicates, the instrument is checking Electrode signal Stability and once the signal is steady it shows the measured pH, mV and temperature.
4.3.1.3 Before performing the pH measurement,
- Select the Temperature Compensation type by pressing “FWD/TEMPO” Key.
- Standardize & Calibrate the Instrument and pH Electrode by pressing “CAL” key.
4.3.1.4 Selecting Temperature Compensation: TEMPCO: There are two options ‘Auto’ and ‘Manual’ for temperature selection at which the automatic temperature compensation is to be considered during Calibration & Measurement.
4.4 Calibration of pH Meter:
4.4.1 Preparation of Buffer Solutions:
The readymade or prepared buffer solutions are used for pH calibration.
4.4.1.1 Potassium Tetra oxalate 0.05 M (pH – 1.68 at 25°C): Dissolve 1.261gm of Potassium Tetra oxalate KH3(C2O4)2.2H2O in carbon dioxide free water to make 100 ml.
4.4.1.2 Potassium Biphthalate 0.05 M (pH- 4.01 at 25°C): Dissolve 1.012gm of Potassium biphthalate (KHC8H4O4) previously dried at 110°C for one hour, in water to make 100 ml.
4.4.1.3 Equimolal Phosphate 0.05 M (pH – 6.86 at 25°C): Dissolve 0.353 gm of Disodium hydrogen phosphate (Na2HPO4) and 0.339 g of Potassium dihydrogen phosphate (KH2PO4) each previously dried at 120°C for two hours, in carbon dioxide free water to make 100 ml.
4.4.1.4 Sodium Tetra Borate 0.01 M (pH – 9.18 at 25°C): Dissolve 0.380 gm of Sodium tetra borate (Na2B4O7.10H2O) in carbon dioxide free water to make 100 ml.
4.4.1.5 Sodium Carbonate & Sodium Bicarbonate (pH – 10.01 at 25°C): Dissolve 7.20 gm of Sodium Carbonate (Na2CO3) and 2.1 gm of Sodium Bicarbonate (NaHCO3) in carbon dioxide free water to make 100 ml.
4.4.1.6 Note: Prepare standard buffer solution for calibration on weekly basis. For readymade buffer solution dispense the buffer solution in glass bottle and use for weekly.
4.4.1.7 Label preparation date and due date on prepared buffer solution and dispense buffer solution bottle.
4.4.2 Calibration Procedure:
4.4.2.1 Select Calibration Mode by pressing ‘CAL’ key.
4.4.2.2 Enter password.
4.4.2.3 Enter ‘1’ to select linear regression interpolation method as standard
from Calibration Method.
4.4.2.4 Enter 1st Buffer value as 1.68 and press enter.
4.4.2.5 Dip the Electrode and temperature probe (RTD) in 1.68 pH solution.
4.4.2.6 ‘Wait! Stabilizing’ message will be displayed. After stable reading press enter.
4.4.2.7 Remove the electrode from the 1.68 pH solution and rinse it thoroughly with purified water.
4.4.2.8 Soak the excess water with tissue paper.
4.4.2.9 Insert the pH electrode & RTD in beaker having 4.01 pH solutions.
4.4.2.10 Repeat same for 4.01, 6.86, 9.18 and 10.01.
4.4.2.11 Record the daily calibration of pH meter in the format.
4.4.2.12 After completion of 5 point buffer, instrument checks the slope of the electrode.
4.4.2.13 If the slope is within limit the final report with value of buffer used and the slope obtained is printed on the printer.
4.4.3 Acceptance Criteria:
Limit of Slope: 80% - 120%
Tolerance: ±0.02 of Standard pH Buffer.
Frequency: Daily
4.5 Verification:
4.5.1 After completion of calibration press “ENTER” key and dip the standard
buffer solution 1.68 and press “ENTER” key.
4.5.2 Repeat same for 4.01, 6.86, 9.18 and 10.01.
4.5.3 After completion of 5 point buffer solution take print out of pH analysis report.
4.6 Precautions:
4.6.1 Clean and dry glass beakers for all sample measurements.
4.6.2 pH electrodes should always be stored in a moist condition with 3M KCl solution.
4.6.3 Tissue paper roll and suitable container for waste disposal.
4.6.4 Discard the left out solution of the buffer after calibration.
5.0 Abbreviation:
QC-Quality Control
QA-Quality Assurance
SOP-Standard operating procedure
KCL-Potassium chloride
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