Title: Operation, Cleaning and Calibration of pH/Conductivity Meter
- Objective:
To lay down the procedure for Operation, Cleaning and Calibration of pH/Conductivity Meter.
- Scope:
This SOP is applicable for Operation, Cleaning and Calibration of pH/Conductivity Meter used to check pH and conductivity of samples and is located in Quality Control Laboratory.
- Responsibility:
- Quality Control Department: To prepare and review the SOP. To follow the procedures laid down for Operation, Cleaning and Calibration of pH/Conductivity Meter as per this SOP.
- Engineering Department: To carry out preventive maintenance as per schedule and procedure defined.
- Quality Assurance Department: To review and approve the SOP and Annexures.
Accountability:
Head Quality Control Department, Head Quality Assurance Department
- Procedure:
| 5.1 | Safety Precautions/Instructions: | |||||
| 5.1.1 | Ensure all the electrical connections are properly earthed. Ensure the power plug of the pH/Conductivity Meter is fixed in the socket properly. | |||||
| 5.1.2 | Wear personal protective equipments such as safety glasses, hand gloves during operation of instrument. | |||||
| 5.1.3 | Ensure that the ON/OFF switch is working properly by switching “ON” the pH/Conductivity Meter. | |||||
| 5.2 | OPERATION UNDER “pH MEASUREMENT MODE”: | |||||
| 5.2.1 | Press “MODE” key to select measurement mode i.e. “pH measurement mode” | |||||
| a) pH MODE: | ||||||
| 5.2.2 | Ensure that the pH electrode is connected to the instrument.
Select “pH mode” and the display shows |
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| 5.2.3 | Note: “Wait! Stabilizing” indicates that the instrument is checking Electrode signal stability and once the signal is steady it shows the measured pH, mV and temperature. | |||||
| 5.2.4 | Remove the pH electrode from the storage solution and rinse it with purified water 2 to 3 times, soak the excess water with tissue paper and insert the pH electrode and temperature sensor into the beaker containing sample solution. | |||||
| 5.2.5 | Stir the sample solution keeping the pH electrode and temperature sensor immersed in it. | |||||
| 5.2.6 | Note: Instrument will print report of single reading taken if printer is connected properly otherwise it will ignore printing and continue the pH measurement. Check if printer is “ON” and paper is loaded in the tray. | |||||
| Update the “Instrument/Equipment Usage Log Book” as per SOP | ||||||
| 5.3 | pH Meter Calibration Procedure: | |||||
| Frequency: Daily or after carrying out any major maintenance work. | ||||||
| 5.3.1 | For issuance of calibration report refer SOP. | |||||
| 5.3.2 | Perform the calibration of instrument as per Annexure and procedure mentioned below. | |||||
| 5.3.3 | Calibrate the instrument using standard buffers pH 1.68, pH 4.01, pH 7.00, pH 9.18 and pH 12.45. | |||||
| 5.3.4 | Ensure that the pH- electrode is connected to the instrument and properly activated and stored. | |||||
| 5.3.5 | Ensure that the temperature sensor and printer is connected to the instrument. | |||||
| 5.3.6 | Rinse the pH electrodes 2 to 3 times, remove the excess water by soaking it with tissue paper and insert the pH electrode and Temperature sensor in the beaker having pH buffer 1.68. | |||||
| 5.3.7 | Now remove the pH electrode from the 1.68 pH buffer and rinse it thoroughly with purified water, soak the excess water with tissue paper. Insert the pH electrode and temperature sensor in the beaker having 4.01 pH buffer. | |||||
| 5.3.8 | Note: The next buffer should not be more than 4 pH unit. | |||||
| 5.3.9 | Enter the second calibration buffer value 4.01 with the numeric keys. | |||||
| 5.3.10 | Repeat the procedure for the calibration buffers 7.00, 9.18 and 12.45. | |||||
| 5.3.11 | When the last (5th) buffer is completed, instrument checks slope obtained i.e. 90% to 105 %. | |||||
| 5.3.12 | Full calibration report is printed with values, buffers used and the slope obtained. | |||||
| 5.3.13 | Enter the details in calibration report as per Annexure. Ensure that the results obtained, comply with the acceptance criteria. | |||||
| 5.3.14 | Update the “Instrument/Equipment Usage Log Book”as per SOP. | |||||
| 5.3.15 | Affix the “Calibration Status Label” on the instrument as per SOP. | |||||
| 5.4 | Operation Under “Conductivity Measurement Mode”: | |||||
| 5.4.1 | Press “MODE” key to select measurement mode i.e. “Conductivity measurement mode” and the instrument will display as: | |||||
| a) Conductivity MODE: | ||||||
| 5.4.2 | Ensure that the conductivity electrode is connected to the instrument.
Select “Conductivity mode” and the display reads, |
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| 5.4.3 | Stir the sample solution keeping Conductivity electrode and temperature sensor immersed in it. | |||||
| 5.4.4 | Display will read the Conductivity of the sample solution. | |||||
| 5.4.5 |
Press “ENTER” and the display will read |
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5.4.6 |
Enter the sample name by using alphanumeric keys, followed by ID No and the press “ENTER”. | |||||
| 5.4.7 | Note: Instrument will print report of single reading taken if printer is connected properly otherwise it will ignore printing and continue the pH measurement. Check if printer is “ON” and paper is loaded in the tray. | |||||
| 5.4.8 | After printing is over, automatically the instrument Display returns to the measurement function. | |||||
| 5.4.9 | Update the “Instrument/Equipment Usage Log Book” as per SOP. | |||||
| 5.5 | Calibration Procedure: | |||||
| 5.5.1 | Frequency: Daily or after carrying out any major maintenance work. | |||||
| 5.5.2 | For issuance of calibration report refer SOP. | |||||
| 5.5.3 | Perform the calibration of instrument as per Annexure and procedure mentioned below. | |||||
| 5.5.4 | Ensure that the Conductivity- electrode is connected to the instrument and properly activated and stored. | |||||
| 5.5.5 | Ensure that the temperature sensor and printer is connected to the instrument. | |||||
| 5.5.6 | Rinse the Conductivity electrodes 2 to 3 times with purified water, remove the excess water by soaking it with tissue paper and insert the Conductivity electrode and Temperature sensor in the beaker having conductivity standard solution 100 μS/cm. | |||||
| 5.5.7 | Press “CAL” | |||||
| 5.5.8 | Press “ENTER” and the instrument checks the calibration limit. | |||||
| 5.5.9 | If the obtained cell constant is within limit, then the display will show the conductivity value of conductivity standard solution. | |||||
| 5.5.10 |
If the obtained cell constant is out of limit, the display reads as |
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| 5.5.11 | Full Calibration report is printed with values of standard used, measured value and Cell constant. | |||||
| 5.5.12 | Enter the details in calibration report as per Annexure. Ensure that the results obtained, comply with the acceptance criteria. | |||||
| 5.5.13 | Update the “Instrument/Equipment Usage Log Book” as per SOP. | |||||
| 5.5.14 | Affix the “Calibration Status Label” on the instrument as per SOP. | |||||
| 5.5.15 | If calibration activity is outsourced, the values are to be transcribed in the Annexure, and external party certificate to be attached. | |||||
| 5.6 | Electrode Storage: | |||||
| 5.6.1 | Store the pH electrode in 3 M KCl solution between routine measurements. | |||||
| 5.6.2 | Store the conductivity electrode in Purified Water. | |||||
| 5.6.3 | After use, the tips of the pH electrode shall be covered with wetting caps filled with KCl solution to prevent damage. | |||||
| 5.6.4 | Activation of pH Electrode: | |||||
| 5.6.5 | Dip the pH electrode in a beaker containing 0.1 M Hydrochloric acid for about 1-2 hours. | |||||
| 5.7 | Cleaning Procedure: | |||||
| 5.7.1 | Clean the instrument with lint free cloth before and after completion of test. | |||||
| 5.7.2 | Change the storage solution of pH electrode once in a week. | |||||
| 5.7.3 | Change the storage solution of Conductivity electrode every day. | |||||
| 5.7.4 | Replace the filled KCl solution in the electrode with 3M KCl solution once in a week. | |||||
| 5.7.5 | If any breakdown occurs, follow procedure as per SOP. | |||||
- Definitions / Abbreviations:
- Definitions:
- Breakdown: Any activity leading to operation of instrument other than the set parameters or unusual sound or vibration observed in the instrument.
- Calibration: Tests performed to ensure that the instrument is functioning as per set parameters. These tests are performed as per predefined frequency and also after any major repair or replacement of parts.
- Preventive Maintenance: Maintenance activity performed to ensure that the instrument will function smoothly and to avoid breakdowns. These activities are performed as per predefined frequency.
- pH: pH is defined as the negative logarithm of the hydrogen ion concentration. Measurement of pH of any aqueous sample solution gives the degree of acidity or alkalinity of the solution.
- Conductivity: Conductivity is the measurement of materials ability to conduct electric current. Measurement of conductivity of sample solution gives the degree of electrical conductance in a defined volume of the solution.
- Abbreviations:
| Abbreviation | Expansion |
| pH | Power of hydrogen |
| KCl | Potassium Chloride |
| % | Percentage |
| mm | millimetre |
| GLP | Good Laboratory Practices |
| N | Normal |
| No. | Number |
| μS/cm | micro Siemens per centimeter |
| ± | Plus or minus |
| ID No. | Identification Number |
Calibration Report (pH Mode)
Observations:
| Buffers used for calibration | Observed pH | Slope obtained |
| pH 1.68 | ||
| pH 4.01 | ||
| pH 7.00 | ||
| pH 9.18 | ||
| pH 12.45 |
Acceptance Criteria:
- The observed pH of buffer solutions should not be more than ± 0.05.
- Slope obtained should be between 90% to 105%.
Calibration Report (Conductivity Mode)
| Sr. No. | Conductivity standard solution at 25oC | Batch No. | Validity |
| 1. | 100 µS/cm |
Observations:
| Cell constant of electrode (K) | Conductivity standard solution used at 25oC | Observed Conductivity |
Acceptance Criteria:
- Displayed value of conductivity should not differ ± 0.5 µS/cm.
*Note – Ready to use SOP available in “DOWNLOAD” Section.