Calibration of pH meter, Purpose :
Calibration of pH meter, The purpose of this SOP is to describe the operation, calibration and cleaning of pH meter (Model: Mettler Toledo Seven Compact S220) used for the measurement of pH in the quality control and microbiology laboratory.
Calibration of pH meter, Scope :
This procedure describes the application of pH meter, for the determination of pH, in the analysis of raw materials, intermediates and formulated drug product in the quality control and microbiology laboratory of xx Pharmaceuticals Ltd.
Definitions / Abbreviation:
[][]SOP: Standard Operating Procedure.
[][]QC: Quality Control.
[][]pH: The pH is a number which represents conventionally the hydrogen ion concentration of an aqueous solution. It is the measurement of the acidity or alkalinity of an aqueous solution.
[][]Calibration: The set of operations which establish, under specified conditions, the relationship between values indicated by a measuring instrument or measuring system or values represented by a material measure and the corresponding known values of a reference standard.
[][]KCl: Potassium chloride.
Procedure:
Precaution(s):
[][]Store the electrode in 3M KCl solution; never store it in distilled or demonized water or any solution containing heavy metal ions as it may block the electrode membrane.
[][]Always keep the pH electrode wet and rinse it thoroughly with the sample to be measured before use.
[][]Avoid high humidity environments and static discharges since these are detrimental for a stable pH reading.
[][]Do not measure pH of a solution with high temperature.
[][]Try to avoid special measuring solutions such as Sulphide, high Alkaline, Albuminous solutions those can reduce the life of electrode.
[][]Never stir the electrode vigorously in solution during measurement of pH.
[][]After washing, dry the electrode with tissue paper but do not wipe the end of with tissue paper.
[][]Never stir the electrode vigorously in solution during measurement of pH.
[][]After washing, dry the electrode with tissue paper but do not wipe the end of with tissue paper.
[][]Always use fresh and unused buffer for calibration.
[][]Perform a recalibration:
[][]When reference electrode is changed.
[][]After testing aggressive chemicals (such as strong acid or base).
Calibration:
[][]Switch on the power from its main.
[][]Power on the pH meter and printer.
[][]Remove the electrode from the potassium chloride (KCl) solution, rinse it with purified water and soak the excess water with tissue paper very carefully.
[][]Calibrate the instrument daily before use by the three buffer solutions of pH values 7.00, 4.00 and 10.0.
[][]Immerse the electrode in buffer solution of pH value of 7.00 and stir gently and press [CAL] .
[][]Wait until a stable endpoint has been reached.
[][]Hear the ‘beep’ point.
[][]See the sign (/A) at the right side of the display.
[][]Rinse the electrode with purified water and soak the excess water with issue paper very carefully.
[][]Repeat the steps from 7.1.5 to 7.1.9 for second and third calibration for the standard solution of pH values respectively 4.00 and 10.00.
[][]Select “End”.
[][]Select “Save”.
[][]Select “Data”.
[][]Select “Calibration Data”.
[][]Select “pH”.
[][]Select “Review”.
[][]Select “Expertpro ISM”.
[][]Select “Transfer”.
[][]Select “Exit” for 5 times to reach the main menu.
[][]The slope should be 90% – 105%, i.e. at print data, S(B1/B2) and S(B2/B3) = 90% – 105% and offset value will be ± 30 mV, i.e. at print data, off.(B1/B2) and off.(B2/B3) = ±30 mV.
Electrode condition:
| Display | Slope value (%) | Condition |
|---|---|---|
| Display Icon | 90 - 105 | Electrode is in good condition. |
| Display Icon | 85 - 89 | Electrode needs cleaning. |
| Display Icon | 84 - 80 | Electrode is faulty. |
Maintenance of the Reference Electrode:
[][]If the electrode slope value falls rapidly, or if the response becomes sluggish or inaccurate, the following procedure should be performed one by one.
[][]Change the reference electrolyte solution every six months.
[][]Degrease the membrane with cotton wool soaked in soap solution.
[][]Soak the tip of the electrode in 0.1M hydrochloric acid overnight.
[][]If all these fail, the electrode must be replaced with a new electrode.
[][]Any replacement of the electrode must be recorded in the log book
[][]Verify the pH of any check buffer (buffer range: 4-9 pH), if reading is within limit (Certificate value ± 0.05), calibration confirms.
[][]Remove the electrode from buffer solution, rinse it with purified water and soak the excess water with tissue paper.
[][]Rinse the electrode with saturated potassium chloride (KCl).
[][]7.1.26 Record the calibration status in Logbook for daily calibration of pH Meter (Seven Compact S220) as per Annexure – I
[][]Power off the pH meter and printer.
[][]Switch off the power from its main.
Operation
[][]Ensure that working area is clean.
[][]Pour enough sample solution into a measuring beaker so that the level of the sample is above the junction of the electrode.
[][]Ensure that the pH meter is cleaned and calibrated on the day use.
[][]Remove the electrode from the potassium chloride (KCl) solution, rinse it with purified water and soak the excess water with tissue paper very carefully. .
[][]Switch on the power its main.
[][]Power on the pH meter and printer.
[][]Gently stir the sample and dip the pH electrode into the solution.
[][]Press [READ] button and wait until a stable endpoint has been reached.
[][]Hear the “beep” sound.
[][]See the sign (/A) at the right side of the display.
[][]Select “Data”.
[][]Select “Measurement Data”.
[][]Select “Review”.
[][]Select “Partial” by using “↓”.
[][]Select “by measurement mode” by using “↓”.
[][]Select “pH”.
[][]Select “transfer”.
[][]Collect the printed result from the printer.
[][]Select “Exit” for 6 (six) times to reach the main display/menu.
[][]Take the electrode out of the solution and rinse with purified water and soak the excess water by tissue paper.
[][]For additional samples repeat the steps from 7.2.7 to 7.2.20 until the sample has been measured.
[][]After taking the measurement, rinse the electrode with saturated potassium chloride (KCl).
[][]Record the measurement data in the Operation Logbook of pH Meter (Seven Compact S220) as per Annexure – II.
[][]Power off the pH meter and printer.
[][]Switch off the power from its main.
Cleaning and maintenance:
[][]Clean the outside case of the pH meter using a mild detergent or disinfectant (e.g.70% ethanol) if required.
[][]Clean the area around the pH meter and wipe away any spillage immediately. Special care should be exercised when cleaning up concentrated HCl (usually) or concentrated NaOH (usually) used for adjusting the pH of solutions.
[][]When required, clean all wires and contacts to avoid corrosion.
[][]Inspect the cables of the electrodes for any signs of broken insulation.
[][]Inspect the pH electrode for any cracks in its stem or bulb.
[][]Rinse off any salt deposits on the top of the electrode using water.
[][]If contamination of the glass bulb is suspected, restoration can be attempted as follows:
[][]Soak electrode in 0.1 M HCl or 0.1 N HNO3 for 15 minutes.
[][]Oily or greasy deposits may be removed by methanol.
[][]After the cleaning stage, rinse the electrode in distilled water and replace the internal filling solution (4M KCl if appropriate) for at least 1 hour before taking any measurements.
[][]Make sure the electrode is always kept filled with the appropriate filling solution.
Annexure: Calibration of pH meter
Annexure-I: Logbook for daily calibration of Seven Compact S220 pH Meter.
Annexure-II: Operation Logbook of Seven Compact S220 pH Meter.