To provide a procedure to operate and maintain the Eutech make Cyberscan 1100 pH meter.
I. PURPOSE :
To provide a procedure to operate and maintain the Eutech make Cyberscan 1100 pH meter.
II. SCOPE:
The procedure is applicable for calibrating the Eutech make Cyberscan 1100 pH meter used at the Quality Control department.
III. RESPONSIBILITY:
It is the responsibility of the Quality Control personnel involved in the pH meters calibration activity to follow the procedure and schedule as mentioned in this Standard Operating Procedure.
IV. DOCUMENT REFERENCE:
SOPs : Core Procedure : Calibration of Equipment
Forms : Standardisation of pH meter
V. OPERATION
1.0 PRELIMINARY CHECK :
1.1 Check that the instrument is clean and free from dust, if not, clean with a soft cloth duster.
1.2 Ensure that the temperature sensor and Electrode are always dipped in tap water or in pH 4.0 Buffer.
2.0 GENERAL CARE AND PRECAUTIONS:
2.1 Do not wipe the pH electrode or temperature probe dry. Wiping the electrode causes static charge, and will create calibration and measurement instability.
3.0 BASIC OPERATION
3.1 Connect the plug to the main power supply.
3.2 Switch on the instrument by pressing the ON/OFF key.
3.3 Ensure that the instrument is calibrated before use.
3.4 To measure pH, insert the electrode, which is previously rinsed with, purified water, into the sample of which the pH is to be measured.
3.5 If the pH meter is not in pH/Temp mode press EXIT and press >/CAL to select pH/Temp mode.
3.6 Record the pH of the sample as displayed on the pH meter.
3.7 Remove the electrode from the sample and rinse with purified water and keep in tap water or in pH 4.0.
3.8 For measurement of mV , If the pH meter is not in mV mode press EXIT and press >/CAL to select mV mode.
3.9 Switch off the instrument by pressing the ON/OFF key.
VI. CALIBRATION
Calibration frequency: Daily/ on the day of usage.
1.1 Standard buffer solution of pH 1.00/1.68, 4.01, 7.00, 9.00/9.18/10.0 and 12.00/12.45 using pH buffer solutions with a certificate of quality traceable to NIST.
1.2 To calibrate instrument at 25 ± 0.5 °C use the following steps:ATC probe Temperature calibration
1.3 Press the >/CAL to enter the pH calibration mode. The display flashes Cal Mode Activated, please wait ….
1.4 Press the >/CAL again , the display will flash Temperature Cal Mode.
1.5 Upper display will read ATC Temp: (Current temperature)
1.6 Lower display will read key in Std: (Current temperature
1.7 Place the temperature probe in DM water and place standard thermometer.
1.8 Wait for five minutes for solution and thermometer to attain equilibrium.
1.9 Key in the temperature observed in thermometer as standard.
2.0 Press enter top confirm .The display flashes Temp Cal Complete, ATC Offset : (Shows off set value).
2.1 The display then shows Sys Updating , Please wait ….., and the meter returns to pH measurement mode.
Acceptance criteria: The variation between temperature displayed by standard temperature and ATC probe should not be more than 10C.
Five point Auto calibration
2.2 Maintain the Buffer solutions of pH
• 1.00/1.68,
• 4.00/4.01,
• 7.00,
• 9.00/9.18 and
• 12.00/12.45 at 25 ± 0.5 °C.
pH buffer setup program
2.3 Enter the pH/Temperature setup mode.
2.4 Press >/CAL key to toggle between USA NIST Bf1 Bf2 Cust.
2.5 Select Cust set.
2.6 Buffer set selected will flash.
2.7 Press ENTER to confirm selection and return to the setup mode.
2.8 Press EXIT to pH/Temperature mode.
2.9 If readymade solutions are not available prepare the buffer solutions.
3.0 When entering the custom calibration , the lower display will show key in ST.
3.1 The upper display shows the pH of the buffer the electrode is dipped into.
3.2 Using the numeric keypad enter the value of the first custom pH buffer.
3.3 If any typographical error is made use the MI or MR to highlight mistake and retype.
3.4 Press the >/CAL to enter the pH calibration mode. The display flashes Cal Mode Activated, please wait ….
3.5 Rinse the electrode with purified water.
3.6 Immerse the electrode and the ATC Probe into standard buffer solution of known pH 7.0 and ensure the temp. is 25 °C ± 0.5 °C.
3.7 Press ENTER when first custom buffer is keyed in. The display will read 1 point Cal Done.
3.8 Rinse the electrode and ATC probe with DM water and immerse into next buffer solution and repeat the above process. Repeat the same with all the remaining three buffer solutions.
3.9 After completing the above process with all the five buffer solutions press EXIT.
4.0 The screen displays Sys. Updating. …Please wait.
4.1 The meter than returns to pH measurement mode.
4.2 At the time of measurement if the reading is not stable change the electrode even after changing the electrode if reading is not stable call for service.Accuracy and Linearity
4.3 Measure the pH, mv for all the five buffer solutions three times and record them.
4.4 Measurement of slope response for pH 4.0 and pH 7.0:
From the observed mean reading of pH and mV calculate the slope value by using the following formula:
mV 7 - mV 4
S = ---------------------------
pH7 - pH4
where,
mV 7 is the value of mean mV of the standard buffer solution pH 7.0
mV 4 is the value of mean mV of the standard buffer solution pH 4.0
pH7 is the value of mean pH of the standard buffer solution pH 7.0
pH4 is the value of mean pH of the standard buffer solution pH 4.0
Acceptance Criteria:
i) Linearity Coefficient for pH 1.68/1.00, 4.01/4.00, 7.00, 9.00/9.18 and 12.00/12.45 should be between –0.999 to-1.000
ii) Accuracy: The pH value should be ± 0.02 of the specific value for the standard buffer solutions at 25°C
iii) Slope value should be between - 55.259 & -59.330
4.5 If the instrument fails in calibration, proceed as per the Core Procedure, “Calibration of Equipment”.
Note:
1. If the pH meter fails to show any of the values as within the mentioned limits, repeat the procedure of washing the electrode using distilled water and then dipping in the specific pH buffer to determine the pH.
2. If the problem persists electrolyte should be changed (3M KCl saturated with Silver chloride) .Even then the problem exists replace the electrodes if the values are found to be not within the limits, send the equipment for repair.
3. After receiving the pH meter, recalibrate the pH meter and if it passes put into regular use.
5.0 ELECTRODE CARE AND MAINTENANCE
5.1 Never store or keep electrodes continuously in pure water this will cause migration of the fill solution from electrode.
5.2 Store the electrodes in water or in pH 4.0 solution
5.3 Before using a new electrode follow the instructions written on it and soak the electrode for 24 hours in 0.1N HCl solution.
5.4 At the time of measurement if the reading is not stable change the electrolyte solution (3M Potassium chloride aqueous solution saturated with Silver chloride).
5.5 If the instrument fails in calibration, proceed as per the Core Procedure, “Calibration of Equipment”.
Cyberscan, electrode, equilibrium, linearity, chloride aqueous
