Operating Procedures for Intelligent Portable pH and Acidity Meter
1、 Preparation before operation
Electrode inspection
Confirm that the glass electrode bulb has no cracks or scratches, the reference electrode ceramic core is unobstructed, and the exudate is clear without crystals.
New or long-term electrodes need to be activated in advance: immerse them in a 3mol/L KCl solution for 24 hours to ensure the integrity of the hydration layer of the glass film.
The electrode wire length is 1.2m, and the plug is tightly matched with the instrument interface without looseness or poor contact.
Calibration solution and reagent verification
Calibration solution: Use standard buffer solutions with pH 4.00 (acidic), 6.86 (neutral), and 9.18 (alkaline) to ensure that they have not expired (shelf life of 6 months), are free of turbidity or precipitation.
Soaking solution: 3mol/L KCl solution should be prepared or commercialized soaking solution should be used to avoid flocculent substances.
Auxiliary tools: distilled water/deionized water (used for electrode cleaning), dedicated pipette (to avoid cross contamination).
Host and environment confirmation
Battery level: The remaining battery level of the lithium battery is ≥ 50% (low battery level can cause circuit instability).
Environment: Avoid strong magnetic fields (such as near motors) and strong corrosive gases (such as ammonia) interference, and control the temperature between 10 ℃ and 35 ℃.
2、 Calibration operation
Two point calibration (common method)
Step 1: Immerse the electrode in pH 6.86 neutral calibration solution, shake the beaker gently for 10 seconds, wait for the reading to stabilize (fluctuation ≤ 0.02pH/10 seconds), and press the "Calibration" button to confirm.
Step 2: Rinse the electrode with distilled water, dry it, and immerse it in a second bottle of calibration solution (pH 4.00 for acidic samples and pH 9.18 for alkaline samples). Repeat the above steps.
Slope verification: After calibration, the host should display a slope value between 95% and 105%. If the slope is greater than 105%, the calibration solution needs to be replaced and retested.
Three point calibration (high-precision requirement)
On the basis of two-point calibration, add a third bottle of calibration solution (such as pH 4.00 → 6.86 → 9.18), following the same steps as above.
Suitable for scenarios that require high analytical accuracy, such as the pharmaceutical and food industries.
3、 Sample determination
Sample pretreatment
Shake well: Heterogeneous samples (such as soil leachate and fruit juice) should be shaken well to avoid layering.
Remove bubbles: Allow to stand for 5 minutes or filter to prevent bubbles from adhering to the glass film and causing fluctuations in readings.
Temperature balance: Place the sample and electrode in the same environment for 10 minutes to ensure consistent temperature (temperature difference affects pH value).
Electrode immersion and reading
Immersion depth: The liquid level should be 1-2cm below the liquid interface to avoid exposing the glass film to the liquid surface.
Stirring: Shake the container gently or stir slowly to accelerate ion diffusion. Do not stir vigorously (to produce bubbles).
Reading: Record after the screen displays "stable" (fluctuation ≤ 0.02pH/10 seconds), and measure in parallel 2-3 times (relative deviation ≤ 0.05pH is qualified).
4、 Post operation processing
Electrode cleaning and preservation
Cleaning: Rinse the electrode with distilled water 3 times, shake off the water, and prohibit wiping the glass film with filter paper (to generate static electricity or damage the hydration layer).
Storage: Immerse the electrode in a 3mol/L KCl solution, avoiding dry storage or immersion in distilled water (to dissolve the hydration layer and shorten the electrode life).
Data recording and registration
Record usage time, sample type, calibration slope, and abnormal conditions (such as reading fluctuations).
Regularly update firmware (via USB connection to the computer) to ensure accurate temperature compensation algorithms.
5、 Maintenance and troubleshooting
Electrode maintenance
Pollution treatment:
Protein contamination (such as serum and soybean milk): soak in 1% pepsin+0.1mol/L hydrochloric acid solution for 30 minutes, and then rinse with distilled water.
Oil contamination (such as cooking oil and engine oil): Soak in anhydrous ethanol for 10 minutes, then rinse with distilled water.
Inorganic pollution (such as calcium carbonate, metal oxides): Soak in 0.1mol/L dilute hydrochloric acid (or dilute sodium hydroxide) for 15 minutes, and then rinse.
Fluid interface blockage:
Mild blockage: Immerse the electrode in a 3mol/L KCl solution and gently shake it (similar to shaking a thermometer).
Severe blockage: Immerse the lower end of the electrode in a warm KCl solution (40-50 ℃) for 1 hour, or inject KCl solution from the upper end of the electrode using a syringe (only applicable to rechargeable electrodes).
Electrode replacement:
Response time: After immersion in calibration solution, the reading stabilizes for more than 2 minutes.
Deviation: When measuring a sample with a known pH, the error is greater than 0.1 pH (which still exists after repeated calibration).
Host maintenance
Physical protection: Avoid falling (circuit chips are susceptible to impact damage), avoid contact with liquids (can be protected with waterproof covers).
Power management: Lithium batteries need to be charged regularly (once every 3 months to avoid excessive discharge); Dry batteries need to be replaced in a timely manner (leakage can corrode the electrode interface).
Calibration solution and reagent management
Preparation requirements: Prepare the calibration solution with ultrapure water (resistivity ≥ 18.2M Ω· cm) to avoid introducing impurities.
Storage method: Calibration solution should be stored in a sealed glass bottle, refrigerated (4 ℃), and used up within one month after opening.
Avoid contamination: Use a dedicated pipette to take the calibration solution, do not dip the electrode directly, and do not pour the remaining liquid back into the original bottle.