⚗️ Water pH Determination
In short
Electrochemical determination of pH value in water and wastewater using a glass electrode. The test is performed according to PN-EN ISO 10523:2012; Measurement range: 0–14 pH. The procedure comprises 11 steps (about 20–24 min in total); it is used for: Drinking water quality control (Dz.U. 2017 poz. 2294), Municipal and industrial wastewater monitoring, Surface water and groundwater testing.
At a glance
- Standard: PN-EN ISO 10523:2012
- Category: Physicochemistry
- Procedure steps: 11
- Total time of stages: 20 min–24 min
- Measurement range: 0–14 pH
- Resolution: 0.01 pH
- Accuracy: ±0.05 pH (routine), ±0.02 pH (precision)
Overview
pH is a measure of hydrogen ion (H⁺) activity in an aqueous solution, expressed on a scale from 0 to 14. A pH value of 7 indicates a neutral solution, below 7 — acidic, above 7 — alkaline. pH is one of the most important quality parameters for drinking water, wastewater, surface water, and groundwater.
pH determination is of key importance in assessing water fitness for consumption (permissible range 6.5–9.5 according to the Polish Ministry of Health Regulation), monitoring wastewater treatment processes, controlling water corrosivity in piping systems, and evaluating the condition of aquatic ecosystems. pH affects heavy metal solubility, chlorine disinfection efficacy, and biological processes in water.
This method is the cornerstone of water analysis — every water laboratory performs this determination dozens of times daily. It is required by Polish and EU regulations concerning the quality of drinking water, industrial and municipal wastewater, and environmental waters.
Method principle
The method is based on potentiometric measurement — the difference in electrical potential between a glass (indicator) electrode and a reference electrode (Ag/AgCl) immersed in the test sample. The glass electrode has a membrane sensitive to H⁺ ions, which generates a potential proportional to the hydrogen ion activity in the solution (according to the Nernst equation: E = E₀ + (RT/nF) × ln[H⁺]). Modern pH meters use a combined electrode incorporating both electrodes in a single housing.
Applications
- Drinking water quality control (Dz.U. 2017 poz. 2294)
- Municipal and industrial wastewater monitoring
- Surface water and groundwater testing
- Water treatment process control
- Water corrosivity assessment in piping systems
- Environmental studies (acid rain, eutrophication)
Key parameters
| Parameter | Value |
|---|---|
| Measurement range | 0–14 pH |
| Resolution | 0.01 pH |
| Accuracy | ±0.05 pH (routine), ±0.02 pH (precision) |
| Measurement temperature | 20–25°C (with temperature compensation) |
| Repeatability | ±0.03 pH |
| Measurement time | 1–3 minutes per sample |
Standard
- Standard number
- PN-EN ISO 10523:2012
- Title (PL)
- Jakość wody — Oznaczanie pH
- Title (EN)
- Water quality — Determination of pH
Step-by-step procedure
-
Workstation preparation
Check the electrode condition (no air bubbles, KCl electrolyte level). Switch on the pH meter 15 min before measurement.
-
Calibration — pH 7.00 buffer
Immerse the electrode in pH 7.00 buffer (25°C). Wait for reading stabilization. Confirm the value.
-
Electrode rinsing
Rinse the electrode with deionized water, gently blot dry with tissue paper (do not rub the membrane!).
-
Calibration — pH 4.00 or 10.00 buffer
Immerse in the second buffer appropriate for the expected sample range. Confirm the value.
-
Calibration verification
Check the slope — it should be 95–105% of the theoretical value (59.16 mV/pH at 25°C). Check the offset.
-
Sample preparation
Bring the sample to 20–25°C. Do not filter (unless specifically required). Record the sample temperature.
-
Sample pH measurement
Immerse the electrode in the sample (min. 2 cm below the surface). Activate gentle stirring. Wait for reading stabilization (±0.01 pH for 30 s).
-
Reading and result recording
Record the pH value to 0.01 accuracy. Record the measurement temperature. Repeat the measurement (duplicate).
-
Post-measurement rinsing
Rinse the electrode with deionized water between successive samples.
-
Quality control
Every 10 samples, measure a control sample (buffer or CRM). Maximum deviation ±0.1 pH from the certified value.
-
Electrode storage
After completing work, immerse the electrode in KCl 3 mol/L solution. Never store in distilled water or dry!
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Laboratory pH meter | Mettler Toledo SevenExcellence S400, WTW inoLab pH 7310, Hanna HI5222 | 3 000–15 000 PLN |
| Combined pH electrode | Mettler Toledo InLab Expert Pro, WTW SenTix 940 | 500–2 000 PLN |
| Temperature sensor | Pt1000 integrated with electrode or external | 200–500 PLN |
| Magnetic stirrer | IKA C-MAG MS 4, Heidolph MR Hei-Standard | 1 500–4 000 PLN |
| Glass beakers 100–250 mL | DURAN / Simax borosilicate | 15–40 PLN/pc. |
| Deionized water system | Millipore Milli-Q or Hydrolab system | system 15 000–40 000 PLN |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Buffer solution pH 4.00 | 77-92-9 | Potassium hydrogen phthalate buffer, certified CRM, traceable to NIST/PTB, 250–500 mL |
| Buffer solution pH 7.00 | 7778-77-0 | Phosphate buffer, certified CRM, 250–500 mL |
| Buffer solution pH 10.00 | 497-19-8 | Borate/carbonate buffer, certified CRM, 250–500 mL |
| KCl solution 3 mol/L | 7447-40-7 | For storage and replenishment of the reference electrode electrolyte |
| Deionized water | — | Conductivity <0.1 mS/m, for rinsing the electrode between measurements |
Health and safety (OHS)
- Buffer solutions — low risk, wear protective gloves
- KCl — non-hazardous, but avoid contact with eyes
- Glass electrode — fragile, handle with care (laceration risk)
- Safety glasses and laboratory coat required
Training and video materials
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 10523:2012 — “Water quality — Determination of pH”.
How does this method work?
The method is based on potentiometric measurement — the difference in electrical potential between a glass (indicator) electrode and a reference electrode (Ag/AgCl) immersed in the test sample. The glass electrode has a membrane sensitive to H⁺ ions, which generates a potential proportional to the hydrogen ion activity in the solution (according to the Nernst equation: E = E₀ + (RT/nF) × ln[H⁺]).
What is the measuring range and accuracy?
Measurement range: 0–14 pH; Resolution: 0.01 pH; Accuracy: ±0.05 pH (routine), ±0.02 pH (precision); Measurement temperature: 20–25°C (with temperature compensation).
How long does the test take?
The times given for the individual stages add up to approximately 20 min–24 min. The procedure comprises 11 steps.
What equipment is required?
Laboratory pH meter, Combined pH electrode, Temperature sensor, Magnetic stirrer, Glass beakers 100–250 mL, Deionized water system. Indicative cost of the core instrument (Laboratory pH meter): 3 000–15 000 PLN.
Where is this test used?
Drinking water quality control (Dz.U. 2017 poz. 2294); Municipal and industrial wastewater monitoring; Surface water and groundwater testing; Water treatment process control; Water corrosivity assessment in piping systems; Environmental studies (acid rain, eutrophication).
What safety precautions apply?
Buffer solutions — low risk, wear protective gloves; KCl — non-hazardous, but avoid contact with eyes; Glass electrode — fragile, handle with care (laceration risk); Safety glasses and laboratory coat required.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN ISO 10523.