βοΈ Water pH Determination
Electrochemical determination of pH value in water and wastewater using a glass electrode. A fundamental water quality parameter.
Overview
pH is a measure of hydrogen ion (HβΊ) activity in an aqueous solution, expressed on a scale from 0 to 14. A pH value of 7 indicates a neutral solution, below 7 β acidic, above 7 β 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 6.5β9.5 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 β 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 β 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 HβΊ ions, which generates a potential proportional to the hydrogen ion activity in the solution (according to the Nernst equation: E = Eβ + (RT/nF) Γ ln[HβΊ]). 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 | 0β14 pH |
| Resolution | 0.01 pH |
| Accuracy | Β±0.05 pH (routine), Β±0.02 pH (precision) |
| Measurement temperature | 20β25Β°C (with temperature compensation) |
| Repeatability | Β±0.03 pH |
| Measurement time | 1β3 minutes per sample |
Standard
- Standard number
- PN-EN ISO 10523:2012
- Title (PL)
- JakoΕΔ wody β Oznaczanie pH
- Title (EN)
- Water quality β Determination of pH
Step-by-step procedure
1. Workstation preparation
Check the electrode condition (no air bubbles, KCl electrolyte level). Switch on the pH meter 15 min before measurement.
2. Calibration β pH 7.00 buffer
Immerse the electrode in pH 7.00 buffer (25Β°C). Wait for reading stabilization. Confirm the value.
3. Electrode rinsing
Rinse the electrode with deionized water, gently blot dry with tissue paper (do not rub the membrane!).
4. Calibration β pH 4.00 or 10.00 buffer
Immerse in the second buffer appropriate for the expected sample range. Confirm the value.
5. Calibration verification
Check the slope β it should be 95β105% of the theoretical value (59.16 mV/pH at 25Β°C). Check the offset.
6. Sample preparation
Bring the sample to 20β25Β°C. Do not filter (unless specifically required). Record the sample temperature.
7. Sample pH measurement
Immerse the electrode in the sample (min. 2 cm below the surface). Activate gentle stirring. Wait for reading stabilization (Β±0.01 pH for 30 s).
8. Reading and result recording
Record the pH value to 0.01 accuracy. Record the measurement temperature. Repeat the measurement (duplicate).
9. Post-measurement rinsing
Rinse the electrode with deionized water between successive samples.
10. Quality control
Every 10 samples, measure a control sample (buffer or CRM). Maximum deviation Β±0.1 pH from the certified value.
11. 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 000β15 000 PLN |
| Combined pH electrode | Mettler Toledo InLab Expert Pro, WTW SenTix 940 | 500β2 000 PLN |
| Temperature sensor | Pt1000 integrated with electrode or external | 200β500 PLN |
| Magnetic stirrer | IKA C-MAG MS 4, Heidolph MR Hei-Standard | 1 500β4 000 PLN |
| Glass beakers 100β250 mL | DURAN / Simax borosilicate | 15β40 PLN/pc. |
| Deionized water system | Millipore Milli-Q or Hydrolab system | system 15 000β40 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, 250β500 mL |
| Buffer solution pH 7.00 | 7778-77-0 | Phosphate buffer, certified CRM, 250β500 mL |
| Buffer solution pH 10.00 | 497-19-8 | Borate/carbonate buffer, certified CRM, 250β500 mL |
| KCl solution 3 mol/L | 7447-40-7 | For storage and replenishment of the reference electrode electrolyte |
| Deionized water | β | Conductivity <0.1 mS/m, for rinsing the electrode between measurements |
Health and safety (OHS)
- Buffer solutions β low risk, wear protective gloves
- KCl β non-hazardous, but avoid contact with eyes
- Glass electrode β fragile, handle with care (laceration risk)
- Safety glasses and laboratory coat required