🔥 Sodium and potassium in water
In short
Determination of sodium and potassium in water by flame photometry (flame emission spectrometry). The test is performed according to PN-EN ISO 9964-3:2001; Range—sodium: 0.01–2 mg/L Na (without dilution). The procedure comprises 8 steps (about 55 min–1 h 1 min in total); it is used for: Drinking water quality control (Na—limit 200 mg/L), Mineral and therapeutic water monitoring, Groundwater testing—mineralization.
At a glance
- Standard: PN-EN ISO 9964-3:2001
- Category: Physicochemistry
- Procedure steps: 8
- Total time of stages: 55 min–1 h 1 min
- Range—sodium: 0.01–2 mg/L Na (without dilution)
- Range—potassium: 0.01–2 mg/L K (without dilution)
- Wavelength—Na: 589 nm (D line)
Overview
Sodium (Na⁺) and potassium (K⁺) are among the main cations present in natural waters. Sodium in drinking water affects taste (detectable above 200 mg/L) and has health significance (hypertension). Potassium is an essential micronutrient, but at high concentrations may indicate wastewater contamination.
The PN-EN ISO 9964-3 standard describes a flame emission spectrometry method (FES / flame photometry) for simultaneous or separate determination of sodium and potassium in water. It is a simple, fast, and economical technique, ideal for routine determinations in waters at concentrations of 0.01–2 mg/L (higher ranges possible after dilution).
The standard also includes ISO 9964-1 (Na by AAS method) and ISO 9964-2 (K by AAS method). Permissible sodium concentration in drinking water: 200 mg/L (Journal of Laws 2017 item 2294). Potassium has no established limit in Polish regulations.
Method principle
In flame photometry, the water sample is aspirated by a pneumatic nebulizer and introduced as an aerosol into a flame (propane–butane/air or acetylene/air, ~1800–2300°C). The thermal energy of the flame excites alkali metal atoms to higher energy states. When returning to ground state, atoms emit radiation at characteristic wavelengths: Na—589 nm (yellow D doublet line), K—766 nm (red). Emission intensity is proportional to element concentration. An interference filter isolates the appropriate wavelength, and a photodetector measures intensity. To eliminate ionization interferences, a suppressor (CsCl or LiCl) is added.
Applications
- Drinking water quality control (Na—limit 200 mg/L)
- Mineral and therapeutic water monitoring
- Groundwater testing—mineralization
- Hemodialysis water control (critical Na and K concentrations)
- Municipal and industrial wastewater monitoring
- Surface water testing—salinity
Key parameters
| Parameter | Value |
|---|---|
| Range—sodium | 0.01–2 mg/L Na (without dilution) |
| Range—potassium | 0.01–2 mg/L K (without dilution) |
| Wavelength—Na | 589 nm (D line) |
| Wavelength—K | 766 nm |
| Flame type | Propane/air or acetylene/air |
| Analysis time | 10–15 seconds per reading |
Standard
- Standard number
- PN-EN ISO 9964-3:2001
- Title (PL)
- Jakość wody — Oznaczanie sodu i potasu — Część 3: Oznaczanie sodu i potasu metodą emisyjnej spektrometrii płomieniowej
- Title (EN)
- Water quality — Determination of sodium and potassium — Part 3: Determination of sodium and potassium by flame emission spectrometry
Step-by-step procedure
-
Photometer startup
Turn on air compressor. Open fuel gas. Ignite photometer flame. Wait for stabilization (~10 min). Select Na filter (589 nm).
-
Standard preparation
From 1000 mg/L Na standard solution, prepare series: 0.1; 0.5; 1; 2; 5; 10 mg/L. To each flask add CsCl (final Cs concentration 1000 µg/mL). Similarly for K.
-
Sample preparation
Dilute water samples to linear range (if needed). Add CsCl as for standards. NOTE: use PE/PP vessels—glass releases Na!
-
Calibration—sodium
Zero photometer on blank (H₂O + CsCl). Set sensitivity on highest standard. Aspirate successive standards and record emission. Plot calibration curve.
-
Na measurement in samples
Aspirate successive samples. Read Na concentration from calibration curve or directly from display (if photometer has concentration mode). Rinse nebulizer with water between samples.
-
Filter change to K (766 nm)
Switch filter to 766 nm (potassium). Repeat calibration and sample measurement analogously.
-
Quality control
Blank, CRM every 10 samples, duplicates. Repeatability <3% CV. Check for glass contamination (Na blank).
-
Shutdown
Aspirate deionized water (rinse). Turn off flame (close gas, then air). Turn off photometer and compressor.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Flame photometer | Jenway PFP7, BWB XP, Sherwood M410, Krüss FP8000 | 25,000–70,000 PLN |
| Oil-free air compressor | Jun-Air, Werther, 3–6 bar with regulator | 5,000–15,000 PLN |
| Fuel gas cylinder | Propane–butane (LPG) or acetylene | 100–300 PLN (exchange) |
| Automatic pipettes | Eppendorf Research Plus (100 µL – 10 mL) | 800–2,500 PLN |
| Volumetric flasks (50, 100, 250 mL) | Class A, borosilicate | 30–100 PLN/piece |
| PE/PP plastic vessels/tubes | Falcon 50 mL, sample cups | 1–5 PLN/piece |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Sodium standard solution 1000 mg/L Na | 7647-14-5 | Certified CRM (NaCl in HNO₃ 0.5 mol/L). Calibration series: 0.1; 0.5; 1.0; 2.0; 5.0; 10.0 mg/L Na. |
| Potassium standard solution 1000 mg/L K | 7447-40-7 | Certified CRM (KCl in HNO₃ 0.5 mol/L). Calibration series: 0.1; 0.5; 1.0; 2.0; 5.0; 10.0 mg/L K. |
| Cesium chloride (CsCl)—ionization suppressor | 7647-17-8 | 10 g/L Cs solution. Add to standards and samples (final concentration ~1000 µg/mL Cs). Cs easily ionizes in flame, providing excess electrons and suppressing Na/K ionization. |
| Deionized water | — | Free from Na and K. Conductivity <0.1 mS/m. Use PE/PP vessels (not glass—releases Na!). |
| Nitric acid (HNO₃) 1% (v/v) | 7697-37-2 | For acidifying samples. Suprapur purity (low Na/K blank). |
Health and safety (OHS)
- Fuel gas (propane–butane / acetylene)—highly flammable, explosive (H220). Check gas connection tightness.
- Open flame—fire and burn risk. Do not leave unattended.
- CsCl—irritating (H315, H319). Use gloves.
- HNO₃—corrosive (H314). Work under fume hood when preparing dilutions from concentrated acid.
- Gas cylinder—secure against tipping. Do not heat. Store vertically.
- Safety glasses and lab coat required.
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 9964-3:2001 — “Water quality — Determination of sodium and potassium — Part 3: Determination of sodium and potassium by flame emission spectrometry”.
How does this method work?
In flame photometry, the water sample is aspirated by a pneumatic nebulizer and introduced as an aerosol into a flame (propane–butane/air or acetylene/air, ~1800–2300°C). The thermal energy of the flame excites alkali metal atoms to higher energy states.
What is the measuring range and accuracy?
Range—sodium: 0.01–2 mg/L Na (without dilution); Range—potassium: 0.01–2 mg/L K (without dilution); Wavelength—Na: 589 nm (D line); Wavelength—K: 766 nm.
How long does the test take?
The times given for the individual stages add up to approximately 55 min–1 h 1 min. The procedure comprises 8 steps.
What equipment is required?
Flame photometer, Oil-free air compressor, Fuel gas cylinder, Automatic pipettes, Volumetric flasks (50, 100, 250 mL), PE/PP plastic vessels/tubes. Indicative cost of the core instrument (Flame photometer): 25,000–70,000 PLN.
Where is this test used?
Drinking water quality control (Na—limit 200 mg/L); Mineral and therapeutic water monitoring; Groundwater testing—mineralization; Hemodialysis water control (critical Na and K concentrations); Municipal and industrial wastewater monitoring; Surface water testing—salinity.
What safety precautions apply?
Fuel gas (propane–butane / acetylene)—highly flammable, explosive (H220). Check gas connection tightness.; Open flame—fire and burn risk. Do not leave unattended.; CsCl—irritating (H315, H319). Use gloves.; HNO₃—corrosive (H314). Work under fume hood when preparing dilutions from concentrated acid.; Gas cylinder—secure against tipping. Do not heat. Store vertically.; Safety glasses and lab 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 9964.