📊 Ion Analysis in Water — Ion Chromatography (IC)
In short
Simultaneous determination of anions (Cl⁻, SO₄²⁻, NO₃⁻, F⁻, PO₄³⁻, Br⁻) and cations (Na⁺, K⁺, Ca²⁺, Mg²⁺, NH₄⁺, Li⁺, Sr²⁺, Ba²⁺) in water by ion chromatography with conductometric detection. The test is performed according to PN-EN ISO 14911:2002; Linear range: 0.01–1,000 mg/L (with dilution). The procedure comprises 10 steps (about 4 h 15 min–6 h 15 min in total); it is used for: Drinking water quality monitoring — chlorides, sulfates, nitrates, fluorides, ammonia, Water hardness (Ca²⁺ + Mg²⁺) and aggressiveness assessment, Mineral and bottled water analysis — ionic balance.
At a glance
- Standard: PN-EN ISO 14911:2002
- Category: Physicochemistry
- Procedure steps: 10
- Total time of stages: 4 h 15 min–6 h 15 min
- Anions (PN-EN ISO 10304-1): F⁻, Cl⁻, NO₂⁻, Br⁻, NO₃⁻, PO₄³⁻, SO₄²⁻
- Cations (PN-EN ISO 14911): Li⁺, Na⁺, NH₄⁺, K⁺, Mn²⁺, Ca²⁺, Mg²⁺, Sr²⁺, Ba²⁺
- Limit of detection: 1–50 µg/L (depending on ion)
Overview
Ion chromatography (IC) is the reference method for determining major inorganic anions and cations in drinking, surface, groundwater, rainwater, mineral waters, and wastewater. Standard PN-EN ISO 14911 covers cations, while anions are covered by PN-EN ISO 10304-1. In laboratory practice, both analyses are performed on one IC system with column exchange or on dual-channel system.
Ion chromatography enables simultaneous determination of many ions in one injection — typically 6–8 anions and 7–9 cations — making it extremely efficient compared to classical titrimetric or spectrophotometric methods. Single chromatogram time is 10–25 minutes, and detection limits reach 1–50 µg/L.
The method is crucial for drinking water quality monitoring (parameters: chlorides, sulfates, nitrates, nitrites, fluorides, ammonia), water hardness assessment (Ca²⁺ + Mg²⁺), mineral water ionic balance, and industrial wastewater control. In water treatment plants, IC allows rapid control of coagulation, iron removal, and manganese removal processes.
Modern IC systems (Thermo Dionex Integrion, Metrohm 940 Professional IC Vario) offer automatic eluent generation (RFIC), electrochemical suppression, and automatic dilution, minimizing operator errors and increasing laboratory efficiency.
Method principle
Water sample is introduced by dosing loop (25–250 µL) onto ion-exchange column — anionic (with quaternary ammonium groups) or cationic (with sulfonic/carboxylic groups). Analyte ions are separated based on affinity differences for ion-exchange resin. Eluent (typically Na₂CO₃/NaHCO₃ for anions or methanesulfonic acid for cations) elutes ions in order of increasing affinity. After column, eluent flows through suppressor (chemical or electrochemical), which eliminates eluent background conductivity and simultaneously converts analytes to highly conductive form (e.g., H₂SO₄ → SO₄²⁻ + H⁺). Conductometric detector measures eluate conductivity. Identification based on retention time, quantification from calibration curve.
Applications
- Drinking water quality monitoring — chlorides, sulfates, nitrates, fluorides, ammonia
- Water hardness (Ca²⁺ + Mg²⁺) and aggressiveness assessment
- Mineral and bottled water analysis — ionic balance
- Municipal and industrial wastewater control
- Rainwater monitoring (acid rain — SO₄²⁻, NO₃⁻)
- Water treatment process control (coagulation, softening, ion exchange)
- Groundwater testing — hydrogeochemistry
- Boiler and circulating water analysis in power industry
Key parameters
| Parameter | Value |
|---|---|
| Anions (PN-EN ISO 10304-1) | F⁻, Cl⁻, NO₂⁻, Br⁻, NO₃⁻, PO₄³⁻, SO₄²⁻ |
| Cations (PN-EN ISO 14911) | Li⁺, Na⁺, NH₄⁺, K⁺, Mn²⁺, Ca²⁺, Mg²⁺, Sr²⁺, Ba²⁺ |
| Limit of detection | 1–50 µg/L (depending on ion) |
| Linear range | 0.01–1,000 mg/L (with dilution) |
| Precision (CV) | 1–5% at concentrations >1 mg/L |
| Chromatogram time | 10–25 minutes |
Standard
- Standard number
- PN-EN ISO 14911:2002
- Title (PL)
- Jakość wody — Oznaczanie rozpuszczonych kationów Li⁺, Na⁺, NH₄⁺, K⁺, Mn²⁺, Ca²⁺, Mg²⁺, Sr²⁺ i Ba²⁺ metodą chromatografii jonowej
- Title (EN)
- Water quality — Determination of dissolved Li⁺, Na⁺, NH₄⁺, K⁺, Mn²⁺, Ca²⁺, Mg²⁺, Sr²⁺ and Ba²⁺ using ion chromatography
Step-by-step procedure
-
Eluent preparation
Anionic eluent: Na₂CO₃ 4.5 mM + NaHCO₃ 0.8 mM in 18.2 MΩ water. Cationic eluent: MSA 20 mM. Degas ultrasonically 15 min. Or use RFIC generator.
-
System conditioning
Flush system with eluent (30 min, 1 mL/min). Check pressure, baseline stability, detector noise (<1 nS/cm).
-
Multi-point calibration
Prepare 5–7 mixed standards (e.g., 0.1; 0.5; 1; 5; 10; 50; 100 mg/L for major ions). Inject sequentially. R² > 0.999 for each ion.
-
Sample filtration
Filter samples through 0.22 µm filters (PVDF or PES). Transfer to PP autosampler vials. Dilute high-concentration samples.
-
Anion analysis
Inject sample (25 µL loop) onto anion column. Flow 1.0 mL/min. Typical sequence: F⁻ (3 min) → Cl⁻ (5 min) → NO₂⁻ (7 min) → Br⁻ (9 min) → NO₃⁻ (11 min) → PO₄³⁻ (15 min) → SO₄²⁻ (18 min).
-
Cation analysis
Switch to cation column (or use second channel). 25 µL loop, MSA 20 mM. Sequence: Li⁺ (3 min) → Na⁺ (4 min) → NH₄⁺ (5 min) → K⁺ (7 min) → Mg²⁺ (12 min) → Ca²⁺ (15 min).
-
Chromatogram integration
Identify peaks based on retention times (±5% window). Integrate peak areas. Read concentrations from calibration curves.
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Quality control
Blank (pure water) every 5–10 samples. CRM (e.g., ION-915, NIST 1643f) every 10 samples. Spike recovery 90–110%. Ionic balance ±5%.
-
Ionic balance verification
Sum of cations (meq/L) ≈ sum of anions (meq/L), difference < 5%. Discrepancy indicates missing ion or analytical error.
-
Column maintenance
After series, flush column with eluent 15 min. Store in working eluents. Regenerate every 200–500 chromatograms.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Ion chromatograph with suppressor | Thermo Dionex Integrion RFIC, Metrohm 940 Professional IC Vario, Shimadzu IC-2010 | 120,000–350,000 PLN |
| Anion-exchange column | Thermo AS23/AS19, Metrohm Metrosep A Supp 7/16 | 3,000–6,000 PLN |
| Cation-exchange column | Thermo CS16/CS12A, Metrohm Metrosep C6 | 3,000–6,000 PLN |
| Autosampler | Thermo AS-DV, Metrohm 858 Professional Sample Processor | 30,000–60,000 PLN |
| Eluent generator (RFIC) | Thermo EGC 500 KOH/MSA, Metrohm Inline Eluent Preparation | 15,000–30,000 PLN |
| Ultrapure water preparation system | Millipore Milli-Q IQ 7000, Merck Direct-Q | 15,000–50,000 PLN |
| Syringe filters | 0.22 µm PVDF or PES, 13 mm, for sample filtration | 1–3 PLN/pc |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Sodium carbonate (Na₂CO₃) | 497-19-8 | Analytical grade, anionic eluent component (4.5 mmol/L) |
| Sodium bicarbonate (NaHCO₃) | 144-55-8 | Analytical grade, anionic eluent component (0.8 mmol/L) |
| Methanesulfonic acid (MSA) | 75-75-2 | Cationic eluent, 20–30 mmol/L, or automatic generation |
| Anion standards — certified CRMs | — | F⁻, Cl⁻, NO₂⁻, Br⁻, NO₃⁻, PO₄³⁻, SO₄²⁻ — 1,000 mg/L solutions, e.g., Merck CertiPUR |
| Cation standards — certified CRMs | — | Li⁺, Na⁺, NH₄⁺, K⁺, Ca²⁺, Mg²⁺, Sr²⁺, Ba²⁺ — 1,000 mg/L solutions |
| Diluted sulfuric acid (H₂SO₄) | 7664-93-9 | Chemical suppressor regenerant, 50 mmol/L |
| Ultrapure water | — | Resistivity >18.2 MΩ·cm, for eluents, standards, and blanks |
Health and safety (OHS)
- Methanesulfonic acid (MSA) — corrosive, causes burns, acid-resistant gloves and glasses
- Sulfuric acid — highly corrosive, work under fume hood during preparation
- Ion standards — low risk, standard protective measures
- Carbonate eluents — low risk, but avoid eye contact
- Lab coat, nitrile gloves, safety glasses mandatory
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 14911:2002 — “Water quality — Determination of dissolved Li⁺, Na⁺, NH₄⁺, K⁺, Mn²⁺, Ca²⁺, Mg²⁺, Sr²⁺ and Ba²⁺ using ion chromatography”.
How does this method work?
Water sample is introduced by dosing loop (25–250 µL) onto ion-exchange column — anionic (with quaternary ammonium groups) or cationic (with sulfonic/carboxylic groups). Analyte ions are separated based on affinity differences for ion-exchange resin.
What is the measuring range and accuracy?
Anions (PN-EN ISO 10304-1): F⁻, Cl⁻, NO₂⁻, Br⁻, NO₃⁻, PO₄³⁻, SO₄²⁻; Cations (PN-EN ISO 14911): Li⁺, Na⁺, NH₄⁺, K⁺, Mn²⁺, Ca²⁺, Mg²⁺, Sr²⁺, Ba²⁺; Limit of detection: 1–50 µg/L (depending on ion); Linear range: 0.01–1,000 mg/L (with dilution).
How long does the test take?
The times given for the individual stages add up to approximately 4 h 15 min–6 h 15 min. The procedure comprises 10 steps.
What equipment is required?
Ion chromatograph with suppressor, Anion-exchange column, Cation-exchange column, Autosampler, Eluent generator (RFIC), Ultrapure water preparation system, Syringe filters. Indicative cost of the core instrument (Ion chromatograph with suppressor): 120,000–350,000 PLN.
Where is this test used?
Drinking water quality monitoring — chlorides, sulfates, nitrates, fluorides, ammonia; Water hardness (Ca²⁺ + Mg²⁺) and aggressiveness assessment; Mineral and bottled water analysis — ionic balance; Municipal and industrial wastewater control; Rainwater monitoring (acid rain — SO₄²⁻, NO₃⁻); Water treatment process control (coagulation, softening, ion exchange); Groundwater testing — hydrogeochemistry; Boiler and circulating water analysis in power industry.
What safety precautions apply?
Methanesulfonic acid (MSA) — corrosive, causes burns, acid-resistant gloves and glasses; Sulfuric acid — highly corrosive, work under fume hood during preparation; Ion standards — low risk, standard protective measures; Carbonate eluents — low risk, but avoid eye contact; Lab coat, nitrile gloves, safety glasses mandatory.
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 14911.