⚗️ Bromides and Bromates in Water
Determination of bromates (BrO₃⁻) and bromides (Br⁻) in drinking water by ion chromatography with conductometric detection. Bromates are a by-product of water ozonation.
Overview
Bromates (BrO₃⁻) are a hazardous by-product of drinking water disinfection with ozone. When water contains natural bromides (Br⁻), ozonation causes their oxidation to bromates — compounds with proven carcinogenic activity (group 2B according to IARC). The EU Directive 98/83/EC and the Polish Ministry of Health Regulation set the maximum permissible concentration of bromates in drinking water at 10 µg/L.
Ion chromatography (IC) is the reference method for bromate determination according to PN-EN ISO 15061. The method allows simultaneous separation and quantitative determination of bromates and bromides in the presence of other inorganic anions (chlorides, sulfates, nitrates). The use of an anion-exchange column and a conductometric detector with suppressor achieves sensitivity in the range of 0.5–5 µg/L.
Bromate determination is required as part of drinking water quality monitoring, especially in treatment plants using ozonation. The method also applies to surface, swimming pool, and bottled waters. In Poland, the obligation to control bromates results from the Ministry of Health Regulation of December 7, 2017.
ISO 15061 covers two techniques: direct conductometric detection (LOD ~3–5 µg/L) and concentration method on ion-exchange cartridges (LOD ~0.5 µg/L). Alternatively, the post-column reaction method (ISO 11206) with UV detection after KI reaction is used, achieving LOD 0.5 µg/L.
Method principle
A water sample is introduced into an ion chromatograph equipped with an anion-exchange column. Anions present in the sample (Br⁻, BrO₃⁻, Cl⁻, NO₃⁻, SO₄²⁻) are separated based on differences in affinity for the ion-exchange resin. Elution is carried out with sodium carbonate/bicarbonate solution or KOH. After separation, the eluent flows through a chemical or electrochemical suppressor, which eliminates background conductivity, and the analyte anions are detected by a conductometric detector. Quantification is performed by comparing peak areas with a calibration curve. For low concentrations, sample concentration on mini-columns in Ba²⁺, Ag⁺, and H⁺ form is used to remove interfering chlorides and sulfates.
Applications
- Drinking water quality control — bromate monitoring (Journal of Laws 2017 item 2294)
- Supervision of water ozonation processes in treatment plants
- Testing of mineral and bottled waters
- Monitoring of swimming pool water subjected to ozonation
- Control of surface and source waters
- Assessment of alternative disinfection effectiveness (UV, chlorination)
- Environmental studies — identification of bromide sources in raw waters
Key parameters
| Parameter | Value |
|---|---|
| Measurement range (bromates) | 0.5–1,000 µg/L |
| Limit of detection (LOD) | 0.5 µg/L (with concentration), 3–5 µg/L (direct) |
| Permissible BrO₃⁻ concentration | 10 µg/L (drinking water, EU/PL) |
| Sample volume | 5–50 mL (depending on concentration) |
| Precision (CV) | 3–8% at concentration >5 µg/L |
| Analysis time | 15–30 minutes per chromatogram |
Standard
- Standard number
- PN-EN ISO 15061:2003
- Title (PL)
- Jakość wody — Oznaczanie rozpuszczonych bromianów — Metoda chromatografii jonowej
- Title (EN)
- Water quality — Determination of dissolved bromate — Method by liquid chromatography of ions
Step-by-step procedure
1. Eluent preparation
Prepare eluent: Na₂CO₃ 4.5 mmol/L + NaHCO₃ 0.8 mmol/L in deionized water (18.2 MΩ). Degas in ultrasonic bath for 15 min.
2. Column conditioning
Flush anion-exchange column with eluent for at least 30 min at 1.0 mL/min flow rate. Check baseline stability.
3. Calibration
Prepare series of bromate standards: 1, 2, 5, 10, 25, 50 µg/L from certified CRM. Inject sequentially, record chromatograms.
4. Sample preparation (direct)
Filter sample through 0.22 µm filter. Transfer to autosampler vial. Analyze samples within 24 h of collection.
5. Concentration (optional, low concentrations)
Pass 50 mL sample through OnGuard Ba → Ag → H cartridges to remove SO₄²⁻, Cl⁻ and reduce ionic strength. Collect filtrate.
6. Sample injection
Inject sample (250 µL or 1 mL loop for concentrated samples) onto column. Start chromatogram recording.
7. Separation and detection
Anions separate on column. BrO₃⁻ typically elutes at 8–12 min, Br⁻ at 12–16 min. Conductometric detection after suppression.
8. Integration and calculations
Identify peaks based on retention times. Calculate concentration from calibration curve (linear regression, R² > 0.999).
9. Quality control
Analyze control sample every 10 samples, blank (deionized water) every 5 samples. Spike recovery 90–110%.
10. Column flushing
After series, flush column with eluent for 15 min. Store in eluents or deionized water.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Ion chromatograph with suppressor | Thermo Dionex Aquion/Integrion, Metrohm 940 Professional IC Vario | 120,000–280,000 PLN |
| Anion-exchange column | Thermo AS19/AS23, Metrohm Metrosep A Supp 7 | 3,000–6,000 PLN |
| Electrochemical suppressor | Thermo ASRS 300/AERS 500e, Metrohm MSM | 8,000–15,000 PLN |
| Autosampler | Thermo AS-DV, Metrohm 858 Professional | 30,000–60,000 PLN |
| Concentration cartridges (Ba²⁺, Ag⁺, H⁺) | Thermo OnGuard II Ba/Ag/H | 200–500 PLN/pc |
| Vials and sample filters | PP vials 0.5 mL, syringe filters 0.22 µm PVDF | 0.50–3 PLN/pc |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Bromate standard solution (BrO₃⁻) | 15541-45-4 | Potassium bromate (KBrO₃), 1,000 mg/L solution, certified CRM |
| Bromide standard solution (Br⁻) | 7647-15-6 | Sodium bromide (NaBr), 1,000 mg/L solution, certified CRM |
| Sodium carbonate (Na₂CO₃) | 497-19-8 | Analytical grade, eluent component (4.5 mmol/L) |
| Sodium bicarbonate (NaHCO₃) | 144-55-8 | Analytical grade, eluent component (0.8 mmol/L) |
| Sulfuric acid (H₂SO₄) | 7664-93-9 | Suppressor regenerant solution, 50 mmol/L |
| Deionized water | — | Resistivity >18.2 MΩ·cm, for eluent and standard preparation |
Health and safety (OHS)
- Potassium bromate (KBrO₃) — oxidizer, carcinogenic cat. 2B, use in fume hood
- Sulfuric acid — corrosive, acid-resistant gloves and safety glasses required
- Sodium carbonate — irritant to eyes, use eye protection
- Drinking water samples — low risk, standard protective measures
- Collect chromatographic waste in chemical waste containers