☠️ Mercury in water
In short
Determination of mercury in water by cold vapor method (CV-AAS) — chemical reduction of Hg²⁺ to Hg⁰ and absorption measurement in gas phase. The test is performed according to PN-EN ISO 12846:2012; Working range (with enrichment): 0.01–1 µg/L. The procedure comprises 6 steps (about 12 h 33 min–12 h 35 min in total); it is used for: Drinking water quality control (standard: ≤ 1 µg/L), Environmental monitoring of surface waters (EQS = 0.07 µg/L), Analysis of industrial wastewater (chlor-alkali, metallurgy).
At a glance
- Standard: PN-EN ISO 12846:2012
- Category: Physicochemistry
- Procedure steps: 6
- Total time of stages: 12 h 33 min–12 h 35 min
- Limit of quantification (with enrichment): 0.008–0.01 µg/L
- Limit of quantification (without enrichment): 0.024–0.05 µg/L
- Working range (with enrichment): 0.01–1 µg/L
Overview
Mercury is one of the most toxic heavy metals, accumulating in the food chain. Even low concentrations are dangerous — the permissible concentration in drinking water is only 1 µg/L (Journal of Laws 2017, item 2294), and environmental standards are even more restrictive (EQS = 0.07 µg/L for surface waters).
PN-EN ISO 12846:2012 specifies two methods for determining mercury in drinking, surface, ground, rainwater, and wastewater: (1) method with enrichment by amalgamation on Au/Pt adsorber — working range 0.01–1 µg/L, and (2) method without enrichment — range from 0.05 µg/L.
The cold vapor (CV) technique is unique to mercury — as the only metal it forms atomic vapor at room temperature after chemical reduction. It does not require flame or graphite furnace, which eliminates thermal interferences and ensures very low detection limits.
Method principle
The water sample is first subjected to acid digestion to release mercury from organic compounds. Then Hg²⁺ ions in solution are reduced to metallic mercury Hg⁰ by adding tin(II) chloride (SnCl₂) or sodium borohydride (NaBH₄).
Elemental mercury Hg⁰ — as the only metal — forms atomic vapor at room temperature. Mercury vapor is released from solution by passing carrier gas stream (argon or nitrogen) and transferred to the absorption cell of the spectrometer.
In the cell, absorption of UV radiation at wavelength 253.7 nm (Hg resonance line) is measured. Absorbance is proportional to mercury concentration in the sample.
In the enrichment method, mercury vapor is first amalgamated (retained) on a gold adsorber, then thermally released — which allows concentration and achievement of lower quantification limits.
Applications
- Drinking water quality control (standard: ≤ 1 µg/L)
- Environmental monitoring of surface waters (EQS = 0.07 µg/L)
- Analysis of industrial wastewater (chlor-alkali, metallurgy)
- Study of groundwater in contaminated areas
- Water monitoring near waste landfills
- Control of mercury emissions to aquatic environment
Key parameters
| Parameter | Value |
|---|---|
| Limit of quantification (with enrichment) | 0.008–0.01 µg/L |
| Limit of quantification (without enrichment) | 0.024–0.05 µg/L |
| Working range (with enrichment) | 0.01–1 µg/L |
| Working range (without enrichment) | 0.05–10 µg/L |
| Wavelength | 253.7 nm (Hg resonance line) |
| Repeatability | RSD < 5–10% (depending on concentration) |
Standard
- Standard number
- PN-EN ISO 12846:2012
- Title (PL)
- Jakość wody — Oznaczanie rtęci — Metoda z zastosowaniem absorpcyjnej spektrometrii atomowej (AAS) z wzbogacaniem i bez wzbogacania
- Title (EN)
- Water quality — Determination of mercury — Method using atomic absorption spectrometry (AAS) with and without enrichment
Step-by-step procedure
-
Sampling
Collect in borosilicate glass or PTFE bottles (not PE — mercury adsorbs on walls). Acidify with 0.5% BrCl or 1% HNO₃. Store in dark.
-
Digestion
Add BrCl (0.5% v/v) and leave for 12h (oxidation of organic Hg forms). Alternatively: acid digestion HNO₃ + H₂O₂ on heating block.
-
Reduction of free halogens
Add hydroxylamine solution (NH₂OH·HCl) to neutralize excess BrCl. Wait 5 min until color disappears.
-
Analyzer calibration
Prepare standard solutions: 0; 0.05; 0.1; 0.5; 1.0 µg/L Hg. Measure and build calibration curve. R² > 0.998.
-
Reduction and measurement
Sample + SnCl₂ in gas-liquid separator. Argon bubbling carries Hg⁰ vapor to cell. Absorbance measurement at 253.7 nm. Optionally enrichment on Au adsorber.
-
Quality control
CRM every 10 samples (recovery 85–115%). Blank sample at beginning and end of series. Duplicates every 20 samples. Check reductant blank.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Mercury analyzer CV-AAS | Lumex RA-915M with RP-92 attachment, Milestone DMA-80, Teledyne Leeman Hydra IIC | 80 000–200 000 PLN |
| Cold vapor generator | Dedicated CV system for AAS spectrometer or standalone analyzer | 40 000–80 000 PLN |
| Au/Pt amalgamator (enrichment option) | Gold adsorber with heater for thermal desorption | included with analyzer |
| Peristaltic pump | For transport of sample and reductant to gas-liquid separator | 5 000–15 000 PLN |
| Digestion system | Heating block or microwave digestion (HNO₃ + H₂O₂ or BrCl) | 15 000–250 000 PLN |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Tin(II) chloride (SnCl₂) | 7772-99-8 | Reductant: 2% (w/v) in 10% HCl. Purify from Hg by argon bubbling 30 min |
| Concentrated nitric acid (HNO₃) | 7697-37-2 | Ultrapur purity (sub-boiling), for digestion and preservation of samples |
| Hydrogen peroxide (H₂O₂) 30% | 7722-84-1 | For assisting digestion of organic matter |
| Hg standard solution (1000 mg/L) | 7439-97-6 | Certified CRM, traceability to NIST. Dilute freshly before use |
| Bromine monochloride (BrCl) | — | For oxidation of organic mercury forms. Prepare from KBrO₃ + HCl |
| Hydroxylamine hydrochloride | 5470-11-1 | For destroying excess BrCl before reduction. 30 g/L in water |
Health and safety (OHS)
- Mercury — highly toxic, accumulates in body. Use nitrile gloves, work in fume hood
- Mercury vapor — poisonous! Absolutely work under exhaust. In case of spill — Hg spill kit
- BrCl — highly corrosive and toxic, causes burns. Prepare only in fume hood
- SnCl₂ — irritating, harmful. Avoid inhalation and skin contact
- Hg-containing waste — collect separately as hazardous waste (code 16 06 01)
- Lab coat, goggles, nitrile gloves mandatory. Hg emergency kit available
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 12846:2012 — “Water quality — Determination of mercury — Method using atomic absorption spectrometry (AAS) with and without enrichment”.
How does this method work?
The water sample is first subjected to acid digestion to release mercury from organic compounds. Then Hg²⁺ ions in solution are reduced to metallic mercury Hg⁰ by adding tin(II) chloride (SnCl₂) or sodium borohydride (NaBH₄).
What is the measuring range and accuracy?
Limit of quantification (with enrichment): 0.008–0.01 µg/L; Limit of quantification (without enrichment): 0.024–0.05 µg/L; Working range (with enrichment): 0.01–1 µg/L; Working range (without enrichment): 0.05–10 µg/L.
How long does the test take?
The times given for the individual stages add up to approximately 12 h 33 min–12 h 35 min. The procedure comprises 6 steps.
What equipment is required?
Mercury analyzer CV-AAS, Cold vapor generator, Au/Pt amalgamator (enrichment option), Peristaltic pump, Digestion system. Indicative cost of the core instrument (Mercury analyzer CV-AAS): 80 000–200 000 PLN.
Where is this test used?
Drinking water quality control (standard: ≤ 1 µg/L); Environmental monitoring of surface waters (EQS = 0.07 µg/L); Analysis of industrial wastewater (chlor-alkali, metallurgy); Study of groundwater in contaminated areas; Water monitoring near waste landfills; Control of mercury emissions to aquatic environment.
What safety precautions apply?
Mercury — highly toxic, accumulates in body. Use nitrile gloves, work in fume hood; Mercury vapor — poisonous! Absolutely work under exhaust. In case of spill — Hg spill kit; BrCl — highly corrosive and toxic, causes burns. Prepare only in fume hood; SnCl₂ — irritating, harmful. Avoid inhalation and skin contact; Hg-containing waste — collect separately as hazardous waste (code 16 06 01); Lab coat, goggles, nitrile gloves mandatory. Hg emergency kit available.
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 12846.