🧪 Aluminium in Water
In short
Determination of aluminium in water by atomic absorption spectrometry (AAS) — flame or graphite furnace. The test is performed according to PN-EN ISO 12020:2002; GF-AAS linear range: 5–200 µg/L. The procedure comprises 10 steps (about 1 days 1 h 3 min–1 days 1 h 4 min in total); it is used for: Drinking water quality control (Al ≤200 µg/L), Monitoring of coagulation process — control of aluminium coagulant dosing, Testing of surface waters (Al toxicity to fish at pH <5).
At a glance
- Standard: PN-EN ISO 12020:2002
- Category: Physicochemistry
- Procedure steps: 10
- Total time of stages: 1 days 1 h 3 min–1 days 1 h 4 min
- Wavelength: 309.3 nm
- GF-AAS detection limit: ~1 µg/L
- FAAS detection limit: ~30 µg/L (N₂O-C₂H₂)
Overview
Aluminium (Al) is the third most abundant element in the Earth's crust, but its presence in drinking water is undesirable. The permissible aluminium concentration in drinking water is 200 µg/L (0.2 mg/L) according to MH Regulation (Journal of Laws 2017, item 2294). The main sources of aluminium in drinking water are aluminium coagulants (aluminium sulfate, polyaluminium chloride) used in the water treatment process — with improper dosing or pH, Al residues can penetrate treated water.
Elevated aluminium concentrations in drinking water raise health controversies — the relationship between aluminium exposure and Alzheimer's disease has been discussed for years. Although epidemiological evidence is inconclusive, the precautionary principle requires minimizing Al in drinking water. Moreover, aluminium deteriorates the organoleptic properties of water (turbidity, color) and can cause problems in installations (deposits).
The PN-EN ISO 12020 standard describes two AAS methods for determining aluminium in water: flame method (FAAS) — with atomization in nitrous oxide-acetylene flame (N₂O-C₂H₂), used for concentrations 5–100 mg/L, and graphite furnace method (GF-AAS) — for concentrations 5–200 µg/L, relevant in drinking water control. Alternatively, spectrophotometric method with chromoazurol S or pyridylazo resorcinol (PAR) is used, as well as ICP-OES.
In practice, drinking water laboratories most commonly use GF-AAS or ICP-OES due to the required low limit of quantification (of the order of 10 µg/L).
Method principle
GF-AAS method: water sample (10–20 µL) is dosed into graphite tube. Temperature program includes: drying (110–130°C), pyrolysis (1200–1500°C — without modifier or with Mg(NO₃)₂), atomization (2400–2600°C — high temperature necessary due to Al thermal resistance), cleaning (2700°C). Free Al atoms absorb HCL radiation at λ = 309.3 nm. FAAS method: sample is aspirated into N₂O-C₂H₂ flame (temp. ~3000°C) — regular air-acetylene flame does not provide sufficient energy for Al atomization.
Applications
- Drinking water quality control (Al ≤200 µg/L)
- Monitoring of coagulation process — control of aluminium coagulant dosing
- Testing of surface waters (Al toxicity to fish at pH <5)
- Monitoring of acidic waters (acid rain mobilizes Al from soils)
- Control of dialysates in dialysis stations (Al <10 µg/L)
- Testing of groundwater in bauxite mining areas
Key parameters
| Parameter | Value |
|---|---|
| Wavelength | 309.3 nm |
| GF-AAS detection limit | ~1 µg/L |
| FAAS detection limit | ~30 µg/L (N₂O-C₂H₂) |
| GF-AAS linear range | 5–200 µg/L |
| FAAS linear range | 5–100 mg/L |
| GF-AAS atomization temperature | 2400–2600°C |
Standard
- Standard number
- PN-EN ISO 12020:2002
- Title (PL)
- Jakość wody — Oznaczanie glinu — Metody atomowej spektrometrii absorpcyjnej
- Title (EN)
- Water quality — Determination of aluminium — Atomic absorption spectrometric methods
Step-by-step procedure
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Preparation of vessels (contamination control)
Aluminium is ubiquitous — PP/PTFE vessels soak in 10% HCl (not HNO₃!) for 24 h, rinse three times with ultrapure water. Work in clean bench recommended.
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Sample acidification
Add Suprapur HNO₃ to pH <2. For drinking water — analysis within 24 h (Al may precipitate at pH >4).
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Preparation of standards (GF-AAS)
Prepare series: 0, 10, 20, 50, 100, 200 µg/L Al in 1% Suprapur HNO₃. Prepare standards immediately before measurement.
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GF-AAS temperature program
Drying: 110°C (30 s), 130°C (20 s). Pyrolysis: 1400°C (20 s, with Mg(NO₃)₂). Atomization: 2500°C (5 s, reading). Cleaning: 2700°C (3 s).
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Dosing modifier
Autosampler doses 5 µL Mg(NO₃)₂ 0.1% + 15 µL sample. Modifier allows raising pyrolysis temp. without Al losses.
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Calibration
Measure calibration standards. Plot curve (peak area vs concentration). R² ≥0.998. Check sensitivity.
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Sample measurement
Measure samples in duplicates. Measurement time approx. 3–4 min/sample. Monitor background (Zeeman correction).
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Quality control
Laboratory blank, field blank, control standard (recovery 90–110%), duplicate (RPD <15%). Special attention to contamination!
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Contamination control
Laboratory blank must be <3 µg/L Al. If higher — search for contamination source (vessels, reagents, air).
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Calculation and reporting
Al concentration from calibration curve. Result in µg/L with accuracy to 1 µg/L. Consider measurement uncertainty.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| AAS spectrometer with graphite furnace | Agilent 280Z AA, Shimadzu AA-7000, Analytik Jena ZEEnit 700P | 150 000–400 000 PLN |
| N₂O-C₂H₂ burner (for FAAS) | Slot-burner type for nitrous oxide — included with FAAS instrument | included |
| Al HCL lamp | Agilent Al HCL, Heraeus — current 10 mA | 600–1 500 PLN |
| Graphite tubes | Pyrolytically coated tubes with L'vov platform | 50–150 PLN/pc. |
| Nitrous oxide N₂O (for FAAS) | 50 L cylinder, purity 2.0, regulator | 300–600 PLN/cylinder |
| PP/PTFE vessels | Aluminium ubiquitous — avoid contamination; do not use aluminosilicate glass | 5–30 PLN/pc. |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Al standard solution 1000 mg/L | 7429-90-5 | Certified CRM in 2% HNO₃ (Merck CertiPUR), traceable to NIST SRM |
| Nitric acid 65% Suprapur | 7697-37-2 | Ultrapure HNO₃ — for acidifying samples and standards (pH <2). Suprapur quality for GF-AAS! |
| Modifier — Mg(NO₃)₂ | 10377-60-3 | Magnesium nitrate 0.1% — matrix modifier for GF-AAS, thermally stabilizes Al |
| Ultrapure water | — | Resistivity ≥18.2 MΩ·cm, Milli-Q system — checked for Al content (<1 µg/L) |
| Hydrochloric acid 30% Suprapur | 7647-01-0 | HCl — for washing vessels; soaking in 10% HCl, 24 h |
Health and safety (OHS)
- Concentrated nitric acid — corrosive, fuming — work under fume hood
- Hydrochloric acid — corrosive, fuming — work under fume hood
- Graphite furnace — temperatures up to 2700°C — do not touch during operation
- Nitrous oxide N₂O (for FAAS) — supports combustion, cylinder under pressure
- Safety goggles, lab coat and gloves mandatory
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 12020:2002 — “Water quality — Determination of aluminium — Atomic absorption spectrometric methods”.
How does this method work?
GF-AAS method: water sample (10–20 µL) is dosed into graphite tube. Temperature program includes: drying (110–130°C), pyrolysis (1200–1500°C — without modifier or with Mg(NO₃)₂), atomization (2400–2600°C — high temperature necessary due to Al thermal resistance), cleaning (2700°C).
What is the measuring range and accuracy?
Wavelength: 309.3 nm; GF-AAS detection limit: ~1 µg/L; FAAS detection limit: ~30 µg/L (N₂O-C₂H₂); GF-AAS linear range: 5–200 µg/L.
How long does the test take?
The times given for the individual stages add up to approximately 1 days 1 h 3 min–1 days 1 h 4 min. The procedure comprises 10 steps.
What equipment is required?
AAS spectrometer with graphite furnace, N₂O-C₂H₂ burner (for FAAS), Al HCL lamp, Graphite tubes, Nitrous oxide N₂O (for FAAS), PP/PTFE vessels. Indicative cost of the core instrument (AAS spectrometer with graphite furnace): 150 000–400 000 PLN.
Where is this test used?
Drinking water quality control (Al ≤200 µg/L); Monitoring of coagulation process — control of aluminium coagulant dosing; Testing of surface waters (Al toxicity to fish at pH <5); Monitoring of acidic waters (acid rain mobilizes Al from soils); Control of dialysates in dialysis stations (Al <10 µg/L); Testing of groundwater in bauxite mining areas.
What safety precautions apply?
Concentrated nitric acid — corrosive, fuming — work under fume hood; Hydrochloric acid — corrosive, fuming — work under fume hood; Graphite furnace — temperatures up to 2700°C — do not touch during operation; Nitrous oxide N₂O (for FAAS) — supports combustion, cylinder under pressure; Safety goggles, lab coat and gloves 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 12020.