⚛️ Lead in Water — GF-AAS
Determination of trace concentrations of lead in water by atomic absorption spectrometry with electrothermal atomization in graphite furnace (GF-AAS). Detection limit of about 0.5 µg/L.
Overview
Lead (Pb) is one of the most dangerous heavy metals contaminating water. Even low lead concentrations are toxic — they affect the nervous system (especially in children), hematopoietic, renal and reproductive systems. The permissible lead concentration in drinking water is 10 µg/L (according to EU Directive 2020/2184) with a tendency to lower to 5 µg/L. The source of lead in drinking water is mainly old installations with lead pipes and brass fittings.
The GF-AAS (Graphite Furnace Atomic Absorption Spectrometry) method is the reference technique for determining lead at trace levels. The graphite furnace provides much higher sensitivity than the flame technique (FAAS) — the detection limit for Pb is about 0.5 µg/L versus about 10 µg/L in FAAS. A small sample volume (10–20 µL) automatically dosed into the graphite tube is subjected to a multi-stage temperature program: drying → pyrolysis (matrix removal) → atomization → cleaning.
The PN-EN ISO 15586 standard is a reference method covering the determination of 17 trace elements (Ag, Al, As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sb, Se, Tl, V, Zn) in surface, groundwater, drinking water and wastewater. For each element, optimal instrumental conditions, matrix modifiers and temperature programs are specified.
Key to quality results is the use of matrix modifiers — for lead, magnesium nitrate Mg(NO₃)₂ or a mixture of Mg(NO₃)₂ + NH₄H₂PO₄ is most commonly used. Modifiers thermally stabilize the analyte, allowing higher pyrolysis temperatures and more effective matrix removal without analyte losses.
Method principle
A water sample (10–20 µL) is dosed by an automatic sampler into a graphite tube placed in the furnace. The temperature program includes: drying (110–130°C — solvent removal), pyrolysis/thermal pretreatment (700–900°C with modifier — decomposition and removal of matrix components), atomization (1700–2100°C — rapid evaporation and atomization of lead), cleaning (2500°C — removal of residues). Free Pb atoms absorb radiation from a hollow cathode lamp at a wavelength of 283.3 nm. Absorbance is proportional to the analyte mass according to the Beer-Lambert law.
Applications
- Drinking water quality control (Pb ≤10 µg/L)
- Monitoring of lead in water installations with old pipes
- Testing of groundwater in contaminated areas
- Industrial wastewater control (metallurgy, battery factories)
- Monitoring of surface waters (Water Framework Directive)
- Water testing for food industry needs
- Analysis of bottom sediments (after mineralization)
Key parameters
| Parameter | Value |
|---|---|
| Wavelength | 283.3 nm |
| Detection limit (LOD) | ~0.5 µg/L |
| Limit of quantification (LOQ) | ~2 µg/L |
| Linear range | 2–50 µg/L |
| Sample volume | 10–20 µL per measurement |
| Atomization temperature | 1700–2100°C |
Standard
- Standard number
- PN-EN ISO 15586:2005
- Title (PL)
- Jakość wody — Oznaczanie pierwiastków śladowych z zastosowaniem atomowej spektrometrii absorpcyjnej z piecem grafitowym
- Title (EN)
- Water quality — Determination of trace elements using atomic absorption spectrometry with graphite furnace
Step-by-step procedure
1. Preparation of laboratory vessels
All vessels (PP, PTFE) soak in 10% HNO₃ for min. 24 h, then rinse three times with ultrapure water. Lead easily adsorbs on glass!
2. Sample acidification
Add 1 mL conc. HNO₃ (Suprapur) per 100 mL sample (pH <2). Store samples in PP or PTFE containers at 4°C.
3. Preparation of calibration standards
From 1000 mg/L Pb solution prepare series: 0 (blank), 5, 10, 20, 30, 50 µg/L in 1% HNO₃.
4. Optimization of temperature program
Drying: 110°C (30 s) → 130°C (20 s). Pyrolysis: 850°C (20 s) with modifier. Atomization: 1800°C (5 s, reading). Cleaning: 2500°C (3 s).
5. Dosing modifier
Set autosampler to dose 5 µL Mg(NO₃)₂ 0.1% (or NH₄H₂PO₄ 1%) together with sample (15 µL).
6. Instrument calibration
Measure calibration standard series. Plot calibration curve as integrated absorbance (peak area) vs concentration. R² ≥0.998.
7. Sample measurement
Measure samples in duplicates. Instrument automatically doses sample and modifier, executes temperature program and records signal.
8. Quality control — blank and control sample
Every 10 samples measure blank (1% HNO₃) and control sample (CRM or spike). Recovery: 90–110%. Blank <LOD.
9. Interference control — standard addition method
For new matrices perform standard addition test — confirm absence of matrix effect.
10. Calculation and reporting
Read Pb concentration from calibration curve. Consider dilution and blank. Report result in µg/L with 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 |
| Autosampler | Agilent GTA 120, Shimadzu ASC-7000 | included with instrument |
| Hollow cathode lamp (HCL) Pb | Agilent Pb HCL, Heraeus, Photron | 800–2 000 PLN |
| Graphite tubes | Tubes with L'vov platform, pyrolytically coated, Agilent/Shimadzu | 50–150 PLN/pc. (100–300 atomizations) |
| Protective gas — argon 5.0 | Ar cylinder 99.999%, two-stage regulator | 300–600 PLN/cylinder 50 L |
| Water cooling system | Recirculating chiller or water circuit | 3 000–10 000 PLN |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Pb standard solution 1000 mg/L | 7439-92-1 | Certified CRM in 2% HNO₃, traceable to NIST SRM. For preparing calibration dilutions. |
| Nitric acid 65% Suprapur | 7697-37-2 | HNO₃ for acidifying samples and preparing dilutions; ultrapure quality (Merck Suprapur or equivalent) |
| Matrix modifier — Mg(NO₃)₂ | 10377-60-3 | Magnesium nitrate 0.1% — thermally stabilizes Pb, allows higher pyrolysis temp. |
| Matrix modifier — NH₄H₂PO₄ | 7722-76-1 | Ammonium dihydrogen phosphate 1% — alternative modifier, particularly effective with chloride matrices |
| Ultrapure water | — | Grade 1 quality (resistivity ≥18.2 MΩ·cm), Milli-Q or Hydrolab system |
| Hydrochloric acid 30% Suprapur | 7647-01-0 | HCl — for washing vessels, soaking in 10% HCl min. 24 h |
Health and safety (OHS)
- Lead compounds — toxic, carcinogenic cat. 2, toxic for reproduction — absolutely gloves and goggles
- Concentrated nitric acid — strongly corrosive, fuming — work under fume hood
- Graphite furnace — temperature up to 2500°C, do not touch during operation, risk of burns
- Argon — inert gas, but in closed room can displace oxygen — ventilation mandatory
- Pb-containing waste — collect separately as hazardous waste