🔬 Copper in Water
Determination of copper in water by flame atomic absorption spectrometry (FAAS) at wavelength 324.8 nm. Fast and reliable method for mg/L level concentrations.
Overview
Copper (Cu) is a microelement essential for living organisms, but in excess shows toxic action — causes gastrointestinal disorders, liver and kidney damage. The permissible copper concentration in drinking water is 2.0 mg/L (according to EU Directive 2020/2184 and MH Regulation). Sources of copper in water are corrosion of copper pipes in water installations, wastewater from electroplating, metallurgical and chemical industry, copper pesticides (vineyards), and natural geological sources.
Flame atomic absorption spectrometry (FAAS) is the most commonly used technique for determining copper in water at mg/L level. The method is fast (30–60 seconds per sample), simple to operate and highly selective. Copper is one of the "easy" elements to determine by FAAS technique — the 324.8 nm resonance line is strong and free from serious spectral interference. The acetylene-air flame provides optimal atomization.
The PN-EN ISO 8288 standard covers simultaneous determination of six heavy metals (Co, Ni, Cu, Zn, Cd, Pb) by FAAS technique in surface, groundwater, drinking water and wastewater. The method requires prior acidification of the sample with nitric acid (pH <2) to stabilize metal ions and prevent adsorption on vessel walls.
For concentrations below the FAAS limit of quantification (about 0.01 mg/L Cu), enrichment technique (extraction, concentration) or transition to GF-AAS (detection limit about 0.1 µg/L) is necessary.
Method principle
A water sample, acidified with HNO₃ to pH <2, is introduced via a nebulizer (atomizer) into an acetylene-air flame (temperature about 2300°C). In the flame, solvent evaporation, dissociation and atomization occur — free copper atoms are formed in the ground state. These atoms absorb radiation emitted by a hollow cathode lamp (HCL) at a characteristic wavelength of 324.8 nm. Absorbance is proportional to the Cu concentration in the sample (Beer-Lambert law). Concentration is read from a calibration curve prepared from standards of known concentrations.
Applications
- Drinking water quality control (Cu ≤2.0 mg/L)
- Monitoring of copper pipe corrosion in water installations
- Control of electroplating and industrial wastewater
- Testing of surface and groundwater
- Water quality control in aquaculture (Cu toxic to fish >0.02 mg/L)
- Monitoring of waters near copper mines (KGHM)
Key parameters
| Parameter | Value |
|---|---|
| Wavelength | 324.8 nm |
| Flame type | acetylene-air (fuel-lean) |
| Detection limit (LOD) | ~0.003 mg/L |
| Limit of quantification (LOQ) | ~0.01 mg/L |
| Linear range | 0.01–5 mg/L |
| Sensitivity (characteristic concentration) | ~0.04 mg/L (1% absorption) |
Standard
- Standard number
- PN-EN ISO 8288:2002
- Title (PL)
- Jakość wody — Oznaczanie kobaltu, niklu, miedzi, cynku, kadmu i ołowiu — Metody płomieniowej absorpcyjnej spektrometrii atomowej
- Title (EN)
- Water quality — Determination of cobalt, nickel, copper, zinc, cadmium and lead — Flame atomic absorption spectrometric methods
Step-by-step procedure
1. Sample acidification
Add 1 mL HNO₃ 65% per 100 mL sample (pH <2). Store samples in PE/PP containers at 4°C. Samples stable for 6 months.
2. Preparation of calibration standards
From 1000 mg/L Cu solution prepare standards: 0 (blank), 0.1, 0.5, 1.0, 2.0, 5.0 mg/L in 1% HNO₃. Standards valid 1 month.
3. Instrument setup
Install Cu HCL lamp. Set wavelength 324.8 nm, slit 0.5 nm. Turn on lamp (current 15 mA) — stabilization 15 min.
4. Flame optimization
Ignite acetylene-air flame. Set fuel/oxidizer ratio to lean flame (blue). Adjust burner position.
5. Calibration
Aspirate blank and calibration standards sequentially. Plot calibration curve (absorbance vs concentration). R² ≥0.999.
6. Sample measurement
Aspirate sample through nebulizer (approx. 5 mL/min). Read absorbance after signal stabilization (5–10 s). Aspirate 1% HNO₃ between samples.
7. Quality control
Every 10 samples measure blank and control standard (e.g., 1.0 mg/L Cu). Recovery: 95–105%. Measure duplicate (RPD <5%).
8. Range verification
For samples with concentration >5 mg/L — dilute and repeat measurement. For concentrations <0.01 mg/L — consider GF-AAS or enrichment.
9. Cleaning after work
Aspirate deionized water for 2 min. Extinguish flame (acetylene first, then air). Rinse nebulizer.
10. Calculation and reporting
Cu concentration from calibration curve. Consider dilution. Result in mg/L with 3 significant figures.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Flame AAS spectrometer | Agilent 240FS AA, Shimadzu AA-7000F, Analytik Jena novAA 800F | 60 000–180 000 PLN |
| Cu HCL lamp | Agilent Cu HCL, Heraeus, Photron — current 15 mA | 600–1 500 PLN |
| Technical acetylene (cylinder) | C₂H₂ 40 L cylinder with regulator, purity 2.6 | 200–400 PLN/cylinder |
| Compressed air (compressor) | Oil-free compressor with dryer, 4–6 bar | 3 000–8 000 PLN |
| Nebulizer and spray chamber | Concentric nebulizer, Scott-type chamber — included with instrument | included |
| Burner exhaust hood | Exhaust with fan for removing combustion gases | 2 000–5 000 PLN |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Cu standard solution 1000 mg/L | 7440-50-8 | Certified CRM in 2% HNO₃ (Merck CertiPUR, Sigma-Aldrich TraceCERT), traceable to NIST SRM |
| Nitric acid 65% analytical grade | 7697-37-2 | HNO₃ for acidifying samples (pH <2) — 1 mL per 100 mL sample. Analytical grade sufficient for FAAS. |
| Deionized water | — | Quality at least grade 2 according to PN-EN ISO 3696 — for preparing dilutions and standards |
| Rinse solution (1% HNO₃) | — | For aspiration between samples — prevents memory effect |
Health and safety (OHS)
- Acetylene — flammable and explosive gas — secured cylinder, not used near fire
- Concentrated nitric acid — corrosive, fuming — work under fume hood
- AAS flame — temperature approx. 2300°C — do not bring hands close, burner exhaust hood mandatory
- Safety goggles, lab coat and gloves mandatory
- Room ventilation — combustion gases from flame must be exhausted outside