⚛️ Cadmium in Water — GF-AAS
In short
Determination of trace concentrations of cadmium in water by atomic absorption spectrometry with graphite furnace (GF-AAS). The test is performed according to PN-EN ISO 15586:2005; Linear range: 0.2–5 µg/L. The procedure comprises 10 steps (about 1 days 58 min in total); it is used for: Drinking water quality control (Cd ≤5 µg/L), Industrial wastewater monitoring (metallurgy, electroplating), Testing of groundwater at waste disposal sites.
At a glance
- Standard: PN-EN ISO 15586:2005
- Category: Physicochemistry
- Procedure steps: 10
- Total time of stages: 1 days 58 min
- Wavelength: 228.8 nm
- Detection limit (LOD): ~0.05 µg/L
- Limit of quantification (LOQ): ~0.2 µg/L
Overview
Cadmium (Cd) is a heavy metal with strong toxic action — it accumulates in the body (half-life in kidneys is 10–30 years), causes kidney damage (cadmium nephropathy), osteoporosis (itai-itai disease), is carcinogenic (group 1 according to IARC). The permissible cadmium concentration in drinking water is 5 µg/L (EU Directive 2020/2184) — one of the lowest limits among heavy metals.
Sources of cadmium in waters are metallurgical industry (zinc, copper), Ni-Cd battery production, phosphorus fertilization (phosphates contain cadmium as contamination), electroplating, and corrosion of galvanized steel pipes. Cadmium is very mobile in the aquatic environment at low pH.
The GF-AAS technique is particularly suited for cadmium determination due to excellent sensitivity — a detection limit of about 0.05 µg/L allows reliable determination at 1/10 of the permissible standard. Cadmium atomizes at a relatively low temperature (1500–1800°C), but is sensitive to chloride interference — excess chlorides can cause premature volatilization of cadmium during pyrolysis. Therefore, use of a matrix modifier (NH₄H₂PO₄) is mandatory.
The PN-EN ISO 15586 standard provides detailed instrumental conditions for cadmium: wavelength 228.8 nm, modifier NH₄H₂PO₄ or mixture Mg(NO₃)₂ + NH₄H₂PO₄, pyrolysis temperature 500–700°C (with modifier), atomization temperature 1500–1800°C.
Method principle
A water sample (10–20 µL) is dosed into a graphite tube in the furnace. The temperature program includes: drying (110–130°C), pyrolysis (500–700°C with NH₄H₂PO₄ modifier — matrix removal without Cd losses), atomization (1500–1800°C — evaporation and atomization of cadmium), cleaning (2400°C). Free Cd atoms absorb radiation from a hollow cathode lamp at 228.8 nm. Absorbance (peak area) is proportional to the cadmium mass in the sample. Background correction (Zeeman or D₂ lamp) eliminates nonspecific absorption from matrix components.
Applications
- Drinking water quality control (Cd ≤5 µg/L)
- Industrial wastewater monitoring (metallurgy, electroplating)
- Testing of groundwater at waste disposal sites
- Control of cadmium in agricultural waters (influence of phosphorus fertilizers)
- Monitoring of surface waters (Water Framework Directive)
- Analysis of cadmium in sewage sludge (after mineralization)
- Food control — water for food production
Key parameters
| Parameter | Value |
|---|---|
| Wavelength | 228.8 nm |
| Detection limit (LOD) | ~0.05 µg/L |
| Limit of quantification (LOQ) | ~0.2 µg/L |
| Linear range | 0.2–5 µg/L |
| Atomization temperature | 1500–1800°C |
| Matrix modifier | NH₄H₂PO₄ + Mg(NO₃)₂ |
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
-
Preparation of vessels
PP/PTFE vessels soak in 10% HNO₃ (min. 24 h), rinse three times with ultrapure water. Do not use glass — cadmium adsorbs on glass.
-
Acidification and storage of samples
Add Suprapur HNO₃ to pH <2 (1 mL conc. HNO₃ per 100 mL sample). Store in PP at 4°C. Analysis within 14 days.
-
Preparation of standards
Prepare calibration series: 0, 0.5, 1, 2, 3, 5 µg/L Cd in 1% HNO₃. Prepare standards immediately before measurement.
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Setting temperature program
Drying: 110°C (30 s), 130°C (20 s). Pyrolysis: 600°C (20 s). Atomization: 1650°C (5 s, reading). Cleaning: 2400°C (3 s). Ar flow: 250 mL/min (stop at atomization).
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Dosing modifier
Autosampler doses 5 µL mixture NH₄H₂PO₄ 1% + Mg(NO₃)₂ 0.1% together with 15 µL sample into graphite tube.
-
Calibration
Measure standard series. Plot calibration curve (peak area vs concentration). R² ≥0.998. Check sensitivity (slope).
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Sample measurement
Measure samples in duplicates. Time of one measurement approx. 3 min (temperature program + cooling). Instrument works automatically.
-
Quality control
Every 10 samples: blank <LOD, control standard (recovery 90–110%), duplicate (RPD <15%). For new matrix — standard addition method.
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Verification of graphite tubes
Monitor tube condition — replace after 100–300 atomizations. Sign of wear is sensitivity drop and repeatability deterioration.
-
Calculation and reporting
Cd concentration from calibration curve. Result in µg/L with measurement uncertainty. For results <LOQ report as "<LOQ (0.2 µg/L)".
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| AAS spectrometer with graphite furnace | Agilent 280Z AA, Analytik Jena ZEEnit 700P, Shimadzu AA-7000 | 150 000–400 000 PLN |
| Autosampler | Agilent GTA 120, Analytik Jena MPE 60 | included with instrument |
| Hollow cathode lamp (HCL) Cd | Agilent Cd HCL, Heraeus, Photron — current 4 mA | 800–2 000 PLN |
| Graphite tubes with L'vov platform | Pyrolytically coated tubes with platform — improved sensitivity and repeatability | 50–150 PLN/pc. |
| Argon 5.0 (protective gas) | 50 L cylinder, two-stage regulator, purity 99.999% | 300–600 PLN/cylinder |
| PP/PTFE vessels | Polypropylene or PTFE containers — do not use glass (Cd adsorption) | 5–30 PLN/pc. |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Cd standard solution 1000 mg/L | 7440-43-9 | Certified CRM in 2% HNO₃ (e.g., Merck CertiPUR), traceable to NIST SRM |
| Nitric acid 65% Suprapur | 7697-37-2 | Ultrapure HNO₃ for acidifying samples (pH <2) and preparing dilutions |
| Modifier — NH₄H₂PO₄ | 7722-76-1 | Ammonium dihydrogen phosphate 1% (w/v) — prevents Cd volatilization with chloride matrices |
| Modifier — Mg(NO₃)₂ | 10377-60-3 | Magnesium nitrate 0.1% (w/v) — used together with NH₄H₂PO₄ for optimal stabilization |
| Ultrapure water | — | Resistivity ≥18.2 MΩ·cm, Milli-Q system — mandatory for trace Cd analysis |
| Diluted nitric acid 1% | — | For rinsing vessels and as blank — prepared from Suprapur HNO₃ and ultrapure water |
Health and safety (OHS)
- Cadmium compounds — carcinogenic cat. 1B (H350), toxic, cumulative — absolutely gloves, goggles, work under fume hood
- Concentrated nitric acid — corrosive, fuming — work under fume hood, acid-resistant gloves
- Graphite furnace — temperatures up to 2500°C — do not touch during operation and cooling
- Cd-containing waste — collect as hazardous waste, do not pour into sewage
- Argon — in closed rooms can displace oxygen, ensure ventilation
- Regular occupational exposure testing for Cd (cadmium in urine) for laboratory workers
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 15586:2005 — “Water quality — Determination of trace elements using atomic absorption spectrometry with graphite furnace”.
How does this method work?
A water sample (10–20 µL) is dosed into a graphite tube in the furnace. The temperature program includes: drying (110–130°C), pyrolysis (500–700°C with NH₄H₂PO₄ modifier — matrix removal without Cd losses), atomization (1500–1800°C — evaporation and atomization of cadmium), cleaning (2400°C).
What is the measuring range and accuracy?
Wavelength: 228.8 nm; Detection limit (LOD): ~0.05 µg/L; Limit of quantification (LOQ): ~0.2 µg/L; Linear range: 0.2–5 µg/L.
How long does the test take?
The times given for the individual stages add up to approximately 1 days 58 min. The procedure comprises 10 steps.
What equipment is required?
AAS spectrometer with graphite furnace, Autosampler, Hollow cathode lamp (HCL) Cd, Graphite tubes with L'vov platform, Argon 5.0 (protective gas), 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 (Cd ≤5 µg/L); Industrial wastewater monitoring (metallurgy, electroplating); Testing of groundwater at waste disposal sites; Control of cadmium in agricultural waters (influence of phosphorus fertilizers); Monitoring of surface waters (Water Framework Directive); Analysis of cadmium in sewage sludge (after mineralization); Food control — water for food production.
What safety precautions apply?
Cadmium compounds — carcinogenic cat. 1B (H350), toxic, cumulative — absolutely gloves, goggles, work under fume hood; Concentrated nitric acid — corrosive, fuming — work under fume hood, acid-resistant gloves; Graphite furnace — temperatures up to 2500°C — do not touch during operation and cooling; Cd-containing waste — collect as hazardous waste, do not pour into sewage; Argon — in closed rooms can displace oxygen, ensure ventilation; Regular occupational exposure testing for Cd (cadmium in urine) for laboratory workers.
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 15586.