🔬 Nickel in Water
Determination of nickel in water by flame atomic absorption spectrometry (FAAS) at wavelength 232.0 nm. Reference method for mg/L level concentrations.
Overview
Nickel (Ni) is a heavy metal of toxicological significance — it is one of the strongest contact allergens (nickel allergy affects about 10–15% of the population), and with chronic oral exposure can cause gastrointestinal disorders, kidney damage and carcinogenicity (nickel compounds — group 1 according to IARC). The permissible nickel concentration in drinking water is 20 µg/L (according to EU Directive 2020/2184 and MH Regulation).
Sources of nickel in waters are wastewater from electroplating (nickel plating), metallurgical industry (nickel steels, alloys), Ni-Cd and Ni-MH battery production, corrosion of stainless steel fittings, fossil fuel combustion, and natural leaching from nickel-bearing minerals.
Flame AAS (FAAS) is the basic method for determining nickel in waters at concentrations of 0.1–10 mg/L. The 232.0 nm resonance line is most commonly used, although the 341.5 nm line may be an alternative at higher concentrations. The acetylene-air flame provides sufficient energy for nickel atomization. The method is simple, fast and economical.
For concentrations below 0.02 mg/L (drinking water standard level), the FAAS technique is insufficient — GF-AAS (detection limit about 0.2 µg/L) or ICP-MS must be used. In laboratory practice, nickel in drinking water is determined mainly by GF-AAS or ICP-MS technique, and FAAS is used for wastewater control.
Method principle
A water sample acidified with HNO₃ is introduced through a nebulizer into an acetylene-air flame (about 2300°C). In the flame, the sample aerosol undergoes desolvation, thermal decomposition and atomization — free nickel atoms are formed. Ni atoms in the ground state absorb radiation from an HCL lamp at a wavelength of 232.0 nm (or alternatively 341.5 nm). Absorbance, proportional to Ni concentration (Beer-Lambert law), is measured by a detector and converted to concentration using a calibration curve.
Applications
- Control of electroplating wastewater (water permit)
- Monitoring of wastewater from metallurgy and metalworking
- Testing of surface waters (Water Framework Directive)
- Drinking water quality control (Ni ≤20 µg/L — by GF-AAS technique)
- Analysis of mine waters
- Control of stainless steel corrosion in water installations
- Testing of groundwater at waste disposal sites
Key parameters
| Parameter | Value |
|---|---|
| Wavelength | 232.0 nm |
| Flame type | acetylene-air (fuel-lean) |
| Detection limit (LOD) | ~0.005 mg/L |
| Limit of quantification (LOQ) | ~0.02 mg/L |
| Linear range | 0.02–5 mg/L |
| Sensitivity (characteristic concentration) | ~0.07 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 HNO₃ 65% to pH <2 (1 mL per 100 mL sample). Store in PE/PP containers at 4°C.
2. Preparation of standards
Prepare calibration series: 0 (blank), 0.1, 0.5, 1.0, 2.0, 5.0 mg/L Ni in 1% HNO₃ from 1000 mg/L solution.
3. Instrument setup
Install Ni HCL lamp. Set wavelength 232.0 nm, slit 0.2 nm, lamp current 4 mA. Stabilize lamp 15 min.
4. Ignition and flame optimization
Ignite acetylene-air flame (flow: air 13.5 L/min, acetylene 2.0 L/min). Set fuel-lean flame (blue).
5. Instrument calibration
Aspirate blank and standards sequentially. Plot calibration curve. Correlation coefficient R² ≥0.999.
6. Sample measurement
Aspirate sample (approx. 5 mL/min). Read absorbance after stabilization (5–10 s). Aspirate 1% HNO₃ between samples (10 s).
7. Quality control
Every 10 samples: blank (A <0.005), control standard (recovery 95–105%), duplicate (RPD <5%).
8. Dilution of high concentration samples
Dilute samples with concentration >5 mg/L to calibration range. Use 1% HNO₃ as diluting medium.
9. Work closure
Aspirate deionized water (2 min). Extinguish flame. Rinse nebulizer and spray chamber. Turn off lamp.
10. Calculation and result reporting
Ni concentration from calibration curve, considering 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 |
| Ni HCL lamp | Agilent Ni HCL, Heraeus, Photron — current 4 mA, slit 0.2 nm | 600–1 500 PLN |
| Technical acetylene | C₂H₂ 40 L cylinder, purity 2.6 | 200–400 PLN/cylinder |
| Compressed air | Oil-free compressor with dryer and filter | 3 000–8 000 PLN |
| Sample aspiration system | Concentric nebulizer + Scott-type spray chamber | included with instrument |
| Burner exhaust system | Exhaust system with fan, connected to ventilation | 2 000–5 000 PLN |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Ni standard solution 1000 mg/L | 7440-02-0 | Certified CRM in 2% HNO₃ (Merck CertiPUR), traceable to NIST SRM |
| Nitric acid 65% analytical grade | 7697-37-2 | HNO₃ for acidifying samples and preparing standards; sample pH <2 |
| Deionized water | — | Quality at least grade 2 according to PN-EN ISO 3696 |
| Rinse solution 1% HNO₃ | — | For aspiration between samples to eliminate memory effect |
Health and safety (OHS)
- Nickel compounds — carcinogenic (H350i — inhalation), strongly sensitizing (H317) — gloves and goggles mandatory
- Acetylene — flammable and explosive gas, cylinder in vertical position, away from heat sources
- Nitric acid — corrosive, work under fume hood
- AAS flame — temperature ~2300°C, burner exhaust hood mandatory
- Nickel-containing waste — collect separately, do not pour into sewage