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ISO 26482 Hardmetals — Determination of Lead and Cadmium Content by FAAS and ICP-AES
Flame Atomic Absorption and ICP Spectrometric Method for Trace Heavy Metal Analysis in Cemented Carbides
ISO 26482:2010 specifies a robust analytical method for determining trace levels of lead (Pb) and cadmium (Cd) in hardmetals (cemented carbides). These heavy metals are strictly regulated under RoHS and global environmental directives, making accurate trace analysis essential for compliance and quality assurance in the powder metallurgy industry. The standard covers a measurement range from 0.0001 % to 0.1 % mass fraction.
The solvent extraction step using dithizone is the critical innovation in this method — it separates Pb and Cd from the dominant tungsten and cobalt matrix, eliminating severe spectral interferences that would otherwise render direct ICP or AAS measurements unreliable.
Principle of the Method
The test sample is first digested in a platinum dish using a mixture of nitric acid (HNO₃) and hydrofluoric acid (HF) to break down the hardmetal matrix. Precipitated tungstic acid is redissolved with sodium hydroxide. After masking residual cobalt with potassium cyanide (KCN), lead and cadmium are selectively extracted using dithizone in chloroform. The extracted analytes are then quantified by either flame atomic absorption spectrometry (FAAS) or inductively coupled plasma atomic emission spectrometry (ICP-AES).
Potassium cyanide is highly toxic — extreme care must be taken during the masking step. Work in a well-ventilated fume hood and follow all local safety regulations for cyanide handling and disposal.
Key Analytical Parameters
| Parameter | FAAS (AAS) | ICP-AES |
|---|---|---|
| Pb wavelength | 283.3 nm | 220.3 nm |
| Cd wavelength | 228.8 nm | 228.8 nm |
| Flame type | Fuel-lean air/acetylene | Argon plasma |
| Detection range | 0.0001 % – 0.1 % | 0.0001 % – 0.1 % |
| Sample mass | 1 g (nearest 0.0001 g) | 1 g (nearest 0.0001 g) |
Engineering Design Insights
Matrix Separation Strategy
The defining feature of ISO 26482 is the dithizone-based liquid-liquid extraction. Hardmetals are primarily tungsten carbide (WC) with cobalt binder — if the sample solution were introduced directly into the plasma or flame, the intense background from tungsten and cobalt would swamp the trace Pb and Cd signals. By selectively chelating Pb²⁺ and Cd²⁺ with dithizone at pH 9.2 and partitioning into chloroform, the analytes are concentrated while the matrix components remain in the aqueous phase. This achieves both separation and a 10× to 20× preconcentration factor.
Instrument Selection Guidance
FAAS is preferred for laboratories with limited budgets or when only a few elements need monitoring — it offers adequate sensitivity for the 0.0001 % – 0.1 % range at lower capital cost. ICP-AES provides multi-element capability, broader linear dynamic range, and better productivity for laboratories handling large sample volumes. The round-robin data in the standard shows that both techniques achieve precision better than 98 %, making them essentially interchangeable for compliance purposes.
Important Practical Considerations
Several subtle points affect measurement quality: (1) the platinum dish must be meticulously cleaned between samples to avoid cross-contamination; (2) the pH adjustment to 9.2 ± 0.2 is critical — outside this window, dithizone extraction efficiency drops sharply; (3) chloroform evaporation temperature must be controlled at 60 °C – 80 °C to prevent analyte loss; (4) blank tests must be run in parallel to correct for reagent impurities. These details separate reliable data from questionable results.
With proper execution, the method achieves relative standard deviations (RSD) of 5 % – 8 % for Pb and 0.8 % – 1.8 % for Cd across the working range, as demonstrated by the inter-laboratory round-robin study in Annex A.
FAQs
Q1: Can this method be used for other matrix types?
Yes, the principle is applicable to various organic and inorganic materials, though sample preparation steps may need adjustment. The standard notes that aliphatic isocyanates and other organic compounds can be analyzed with modified sample masses.
Yes, the principle is applicable to various organic and inorganic materials, though sample preparation steps may need adjustment. The standard notes that aliphatic isocyanates and other organic compounds can be analyzed with modified sample masses.
Q2: What is the advantage of using a platinum dish versus PTFE?
Platinum dishes withstand the perchloric acid fuming step at high temperatures, whereas PTFE beakers are limited to lower temperatures. The HF digestion requires a PTFE or platinum vessel — glass is attacked by HF.
Platinum dishes withstand the perchloric acid fuming step at high temperatures, whereas PTFE beakers are limited to lower temperatures. The HF digestion requires a PTFE or platinum vessel — glass is attacked by HF.
Q3: How should laboratory waste containing dithizone and chloroform be handled?
Chloroform is a suspected carcinogen and dithizone contains heavy metals. All organic waste must be collected separately, labeled, and disposed of through licensed hazardous waste contractors in accordance with local regulations.
Chloroform is a suspected carcinogen and dithizone contains heavy metals. All organic waste must be collected separately, labeled, and disposed of through licensed hazardous waste contractors in accordance with local regulations.
Q4: What is the shelf life of the dithizone reagent?
Dithizone solutions degrade under light. Store in brown bottles and prepare fresh weekly. A color change from green to brown indicates decomposition and requires fresh preparation.
Dithizone solutions degrade under light. Store in brown bottles and prepare fresh weekly. A color change from green to brown indicates decomposition and requires fresh preparation.
