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ISO 27085:2009 — Animal Feeding Stuffs — ICP-OES Determination of Minerals and Trace Elements
ICP-AES analysis of calcium, phosphorus, trace elements and contaminants in animal feed
1. Scope and Principle of ICP-AES Analysis for Animal Feed
ISO 27085:2009 specifies an inductively coupled plasma atomic emission spectroscopic (ICP-AES) method for determining minerals and trace elements in animal feeding stuffs. The method covers 14 elements essential for nutritional assessment and safety monitoring: calcium, sodium, phosphorus, magnesium, potassium, iron, zinc, copper, manganese, cobalt, molybdenum, arsenic, lead, and cadmium. It applies to both major minerals present at percentage levels and potentially toxic trace elements, making it versatile for nutritional labelling, quality control, and regulatory compliance. The standard was developed through CEN/TC 327 and adopted by ISO/TC 34/SC 10 under a fast-track procedure.
The method detection limit depends on the sample matrix and instrument configuration, with a limit of quantification of 3 mg/kg or lower for most elements. ICP-AES offers multi-element analysis capability with wide dynamic range across several orders of magnitude, making it ideal for feed testing where both major minerals above 5 percent mass fraction and trace elements at mg/kg levels need quantification in a single analytical run. The standard notes that for products with very high mineral content exceeding 5 percent, alternative analytical techniques may provide better accuracy.
ICP-AES offers simultaneous multi-element analysis across a wide dynamic range, ideal for animal feed testing where both major minerals at percentage levels and trace elements at mg/kg levels must be quantified in a single run. Modern instruments can analyze all 14 elements in under 3 minutes per sample after digestion.
| Element Group | Elements | Typical Concentration Range | Primary Application |
|---|---|---|---|
| Major Minerals | Ca, Na, P, Mg, K | 0.1% to 5% | Nutritional formulation |
| Trace Elements | Fe, Zn, Cu, Mn, Co, Mo | 1 to 500 mg/kg | Micronutrient assessment |
| Contaminants | As, Pb, Cd | 0.1 to 10 mg/kg | Safety monitoring |
2. Analytical Procedure and Quality Control Requirements
The procedure involves sample digestion using mineral acids, typically nitric acid with hydrogen peroxide, followed by ICP-AES measurement at element-specific wavelengths. The standard provides detailed guidance on wavelength selection to minimize spectral interferences common in complex feed matrices containing high levels of aluminium, iron, or calcium. Matrix effects can cause signal suppression or enhancement, and the standard recommends matrix-matched calibration standards for accurate quantification. Sample digestion must be complete — undigested organic matter can cause physical interferences including nebulizer clogging and carbon buildup on the torch.
Quality control requirements are comprehensive: reagent blanks to check contamination, certified reference materials (CRMs) for accuracy verification, duplicate analyses for precision assessment, and spike recovery tests for matrix effect evaluation. Acceptance criteria include CRM recoveries typically within 90 to 110 percent depending on concentration level, duplicate relative standard deviation below 10 percent, and spike recoveries within 80 to 120 percent. The standard specifies the limit of detection as three times the standard deviation of blank determinations and the limit of quantification as ten times, providing clear statistical definitions for method performance characterization across different sample types.
Spectral interferences are a significant concern in ICP-AES analysis of animal feeds containing high levels of Al, Fe, or Ca. The standard recommends using interference correction equations or alternative wavelengths when significant overlaps are identified. Matrix-matched calibration is strongly advised for complex sample types such as mineral premixes and compound feeds with diverse ingredient compositions.
Precision data from interlaboratory studies are provided in informative annexes. Repeatability relative standard deviation (RSDr) typically ranges from 2 to 8 percent depending on element and concentration, while reproducibility relative standard deviation (RSDR) ranges from 6 to 20 percent. The standard includes detailed guidance on interference correction and quantification strategies for each element, with specific notes on arsenic determination where hydride generation ICP-AES may be needed for very low concentrations. Sample preparation guidelines reference ISO 6498 for sample grinding and homogenization procedures.
3. Engineering Insights for Feed Analysis Laboratories
Successful implementation requires careful attention to sample preparation — the largest source of analytical variability. Microwave-assisted digestion systems are recommended for their efficiency, consistency, and reduced contamination risk compared to conventional hot plate digestion. Laboratories should establish instrument-specific performance criteria including detection limits, precision, and long-term stability monitored through control charting. Regular maintenance of the sample introduction system — nebulizer, spray chamber, torch, and peristaltic pump tubing — is critical for reliable results, as these components are prone to salt deposition, blockage, and wear.
The multi-element capability of ICP-AES makes it highly cost-effective for feed analysis laboratories. A single method can replace multiple traditional wet chemistry procedures for individual elements, reducing reagent consumption, analyst time, and overall cost per sample. However, the standard cautions that for high-mineral products exceeding 5 percent calcium or phosphorus, alternative techniques such as titrimetric or gravimetric methods may provide better accuracy. Laboratories should validate the method for their specific sample types and instrument configurations before routine use, establishing their own method performance characteristics rather than relying solely on the interlaboratory data provided in the standard.
Laboratories implementing ISO 27085 can achieve significant productivity improvements — analyzing 14 elements simultaneously in under 3 minutes per sample after digestion. Compared to traditional atomic absorption spectroscopy (AAS) which analyzes one element at a time, ICP-AES improves laboratory throughput by 5 to 10 times while maintaining comparable or better detection limits for most feed-relevant elements.
The informative annexes provide valuable guidance on interference correction strategies and quantification approaches. For arsenic determination at very low concentrations, the standard notes that hydride generation ICP-AES may provide improved detection limits compared to conventional pneumatic nebulization. The annex on interlaboratory test results allows laboratories to benchmark their performance against international study data. The standard also addresses the determination of elements in mineral additives and premixtures where high concentration differences between analytes present additional analytical challenges requiring careful wavelength selection and detector linearity verification.
FAQs
Q: What is the detection limit for lead determination in animal feed by this method?
A: The typical limit of quantification is 3 mg/kg or lower for most elements, depending on the sample matrix and instrument configuration. Detection limits vary by element and instrument.
A: The typical limit of quantification is 3 mg/kg or lower for most elements, depending on the sample matrix and instrument configuration. Detection limits vary by element and instrument.
Q: Can this method be used for high-mineral products like calcium supplements?
A: Yes, but the standard notes that other more precise techniques may be better for products with mineral content exceeding 5 percent mass fraction due to potential accuracy limitations at high concentrations.
A: Yes, but the standard notes that other more precise techniques may be better for products with mineral content exceeding 5 percent mass fraction due to potential accuracy limitations at high concentrations.
Q: How should samples be prepared for ISO 27085 analysis?
A: Samples are digested with nitric acid and hydrogen peroxide using either conventional hot plate or microwave-assisted digestion systems following the procedures in Clause 8. Complete digestion is critical for accurate results.
A: Samples are digested with nitric acid and hydrogen peroxide using either conventional hot plate or microwave-assisted digestion systems following the procedures in Clause 8. Complete digestion is critical for accurate results.
Q: Is ICP-MS also covered by this standard?
A: No, this standard specifically covers ICP-AES (also called ICP-OES). ICP-MS analysis would require a different standard method, though similar sample preparation procedures may apply.
A: No, this standard specifically covers ICP-AES (also called ICP-OES). ICP-MS analysis would require a different standard method, though similar sample preparation procedures may apply.
