Overview
ISO 5738:2004 (IDF 76:2004) - "Milk and milk products - Determination of copper content - Photometric method" - specifies a reference photometric method for measuring copper in a wide range of dairy matrices. The standard covers milk, cream, butter and butterfat, milk powders, evaporated and condensed milks, ice‑cream, cheeses (hard to soft), processed cheese, and caseins/caseinates. It is designed for accurate, comparable determination of copper content in dairy testing, with suitability down to 0.05 mg/kg in butter and butterfat.
Key topics and technical requirements
- Analytical principle: organic matter is digested (nitric + sulfuric acids), the solution is neutralized, copper is complexed as a diethyl dithiocarbamate salt, extracted into amyl acetate (or xylene), and quantified photometrically.
- Instrumentation: spectrophotometer operating at 436 nm with 10 mm cells; analytical balance; Kjeldahl digestion flasks; temperature‑controlled water baths.
- Reagents: copper‑free, analytical grade reagents including concentrated/dilute nitric and sulfuric acid, sodium diethyl dithiocarbamate solution, citrate/EDTA solution, amyl acetate (dried/distilled), and prepared copper standard solutions.
- Contamination control: stringent requirement for copper‑free glassware, distilled solvents, and procedures to avoid environmental copper contamination during sampling and analysis.
- Interferences and checks: bismuth and tellurium interfere and the method includes checks and removal steps (see clause 8.6). A blank test, calibration curve and multiple determinations are specified for reliable results.
- Performance and quality: clauses on precision (repeatability, reproducibility) and an interlaboratory test (Annex A) provide performance context for laboratories.
Applications and users
- Who uses it: national reference laboratories, regulatory and food safety authorities, dairy quality control (QC) labs, contract testing laboratories, and research groups working with trace metals in dairy.
- Why use it: provides a validated, internationally recognized reference method for compliance testing, method validation, interlaboratory comparability, and routine QC where reliable copper quantification is required.
- Practical value: suitable for low‑level copper monitoring in sensitive dairy products (e.g., butterfat), verification of supplier/raw material quality, and investigation of contamination sources.
Related standards
- ISO 707 - Sampling of milk (recommended sampling practices to obtain representative laboratory samples).
- IDF 68 - Details on butterfat (referenced for fat removal/preparation).
- ISO/IDF precision and analytical standards referenced within ISO 5738:2004 (see clause 2 and clause 10 for interlaboratory precision data).
Keywords: ISO 5738:2004, copper determination, photometric method, milk and milk products, dairy testing, copper content, spectrophotometry 436 nm, reference method.