Determination of Melamine Residue in Milk Powder and Egg Using Agilent SampliQ Polymer SCX Solid Phase Extraction and the Agilent 1200 Series HPLC/UV

Significance of the Topic

The 2008 melamine contamination crisis underscored the need for reliable analytical methods to detect trace levels of melamine in food products. Milk powder and egg are widely consumed ingredients, and ensuring they meet regulatory limits for melamine is essential for public health and international trade compliance.

Objectives and Study Overview

This study aimed to implement and optimize the Chinese national standard GB/T 22388-2008 for determining melamine residues in milk powder and egg. The method combines polymeric strong cation exchange (SCX) solid phase extraction (SPE) with high-performance liquid chromatography and UV detection (HPLC/UV) to achieve sensitive, accurate quantification of melamine at regulatory levels.

Methodology

• Sample preparation: 2 g of homogenized milk powder or egg is extracted with 15 mL 1% trichloroacetic acid and 5 mL acetonitrile, followed by sonication, shaking, centrifugation, and filtration.
• SPE cleanup: Agilent SampliQ SCX cartridges are conditioned with methanol and water. A 10 mL aliquot of diluted extract is loaded, washed sequentially with water and methanol, then dried under vacuum. Analytes are eluted with 5% ammonium hydroxide in methanol, evaporated under nitrogen, reconstituted in mobile phase, and filtered.

Instrumentation Used

• HPLC system: Agilent 1200 Series with diode array detector at 240 nm.
• Analytical column: ZORBAX SB-C8 (5 µm, 250 × 4.6 mm).
• Mobile phase: isocratic mixture of acetonitrile and 10 mmol/L citric acid/10 mmol/L sodium octanesulfonate buffer (15:85, pH 3.0).
• Flow rate: 1.0 mL/min; column temperature: 40 °C; injection volume: 20 µL.

Main Results and Discussion

Calibration was linear over 1–20 mg/kg for melamine with correlation coefficient of 0.9999. The limit of detection was 10 µg/kg, well below the maximum residue limit of 2 mg/kg. Recovery tests at 2, 5, and 10 mg/kg spiking levels yielded 84–87% in milk powder and 93–96% in egg, with RSDs below 3%. Chromatograms showed clean baselines and no matrix interference, confirming method specificity and robustness.

Benefits and Practical Applications

The Agilent SampliQ SCX SPE-HPLC/UV workflow offers a rapid, cost-effective approach for routine monitoring of melamine in dairy and egg matrices. Its high recoveries, low detection limits, and minimal matrix effects make it suitable for quality control laboratories and regulatory compliance testing.

Future Trends and Opportunities for Application

Integration of this SPE procedure with tandem mass spectrometry (LC-MS/MS) could further lower detection limits and expand applicability to complex food matrices. Automation of the SPE steps and miniaturization of the workflow may increase throughput for large-scale screening programs.

Conclusion

The described method meets regulatory requirements for melamine residue determination in milk powder and egg, combining effective SPE cleanup with reliable HPLC/UV quantification. Its simplicity, precision, and sensitivity support broad adoption in food safety laboratories.

Reference

• GB/T 22388-2008, Determination of Melamine in Raw Milk and Dairy Products