Trace-Level Analysis of Melamine in Milk Products on Agilent 7890A/5975C GC/MSD Using a New Agilent J&W DB-5ms Ultra Inert Column and SampliQ SCX Cartridges

Significance of the Topic

The melamine contamination crisis highlighted the critical need for sensitive, reliable methods to detect trace levels of melamine in milk and dairy products. Accurate quantification at low concentrations is essential to ensure consumer safety, comply with regulatory limits, and protect public health.

Objectives and Study Overview

This study aims to develop and validate a gas chromatography–mass spectrometry (GC/MS) method for quantitative determination and confirmation of melamine residues in milk products. The approach leverages a novel ultrainert GC column and mixed-mode solid‐phase extraction to achieve trace‐level sensitivity and robust matrix cleanup.

Methodology

• Sample extraction: 5 g milk powder was treated with 1 % trichloroacetic acid and lead acetate, then centrifuged to remove precipitated proteins.
• SPE cleanup: Agilent SampliQ SCX cartridges were conditioned (methanol, water), loaded with supernatant, washed (water, methanol), and eluted with 5 % ammonium hydroxide in methanol. Cartridges were dried under nitrogen.
• Derivatization: Dried extract was reacted with 600 µL pyridine and 200 µL BSTFA+1 % TMCS at 70 °C for 30 min to form trimethylsilyl derivatives.
• Calibration: Standard solutions of melamine tri‐TMS (0.025–2.000 µg/mL) were prepared to assess linearity.

Instrumentation Used

• GC/MS system: Agilent 7890A GC coupled to 5975C MSD with 7683 autosampler.
• Column: Agilent J&W DB-5ms Ultra Inert (30 m × 0.25 mm × 0.25 µm).
• Injection: 1 µL split 3:1 at 250 °C; helium carrier at 1.3 mL/min.
• Oven program: 75 °C (1 min) ramped at 30 °C/min to 300 °C (2 min).
• MS conditions: EI source; SIM/scan mode; transfer line 290 °C; source 230 °C; quadrupole 150 °C.
• Quantitative ions monitored: m/z 342 (quantifier), 327, 171, 99.

Main Results and Discussion

• SPE cleanup removed most matrix interferences, yielding sharp, symmetric peaks and reducing detector contamination compared to direct methanol extracts.
• Chromatographic inertness of the DB-5ms Ultra Inert column enhanced signal‐to‐noise ratios and reproducibility for active analytes.
• Calibration was linear from 0.025 to 2.000 µg/mL (r = 0.9986).
• Average recoveries at 0.080, 0.800, and 1.600 mg/kg were 82.1–82.8 % with RSDs below 5 % (n = 6).
• Limit of detection was 0.0025 mg/kg in milk matrix (S/N = 3), meeting trace‐level requirements.

Benefits and Practical Applications

The method combines cost‐effective GC/MS instrumentation with straightforward SPE cleanup to deliver reliable trace‐level screening for melamine. It is well suited for routine quality control and food‐safety laboratories, enabling rapid confirmation of compliance with regulatory standards.

Future Trends and Opportunities

• Integration of automated on‐line SPE to increase throughput and reduce manual handling.
• Application of high‐resolution MS for enhanced selectivity in complex matrices.
• Expansion to multiplexed screening of multiple adulterants in dairy and other food products.
• Development of more inert stationary phases to further improve sensitivity for polar analytes.

Conclusion

The presented GC/MS method, utilizing SampliQ SCX SPE and the Agilent J&W DB-5ms Ultra Inert column, achieves sensitive, accurate, and reproducible trace‐level analysis of melamine in milk products. Its robust cleanup and high inertness support reliable quantification down to the low microgram per kilogram range.

References

1. GB/T 22388-2008. Determination of Melamine in Raw Milk and Dairy Products. Standards Press of China.
2. U.S. Food and Drug Administration. GC-MS Screen for the Presence of Melamine and Cyanuric Acid. Revised April 25, 2007.
3. Agilent Technologies. Agilent J&W Ultra Inert GC Columns: A New Tool to Battle Challenging Active Analytes. Publication 5989-8685EN, May 29, 2008.
4. Agilent Technologies. Rapid Screening of Melamine and Cyanuric Acid in Milk Products Using Agilent J&W HP-5ms GC Column and Agilent 7890A/5975C GC/MSD with Column Backflushing. Publication 5989-9866EN, October 2008.