Analysis of Dicyandiamide and Melamine in Milk Powders by LC/MS/MS Method

Significance of the topic

Concerns over melamine adulteration in dairy products have highlighted the need to detect not only melamine but also other nitrogen-rich adulterants such as dicyandiamide (DCD). High-sensitivity analytical methods are critical to ensure food safety and consumer protection.

Aims and Overview of the Application

This study aimed to develop and validate a rapid and sensitive UHPLC-ESI-MS/MS method for simultaneous quantification of DCD and melamine in infant milk powder matrices.

Methodology and Instrumentation

Sample pretreatment involved acid extraction with 2.5% formic acid, sonication, centrifugation, ultrafiltration (MWCO 5 kDa), PTFE filtration and dilution with acetonitrile. Analyses were performed on a Shimadzu LCMS-8040 triple quadrupole system coupled to UHPLC. Separation used an Alltima HP HILIC column (2.1×150 mm) at 40 °C with gradient elution: mobile phase A (0.1% formic acid in H2O/ACN 5:95 v/v) and B (20 mM ammonium formate in H2O/ACN 50:50 v/v), flow rate 0.2 mL/min, injection volume 5 µL. ESI positive mode monitored MRM transitions: DCD 85.1>68.05, 85.1>43.00; melamine 127.1>85.10, 127.1>68.05.

Main Results and Discussion

DCD and melamine eluted at 2.55 min and 6.29 min, respectively. Calibration curves in the 0.5–10 ng/mL range exhibited linearity (R2>0.997). Method limits of quantitation in matrix were 0.16 ng/mL for DCD and 0.15 ng/mL for melamine. Repeatability at 0.5 and 1.0 ng/mL levels showed RSDs <9.2%. Matrix effects ranged between 64–70% for DCD and 62–73% for melamine. Recoveries from pre- and post-spiked samples at 2.5 ng/mL were 102.9% for DCD and 104.6% for melamine, demonstrating accuracy in complex matrices.

Benefits and Practical Applications

• Sub-ppb sensitivity enables detection of trace residues.
• Simultaneous screening of multiple nitrogen-rich adulterants.
• Robust performance in infant milk powder matrices.
• Suitable for regulatory compliance and routine QA/QC in dairy analysis.

Future Trends and Possibilities

Further developments may include integration of high-resolution mass spectrometry for increased specificity, automated sample preparation workflows, expansion to multi-residue panels including other emerging adulterants, and portable MS platforms for on-site monitoring.

Conclusion

The validated UHPLC-ESI-MS/MS method on the Shimadzu LCMS-8040 offers rapid, precise and accurate quantitation of DCD and melamine in milk powders at sub-ppb levels, supporting enhanced food safety surveillance.

References

• Turnipseed S., Casey C., Nochetto C., Heller D.N., FDA Food, LIB No. 4421, Vol. 24, October 2008.
• McMahon S., Begley T.H., Diachenko G.W., Stromgren S.A., Journal of Chromatography A, 1220, 101–107 (2012).
• Natural News. Fonterra milk powder dicyandiamide adulteration report (2013).
• Lucas G.N., Sri Lanka Journal of Child Health, 42(2), 63–64 (2013).