Analysis of Melamine and Cyanuric Acid in Food Matrices by LC–MS–MS

Peter Varelis,¹ Jonathan Beck,² Kefei Wang² and Dipankar Ghosh,²

¹ National Center for Food Safety and Technology, Illinois Institute of Technology, Illinois, USA, ² Thermo Fisher Scientific, San Jose, California, USA.

Introduction

In March 2007, several North American manufacturers of pet food voluntarily issued nationwide recall notices for some of their products that were reportedly associated with renal failure in pets. The raw material wheat gluten, used to manufacture the pet food, was imported from China and was identified as the source of contamination.

Figure 1

Although initial reports suggested that contamination was confined to pet food, further investigations revealed that melamine-tainted fodder may have been used to feed animals intended for human consumption.^1,2 In particular, it was discovered that melamine-contaminated ingredients had been used to prepare feed for chickens, swine and catfish.^1,2 Consequently, the US Food and Drug Administration (FDA)¹ and the US Department of Agriculture (USDA)² have developed methods for the analysis of melamine residues in animal tissue. This note describes a method for the detection and analysis of melamine and cyanuric acid in food matrices by LC–MS–MS using the Thermo Scientific TSQ Quantum Ultra mass spectrometry system.

Sample Preparation

Solid samples were homogenized using an Ultra-Turrax (IKA-Werke GmbH & Co. KG, Staufen, Germany) homogenizer. After extraction into aqueous 1:1 Water:MeOH and addition of the internal standards, the samples were prepared by off-line ion exchange chromatography using SPE cartridges.

Liquid Chromatography

Aliquots (10–25 µL) of the above extract were chromatographed on a BioBasic AX (Thermo Fisher Scientific, Bellefonte, Pennsylvania, USA) analytical column (2.1 × 150 mm, 5 µm), which was kept at 30 °C in an oven.

MS Conditions

MS: TSQ Quantum Ultra

Source: Heated Electrospray (H-ESI)

Ionization: Positive ESI

SRM Transitions

Melamine: Melamine ¹³ C₃ (Internal Standard):

m/z 127→68 @ 32 eV m/z 130→70 @ 32 eV

m/z 127→85 @ 18 eV m/z 130→87 @ 18 eV

Cyanuric acid: Cyanuric acid ¹³ C₃:

m/z 128→42 @ 17 eV m/z 131→43 @ 17 eV

m/z 128→85 @ 11 eV m/z 131→87 @ 11 eV

Results

Calibration curves ranged from 1–1000 ppb for melamine and cyanuric acid, respectively. Melamine and cyanuric acid were spiked into a matrix of catfish and processed as described above. A chromatogram of this sample, spiked at 10 ppb for melamine and 50 ppb for cyanuric acid, is shown in Figure 1. Very low noise is observed, emphasizing the effectiveness of the clean-up procedure for a complicated matrix.

Conclusion

A simple, sensitive, and specific method for the detection and quantification of melamine and cyanuric acid in food matrices has been demonstrated. The method is robust and allows for the analysis of a large number of samples, without degradation in column performance.

References

1. Weise, E. and Schmit, J. Melamine in pet food may not be accidental. USA Today. Available at www.usatoday.com/money/industries/2007-04-24-fda-pet-food-probe_N.htm.

2. Fish on US fish farms fed melamine-contaminated feed; FDA discovers contaminated food products from China mislabeled. American Veterinary Medical Association. Available at www.avma.org/press/releases/070508_petfoodrecall.asp. Accessed 10 December 2007.

Ultra-Turrax is a registered trademark of IKA-Werke GmbH & Co. KG. The TSQ Quantum Ultra and BioBasic trademarks are the property of Thermo Fisher Scientific Inc. and its subsidiaries.

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