HPLC or IC with UV Detection: Melamine in Pet Food & Milk
After the ongoing serious health challenges of melamine contamination in milk, milk products, and pet food for the last couple of years, the Chinese government has established standard test methods for the determination of melamine in milk and milk powders by HPLC-UV, LC-MS, and GC-MS methods. Currently, the HPLC-UV method is the most popular analytical method in milk product factories because of the high cost of operation and maintenance of GC-MS and LC-MS systems, and the labor-intensive derivatization required by GC-MS.
Melamine--a common component of plastic manufacturing--and cyanuric acid, a compound often used for pool chlorination, are closely related chemicals that, by themselves, are non-toxic. However, when combined these components form a toxic, insoluble crystal that causes kidney stones and can lead to renal failure. Because melamine has high nitrogen content, it has been added to low-quality wheat gluten and milk products to make them appear higher in protein. For those not familiar with this adulteration, here is a great WHO FAQ on melamine adulteration
Here we present two methods: one featuring reversed-phase HPLC with UV detection and other other using ion chromatography (IC).
HPLC & UV Detection of Melamine
Application Note 244, Determination of Melamine in Milk Powder by Reversed-Phase HPLC with UV Detection, (downloadable PDF) describes the determination of melamine in milk powder samples following the regulated method. Melamine was separated from other components in the powdered milk samples using our unique, high-efficiency, silica-based LC column (Thermo Scientific Acclaim 120 C18 column) and our HPLC system (Thermo Scientific UltiMate 3000 HPLC) with UV detection. The results of method detection limits (MDL), recovery, and permitted detection deviation match the requirements in the regulated method.
Application Note 221, Rapid Determination of Melamine in Liquid Milk and Milk Powder by HPLC on the Acclaim Mixed-Mode WCX-1 Column with UV Detection, (downloadable PDF) describes a simple HPLC method for rapid analysis of melamine in liquid milk and milk powder samples. The column used in this method provides reversed-phase and weak cation-exchange properties on a single column!
By the way, the Wadsworth Center of the New York State Department of Health, in Albany, New York, also used one of our mixed-mode columns (Thermo Scientific Dionex Acclaim Trinity P1 column) in the development of a HPLC method for the simultaneous separation of melamine and cyanuric acid residues in dairy products and pet foods. The Center developed this method in response to the acetonitrile shortage by using methanol (replacing acetonitrile) in the mobile phase. Dr. Tran, B.N. et. al,. describes this validated method in the publication titled, Use of Methanol for the Efficient Extraction and Analysis of Melamine and Cyanuric Acid Residues in Dairy Products and Pet Foods, published in J. Agric. Food Chem. 2010, 58, 101-107. It states that excellent linearity was achieved using methanol and the results are “comparable to those published by the FDA.”
Ion Chromatography Detection of Melamine
If you are using IC for your analysis, check out Application Note 231, Determination of Melamine in Milk by Ion Chromatography with UV Detection, (downloadable PDF) which demonstrates the determination of melamine in milk, powdered milk, and a milk-containing candy by IC using a cation-exchange column (Thermo Scientific Dionex IonPac CS17 column) and UV detection at 240 nm.
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