Quantification of Melamine in Milk and Dairy Products by Liquid Chromatography after a Simple Sample Clean-Up Procedure

Abstract

In this work, a simple procedure of melamine determination in dairy products is reported. This is based first on melamine extraction from dairy products by 1% acetic acid, sonication, centrifugation and filtration by 0.45 µm filter. The proposed method has a low detection limit (0.50 mg kg−1), high accuracy (%recovery 98.9%), high precision (%RSD range 1.6–2.5%), high calibration sensitivity (19,335 (mg l−1)−1), and a wide dynamic range (1.0–50.0 mg l−1). Melamine was accurately quantified in spiked powdered milk, infant powder milk, full-fat liquid milk, fat-free liquid milk, local yoghurt, and local soft cheese (spiking levels 0.5, 50, and 1000 mg kg−1). The samples have variable amounts of fat (0–29%) and protein (3–23%) indicating the wide applicability of the proposed method. The %recoveries with %RSD were 78.2–103.6(2.5), 92.7–98.8(4.7), 79.3–101.5(3.8), 86.3–101.0(2.6), 78.0–89.2 (8.3), and 91.8–103.8(3.2) for soft cheese, yoghurt, powdered milk, infant powder, full-fat liquid milk, fat-free liquid milk, respectively. Practical Applications A simple and accurate analytical method was proposed for quick melamine detection and quantification in milk and dairy products having variable amounts of fat (0–29%) and protein (3–23%) with minimal sample clean up. The method is mainly based on melamine extraction by 1% acetic acid, sonication, centrifugation for 4.0 min, and filtration by 0.45 μm cellulose filter. The method could detect melamine down to 0.50 mg kg−1 with acceptable accuracy and precision (2.5 mg kg−1 is the upper limit of melamine in milk and dairy products). The proposed method was found effective for melamine quantification at three variable spiked levels (0.5, 10, and 1000 mg kg−1) in local soft cheese, local yoghurt, powdered milk, infant powder, full-fat liquid milk, fat-free liquid milk with %recoveries (%RSD) of 78.2–103.6 (2.5), 92.7–98.8 (4.7), 79.3–101.5 (3.8), 86.3–101.0 (2.6), 78.0–89.2 (8.3), and 91.8–103.8(3.2), respectively.