Determination of Melamine in Liquid Milk and Milk Powder by Titania-Based Ligand-Exchange Hydrophilic Interaction Liquid Chromatography

Abstract

A simple and rapid high-performance liquid chromatography (HPLC) procedure for the analysis of melamine in liquid milk and milk powder has been developed. Decrease of acetonitrile percentage and phosphate buffer concentration in mobile phase, and lowering of buffer pH and column temperature would benefit the retention of melamine on titania. Taking advantage of the ligand-exchange and hydrophilic interaction mixed retention mode on bare titania column, neither complex pretreatment nor ion-pair reagent was required. The whole analysis for one sample including sample pretreatment and HPLC analysis could be accomplished within 30 min. The method presented good linearity (R 2 = 0.9998) in a wide range of 0.02–10 μg mL−1. The limit of detection (3σ) and limit of quantification (10σ) of the method were 6 and 20 μg L−1, respectively, which were equivalent to 15 and 50 μg kg−1 melamine in liquid milk, 60 and 200 μg kg−1 melamine in milk powder, respectively. Such sensitivity could be compared with those obtained by HPLC with solid-phase extraction or HPLC coupled with tandem mass spectrometry and was adequate for the screening of melamine in tainted dairy products. The repeatability (RSDs) of the retention times and peak areas of 11 replicate detections of 1.0 μg mL−1 melamine were 0.32% and 2.5%, respectively. The intermediate precision on three consecutive days (RSDs, n = 6) of the retention times and peak areas were 1.1% and 2.3%, respectively. The recovery of spiked melamine in dairy samples ranged from 95.2% to 105%. The simplicity, sensitivity and rapidity of the proposed method make it an effective alternative detecting technique for melamine.