Determination of Melamine in Fresh Milk with Hollow Fiber Liquid Phase Microextraction Based on Ion-Pair Mechanism Combined with High Performance Liquid Chromatography

Abstract

In this work, a novel analytical method based on hollow fiber liquid phase microextraction (HF-LPME) and high performance liquid chromatography (HPLC) was developed for the analysis of melamine in fresh milk. The conditions of the HF-LPME were investigated and optimized. As a result, a supported liquid membrane containing 6-undecanone and di-2-ethylhexyl phosphoric acid (D2EHPA) was selected. The extractions were made from 25 mL aqueous donor phase (prepared from milk) with pH 5.0 to a more acidic acceptor phase (36 µL 1 M HCl) and the mass transfer was driven by the proton gradient between these phases. Other optimum conditions of the HF-LPME were 60 min extraction time at 360 rpm stirring rate and an extraction factor of 21 times (extraction efficiency 3%) was obtained. The C8 column was operated at 1 mL/min at room temperature and the UV detection wavelength was 240 nm for HPLC. The mobile phase was 10 mM sodium n-octanesulfonate (pH 3.0) mixed with acetonitrile (85:15, v/v). The relative recovery of melamine for milk samples spiked with 0.5–25 mg/kg was in the range of 89.1–120.6% with the RSDs (n = 4) of 4.0–8.5%. It was found that the proposed method provided a linear range from 0.1 to 50 mg/kg (r ²  = 0.9993), method detection limit (MDL) of 0.003 mg/kg and method quantification limit (MQL) of 0.01 mg/kg. The obtained results demonstrated that HF-LPME combined with HPLC is a simple and cheap method for the determination of melamine in fresh milk.

Keywords:

• HF-LPME
• Hollow fiber liquid phase microextraction
• HPLC
• Melamine
• Milk

Acknowledgments

Funding was provided by Education and Teaching Projects of Polytechnic College of Hebei University of Science and Technology (No. 2010Y03). Technical support from Abolfazl Saleh, Teris A. van Beek, Murtaza Hyder, Ayman Rabayah, and Estelle Larsson are gratefully acknowledged.