Detection of melamine in liquid milk using surface-enhanced Raman scattering spectroscopy

Melamine, a nitrogen-rich chemical, has recently caused enormous economic losses to the food industry due to the cases of milk products adulterated by melamine. This has led to an urgent need of rapid and reliable methods for detection of melamine in food. In this study, surface-enhanced Raman scattering (SERS) spectroscopy was used to detect melamine in liquid milk. The sample preparation with liquid milk is very easy; it has to be only diluted with double-distilled water followed by centrifugation. By using a silver colloid, at least a 10(5)-fold enhancement of the Raman signal was achieved for the measurement of melamine. The limit of detection by this method was 0.01 mu g ml(-1) for melamine standard samples. Based on the intensity of the Raman vibrational bands normalised to that of the band at 928 cm(-1) (CH2), an external standard method was employed for quantitative analysis. The linear regression square (R-2) of the curve was 0.9998; the limit of quantitation using this approach was 0.5 mu g ml(-1) of melamine in liquid milk; the relative standard deviation was <= 10%; and recoveries were from 93 to 109%. The test results for SERS were very precise and as good as those obtained by liquid chromatography/tandem mass spectrometry. The method was simple, fast(only needs about 3 min), cost effective, and sensitive for the detection of melamine in liquid milk samples. Therefore, it is more suitable for the field detection of melamine in liquid milk. Copyright (C) 2010 John Wiley & Sons, Ltd.