Application Of Surface-Enhanced Raman Spectroscopy To Determination Of Thiocyanate,Melamine And Nitrite

In recent years, with the development of economic and the improvement of living standard, food safety becomes a growing concern in China. It is imperative to develop rapid and sensitive detection methods for assuring the interests and health of food consumers.In this study, a simple and rapid method based on surface-enhanced Raman spectroscopy (SERS) to detect thiocyanate and melamine in milk and milk powder was developed. Silver nanoparticles (AgNPs), sodium chloride (NaCl) and sodium hydroxide (NaOH) were used as the substrate, the aggregating agent and the alkaline adjusting agent for the SERS process, respectively. The characteristic peak of thiocyanate is different from melamine. Besides, determination of thiocyanate needs low concentration of NaCl, while determination of melamine need high concentration of NaCl and some mixing time under alkaline condition. So we designed a method to simultaneously determination thiocyanate and melamine in milk and milk powder. The determination conditions for SERS, including the amount of AgNPs, NaCl and NaOH, and the mixing time before measurement, were optimized. By the present method, good linear responses were obtained for thiocyanate and melamine in the concentration ranges of 2.00-191.00 mg L-1 andO.01-4.80 mg L-1 respectively, with correlation coefficients higher than 0.998. The detection method was applied to the simultaneous determination of thiocyanate and melamine in four spiked milk samples and three certified milk powder samples. The recoveries of thiocyanate and melamine in spiked milk samples were 95.15-100.47%and 94.43-102.84%, respectively. The relative standard deviations (RSDs) for determining melamine in certified milk powder samples were lower than 1.6%.A selective and sensitive method was established to detect nitrite in meat products and drinking water by SERS, based on the diazo reaction of nitrite with p-nitroaniline and 1-naphthylamine in acidic solution. The azo dye (4-(4-nitrophenyldiazenyl) naphthalene-1-aminium, NNA), which was derived from the diazo reaction, was determined by SERS using AgNPs as SERS substrates. The concentrations of nitrite in samples were finally calculated from the intensities of SERS signals generated by NNA in the testing solutions. The effects of several test parameters on the intensity of SERS signals, such as the volume of AgNPs solution and the mixing time of AgNPs and NNA, were investigated. The linear range of the method was 0.1-10.0 mg L-1. The limits of detection (LODs) were 0.01,0.03 and 0.05 mg L-1 at 720,1459 and 1609 cm-1, respectively. The method was applied to the determination of nitrite in meat products and drinking water samples, with recoveries in the range of 86.9-103.4%. By using the present method combined with a portable miniature Raman spectrometer, on-site determination of nitrite could be performed easily and efficiently.