Abstract: 【Objective】Vanillin (3-Methoxy-4-hydroxybenzaldehyde) is a kind of food additives with rich milk flavor that is commonly used in infant food. Excessive use of vanillin may cause liver and kidney damage in infants. Therefore the detection method and the control of vanillin in infant milk powder has an important practical significance. At present, the government has not released relevant inspection standards, also have no on-site test methods. In this paper, a rapid qualitative and quantitative analysis of vanillin in infant formulas milk powder was set up by surface enhanced Raman spectroscopy, which is stable, reliable and suitable for the on-site detection, thus providing technical support for government regulations.【Method】In this study, the optimization of the pretreatment, the synthesis of enhanced substrates and the choice of operating parameters were studied, respectively. By comparing the effect of different extraction solvents on extraction, the optimum conditions were established. The effect of different sizes of Au nanoparticles on SERS intensity and the influence of pH or the ionic strength on the testing solutions were investigated in order to obtain the optimum enhanced substrates and detection conditions 【Result】The optimum pretreatment method was described as follows: Firstly, the proteins in the matrix were removed by using lead acetate solution. Secondly, the vanillin was extracted by using methylene chloride. Finally, the extraction was purified by sodium hydroxide solution with pH of 9. With approximate 58 nm of gold colloidal solution as enhanced substrates, 200 μL 1% salpeter solution and 50 μL 1% potassium nitrate solution were used in order to make the characteristic Raman signal of vanillin stronger and the qualitative and quantitative analysis available. The 1 149, 1 497 and 1 542 cm-1 Raman shifts were chosen as the qualitative basis. The intensity of 1 531 cm-1 peak was used as a normalization standard. The optimized method has a good linear correlation (calibration coefficient=0.9913) between the intensity of quantitative Raman peak and the concentration of vanillin over a large working range (30-300 μg•mL-1). The limit of detection (LOD) was 10 μg•mL-1. The recoveries for vanillin spikes (50, 100, 200 μg•mL-1) in milk powder ranged from 80.5% to 86.9% and the relative standard deviations (RSD) were lower than 8.6%.【Conclusion】The actual samples purchased from the local markets were tested by the method of this study and the latest reported methods. The established method was true and reliable compared with the latest reported methods, which is suitable to the on-site and rapid detection of vanillin in infant formulas milk powder with the advantages of simple sample preparation and fast analysis of 5 min per sample.

Key words: surface enhanced Raman spectroscopy , infant formulas , vanillin , rapid determination