Development and Optimization of a SERS Method for On-site Determination of Nitrite in Foods and Water

A rapid, sensitive, and selective detection method of nitrite in foods and water was established by surface-enhanced Raman spectroscopy (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 citrate-coated silver nanoparticles (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. By using the present method combined with a portable miniature Raman spectrometer, on-site determination of nitrite could be performed easily and efficiently. The effects of several experimental parameters on the intensity of SERS signals, such as the volume of AgNP 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, 1,459, and 1,609 cm^?1, respectively. The method was applied to the determination of nitrite in real food and water samples, with recoveries in the range of 86.9–103.4 % and relative standard deviations (RSDs) less than 9.64 %.