Stable isotope ratio analysis of carbon to distinguish sialic acid from freshly stewed bird's nest products.

Freshly stewed bird's nest products are easily adulterated with exogenous synthetic sialic acid to enhance the grade of the products and sell at high prices. This paper identifies the carbon stable isotope characteristics of sialic acid from natural and commercially synthetic sources using stable isotope ratio mass spectrometry (IRMS). Specifically, an off-line pretreatment technique combined with on-line LC-IRMS was developed to accurately determine C values of sialic acid in a freshly stewed bird's nest. This method has no obvious isotope fractionation and good reproducibility. EA-IRMS was used to determine the C values of commercial sialic acid. The results showed that the C values of sialic acid from natural and synthetic sources were -29.90% ± 0.42% and -16.26% ± 3.91%, respectively, with distinct carbon stable isotope distribution characteristics. By defining a C threshold value of -28.54% for natural SA, additional commercial SA from a minimum of 10% can be identified. Therefore, C was proposed as a suitable tool for verifying the authenticity of fresh stewed bird's nests on the market.