Determination of 4 Characteristic Aldehyde Compounds in Infant Formula by Gas Chromatography with Precolumn Derivatization

In order to provide accurate quantitative means for the shelf life index of infant formula, the work as mentioned by the article was carried out. The sample (about 2.0 g) was taken, and 10.0 mL of derivative solution ［a mixture of 0.5 g·L^-1 of 2,4-dinitrophenylhydrazine acetonitrile solution and phosphate buffer solution (pH 5) at volume ratio of 1∶1］ and 5.0 mL of acetonitrile-saturated n-hexane solution were added. After mixing well and centrifugation, the lower solution was placed in a water bath at 60 ℃ to react for 1 h, and 5 g of ammonium sulfate was added to settle for 5 min, then 5.0 mL of cyclohexane was added to vortex for 1 min. After centrifugation, the supernatant was taken and dried with about 1.0 g of anhydrous sodium sulfate for gas chromatography analysis. It was shown that linear relationships between values of mass of benzaldehyde, 2,4-nonadienal, 2-undecanonal and 1-nonanal and their peak areas were kept within 10 μg, with detection limits (3S/N) in the range of 0.05-0.1 mg·kg^-1. Test for recovery was made on blank sample, giving values of recovery in the range of 85.0%-95.4%, and RSDs (n=6) of the determined values less than 10%. This method has been applied to the analysis of infant formula stored open for a period of time. When the infant formula was stored open for more than 21 d, the contents of 4 characteristic aldehyde compounds gradually increased with the extension of time.