A fast and reliable method to quantify neral and geranial (citral) in essential oils using 1H NMR spectroscopy

Citral (3,7-dimethyl-2,6-octadienal), a mixture of geranial and neral (two stereoisomeric monoterpene aldehydes), is considered an important raw material in the fields of fragrance, pharmaceutical, food and cosmetic industries. It is a well-known biologically active compound present in various essential oils. A fast and reliable experimental method was developed and validated in order to quantify citral in essential oils using ¹H NMR spectroscopy (experiment time at the minute level). The quantitative procedure, using anisole as internal standard, showed a perfect linearity of measurements (R² = 0.9999), a very good accuracy (relative errors comprised between −1.9% and 0.3%) and an excellent precision (reproducibility 17.8 mg ± 1.0%). The procedure was also checked with three mixtures of weighted monoterpenes and the contents of citral, measured by GC and ¹H NMR, were absolutely comparable. Then, the method was successfully applied to measure the contents of citral in 10 commercially available essential oils. Among the investigated samples, citral varied from 2.9% (Zingiber officinalis) to 90.6% (Bakhousia citriodora).