Rapid Screening of Illegal Added Lidocaine and Cinchocaine in Cosmetics by Surface-Enhanced Raman Spectrometry

The sample of 0.5 g was taken, and saturated sodium chloride solution of 0.5 mL was added. After swirling for 1 min, n-hexane of 3 mL was added, and the mixture obtained was extracted for 3 min by ultrasound, and centrifuged for 30 s. The supernatant of 2 mL was taken, and 0.1 mol·L^-1 hydrochloric acid solution of 0.5 mL was added. After swirling for 30 s and centrifuging for 15 s, the lower layer of extract was collected. Colloridal gold nanoparticles of 150 μL was taken, and the lower layer extract of 50 μL and 1 mol·L^-1 sodium chloride solution of 50 μL were added. The mixed solution was swirled for 10 s, and detected by portable Raman spectrometer. As shown by the results, the surfance-enhanced Raman characteristic peaks of lidocaine and cinchocaine were 505, 670, 1 081, 1 254 cm^-1 and 509, 774, 1 379, 1 599 cm^-1, and lidocaine and cinchocaine could be effectively distinguished from other local anesthetics by the above Raman characteristic peaks. Instrument detection limits of lidocaine and cinchocaine were 0.10 mg·L^-1, and method detection limits were 5 mg·kg^-1. The proposed method was suitable for rapid screening of the 2 local anesthtics (lidocaine and cinchocaine) in common cosmetic substrates, such as solid cream, lotion and gel essence.