Discrimination of sibutramine and its analogues based on surface-enhanced Raman spectroscopy and chemometrics: toward the rapid detection of synthetic anorexic drugs in natural slimming products

Nowadays there is growing concern about the adulteration of synthetic anorexics in natural slimming products (NSP) due to the increasing use of weight-reducing aids. Here, we report surface-enhanced Raman spectroscopy (SERS) coupled with chemometrics for rapid discrimination and detection of sibutramine (SIB) and its analogues (mono-desmethylsibutramine, MDS; di-desmethylsibutramine, DDS) in konjac pressed candy (KPC), which is a NSP used in the treatment of obesity. It has been demonstrated that the two characteristic peaks at 1060 cm(-1) (in SERS spectrum of SIB) and 1407 cm(-1) (in SERS spectrum of MDS) were used to discriminate between SIB, MDS and DDS. Moreover, the two spectra for KPC with MDS and KPC with DDS only exhibited some slight differences. After the second derivative transformation, the differences were much more clear, especially for the peak at 1407 cm(-1) in the SERS spectrum of KPC with MDS. Meanwhile, partial least-squares regression was used for quantitative analysis of the samples. The limit of detection for SIB, MDS and DDS was 5.00 x 10(-8) M, 5.00 x 10(-7) M and 1.00 x 10(-6) M, respectively. Compared with previously reported studies, the method is simple (no pretreatment), less time-consuming and inexpensive, and can be applied to rapidly screen SIB and its analogues in NSP.