Determination of Four Diping Anti-Hypertensive Drugs Illegally Added in Healthcare Foodstuffs by Nano-Silver Surface Enhanced Raman Spectroscopy

Surface enhanced Raman spectroscopy (SERS) was applied to the determination of illegally added anti-hypertensive drugs4 of which were chosen to be studied in this work, namely benidipine hydrochloride (BNDP), nicardipin hydrochloride (NCDP), nifedipine (NFDP) and adipine (ADP) in health-care foodstuffs. As shown by their molecular structures, these 4 drugs were classified to dihydropyridines. A portion (0.103 0 g) of the crushed sample, suspected for adding the contraband drugs, was ultra-sonicated for 5 min with 10.0 mL of methanol to extract the drugs into the solvent. After centrifugation, 1.0 mL of the supernatant was taken and made its volume to 10.0 mL with methanol. An aliquot of 100 μL of the solution was taken and 200 μL of the nano-silver solution (as surface enhancer) together with 20 μL of hydrochloric acid solution with a volume ratio of 2:7 (as auxiliary) were added. After shaking for 10 s at a rotation rate of 400 r·min^-1, the solution was ready for SERS determination under the prescribed working condition of the instrument. Linear relationships between values of intensity ratios of the characteristic peaks found and relative mass concentrations of the 4 drugs were found in the following ranges:1 from 1.0-10.0 mg·L^-1, same for DNDP and NCDP; 2 from 2.0-9.0 mg·L^-1 for NFDP; and 3 from 1.0-9.0 mg·L^-1 for ADP. Values of detection limits (3S/N) found of the 4 drugs were 0.40, 0.45, 0.75, 0.75 mg·L^-1 respectively. Recovery was tested by standard addition method, giving results of recovery of 96% for ADP, and at same value of 108% for the remainder 3 drugs. Values of RSDs (n=5) found were ranged between 1.0% and 5.9%. A seized sample was analyzed by the present method, NCDP was found with its content of 10.4%.