Determination of 6 Illegally Additive Weight-Reducing Drugs in Meal Replacement Foods by High Performance Liquid Chromatography-Triple Quadrupole Composite Linear Ion Trap Mass Spectrometry with QuEChERS

After the meal replacement biscuit, meal replacement congee or meal replacement milkshake sample was ground, an aliquot (1.00 g) was taken, and 8.00 mL of methanol was added. The mixture was shaken for 2 min,extracted by vortex for 5 min, diluted to 10.00 mL by methanol, and centrifuged for 5 min. The 6.00 mL of supernatant was taken, and placed into a purification tube containing 25 mg of N-propyletyhlenediamine (PSA), 25 mg of octadecylsilane bonded silica gel (C₁₈), and 150 mg of magnesium sulfate. The mixture was vortexed for 2 min,and centrifuged for 5 min。The supernatant was passed through a 0.22 μm organic filter membrane, and the filtrate was determined by high performance liquid chromatography-triple quadrupole composite linear ion trap mass spectrometry. In the chromatographic analysis, a ZORBAX Eclipse Plus C₁₈ column (50 mm×2.1 mm, 1.8 μm) was used as the stationary phase, and mixed solutions of 0.1% (volume fraction) formic acid solution containing 5 mmol·L⁻¹ ammonium acetate and methanol at different volume ratios were used as the mobile phase for gradient elution. In the mass spectrometry analysis, the positive ion mode of the electrospray ion source was used for ionization, multiple reaction monitoring-information dependent acquisition-enhanced product ion (MRM-IDA-EPI) mode was used for scanning, and external standard method was used for quantitative analysis. It was shown that linear relationships between values of the mass concentration and peak area of 6 illegally additive weight-reducing drugs, including sibutramine, N-desmethyl sibutramine, N,N-didesmethyl sibutramine, ephedrine, fenflutamine, and phenolphthalein, were kept in the range of 0.5-20.0 μg·L⁻¹, with lower limits of determination (10S/N) in the range of 5.0-10 μg·kg⁻¹. Test for recovery was made according to the standard addition method, giving recoveries in the range of 79.5%-102%, and RSDs (n=6) of the determined values were less than 5.0%. The proposed method was used for the analysis of actual samples, and sibutramine was detected in 3 meal replacement milkshake samples out of 40 batches of samples, with detection amounts of 2.60×10⁷, 2.62×10⁷, 1.86×10⁷ μg·kg⁻¹, respectively.