Simultaneous Determination of Residual Amount of Eleven Plant Growth Regulators in Bean Sprout by QuEChERS-HPLC-MS/MS

A portion (10.0 g) of crashed and blent fresh bean sprouts was homogenized for 2 min at high speed with 20 mL of a mixture of 5% (volume fraction, the same below) HCOOH-CH₃CN solution to extract 11 plant growth regulators (PGRs) into CH₃CN. 4 g of anhydrous MgSO₄ and 1 g of anhydrous Na₂SO₄ were added to the mixed solution, which was mixed and centrifuged. 4 mL of the upper CH₃CN layer were taken and added to a centrifuging tube in which 300 mg of anhydrous MgSO₄, 30 mg of PSA and 50 mg of C₁₈ were added preliminarity. The mixture was swirled and centrifuged to have the extract in CH₃CN to be purified. All of the supernatant was taken and evaporated to near-dryness by N₂-blowing at 45 ℃. The residue was taken up and diluted to 1.0 mL with CH₃OH. The solution was filtered through 0.22 μm filtering membrane and the filtrate was used for HPLC-MS/MS analysis under the optimized conditions. Agilent ZORBAX Eclipse plus C₁₈ column was selected for chromatographic separation. Mixtures of (A) 5 mmol·L^-1 NH₄OAc solution containing 1% HCOOH and (B) CH₃OH in various ratios were used as mobile phase in gradient elution. Retention time for the 11 PGRs were found in the range from 6.2 min to 8.6 min under this condition. Due to difference in properties of the 11 PGRs, switching of ESI⁺ and ESI^- was taken as the mode of ionization in MS/MS analysis, and some other MS parameters were also optimized, and the determination was made under MRM mode. Blank sample was used as matrix in preparation of standard solution series to overcome the matrix effect. As shown by the experimental results, linearity ranges of the standard curves of the 11 PGRs were same in the range of 5.0-200.0 μg·L^-1, with detection limits (3S/N) in the range from 0.01 to 0.40 μg·kg^-1. Test for recovery was made by addition of standard solutions at 3 concentration levels to a matrix sample, giving values of average recovery ranged from 66.9% to 109%, with RSDs (n=10) of the determined values in the range of 3.6% to 8.9%.