## 3 Results and Discussion
### Adsorption Performance Results of Actual Samples  
Adsorption effect analysis of melamine samples: The melamine standard was prepared with acetonitrile to 1000 ug/L and stored at \(-18\)\({}^{\circ}\)C. The standard solution was diluted to 10 ug/L, 20 ug/L, 50 ug/L, 100 ug/L, 200 ug/L and 300 ug/L standard working solutions with formic acid aqueous solution, followed by oscillation and vortex. The standard curve was plotted according to the test results of HPLC-MS/MS, with the results shown in Figure 6a. Adsorption effect analysis of \(\beta\)-agonists: Mixed standard solution: An appropriate amount of single standard stock solutions of clenbuterol hydrochloride, ratopamine and salbutamol were taken and diluted with methanol to 1000 ug/L mixed standard solutions. These solutions were stored in the dark at \(-18\)\({}^{\circ}\)C. Mixed working solution of isotope internal standard: An appropriate amount of single-standard internal standard storage solutions of clenbuterol-D9, ratopamine-D6 and salbutamol-D3 isotopes were, respectively, taken and diluted with methanol to 1000 ug/L mixed isotope internal standard solutions. These solutions were stored in the dark at \(-18\)\({}^{\circ}\)C. The mixed standard solutions were diluted with acetonitrile to obtain standard working solutions with external standardconcentrations of 1 \(\mu\)g/L, 2 \(\mu\)g/L, 5 \(\mu\)g/L, 10 \(\mu\)g/L, and 20 \(\mu\)g/L (all isotope internal standards were 10 \(\mu\)g/L). The standard curve was plotted according to the test results of HPLC-MS/MS, with the results shown in Figure 6b. The blank sample milk was used as the matrix for the standard addition recovery experiment. The standard addition concentrations were 20 \(\mu\)g/L, 50 \(\mu\)g/L, 100 \(\mu\)g/L, 150 \(\mu\)g/L, and 200 \(\mu\)g/L, respectively. The spiked samples and blank samples were tested after pretreatment, with the results listed in Table 2. It can be seen from the table that the adsorption amount of melamine on Fe\({}_{3}\)O\({}_{4}\)@SPS microspheres reaches about 55% at the spiked concentration of 20 \(\mu\)g/L. In addition, the recovery rate increases with the increase in the concentration of melamine. This indicates that there is a remarkable adsorption effect of Fe\({}_{3}\)O\({}_{4}\)@SPS microspheres on melamine. After 8 blank matrix samples of pork, mutton, and meat pine in 2 g were weighed and placed in a 50 mL centrifuge tube, clenbuterol hydrochloride, salbutamol and ratcopamine standard solutions were added to 6 samples to reach a concentration of 0.5 \(\mu\)g/kg. The remaining 2 samples were used as blank matrix samples which were tested on the machine. Each centrifuge tube was added with 10 mg of Fe\({}_{3}\)O\({}_{4}\)@SPS, in turn, followed by oscillation and vortex at 25 \({}^{\circ}\)C for 24 h. The supernatant was separated by strong magnetic separation and determined by HPLC-MS/MS. The test results are listed in Table 3. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Concentration** & **Result of** & **Mean Value** & **Average** & **Relative Standard** \\ (\#g/L) & **Survey (\#g/L)** & **(\#g/L)** & **Recoveries/\%** & **Deviation/\%** \\ \hline
20 & 8.979 & & & \\
9.012 & 8.996 & & 55.92 & \\
50 & 8.957 & & & \\
9.189 & 9.073 & 81.85 & & \\
100 & 8.995 & & & \\  & 8.920 & 8.958 & 91.04 & 0.9959 \\  & 8.906 & & & \\
150 & 8.899 & 8.903 & 94.10 & \\
200 & 8.964 & 9.006 & 95.50 & \\  & 9.048 & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Experimental records of precision and recovery of melamine spiked samples. Figure 6: Standard curve of melamine solution at 10–300 ng/mL concentration (**a**); standard curves of three \(\beta\)-agonist mixture solutions at concentrations of 1–20 ng/mL (**b**). It can be seen from the table that the recovery rate of clenbuterol hydrochloride, salbutamol and ratcopamine in pork, mutton, and fried pork flakes were 92-102%, 90-100% and 94-104%; 94-102%, 90-102% and 90-98%; 90-102%, 90-98% and 92-102%, respectively.