3.3. Loading of Pyrimethanil into Mesoporous Silica Nanoparticles

Thirty milligrams of synthesized MSNs was added into the pyrimethanil-toluene solution (6.0 mg/mL, 5.0 mL). The mixture was magnetic stirred for 6 h, and the supernatant was then removed by centrifugation at 10,000 rpm for 10 min. The pyrimethanil-loaded MSNs was dried at 50 °C for 5 h to remove the supernatant completely.

The pyrimethanil loading efficiency of the proposed method was determined by high performance liquid chromatography (HPLC, 1200-DAD (Diode Array Detector), Agilent, Santa Clara, CA, USA). In brief, 10.0 mg of Py-MSNs were dissolved in 25.0 mL of methanol under sonication for 2 h. This process was repeated several times, and the methanol solution was combined for HPLC analysis, until the concentration level of pyrimethanil in the solution lower than the limit of detection.

For the HPLC analysis, Venusil XBP-C18 column (Bonna-Agela Technologies Inc., Tianjin, China) (2.5 mm × 4.6 mm, 5 µm) was used to separate the target compound from others at 30 °C. Methanol/water (80/20) was used as mobile phase at a flow rate of 1.0 mL/min. DAD signals was used as 275 nm. Loading efficiency (%) = (weight of pesticide in nanoparticles/weight of nanoparticles) × 100%. In this study, the loading efficiency of MSNs was 29.77%.

The nitrogen adsorption of MSNs and Py-MSNs was studied to show the typical pore characteristics using a surface area and pore size analyzer (TriStarII 3020, Micromeritics Instruments Corp, Norcross, GA, USA) at 196 °C. Samples were degassed at 80 °C for 12 h prior to analysis. The characteristics of mesoporous structure were analyzed by the BET and BJH procedures from the adsorption branches of the isotherms.