It was diluted to the required volume with n-hexane and shaken
for 1 min. Then, 2 mL of the sample solution was loaded onto a 300
mg pollen grain SPE cartridge (sorbent materials were packed into a 3
mL polypropylene syringe and retained by two polyethylene frits),
which was sequentially preconditioned with 3 mL of acetone and 2 mL
of n-hexane for activation (in Figure 1).