The characteristics of XAD-16, SP-825, HP-20 and HP-2MGL
resins were summarized in Table 1. In order to remove the undesired
substances trapped inside the resin pores during resin manufacturing
such as the monomers and porogenic agents, the
MARs were subjected to pretreatments: The resins were first
soaked in ethanol for 24 h, washed with deionized water until
complete removal of ethanol, soaked in 1 M NaOH for 5 h and then
1 M HCl for 5 h, and finally washed thoroughly with deionized
water until the pH of resin is 7. Such pretreated resins were dried
at 60 C to constant weight in an oven (101-3A, Pudong Rong-feng
Scientific Instrument Co., Ltd., Shanghai, China).