Ontwsep™ PSA is an ethylenediamine-N-propyl extraction cartridge made from high-purity spherical silica gel, an adsorbent similar to NH2. PSA has two amino groups, with pKa values of 10.1 and 10.9, respectively. It has a higher ion exchange capacity than the NH2 column. Simultaneously, PSA can generate chelation with metal ions and is utilised to remove them. It is commonly used to remove organic acids, pigments, metal ions, and phenols from pesticide residue samples before examination.