Ontwsep™ NH₂ (amino) is an aminopropyl extraction cartridge made from highpurity spherical silica gel. It features a polar stationary phase and a weak anion exchanger. When used in a non-polar solvent (such as n-hexane) for pretreatment, it can create hydrogen bonds with molecules containing -OH, -NH, or -SH groups. Amino pKa = 9.8; in an aqueous solution with pH < 7.8, it can act as a weak anion exchanger, removing strong anions like sulfonate radicals from the sample. It is commonly used for sample preparation in pesticide residue analysis.