Developing　a　functional　affinity　monolithic　column　towards　in-tube　solid-phase　microextraction　(IT-SPME)　for　selective　sample　pretreatment　is　critical.　Herein,　a　high-performance　capillary　affinity　monolithic　column　with　an　ultra-high　aptamer　coverage　density　was　rapidly　fabricated　via　a　simple　adsorption　strategy,　in　which　aptamers　with　natural　sequences　were　directly　immobilized　on　an　ammonium-based　strongly　cationic　matrix.　Limitations　of　the　traditional　biological　or　covalent　methods　such　as　time-consuming　modification　reactions,　special　requirement　of　active　groups　(e.g.　-NH2　and　-SH)　on　the　aptamer,　and　low　aptamer　coverage　density　levels　were　avoided.　An　ultra-high　coverage　density　of　8616　pmol　μL-1　was　achieved　with　excellent　stability,　and　the　highest　aptamer-modification　level　among　all　the　current　methods　was　reached.　Selective　recognition　and　high　recovery　yields　of　the　model　mycotoxin　ochratoxin　A　(OTA)　were　achieved　in　95.9　±　0.98%-97.9　±　0.28%　(n　=　3).　In　particular,　there　was　little　cross-reactivity　towards　the　OTB　analogue　of　only　0.5%　even　in　the　case　of　250　fold　of　the　analogue　OTB,　which　was　not　reported　in　previous　affinity　monoliths.　Upon　sample　analysis,　satisfactory　discriminations　of　trace　OTA　were　obtained　at　93.7　±　1.4%-95.5　±　2.5%　(n　=　3)　in　beer　and　wheat.　A　facile　and　direct　method　for　efficiently　fabricating　an　aptamer-based　affinity　monolith　towards　online　selective　IT-SPME　was　proposed.　This　journal　is　©　The　Royal　Society　of　Chemistry.